Effects of nitrogen application rates on root recover growth of maize after waterlogging

Effects of nitrogen application rates on root recover growth of maize after waterlogging | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of nitrogen application rates on root recover growth of maize after waterlogging Yonggang Duan, Weihan Wang, Dongliang Qi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8598554/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Aims The growth and development of the root system are of critical significance for crop yield and nutrient utilization. Nitrogen fertilization is frequently utilized to modulate and augment plants' tolerance to abiotic stresses. This study aimed to investigate the effects of nitrogen fertilization on the recovery growth of maize (Zea mays L.) roots and their correlations with grain yield and nitrogen use efficiency after waterlogging stress. Methods A two-year experiment was conducted to examine effects of nitrogen fertilizer application rates (0, 90, 180, 270, and 360 kg N ha-1, designated as N1, N2, N3, N4 and N5, respectively) on root morphological and physiological characteristics under well-watered (W1) conditions across the maize grown season and waterlogging for 6 days at the sixth leaf (V6) growth stage (W2). Results In comparison to W1, W2 significantly decreased length, dry weight, surface area, volume, oxidation activity, zeatin + zeatin riboside, and indole-3-acetic acid contents in roots at the tasselling, filling, and maturity stages regardless of nitrogen rates. Furthermore, these parameters increased with the increase in nitrogen rates (up to N5) under W2, indicating that a high nitrogen rate (such as N5) could enhance the root recovery growth of maize after early(V6)-stage waterlogging. Moreover, the N5 led to a more developed root system, contributing to the improved nitrogen use efficiency under the W2 condition. Conclusion Collectively, a high nitrogen application rate (N5) promoted root recovery growth after waterlogging at the V6 stage, and thus obtained relatively high grain yield and nitrogen use efficiency in maize. Root length density Root distribution Economic yield Nitrogen uptake Zea mays Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Waterlogging or flooding commonly occurs in regions characterized by substantial precipitation, excessive irrigation, and notable fluctuations in the elevated groundwater level (Ren et al., 2016 ; Tian et al., 2019a ). It is reckoned that roughly 16% of global cropped areas are affected by waterlogging stress (Shabala 2011 ), resulting in 15%-80% reductions of crop yields (Prasanna and Rao 2014 ; Huang et al., 2022 ). Owing to global climate change, the severity and incidence of waterlogging are projected to rise, especially in mid- and high-latitude regions (Herzog et al., 2016 ). For instance, the Huang-Huai-Hai Plain and the Jianghan Plain in the People's Republic of China are affected (Ren et al., 2017 ; Qi and Pan 2022 ). When waterlogging takes place, the gas exchange between the soil and the atmosphere decreases. In this circumstance, the soil become hypoxic (low-oxygen) or anoxic (oxygen-free) within one day (Araki et al. 2012a ; Ghobadi et al., 2017 ). Waterlogging enhanced anaerobic respiration, consequently leading to the accumulation of toxins in the rhizosphere, such as hydrogen sulfide (H 2 S) and ferrous sulfide (FeS)(Ashraf and Rehman 1999 ). This toxic environment resulted in the degradation of the rhizosphere environment, causing a reduction in the absorption of mineral ions and beneficial trace elements, inhibiting the growth and development of the root system (Ren et al., 2016 ; Zhang et al., 2021 ). Waterlogging also induced the generation of reactive oxygen species (ROS) and free radicals, and expedited leaf senescence, and consequently a significant drop in grain yield (Araki et al., 2012b ; Tian et al., 2021 ). Moreover, the lower levels or free of soil oxygen supply inhibited both carbon and nitrogen metabolism in plants (Ren et al., 2017 ; Tian et al., 2021 ; Zhang et al., 2021 ). In addition, waterlogging elevated denitrification and leaching of nitrogen from crop field, lowering the soil nitrogen availability (Limami et al., 2014 ; Kaur et al., 2020 ). Previous studies have demonstrated that a high nitrogen application rate contributes to improve the activities of superoxide dismutase, peroxidase, and catalase, net photosynthetic rate, allocation proportion of shoot biomass to grain parts, and nitrogen accumulation (Tian et al., 2021 ; Qi and Pan 2022 ). Consequently, enough nitrogen fertilization helped to stabilize grain yield of maize following six days of waterlogging at the V6 stage. However, it was observed that a high nitrogen treatment decreased biomass and nitrogen accumulation and the redistribution to the grain of waterlogged wheat, and thus inducing more grain yield losses (Jiang et al., 2008 ). Furthermore, appropriate nitrogen application (240 kg N ha − 1 ) demonstrated potential in augmenting the activity of antioxidant enzymes and mitigating lipid peroxidation, thereby reducing the yield loss of waterlogged cotton (Guo et al., 2010 ). Conversely, an excessive nitrogen application rate (480 kg N ha − 1 ) presenting an opposite trend. Therefore, the application rate of nitrogen fertilizer requires meticulous consideration to mitigate stress-induced damage and facilitate the recovery of crop growth following the alleviation of waterlogging stress. Plant roots, as a vital constituent of the plant life system, not only execute essential functions such as the uptake of nutrients and water and the anchorage of shoots. Additionally, they can synthesize hormones and amino acids and interact with soil microorganisms, thereby playing an indispensable role in yield formation and resource utilization (Li et al., 2022 ; Jing and Shi 2025 ). The growth and development of shoots rely heavily on root systems (Qi et al., 2023 ). The capacity of a plant to assimilate nutrients and uptake water is dictated by the morphology and physiology of the root system within the soil profile (Qi and Hu 2022 ; Liu et al. 2023 ). Root morphology is predominantly characterized by crucial indicators including root dry weight, volume, length, and surface area (Xu et al. 2018 ; Liu et al. 2023 ). Moreover, the physiological activity of roots can be evaluated through parameters including oxidation activity, the content of zeatin (Z) combined with zeatin riboside (ZR), and the content of indole-3-acetic acid (IAA) (Yang et al. 2012 ; Qi et al. 2023 ). As the primary organ directly affected by waterlogging, maintaining root function or improve its recovery growth is crucial for plant adaptation to this stress.(Ren et al., 2016 ; Gao et al., 2025 ). It has been shown that nitrogen fertilization improve the dry weight, length, quantity, oxidation activity, and Z + ZR content of rice roots under normal water supply condition (Liu et al., 2023 ). Nevertheless, there is relatively limited evidence concerning the impacts of nitrogen application rates on the recovery growth of roots after waterlogging, as well as their correlations with crop yield and nitrogen use efficiency (NUE). In the Jianghan Plain, the majority of precipitation occurs during the growth season of spring maize, generally ranging from the sixth leaf (V6) stage to maturity (Qi and Hu, 2022 ). In this area, the growth and yield of spring maize are significantly affected by excessive precipitation. Furthermore, the early growth stages of maize, such as the V6 stage, are vulnerable to waterlogging-induced damage (Ren et al., 2016 ; Tian et al., 2019a , b ). Understanding the effects of nitrogen application rates on root recovery growth after waterlooging is of great significance for stabilizing maize productivity under global climate change. Therefore, the present study aimed to investigate (1) the characteristics of root growth and activity under well-watered conditions and waterlogging scenarios with different nitrogen application rates, and (2) the correlations between root characteristics and grain yield in maize. It was hypothesized that increasing nitrogen application rates could provide suitable soil nutrient conditions to improve the root morphology and physiology of waterlogged maize plants, thereby achieving high grain yield and NUE. The results emphasize the importance of a balanced nitrogen management strategy in the adverse effects of waterlogging on maize through the regulation of root recovery growth. Materials and methods Experimental site A two-year field experiment (2018–2019) was carried out at the agricultural test station in Jingzhou City, central China (30° 21′N, 112° 31′E, 30 m above sea level). This region is characterized by a typical subtropical monsoon climate, with an average annual precipitation of approximately 1,095 mm. The region experiences a mean annual sunshine duration exceeding 1,718 hours and an average annual temperature of 16.5℃. In accordance with the criteria of the Food and Agriculture Organization (FAO), the soil at the experimental site is classified as calcareous alluvial soil. The fundamental physicochemical properties of the experimental soil are elaborated in Table S1. The mean air temperature, precipitation, and sunshine hours during the maize growing season are presented in Table S2. Experimental design A split-plot experimental design was devised, where the water regime was designated as the main plots and the nitrogen rate as the sub-plots. Each treatment (sub-plot) was replicated thrice. The area of each plot was 16 m 2 (4 m× 4 m). Polyvinyl chloride (PVC) boards (4 m × 2.3 m) were installed around the plots, with 2.0 m inserted below the soil surface and 0.4 m remaining above the ground to impede water movement. The water regimes included well-watered (W1), characterized by a relative soil mass water content of 70–85% of the field capacity (Fc), which was a rational control during the maize growing season, and W2, where a 2–3 cm water layer was maintained for 6 days above the soil surface at the V6 stage (Qi and Pan 2022 ). In 2018, W2 commenced 41 days after the crop was planted (DAP), and in 2019, it started 42 DAP. At the conclusion of the waterlogging period, the surface water in the W2 plots was removed via a siphon, and the soil moisture content was gradually reduced to that of the control (the soil moisture content of W1) over a period of 5–7 days. The nitrogen application rates were 0 (N1), 90 (N2), 180 (N3), 270 (N4), and 360 (N5) kg N ha − 1 , which were applied to each water regime. The nitrogen fertilizer (urea, N 46%) was split into a basal application (one day before sowing, 40%) on 31 March 2018 and 3 April 2019, and a top-dressing fertilization at the twelfth leaf growth stage (V12, 60%) on 25 June 2018 and 28 June 2019. Field management Tian et al. ( 2021 ) presented a comprehensive account of the crop management strategies. Briefly, ditches were established for each sub-plot to eliminate excess water resulting from heavy rainfall during the crop growth season (excluding the V6 stage of maize under the waterlogging treatment). Water was pumped onto the W2 plots 4–6 times per day to maintain a 2–3 cm layer of free water on the field surface throughout the waterlogging period. Due to a substantial amount of precipitation in the two experimental years (Table S2), no irrigation water was provided to the maize (excluding waterlogging conditions). Prior to sowing, calcium superphosphate and potash muriate were applied at rates of 329 kg ha − 1 (P 2 O 5 17%) and 300 kg ha − 1 (K 2 O 60%), respectively. Maize (cultivar Yidan No.629) was sow at a density of 73,000 plants ha − 1 on 1 April 2018 and 4 April 2019, and the crops were harvested on 9 August 2018 and 11 August 2019. Data collection Root characteristics In 2018 and 2019, at the tasseling (VT), filling (R2), and maturity (R6) stages, corresponding to 92 and 91, 109 and 110, and 125 and 126 days after planting (DAP), respectively, tests were conducted on the length, number, dry weight, surface area, oxidation activity, Z + ZR content, and IAA content of the roots. A hand-driven auger with a diameter of 10 cm and a length of 1.25 m was used for root sampling. The samples were collected from soil depths of 0–20, 20–40, 40–60, 60–80, and 80–100 cm beneath the plant. A portion of each root sample was employed to determine the morphological and physiological parameters of the roots. To measure the length, quantity, and surface area, the roots were floated in shallow water within a 30 × 30 cm glass tray and scanned (Epson Expression 1680 Scanner, Seiko Epson Corp., Tokyo, Japan). The WinRHIZO Root Analyzer System (Regent Instruments Inc, Quebec, Canada) was utilized to quantify the corresponding parameters. Subsequently, the roots were dried in an oven at 75°C until a constant weight was achieved, and their dry weight was measured. The oxidation activity of (fresh) roots was determined in accordance with the method described by Ramasamy et al. ( 1997 ). Z, ZR, and IAA were extracted from (fresh) roots and then purified using the methods provided by Bollmark et al. ( 1988 ). The concentrations of these compounds were determined as described by Xu et al. ( 2018 ). Nitrogen uptake and grain yield The semimicro Kjeldahl method (AOAC, 1984) was utilized to analyze nitrogen concentrations in mature plants. The shoot nitrogen uptake was computed by calculating the products of biomass and tissue nitrogen contents. To determine grain yield (adjusted to 14.5% moisture), a 6.0 m 2 area at the center of each plot was harvested. As per Ju et al. ( 2015 ), the NUE is computed as the ratio of grain yield to the total shoot nitrogen uptake. The relative root-to-shoot ratio was computed as the ratio of the total root biomass within the 0-100 cm soil depth (the sum of root biomass at the 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm soil layers) to the shoot biomass. Statistical analysis All the collected data were individually analyzed via a randomized complete block design (RCBD) method using the PROC GLM procedure in SAS for variance assessment. The means were compared by Duncan’s multiple range test at a significance level of P < 0.05. Although most of the measured root morphological and physiological parameters exhibited variability over the years, no year × waterlogging regime or year × N interactions were detected (Table 1 ). Therefore, we pooled the data from the two different years. Table 1 Analysis of variance of root length, root surface area (RSA), root weight (RW), root volume (RV), root length density (RLD), root oxidation activity (ROA), root zeatin (Z) + zeatin riboside (ZR) content, and indole-3-acetic acid (IAA) content under condition of waterlogging regimes and nitrogen management strategies interaction. Source of variation Degree of freedom Root length (cm) RSA(cm 2 ) RW(g) RV(cm 3 ) RLD (m 3 m − 3 ) ROA (µgα-NA h −1 g − 1 ) Z + ZR content (nmol g − 1 DW) IAA content (nmol g − 1 DW) Y 1 NS NS NS NS NS NS NS NS W 1 ** ** ** ** ** ** ** ** N 4 ** ** ** ** ** ** ** ** Y⋅W 1 NS NS NS NS NS NS NS NS Y⋅N 4 NS NS NS NS NS NS NS NS W⋅N 4 ** ** ** ** * ** ** * Y⋅W⋅N 4 NS NS NS NS NS NS NS NS Note: NS indicates statistical significance at P > 0.05 within a column. * and** represents statistical significance at P < 0.05 and P < 0.01 respectively. Y, D and N represents year, drainage regime and nitrogen rate, respectively. Results Root morphology traits Within the 0-100 cm soil depth, root morphological characteristics, including length, surface area, biomass, and volume, attained their maxima during the R2 and VT stages under W1 and W2 conditions, respectively (Table 2 ). In plants treated with W1, the root morphological parameters at the VT, R2, and R6 stages exhibited an increase ranging from 12.5% to 48.7% as the nitrogen application rates increased up to N4, followed by a subsequent decline under N5. However, these parameters demonstrated an increase spanning from 6.7% to 67.9% with the elevation of nitrogen application rates (up to N5). In most instances, there were statistically significant disparities among different nitrogen rates for plants treated with W1. Additionally, in comparison to W1, W2 notably diminished the total length, surface area, weight, and volume of the roots (decreased by 14.6%-69.0%) at each nitrogen rate (Table 2 ). The W1N4 treatment resulted in the maximum root length, while the W2N1 treatment led to the minimum root length at the three growth stages (Table 2 ). Furthermore, the total root length at the R6 stage was comparable between the W1N4 and W1N5 treatments. Root surface area, root weight, and root volume at the VT, R1, and R6 stages among different treatments, which exhibited a highly similar variation pattern to that of root length (Table 2 ). These suggest that a high nitrogen rate (as in N5) help to improve root growth morphology at the the middle and later growth stage of maize under waterlogging at the V6 stage. Table 2 Total root length, root surface area, root weight (RW), and root volume (RV) in the 0-100 cm soil profile at the tasseling (VT), Filling (R1), and maturity (R6) stages of maize as affected by different nitrogen application rates and waterlogging regimes Treatment Root length (cm) Root surface area (cm 2 ) Root weight (g) Root volume (cm 3 ) VT R2 R6 VT R2 R6 VT R2 R6 VT R2 R6 W1N1 5381c 5413d 2871c 997c 1109c 411c 7.6c 8.2c 4.9c 35.8c 36.7c 24.9c W1N2 6325b 6214c 3328b 1365b 1454b 632b 10.7b 11.8b 7.6b 41.4b 42.4b 32.8b W1N3 6425b 6712b 3564b 1498b 1599b 715b 11.6b 12.6b 8.1b 42.8b 44.1b 34.1b W1N4 6938a 7325a 4125a 1729a 1899a 921a 13.8a 14.5a 10.3a 49.1a 54.3a 39.3a W1N5 6432b 6813b 3095a 1501b 1664b 887a 13.1a 14.1a 10.1a 47.1b 51.5a 38.1a W2N1 3587g 3313h 1211g 387f 369f 87f 3.1e 2.6f 1.3g 19.3g 15.8h 10.1h W2N2 4013f 3821g 1698f 598e 551e 198e 5.5d 5.1e 2.6f 26.1f 22.7g 14.6g W2N3 4658e 4305f 1798f 654e 621e 245e 6.1d 5.3e 3.1e 28.3e 26.4f 16.2f W2N4 5010d 4731e 2102e 827d 801d 336d 7.2c 6.4d 4.0d 32.2d 30.2e 18.7e W2N5 5489c 5234d 2487d 1010c 945c 454c 8.1c 7.7c 5.1c 36.1c 33.1d 22.1d Note: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha − 1 , respectively. Values are mean of 2 years and three replicates. Means followed by different letters within each column are significantly different at the probability level of 0.05. Root vertical distribution This study measured the RLD at the R2 stage to evaluate the vertical distribution of roots, as this stage is crucial for determining yield formation (Wang et al. 2018 ). In all treatments, the RLD declined with increasing soil depth (Fig. 1 ). The root system was predominantly concentrated in the topsoil. Specifically, the root length within the 0–40 cm soil layer constituted 60.9% − 66.1% of the total root system within the 0-100 cm depth (Table 3 ). The waterlogging conditions and nitrogen application rates in this study had an impact on the maize root distribution (Fig. 1 ).. Compared to W1, W2 led to a significant reduction in RLD ranging from 19.4% to 46.7% across the 0-100 cm soil depth. The W1N4 treatment generated the greatest RLD across the 0-100 cm soil depth while the W2N1 treatment led to the smallest RLD. Within the 0–60 cm soil depth, the root length density of plants treated with W1 demonstrated an increment with the augmentation of nitrogen application rates up to the N4 level, followed by a decline under the N5 treatment. In the 0–40 cm soil depth, the RLD of plants treated with W2 showed an increase as the N application rates increased up to the N5 level. Within the 60–100 cm soil depth, in comparison to the N1, the other nitrogen treatments led to a significant increase in RLD ranging from 23.4% to 55.1% under the two watering regimes. Table 3 The percentage of total root length in each soil depth to the sum of 0-100 cm soil depth (%) in maize as affected by different nitrogen application rates and waterlogging regimes Soil depth W1N1 W1N2 W1N3 W1N4 W1N5 W2N1 W2N2 W2N3 W2N4 W2N5 0–20 cm 33.2 33.7 32.8 34.8 33.8 36.8 36.8 36.6 37.0 38.5 20–40 cm 32.6 32.4 32.4 31.5 31.5 24.6 24.1 24.8 26.7 26.9 40–60 cm 12.7 15.3 16.8 16.9 16.8 12.9 14.0 14.2 14.1 14.1 60–80 cm 10.6 9.4 9.4 8.9 10.0 13.5 13.6 13.4 11.9 11.2 80–100 cm 10.9 9.2 8.7 7.9 7.9 12.3 11.4 11.0 10.4 9.3 Note: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha − 1 , respectively. Values are mean of 2 years and three replicates. Furthermore, under a specific nitrogen application rate (Table 3 ), W2 rather than the W1, increased the proportion of root length in the surface soil layer (0–20 cm) and the deep soil layer (60–100 cm). Conversely, W2 decreased the proportion of root length at a soil depth of 40–60 cm. Under W1, N1 resulted in the highest proportion of root length in the deep soil layer, whereas N4 led to the lowest proportion. Under W2, in comparison with other N treatments, N4 and N5 enhanced the proportion of root length at a soil depth of 0–40 cm and reduced the proportion of root length in the deep soil layer. This indicates that high nitrogen application rates (N4 and N5) primarily promoted the root growth recovery in the 0–40 cm soil depth after waterlogging at the V6 stage. Relative root-to-shoot ratio In maize, the root-to-shoot ratio gradually decreased during growth and was at its lowest at the R6 stage (Fig. 2 ). Irrespective of the nitrogen application rate, compared with W1, W2 significantly decreased the root-to-shoot ratio (by 14.5%-31.8%) at the VT, R2, and R6 stages. Moreover, under both W1 and W2 conditions, the root-to-shoot ratio declined by 8.7%-24.8% with the increase in nitrogen rates. The W1N1 treatment resulted in the highest root-to-shoot ratio at the three growth stages, whereas the W2N5 treatment led to the lowest root-to-shoot ratio (Fig. 2 ). This indicates that a high nitrogen application rate (as in N5) enhances the shoot growth of maize more significantly than its root growth under waterlogging at the V6 stage. Root oxidation activity and Z + ZR and IAA Contents As maize plants grow and develop, their root oxidation activity gradually declines (Fig. 3 ). In contrast to W1, W2 notably decreased the root oxidation activity varied nitrogen rates. In plants treated with W1, the root oxidation activity at the VT, R2, and R6 stages demonstrated an elevation as nitrogen levels increased up to N4, followed by a decline under N5. In contrast, during these stages, the activity presented an increase with the increment of nitrogen application rates (up to N5) in W2-treated plants. The contents of Z + ZR and IAA in the roots reached their peak at the VT stage and then declined as maize plants grew and developed (Figs. 4 and 5 ). At the three growth stages, the variations in Z + ZR and IAA contents among the different treatments showed a very similar variation compared to root oxidation activity (Figs. 3 , 4 , and 5 ). These suggest that a high nitrogen rate (as in N5) help to improve root growth physiology at the the middle and later growth stage of maize under waterlogging at the V6 stage. Grain yield and NUE In comparison with the W2, the grain yield and NUE in the W1 treatment were significantly higher by 19.7%-44.6%, regardless of the nitrogen application rate (Fig. 6 ). Under W1, the grain yield increased from N1 to N4, and then decreased at N5. In contrast, under the W2 condition, the grain yield increased from N1 to N5. This indicates that a high nitrogen application rate, such as that in the N5, contributes to a greater enhancement of grain yield under waterlogging stress at the V6 stage. The NUE increased with the increase in nitrogen application up to N4 and then remained stable at N5 under both the W1 and W2 waterlogging conditions. The highest grain yield and NUE were obtained in the W1N4 treatment, while the lowest grain yield and NUE were observed in the W2N1 treatment (Fig. 6 ). Correlation of root characteristics with grain yield and NUE Pearson's correlation analysis revealed a significant or highly significant positive correlation between the length, dry weight, surface area, weight, volume, oxidation activity, and the contents of Z + ZR and IAA in roots at the VT and R2 stages and the grain yield (r = 0.712*−0.911**). Additionally, a significant positive correlation was detected between the aforementioned root parameters at the VT and R2 stages and NUE (r = 0.654*−0.889**). Moreover, the length, volume, surface area, weight, oxidation activity, and the contents of Z + ZR and IAA in roots at the R6 stage also exhibited a significant positive correlation with grain yield (r = 0.638*−0.798*) and NUE (r = 0.631*−0.779**). Discussion Early-stage (V3 and V6) waterlogging exerted long-term negative effects on maize growth, as manifested by the continuous decline in shoot dry matter accumulation and its allocation to grains, premature leaf senescence, a decrease in the crop growth rate, the suppression of carbon and nitrogen metabolism, and a reduction in the net photosynthetic rate during the later growth stages (Ren et al., 2016 ; Hu et al., 2021 ; Qi and Pan 2022 ). In this study, waterlogging resulted in a continuous decrease in root morphological (Table 2 ) and physiological (Figs. 3 – 5 ) parameters. This is consistent with previous research on cotton (Guo et al., 2009 ), winter wheat (Wu et al., 2018 ), winter rapeseed (Liu et al., 2017 ), and pea (Ploschuk et al., 2018 ). These findings imply that it is infeasible for the maize roots to fully recover their growth when subjected to waterlogging at the V6 stage. The causes can be elucidated as follows: Firstly, the exchange of oxygen between soil and roots was greatly impeded by soil waterlogging, as the diffusion rate of gases in water was 10,000 times less than that in air (Armstrong, 1979 ). Once hypoxia occurs in the rhizosphere soil, the soil redox potential (Eh) declines, and reductive metal ions, particularly accumulation of Fe 2+ , Mn 2+ , S 2− , and HS − , exerting toxic impacts on crop roots (Visser and Voesenek 2005 ). Through anaerobic respiration, anaerobic microorganisms in the soil produced organic acids like acetic acid, lactic acid, and butyric acid, which in turn boosted soil acidity (Mohammad et al., 2017 ). The microbial population in the rhizosphere undergoes succession, with aerobic microorganisms being supplanted by anaerobic ones. The substitution of substances resulted in more rapid bacterial reproduction compared to fungi and actinomycetes, inhibiting beneficial bacteria and deteriorating the growth environment of the root system (Manghwar et al., 2024 ). Secondly, under waterlogging, the metabolic process of the roots transitions from an aerobic mode to an anaerobic mode. The efficiency of anaerobic respiration decreases, and the intermediate products, such as lactic acid, acetaldehyde, and ethanol, produced have toxic effects on the cells (Ahmed et al., 2013 ). The generated ATP energy was decreased by 70% to 97%, weakening the root system's capacity to absorb and transport water, minerals, and nutrients (such as N, P, and K) upward, and consequently restrained shoot growth, nutrient utilization and yield formation (Qiu et al., 2025 ). This was evidenced by reduced grain yield and NUE under W2 (Fig. 6 ). In turn, the inhibited photosynthate accumulation in shoot hinder root growth (Ren et al., 2016 ). Thirdly, waterlogging enhanced denitrification and nitrogen leaching, resulting in the low soil nitrogen availability (Table S3, Kaur et al., 2020 ). Nitrogen deficiency inhibited root growth has been widely observed on maize, cotton, wheat, and rapeseed (Guo et al., 2010 ; Men et al., 2020 ; Qi and Hu 2022 ; Tian et al., 2023 ). In support, under the W1 condition, the N4 resulted in larger root morphological and physiological parameters, while such an effect was not observed under the W2 condition (the N5 showed this effect). We noticed as well that applying nitrogen at a high rate (like in N5) boosted root growth and development after waterlogging. This corresponds with previous findings on nitrogen fertilization positive alleviated detrimental effects of waterlogging on shoot growth in maize (Kaur et al., 2017 ; Tian et al., 2021 ; Qi and Pan 2022 ), indicating that suitable increases in nitrogen fertilization could enhance root tolerance to waterlogging stress and promote it recovery growth. The possible explanations are as follows. Firstly, Plant hormones are known to play a crucial role in the post-waterlogging recovery process (Bashar, 2018 ), and their sophisticated regulation serves as a central driver coordinating the developmental changes of the waterlogging recovery phase, particularly lateral root initiation (Gao et al., 2025 ). Nitrogen serves as a crucial element in plant hormones, therefore, the use of nitrogen facilitated the generation and functioning of Z + ZR and IAA (Guo et al., 2010 ). The enhanced hormones contents in roots (Figs. 4 and 5 ) at high nitrogen rate helped to strengthen recovery growth after waterlogging (Zhang et al., 2025 ). Secondly, higher nitrogen treatments compensated for nitrogen loss caused by denitrification and leaching due to waterlogging (Kaur et al., 2017 ), resulting in relatively high soil nitrogen availability (Table S3). Root growth was positively correlated with soil nitrogen contents under nitrogen deficit condition (Tian et al., 2023 ; Qi et al., 2023 ). The enhanced NUE (Fig. 6 ) verified the improvement of root growth for the W2N5 treatment. Alternatively, it has been shown fertilizer nitrogen uptake by maize plant was positively correlated with RLD in the 0–40 cm soil depth (Qi et al., 2020b ). Moreover, the application of higher nitrogen fertilizer early could enhance the root vitality of waterlogged plants (Zhou and Oosterhuis, 2012 ). In this situation, 40% of the nitrogen fertilizer was used for the basal application. Thirdly, nitrogen fertilization could induce the expression of antioxidant enzyme genes in waterlogged plants (Ozcubukcu et al. 2014 ), enhancing recovery growth of plants after abiotic stresses (Manghwar et al., 2024 ). Lastly but not least, the increased leaf area index, SPAD value, and net photosynthetic rate at higher nitrogen levels at the end of waterlogging and during the later growth stages aid in carbohydrate production (Tian et al., 2021 ). The enhanced accumulation of shoot biomass was useful to root growth (Ren et al., 2016 ). Alternatively, supplemental nitrogen could boost the net photosynthetic rate by enhancing the synthesis of photosynthetic enzymes, inhibiting abscisic acid production, and promoting gibberellic and cytokinin synthesis under soil deficit condition (Ma et al., 2008 ). Furthermore, compared with the zero nitrogen (N1) treatment, all the nitrogen fertilization treatments promoted root growth of waterlogged maize at VT, R2, and R6 stages (Table 4 ). Table S1 Basic physicochemical properties for test soil in the 0–40 cm soil layer Total N (g kg − 1 ) Total P (g kg − 1 ) Available N(mg kg − 1 ) Olsen-P (mg kg − 1 ) Exchangeable K (mg kg − 1 ) pH Field capacity (cm 3 cm − 3 ) Soil bulk density (g cm − 3 ) 0.91 0.35 29.5 19.5 85.1 6.8 0.36 1.54 Table S2 Precipitation, sunshine hours, and mean temperature during the growing season of maize in 2018 and 2019 at the experimental site. April May June July August Precipitation (mm) 2018 86 101 120 141 157 2019 91 93 117 126 140 Sunshine duration (h) 2018 74 87 98 188 245 2019 87 91 104 191 287 Average temperature (℃) 2018 21.2 22.9 26.7 28.9 29.1 2019 21.7 23.4 27.2 31.2 29.7 Table S3 Soil available nitrogen (NH 4 + -N + NO 3 – -N) content (mg kg − 1 ) in the 0-100 cm soil depth at the filling stage (R2) as affected by different nitrogen application rates and waterlogging regimes Treatment Soil depth (cm) 0–20 20–40 40–60 60–80 80–100 W1N1 21.3g 18.7f 12.5e 8.9d 7.1c W1N2 84.0c 72.2c 50.2b 32.4b 29.1a W1N3 89.5c 77.5c 55.3b 33.6b 30.2a W1N4 106.8b 94.3a 73.2a 40.6a 33.5a W1N5 121.2a 105.1a 75.2a 41.6a 34.1a W2N1 11.5h 9.5g 7.8f 4.6e 3.8d W2N2 42.4f 34.1e 20.8d 10.2d 9.4c W2N3 53.3e 42.2e 22.6d 12.6d 11.2c W2N4 64.5d 55.5d 38.1c 24.3c 18.5b W2N5 78.6c 67.2c 46.1b 25.8c 22.1b Note: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha − 1 , respectively. Values are mean of 2 years and three replicates. Means followed by different letters within each soil depth are significantly different at the probability level of 0.05. Table 4 Correlation coefficients of root characteristics at the tasseling, filling and maturity stages, grain yield and nitrogen use efficiency (NUE) of maize Root parameter Correlation coefficients between grain yields Correlation coefficients between NUE VT R2 R6 VT R2 R6 Root length 0.762* 0.814** 0.721* 0.748* 0.801** 0.711* Root surface area 0.712* 0.745* 0.638* 0.698* 0.725* 0.631* Root weight 0.724* 0.804** 0.713* 0.701* 0.798* 0.697* Root volume 0.698* 0.716* 0.572 0.654* 0.701* 0.505 Root oxidation activity 0.819* 0.889** 0.798* 0.802** 0.868** 0.779* Z + ZR in roots 0.827** 0.901** 0.758* 0.811** 0.878** 0.734* IAA in roots 0.834** 0.911** 0.784* 0.812** 0.889** 0.757* *and ** indicate significant difference at the 0.05 and 0.01 levels, respectively Apart from the root morphology, the spatial layout of the root system within the soil profile significantly influenced the absorption of soil water and nutrients, thereby impacting crop productivity and resource-use efficiency (Xu et al. 2021 ). The architecture and distribution pattern of the root system can exhibit considerable plasticity and may be regulated by changes in soil water, nutrients, and numerous other factors (Jing and Shi 2025 ). In the present study, W2 elevated the proportion of root length within the surface soil layer (0–20 cm) could be related to the formation of adventitious roots caused by waterlogging (Qiu et al., 2025 ). The interaction among these strategies—quiescence securing survival during flooding, escape offering temporary relief, and compensatory aiding recovery—discloses a hierarchical trade-off in adaptation (Zhang et al., 2021 ). Alternatively, maize focused on hormonal regulation via ZmEREB180, increasing the mRNA levels of genes related to endogenous hormones, thus triggering adventitious root development through auxin and ethylene signaling to aid in the formation of escape structures (Reynoso et al., 2019 ). Moreover, the root system of maize is mainly concentrated in the topsoil layer (0–40 cm), indicating that appropriate soil water and nitrogen availability in the upper layer rather than the deep layer (60–100 cm) contributed to maintaining an extensive root system (Qi and Hu 2022 ). Therefore, it is of great importance to balance root growth and distribution through adjusting water and nitrogen supply for enhancing resource use efficiency and crop yield (Xu et al. 2018 ). Notably, when compared with other nitrogen treatments, under waterlogging conditions, only the N5 treatment resulted in the highest RLD within the 0–40 cm soil depth, suggesting that a high nitrogen application rate predominantly facilitated root recovery growth in the topsoil stratum. The root-shoot ratio acts as a sign of biomass distribution between aboveground and belowground parts of plants, showing the redundancy and functional condition of root growth (Wang et al., 2020 ). Therefore, harmonizing root and shoot development is crucial for crop output and resource utilization. A high level of water and nitrogen fertilizer supply led to a reduced root-to-shoot ratio in wheat (Wang et al. 2014 ). In the current study, waterlogging led to a reduction in the relative root-to-shoot ratio (Fig. 2 ), suggesting that waterlogging inhibit root growth to a greater extent than shoot growth. Soil oxygen deficiency can directly restrict plant growth and final yield by changing root metabolism (Ghobadi et al., 2017 ). On the other hand, the suppression of root recovery growth caused by insufficient oxygen is a primary limiting factor for plant growth after waterlogging (Manghwar et al., 2024 ). Moreover, increasing nitrogen application rate boosted recovery growth of shoot more than its of root after waterlogging, as indicated by the reduced relative root-to-shoot ratios for the W2N5 treatment (Fig. 2 ). Roots serve as the primary storage for assimilates and require twice the photosynthesis to produce dry matter compared to shoots (Passioura 1983 ). This indicates that crops with a lower root-to-shoot ratio can direct more carbohydrates to shoots (Xu et al. 2018 ; Qi and Hu 2022 ), enhancing shoot growth and nitrogen use efficiency. In line with this reasoning, the W2N5 achieved a relatively high grain yield (Fig. 6 ). However, the W2N1 treatment, despite had a low relative root-to-shoot ratio, exhibited the smallest grain yield. Given that the combined stress of waterlogging and nitrogen deficiency significantly diminished shoot biomass accumulation and its distribution to grain components, along with the SPAD value, the net photosynthetic rate, and the leaf area index, it also accelerated leaf senescence (Tian et al., 2021 ; Qi and Pan, 2022 ). Root dry weight, volume, length, surface area, ROA, Z + ZR, and IAA contents showed a significant and positive correlation with rice yield and NUE (Xu et al. 2018 ; Chu et al., 2021 ). Similarly, our research discovered that root morphological and physiological parameters at the VT, R2, and R6 stages are closely associated with maize yield and NUE (Table 4 ). This connection might be associated with the boosted root development during the middle and late growth phases, which enhances the leaf size (Qi et al., 2020a ), aiding in prolonged photosynthesis (Jing et al., 2025). This established a firm groundwork for improvement of crop production (Fig. 6 ). At the same time, the improvement of root system showed an increased demand for nutrients and water to support shoot growth (Xu et al., 2018 ), enhancing the nitrogen nutrition status of rice plants (Qi et al., 2023 ). Moreover, the connection among grain yield, NUE, and the oxidation activity, Z + ZR levels, and IAA levels in roots were stronger than their connection with root morphological traits. This indicated that physiological factors of root are more closely related to grain yield and nitrogen utilization in maize plants. One limitation of this study is that the changes in soil redox and the processes of toxin accumulation during and after waterlogging were not determined. Moreover, root growth at the end of waterlogging was not observed timely. These confine the understanding mechanism underlying root recover growth in maize with varying nitrogen application rates after waterlogging, which merits a further study. Additionally, increasing the nitrogen application rate to mitigate stress damage would also increase the probability of nitrogen loss from agricultural land, thus leading to the waste of limited agricultural resources and ecological deterioration (Ju et al. 2009). Therefore, accurately quantifying the amount of nitrogen loss from maize fields via ammonia generation, denitrification, deep leaching, and surface runoff is essential for enhancing the NUE of crops under different nitrogen application rates and waterlogging conditions. Besides, in the future, the underlying mechanisms by which nitrogen fertilization contributes to a relatively high grain yield of waterlogged maize should be investigated from the perspective of soil microbial community structure. Conclusion At the early (sixth leaf) stage, 6 days of waterlogging limited the roots' length, dry weight, surface area, volume, oxidation activity, zeatin + zeatin riboside and indole-3 -acetic acid contents of maize, suggesting that it is infeasible for the roots to fully recover their growth when subjected to waterlogging at the early stage. The inhibited root growth was responsible for low grain yield and nitrogen use efficiency under waterlogging. Nevertheless, increasing the nitrogen fertilization rates could partially compensate for grain yield loss caused by early-stage waterlogging by boosting both root morphological and physiological traits. The enhanced root growth was associated with the increased soil nitrogen availability due to a high nitrogen rate under waterlogged conditions. Therefore, we concluded that appropriate increases in the nitrogen application rate (up to 360 kg N ha − 1 ) could stimulate root recover growth, resulting in high grain yield in maize after early-stage waterlogging. The results also reveal the physiological mechanisms underlying the responses of grain yield and nitrogen use efficiency to nitrogen application rates from the perspective of root recovery growth under excessive soil water conditions. Declarations Acknowledgement We are grateful to Scientific Research Foundation of Zhejiang University of Water Resources and Electric Power (Grant No. JBGS2025005) and Open-ended Found of Agricultural Environmental Science Observation Experiment Stations of Shangqiu, CAAS (FIRI2018-07-01). References Bashar KK (2018) Hormone dependent survival mechanisms of plants during postwaterlogging stress. Plant Signal Behav 13:e1529522. https://doi.org/10.1080/15592324.2018.1529522 Bollmark M, Kubat B, Eliasson L (1988) Variations in endogenous cytokinin content during adventitious root formation in pea cuttings. J Plant Physiol 132:262–265. 10.1007/s00344-008-9048-5 Ahmed F, Rafii MY, Ismail MR, Ismail MR, Juraimi AS, Rahim HA et al (2013) Waterlogging tolerance of crops: breeding, mechanism of tolerance, molecular approaches, and future prospects. 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Am J Plant Sci 3:721–730. 10.4236/ajps.2012.36087 Supplementary Files TableS.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Major revisions 26 Feb, 2026 Reviewers agreed at journal 04 Feb, 2026 Reviewers invited by journal 03 Feb, 2026 Editor invited by journal 01 Feb, 2026 Editor assigned by journal 01 Feb, 2026 First submitted to journal 26 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8598554","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":585077416,"identity":"123d7974-1a19-4a96-9852-e7023d53065f","order_by":0,"name":"Yonggang Duan","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yonggang","middleName":"","lastName":"Duan","suffix":""},{"id":585077417,"identity":"43105afe-c1b0-4ed0-bcd5-950a7111b432","order_by":1,"name":"Weihan Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Weihan","middleName":"","lastName":"Wang","suffix":""},{"id":585077418,"identity":"3e78e65f-844d-4014-b586-52e99c260e9f","order_by":2,"name":"Dongliang Qi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0UlEQVRIiWNgGAWjYFCC5IYDHyr+y/GzNzY++ECclsTGgzPOMBtL9hxuNpxBpJbmw7xtzIkbbqS3SXMQo4HveGLDYZ4zbIkbbj5skGZgsJPTbSCgRfLMw4aDcyp4jGfeTmwwLmBINjY7QECLwY3EhgNvzkjI9gG1JM9gOJC4jSgtvG0GjA03DwJdSKyWg7xtCYoTbjA2NhOlBeyXGWcOAAM5sZlxhgERfuE7nnz4w4eKA8CoPP78x4cKOzmCWhhQFRgQUo6pZRSMglEwCkYBFgAAq89VHKDIIGIAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-3851-6304","institution":"Yangtze University","correspondingAuthor":true,"prefix":"","firstName":"Dongliang","middleName":"","lastName":"Qi","suffix":""}],"badges":[],"createdAt":"2026-01-14 07:13:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8598554/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8598554/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101945169,"identity":"2a9fe883-cfce-475e-b066-617b0b674617","added_by":"auto","created_at":"2026-02-05 09:56:25","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":188858,"visible":true,"origin":"","legend":"\u003cp\u003eRoot length density at the filling (R2) stage across 0-100\u0026nbsp;cm soil depth (%) in maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e\n\u003cp\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e−1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Vertical bars represent ± standard error of the mean (n = 6). Means followed by different letters within each soil depth are significantly different at the probability level of 0.05.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/cbc60f4e56b48beaccbd7874.jpg"},{"id":101945139,"identity":"1317efa1-1ffd-419c-9b75-5e6810872705","added_by":"auto","created_at":"2026-02-05 09:55:44","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":165436,"visible":true,"origin":"","legend":"\u003cp\u003eRoot to shoot ratio at the tasseling (VT), filling (R2) and maturity (R6) stages in maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e\n\u003cp\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e−1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Vertical bars represent ± standard error of the mean (n = 6). Means followed by different letters within each growth stage are significantly different at the probability level of 0.05.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/f97aa568307f60b657583bda.jpg"},{"id":101946535,"identity":"5b434cd4-fb23-4a7e-a305-d0f914b7e33c","added_by":"auto","created_at":"2026-02-05 10:01:49","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":153540,"visible":true,"origin":"","legend":"\u003cp\u003eRoot oxidation activity at the tasseling (VT), filling (R2) and maturity (R6) stages in maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e\n\u003cp\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e−1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Vertical bars represent ± standard error of the mean (n = 6). Means followed by different letters within each growth stage are significantly different at the probability level of 0.05.\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/6074146d37cb918c091759cf.jpg"},{"id":101945217,"identity":"520e5e26-7f31-434d-8ec9-fbb2ce08c84c","added_by":"auto","created_at":"2026-02-05 09:56:34","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":142869,"visible":true,"origin":"","legend":"\u003cp\u003eZeatin (Z) + zeatin riboside (ZR) content of roots at the tasseling (VT), filling (R2) and maturity (R6) stages in maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e\n\u003cp\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e−1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Vertical bars represent ± standard error of the mean (n = 6). Means followed by different letters within each growth stage are significantly different at the probability level of 0.05\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/9ecf581b38d1ee5069f2587b.jpg"},{"id":101945717,"identity":"68f92834-cf53-4863-8988-6e193df02747","added_by":"auto","created_at":"2026-02-05 09:58:19","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":140845,"visible":true,"origin":"","legend":"\u003cp\u003eIndole-3-acetic acid(IAA) content of roots at the tasseling (VT), filling (R2) and maturity (R6) stages in maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e\n\u003cp\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e−1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Vertical bars represent ± standard error of the mean (n = 6). Means followed by different letters within each growth stage are significantly different at the probability level of 0.05.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/c6b191eab0ef77ef322643c2.jpg"},{"id":101945133,"identity":"8959fbf3-e47f-4d37-bbbe-24090779bcc1","added_by":"auto","created_at":"2026-02-05 09:55:38","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":157902,"visible":true,"origin":"","legend":"\u003cp\u003eGrain yield and nitrogen use efficiency (NUE) of maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e\n\u003cp\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e−1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Vertical bars represent ± standard error of the mean (n = 6). Means followed by different letters are significantly different at the probability level of 0.05.\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/23ead48dacbcd213049fc84e.jpg"},{"id":101947285,"identity":"ab69bc66-6bcb-405b-ba0e-31c1e363d9bb","added_by":"auto","created_at":"2026-02-05 10:04:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1952199,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/8af2d11a-7135-4352-9254-8208597edca7.pdf"},{"id":101945899,"identity":"f5425374-a8ef-40c7-9c46-2aff4d99ea32","added_by":"auto","created_at":"2026-02-05 09:59:17","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":18540,"visible":true,"origin":"","legend":"","description":"","filename":"TableS.docx","url":"https://assets-eu.researchsquare.com/files/rs-8598554/v1/0445a8cfa499702312a55dab.docx"}],"financialInterests":"","formattedTitle":"Effects of nitrogen application rates on root recover growth of maize after waterlogging","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWaterlogging or flooding commonly occurs in regions characterized by substantial precipitation, excessive irrigation, and notable fluctuations in the elevated groundwater level (Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e). It is reckoned that roughly 16% of global cropped areas are affected by waterlogging stress (Shabala \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), resulting in 15%-80% reductions of crop yields (Prasanna and Rao \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Owing to global climate change, the severity and incidence of waterlogging are projected to rise, especially in mid- and high-latitude regions (Herzog et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). For instance, the Huang-Huai-Hai Plain and the Jianghan Plain in the People's Republic of China are affected (Ren et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Qi and Pan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWhen waterlogging takes place, the gas exchange between the soil and the atmosphere decreases. In this circumstance, the soil become hypoxic (low-oxygen) or anoxic (oxygen-free) within one day (Araki et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2012a\u003c/span\u003e; Ghobadi et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Waterlogging enhanced anaerobic respiration, consequently leading to the accumulation of toxins in the rhizosphere, such as hydrogen sulfide (H\u003csub\u003e2\u003c/sub\u003eS) and ferrous sulfide (FeS)(Ashraf and Rehman \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). This toxic environment resulted in the degradation of the rhizosphere environment, causing a reduction in the absorption of mineral ions and beneficial trace elements, inhibiting the growth and development of the root system (Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Waterlogging also induced the generation of reactive oxygen species (ROS) and free radicals, and expedited leaf senescence, and consequently a significant drop in grain yield (Araki et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2012b\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Moreover, the lower levels or free of soil oxygen supply inhibited both carbon and nitrogen metabolism in plants (Ren et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition, waterlogging elevated denitrification and leaching of nitrogen from crop field, lowering the soil nitrogen availability (Limami et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Kaur et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious studies have demonstrated that a high nitrogen application rate contributes to improve the activities of superoxide dismutase, peroxidase, and catalase, net photosynthetic rate, allocation proportion of shoot biomass to grain parts, and nitrogen accumulation (Tian et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Qi and Pan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Consequently, enough nitrogen fertilization helped to stabilize grain yield of maize following six days of waterlogging at the V6 stage. However, it was observed that a high nitrogen treatment decreased biomass and nitrogen accumulation and the redistribution to the grain of waterlogged wheat, and thus inducing more grain yield losses (Jiang et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Furthermore, appropriate nitrogen application (240 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) demonstrated potential in augmenting the activity of antioxidant enzymes and mitigating lipid peroxidation, thereby reducing the yield loss of waterlogged cotton (Guo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Conversely, an excessive nitrogen application rate (480 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) presenting an opposite trend. Therefore, the application rate of nitrogen fertilizer requires meticulous consideration to mitigate stress-induced damage and facilitate the recovery of crop growth following the alleviation of waterlogging stress.\u003c/p\u003e \u003cp\u003ePlant roots, as a vital constituent of the plant life system, not only execute essential functions such as the uptake of nutrients and water and the anchorage of shoots. Additionally, they can synthesize hormones and amino acids and interact with soil microorganisms, thereby playing an indispensable role in yield formation and resource utilization (Li et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Jing and Shi \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The growth and development of shoots rely heavily on root systems (Qi et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The capacity of a plant to assimilate nutrients and uptake water is dictated by the morphology and physiology of the root system within the soil profile (Qi and Hu \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Root morphology is predominantly characterized by crucial indicators including root dry weight, volume, length, and surface area (Xu et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, the physiological activity of roots can be evaluated through parameters including oxidation activity, the content of zeatin (Z) combined with zeatin riboside (ZR), and the content of indole-3-acetic acid (IAA) (Yang et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Qi et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). As the primary organ directly affected by waterlogging, maintaining root function or improve its recovery growth is crucial for plant adaptation to this stress.(Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Gao et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). It has been shown that nitrogen fertilization improve the dry weight, length, quantity, oxidation activity, and Z\u0026thinsp;+\u0026thinsp;ZR content of rice roots under normal water supply condition (Liu et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Nevertheless, there is relatively limited evidence concerning the impacts of nitrogen application rates on the recovery growth of roots after waterlogging, as well as their correlations with crop yield and nitrogen use efficiency (NUE).\u003c/p\u003e \u003cp\u003eIn the Jianghan Plain, the majority of precipitation occurs during the growth season of spring maize, generally ranging from the sixth leaf (V6) stage to maturity (Qi and Hu, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this area, the growth and yield of spring maize are significantly affected by excessive precipitation. Furthermore, the early growth stages of maize, such as the V6 stage, are vulnerable to waterlogging-induced damage (Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003eb\u003c/span\u003e). Understanding the effects of nitrogen application rates on root recovery growth after waterlooging is of great significance for stabilizing maize productivity under global climate change. Therefore, the present study aimed to investigate (1) the characteristics of root growth and activity under well-watered conditions and waterlogging scenarios with different nitrogen application rates, and (2) the correlations between root characteristics and grain yield in maize. It was hypothesized that increasing nitrogen application rates could provide suitable soil nutrient conditions to improve the root morphology and physiology of waterlogged maize plants, thereby achieving high grain yield and NUE. The results emphasize the importance of a balanced nitrogen management strategy in the adverse effects of waterlogging on maize through the regulation of root recovery growth.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eExperimental site\u003c/p\u003e \u003cp\u003eA two-year field experiment (2018\u0026ndash;2019) was carried out at the agricultural test station in Jingzhou City, central China (30\u0026deg; 21\u0026prime;N, 112\u0026deg; 31\u0026prime;E, 30 m above sea level). This region is characterized by a typical subtropical monsoon climate, with an average annual precipitation of approximately 1,095 mm. The region experiences a mean annual sunshine duration exceeding 1,718 hours and an average annual temperature of 16.5℃. In accordance with the criteria of the Food and Agriculture Organization (FAO), the soil at the experimental site is classified as calcareous alluvial soil. The fundamental physicochemical properties of the experimental soil are elaborated in Table S1. The mean air temperature, precipitation, and sunshine hours during the maize growing season are presented in Table S2.\u003c/p\u003e \u003cp\u003eExperimental design\u003c/p\u003e \u003cp\u003eA split-plot experimental design was devised, where the water regime was designated as the main plots and the nitrogen rate as the sub-plots. Each treatment (sub-plot) was replicated thrice. The area of each plot was 16 m\u003csup\u003e2\u003c/sup\u003e (4 m\u0026times; 4 m). Polyvinyl chloride (PVC) boards (4 m \u0026times; 2.3 m) were installed around the plots, with 2.0 m inserted below the soil surface and 0.4 m remaining above the ground to impede water movement.\u003c/p\u003e \u003cp\u003eThe water regimes included well-watered (W1), characterized by a relative soil mass water content of 70\u0026ndash;85% of the field capacity (Fc), which was a rational control during the maize growing season, and W2, where a 2\u0026ndash;3 cm water layer was maintained for 6 days above the soil surface at the V6 stage (Qi and Pan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In 2018, W2 commenced 41 days after the crop was planted (DAP), and in 2019, it started 42 DAP. At the conclusion of the waterlogging period, the surface water in the W2 plots was removed via a siphon, and the soil moisture content was gradually reduced to that of the control (the soil moisture content of W1) over a period of 5\u0026ndash;7 days.\u003c/p\u003e \u003cp\u003eThe nitrogen application rates were 0 (N1), 90 (N2), 180 (N3), 270 (N4), and 360 (N5) kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which were applied to each water regime. The nitrogen fertilizer (urea, N 46%) was split into a basal application (one day before sowing, 40%) on 31 March 2018 and 3 April 2019, and a top-dressing fertilization at the twelfth leaf growth stage (V12, 60%) on 25 June 2018 and 28 June 2019.\u003c/p\u003e \u003cp\u003eField management\u003c/p\u003e \u003cp\u003eTian et al. (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) presented a comprehensive account of the crop management strategies. Briefly, ditches were established for each sub-plot to eliminate excess water resulting from heavy rainfall during the crop growth season (excluding the V6 stage of maize under the waterlogging treatment). Water was pumped onto the W2 plots 4\u0026ndash;6 times per day to maintain a 2\u0026ndash;3 cm layer of free water on the field surface throughout the waterlogging period. Due to a substantial amount of precipitation in the two experimental years (Table S2), no irrigation water was provided to the maize (excluding waterlogging conditions). Prior to sowing, calcium superphosphate and potash muriate were applied at rates of 329 kg ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e 17%) and 300 kg ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (K\u003csub\u003e2\u003c/sub\u003eO 60%), respectively. Maize (cultivar Yidan No.629) was sow at a density of 73,000 plants ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e on 1 April 2018 and 4 April 2019, and the crops were harvested on 9 August 2018 and 11 August 2019.\u003c/p\u003e \u003cp\u003eData collection\u003c/p\u003e \u003cp\u003eRoot characteristics\u003c/p\u003e \u003cp\u003eIn 2018 and 2019, at the tasseling (VT), filling (R2), and maturity (R6) stages, corresponding to 92 and 91, 109 and 110, and 125 and 126 days after planting (DAP), respectively, tests were conducted on the length, number, dry weight, surface area, oxidation activity, Z\u0026thinsp;+\u0026thinsp;ZR content, and IAA content of the roots. A hand-driven auger with a diameter of 10 cm and a length of 1.25 m was used for root sampling. The samples were collected from soil depths of 0\u0026ndash;20, 20\u0026ndash;40, 40\u0026ndash;60, 60\u0026ndash;80, and 80\u0026ndash;100 cm beneath the plant. A portion of each root sample was employed to determine the morphological and physiological parameters of the roots. To measure the length, quantity, and surface area, the roots were floated in shallow water within a 30 \u0026times; 30 cm glass tray and scanned (Epson Expression 1680 Scanner, Seiko Epson Corp., Tokyo, Japan). The WinRHIZO Root Analyzer System (Regent Instruments Inc, Quebec, Canada) was utilized to quantify the corresponding parameters. Subsequently, the roots were dried in an oven at 75\u0026deg;C until a constant weight was achieved, and their dry weight was measured. The oxidation activity of (fresh) roots was determined in accordance with the method described by Ramasamy et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Z, ZR, and IAA were extracted from (fresh) roots and then purified using the methods provided by Bollmark et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The concentrations of these compounds were determined as described by Xu et al. (\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNitrogen uptake and grain yield\u003c/p\u003e \u003cp\u003eThe semimicro Kjeldahl method (AOAC, 1984) was utilized to analyze nitrogen concentrations in mature plants. The shoot nitrogen uptake was computed by calculating the products of biomass and tissue nitrogen contents. To determine grain yield (adjusted to 14.5% moisture), a 6.0 m\u003csup\u003e2\u003c/sup\u003e area at the center of each plot was harvested. As per Ju et al. (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), the NUE is computed as the ratio of grain yield to the total shoot nitrogen uptake. The relative root-to-shoot ratio was computed as the ratio of the total root biomass within the 0-100 cm soil depth (the sum of root biomass at the 0\u0026ndash;20 cm, 20\u0026ndash;40 cm, 40\u0026ndash;60 cm, 60\u0026ndash;80 cm, and 80\u0026ndash;100 cm soil layers) to the shoot biomass.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll the collected data were individually analyzed via a randomized complete block design (RCBD) method using the PROC GLM procedure in SAS for variance assessment. The means were compared by Duncan\u0026rsquo;s multiple range test at a significance level of \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Although most of the measured root morphological and physiological parameters exhibited variability over the years, no year \u0026times; waterlogging regime or year \u0026times; N interactions were detected (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Therefore, we pooled the data from the two different years.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAnalysis of variance of root length, root surface area (RSA), root weight (RW), root volume (RV), root length density (RLD), root oxidation activity (ROA), root zeatin (Z) + zeatin riboside (ZR) content, and indole-3-acetic acid (IAA) content under condition of waterlogging regimes and nitrogen management strategies interaction.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource of\u003c/p\u003e \u003cp\u003evariation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDegree of\u003c/p\u003e \u003cp\u003efreedom\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRoot length (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRSA(cm \u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRW(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRV(cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRLD (m\u003csup\u003e3\u003c/sup\u003e m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eROA (\u0026micro;gα-NA h\u003csup\u003e\u0026minus;1\u003c/sup\u003eg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e )\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eZ\u0026thinsp;+\u0026thinsp;ZR content (nmol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e DW)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eIAA content (nmol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e DW)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eY\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eY\u0026sdot;W\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eY\u0026sdot;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW\u0026sdot;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eY\u0026sdot;W\u0026sdot;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"10\"\u003eNote: NS indicates statistical significance at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05 within a column. * and** represents statistical significance at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 and \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01 respectively. Y, D and N represents year, drainage regime and nitrogen rate, respectively.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eRoot morphology traits\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eWithin the 0-100 cm soil depth, root morphological characteristics, including length, surface area, biomass, and volume, attained their maxima during the R2 and VT stages under W1 and W2 conditions, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In plants treated with W1, the root morphological parameters at the VT, R2, and R6 stages exhibited an increase ranging from 12.5% to 48.7% as the nitrogen application rates increased up to N4, followed by a subsequent decline under N5. However, these parameters demonstrated an increase spanning from 6.7% to 67.9% with the elevation of nitrogen application rates (up to N5). In most instances, there were statistically significant disparities among different nitrogen rates for plants treated with W1. Additionally, in comparison to W1, W2 notably diminished the total length, surface area, weight, and volume of the roots (decreased by 14.6%-69.0%) at each nitrogen rate (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The W1N4 treatment resulted in the maximum root length, while the W2N1 treatment led to the minimum root length at the three growth stages (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Furthermore, the total root length at the R6 stage was comparable between the W1N4 and W1N5 treatments. Root surface area, root weight, and root volume at the VT, R1, and R6 stages among different treatments, which exhibited a highly similar variation pattern to that of root length (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These suggest that a high nitrogen rate (as in N5) help to improve root growth morphology at the the middle and later growth stage of maize under waterlogging at the V6 stage.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTotal root length, root surface area, root weight (RW), and root volume (RV) in the 0-100 cm soil profile at the tasseling (VT), Filling (R1), and maturity (R6) stages of maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eRoot length (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eRoot surface area (cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e \u003cp\u003eRoot weight (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c13\" namest=\"c11\"\u003e \u003cp\u003eRoot volume (cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eR6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eVT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eR6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eVT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eR6\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5381c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5413d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2871c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e997c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1109c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e411c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e7.6c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e8.2c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e4.9c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e 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\u003cp\u003e10.7b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e11.8b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.6b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e41.4b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e42.4b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e32.8b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6425b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6712b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3564b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1498b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1599b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e715b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e11.6b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e12.6b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.1b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e42.8b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e44.1b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e34.1b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6938a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7325a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4125a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1729a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1899a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e921a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e13.8a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14.5a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e10.3a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e49.1a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e54.3a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e39.3a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6432b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6813b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3095a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1501b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1664b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e887a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e13.1a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14.1a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e10.1a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e47.1b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e51.5a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e38.1a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3587g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3313h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1211g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e387f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e369f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e87f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.1e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.6f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.3g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e19.3g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e15.8h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e10.1h\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4013f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3821g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1698f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e598e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e551e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e198e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5.5d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5.1e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e2.6f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e26.1f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e22.7g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e14.6g\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4658e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4305f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1798f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e654e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e621e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e245e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6.1d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5.3e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e3.1e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e28.3e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e26.4f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e16.2f\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5010d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4731e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2102e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e827d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e801d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e336d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e7.2c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.4d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e4.0d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e32.2d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e30.2e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e18.7e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5489c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5234d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2487d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1010c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e945c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e454c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e8.1c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e7.7c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.1c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e36.1c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e33.1d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e22.1d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"13\"\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Means followed by different letters within each column are significantly different at the probability level of 0.05.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eRoot vertical distribution\u003c/p\u003e \u003cp\u003eThis study measured the RLD at the R2 stage to evaluate the vertical distribution of roots, as this stage is crucial for determining yield formation (Wang et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In all treatments, the RLD declined with increasing soil depth (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The root system was predominantly concentrated in the topsoil. Specifically, the root length within the 0\u0026ndash;40 cm soil layer constituted 60.9% \u0026minus;\u0026thinsp;66.1% of the total root system within the 0-100 cm depth (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The waterlogging conditions and nitrogen application rates in this study had an impact on the maize root distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).. Compared to W1, W2 led to a significant reduction in RLD ranging from 19.4% to 46.7% across the 0-100 cm soil depth. The W1N4 treatment generated the greatest RLD across the 0-100 cm soil depth while the W2N1 treatment led to the smallest RLD. Within the 0\u0026ndash;60 cm soil depth, the root length density of plants treated with W1 demonstrated an increment with the augmentation of nitrogen application rates up to the N4 level, followed by a decline under the N5 treatment. In the 0\u0026ndash;40 cm soil depth, the RLD of plants treated with W2 showed an increase as the N application rates increased up to the N5 level. Within the 60\u0026ndash;100 cm soil depth, in comparison to the N1, the other nitrogen treatments led to a significant increase in RLD ranging from 23.4% to 55.1% under the two watering regimes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe percentage of total root length in each soil depth to the sum of 0-100 cm soil depth (%) in maize as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoil depth\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eW1N1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eW1N2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eW1N3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eW1N4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eW1N5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eW2N1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eW2N2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eW2N3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eW2N4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eW2N5\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u0026ndash;20 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e33.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e32.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e34.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e33.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e36.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e36.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e36.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e37.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e38.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20\u0026ndash;40 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e32.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e31.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e24.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e24.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e24.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e26.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e26.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e40\u0026ndash;60 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e12.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e16.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e16.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e16.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e14.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e14.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e14.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e60\u0026ndash;80 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e13.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e13.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e11.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e11.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e80\u0026ndash;100 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e11.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e11.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e10.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"11\"\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFurthermore, under a specific nitrogen application rate (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), W2 rather than the W1, increased the proportion of root length in the surface soil layer (0\u0026ndash;20 cm) and the deep soil layer (60\u0026ndash;100 cm). Conversely, W2 decreased the proportion of root length at a soil depth of 40\u0026ndash;60 cm. Under W1, N1 resulted in the highest proportion of root length in the deep soil layer, whereas N4 led to the lowest proportion. Under W2, in comparison with other N treatments, N4 and N5 enhanced the proportion of root length at a soil depth of 0\u0026ndash;40 cm and reduced the proportion of root length in the deep soil layer. This indicates that high nitrogen application rates (N4 and N5) primarily promoted the root growth recovery in the 0\u0026ndash;40 cm soil depth after waterlogging at the V6 stage.\u003c/p\u003e \u003cp\u003eRelative root-to-shoot ratio\u003c/p\u003e \u003cp\u003eIn maize, the root-to-shoot ratio gradually decreased during growth and was at its lowest at the R6 stage (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Irrespective of the nitrogen application rate, compared with W1, W2 significantly decreased the root-to-shoot ratio (by 14.5%-31.8%) at the VT, R2, and R6 stages. Moreover, under both W1 and W2 conditions, the root-to-shoot ratio declined by 8.7%-24.8% with the increase in nitrogen rates. The W1N1 treatment resulted in the highest root-to-shoot ratio at the three growth stages, whereas the W2N5 treatment led to the lowest root-to-shoot ratio (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This indicates that a high nitrogen application rate (as in N5) enhances the shoot growth of maize more significantly than its root growth under waterlogging at the V6 stage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRoot oxidation activity and Z\u0026thinsp;+\u0026thinsp;ZR and IAA Contents\u003c/p\u003e \u003cp\u003eAs maize plants grow and develop, their root oxidation activity gradually declines (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In contrast to W1, W2 notably decreased the root oxidation activity varied nitrogen rates. In plants treated with W1, the root oxidation activity at the VT, R2, and R6 stages demonstrated an elevation as nitrogen levels increased up to N4, followed by a decline under N5. In contrast, during these stages, the activity presented an increase with the increment of nitrogen application rates (up to N5) in W2-treated plants.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe contents of Z\u0026thinsp;+\u0026thinsp;ZR and IAA in the roots reached their peak at the VT stage and then declined as maize plants grew and developed (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). At the three growth stages, the variations in Z\u0026thinsp;+\u0026thinsp;ZR and IAA contents among the different treatments showed a very similar variation compared to root oxidation activity (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). These suggest that a high nitrogen rate (as in N5) help to improve root growth physiology at the the middle and later growth stage of maize under waterlogging at the V6 stage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGrain yield and NUE\u003c/p\u003e \u003cp\u003eIn comparison with the W2, the grain yield and NUE in the W1 treatment were significantly higher by 19.7%-44.6%, regardless of the nitrogen application rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Under W1, the grain yield increased from N1 to N4, and then decreased at N5. In contrast, under the W2 condition, the grain yield increased from N1 to N5. This indicates that a high nitrogen application rate, such as that in the N5, contributes to a greater enhancement of grain yield under waterlogging stress at the V6 stage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe NUE increased with the increase in nitrogen application up to N4 and then remained stable at N5 under both the W1 and W2 waterlogging conditions. The highest grain yield and NUE were obtained in the W1N4 treatment, while the lowest grain yield and NUE were observed in the W2N1 treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCorrelation of root characteristics with grain yield and NUE\u003c/p\u003e \u003cp\u003ePearson's correlation analysis revealed a significant or highly significant positive correlation between the length, dry weight, surface area, weight, volume, oxidation activity, and the contents of Z\u0026thinsp;+\u0026thinsp;ZR and IAA in roots at the VT and R2 stages and the grain yield (r\u0026thinsp;=\u0026thinsp;0.712*\u0026minus;0.911**). Additionally, a significant positive correlation was detected between the aforementioned root parameters at the VT and R2 stages and NUE (r\u0026thinsp;=\u0026thinsp;0.654*\u0026minus;0.889**). Moreover, the length, volume, surface area, weight, oxidation activity, and the contents of Z\u0026thinsp;+\u0026thinsp;ZR and IAA in roots at the R6 stage also exhibited a significant positive correlation with grain yield (r\u0026thinsp;=\u0026thinsp;0.638*\u0026minus;0.798*) and NUE (r\u0026thinsp;=\u0026thinsp;0.631*\u0026minus;0.779**).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eEarly-stage (V3 and V6) waterlogging exerted long-term negative effects on maize growth, as manifested by the continuous decline in shoot dry matter accumulation and its allocation to grains, premature leaf senescence, a decrease in the crop growth rate, the suppression of carbon and nitrogen metabolism, and a reduction in the net photosynthetic rate during the later growth stages (Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Hu et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Qi and Pan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this study, waterlogging resulted in a continuous decrease in root morphological (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and physiological (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) parameters. This is consistent with previous research on cotton (Guo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), winter wheat (Wu et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), winter rapeseed (Liu et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), and pea (Ploschuk et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). These findings imply that it is infeasible for the maize roots to fully recover their growth when subjected to waterlogging at the V6 stage. The causes can be elucidated as follows: Firstly, the exchange of oxygen between soil and roots was greatly impeded by soil waterlogging, as the diffusion rate of gases in water was 10,000 times less than that in air (Armstrong, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1979\u003c/span\u003e). Once hypoxia occurs in the rhizosphere soil, the soil redox potential (Eh) declines, and reductive metal ions, particularly accumulation of Fe\u003csup\u003e2+\u003c/sup\u003e, Mn\u003csup\u003e2+\u003c/sup\u003e, S\u003csup\u003e2\u0026minus;\u003c/sup\u003e, and HS\u003csup\u003e\u0026minus;\u003c/sup\u003e, exerting toxic impacts on crop roots (Visser and Voesenek \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Through anaerobic respiration, anaerobic microorganisms in the soil produced organic acids like acetic acid, lactic acid, and butyric acid, which in turn boosted soil acidity (Mohammad et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The microbial population in the rhizosphere undergoes succession, with aerobic microorganisms being supplanted by anaerobic ones. The substitution of substances resulted in more rapid bacterial reproduction compared to fungi and actinomycetes, inhibiting beneficial bacteria and deteriorating the growth environment of the root system (Manghwar et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Secondly, under waterlogging, the metabolic process of the roots transitions from an aerobic mode to an anaerobic mode. The efficiency of anaerobic respiration decreases, and the intermediate products, such as lactic acid, acetaldehyde, and ethanol, produced have toxic effects on the cells (Ahmed et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The generated ATP energy was decreased by 70% to 97%, weakening the root system's capacity to absorb and transport water, minerals, and nutrients (such as N, P, and K) upward, and consequently restrained shoot growth, nutrient utilization and yield formation (Qiu et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). This was evidenced by reduced grain yield and NUE under W2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). In turn, the inhibited photosynthate accumulation in shoot hinder root growth (Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Thirdly, waterlogging enhanced denitrification and nitrogen leaching, resulting in the low soil nitrogen availability (Table S3, Kaur et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Nitrogen deficiency inhibited root growth has been widely observed on maize, cotton, wheat, and rapeseed (Guo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Men et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Qi and Hu \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In support, under the W1 condition, the N4 resulted in larger root morphological and physiological parameters, while such an effect was not observed under the W2 condition (the N5 showed this effect).\u003c/p\u003e \u003cp\u003eWe noticed as well that applying nitrogen at a high rate (like in N5) boosted root growth and development after waterlogging. This corresponds with previous findings on nitrogen fertilization positive alleviated detrimental effects of waterlogging on shoot growth in maize (Kaur et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Tian et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Qi and Pan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), indicating that suitable increases in nitrogen fertilization could enhance root tolerance to waterlogging stress and promote it recovery growth. The possible explanations are as follows. Firstly, Plant hormones are known to play a crucial role in the post-waterlogging recovery process (Bashar, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), and their sophisticated regulation serves as a central driver coordinating the developmental changes of the waterlogging recovery phase, particularly lateral root initiation (Gao et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Nitrogen serves as a crucial element in plant hormones, therefore, the use of nitrogen facilitated the generation and functioning of Z\u0026thinsp;+\u0026thinsp;ZR and IAA (Guo et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). The enhanced hormones contents in roots (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) at high nitrogen rate helped to strengthen recovery growth after waterlogging (Zhang et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Secondly, higher nitrogen treatments compensated for nitrogen loss caused by denitrification and leaching due to waterlogging (Kaur et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), resulting in relatively high soil nitrogen availability (Table S3). Root growth was positively correlated with soil nitrogen contents under nitrogen deficit condition (Tian et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Qi et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The enhanced NUE (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) verified the improvement of root growth for the W2N5 treatment. Alternatively, it has been shown fertilizer nitrogen uptake by maize plant was positively correlated with RLD in the 0\u0026ndash;40 cm soil depth (Qi et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e). Moreover, the application of higher nitrogen fertilizer early could enhance the root vitality of waterlogged plants (Zhou and Oosterhuis, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In this situation, 40% of the nitrogen fertilizer was used for the basal application. Thirdly, nitrogen fertilization could induce the expression of antioxidant enzyme genes in waterlogged plants (Ozcubukcu et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), enhancing recovery growth of plants after abiotic stresses (Manghwar et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Lastly but not least, the increased leaf area index, \u003cem\u003eSPAD\u003c/em\u003e value, and net photosynthetic rate at higher nitrogen levels at the end of waterlogging and during the later growth stages aid in carbohydrate production (Tian et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The enhanced accumulation of shoot biomass was useful to root growth (Ren et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Alternatively, supplemental nitrogen could boost the net photosynthetic rate by enhancing the synthesis of photosynthetic enzymes, inhibiting abscisic acid production, and promoting gibberellic and cytokinin synthesis under soil deficit condition (Ma et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Furthermore, compared with the zero nitrogen (N1) treatment, all the nitrogen fertilization treatments promoted root growth of waterlogged maize at VT, R2, and R6 stages (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable S1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBasic physicochemical properties for test soil in the 0\u0026ndash;40 cm soil layer\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal N\u003c/p\u003e \u003cp\u003e(g kg\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal P\u003c/p\u003e \u003cp\u003e(g kg\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAvailable N(mg kg\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e )\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOlsen-P\u003c/p\u003e \u003cp\u003e(mg kg\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eExchangeable K (mg kg\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eField capacity\u003c/p\u003e \u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003ecm\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSoil bulk density\u003c/p\u003e \u003cp\u003e(g cm\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e85.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable S2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePrecipitation, sunshine hours, and mean temperature during the growing season of maize in 2018 and 2019 at the experimental site.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eApril\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMay\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eJune\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eJuly\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAugust\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003ePrecipitation (mm)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e101\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e141\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2019\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e117\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e126\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e140\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eSunshine duration (h)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e188\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e245\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2019\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e191\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e287\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eAverage temperature (℃)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e26.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e28.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2019\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable S3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSoil available nitrogen (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N\u0026thinsp;+\u0026thinsp;NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e-N) content (mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in the 0-100 cm soil depth at the filling stage (R2) as affected by different nitrogen application rates and waterlogging regimes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eSoil depth (cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026ndash;20\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u0026ndash;40\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e40\u0026ndash;60\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e60\u0026ndash;80\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e80\u0026ndash;100\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21.3g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.7f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.5e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.9d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.1c\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.0c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e72.2c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50.2b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e32.4b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.1a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e89.5c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e77.5c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e55.3b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e33.6b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e30.2a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e106.8b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e94.3a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e73.2a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40.6a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e33.5a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1N5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e121.2a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e105.1a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75.2a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e41.6a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e34.1a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.5h\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.5g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.8f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.6e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.8d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e42.4f\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34.1e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.8d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.2d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e9.4c\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53.3e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42.2e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22.6d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12.6d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e11.2c\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64.5d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55.5d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e38.1c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24.3c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e18.5b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2N5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e78.6c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67.2c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e46.1b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.8c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.1b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003eNote: W1 and W2 represents well-watered and waterlogging for six days at the sixth leaf stage, respectively; N1, N2, N3, N4 and N5 represents 0, 90, 180, 270 and 360 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Values are mean of 2 years and three replicates. Means followed by different letters within each soil depth are significantly different at the probability level of 0.05.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCorrelation coefficients of root characteristics at the tasseling, filling and maturity stages, grain yield and nitrogen use efficiency (NUE) of maize\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRoot parameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eCorrelation coefficients between grain yields\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eCorrelation coefficients between NUE\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eR6\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot length\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.762*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.814**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.721*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.748*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.801**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.711*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot surface area\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.712*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.745*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.638*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.698*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.725*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.631*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot weight\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.724*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.804**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.713*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.701*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.798*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.697*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot volume\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.698*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.716*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.572\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.654*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.701*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.505\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRoot oxidation activity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.819*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.889**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.798*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.802**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.868**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.779*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZ\u0026thinsp;+\u0026thinsp;ZR in roots\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.827**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.901**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.758*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.811**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.878**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.734*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIAA in roots\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.834**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.911**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.784*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.812**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.889**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.757*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e*and ** indicate significant difference at the 0.05 and 0.01 levels, respectively\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eApart from the root morphology, the spatial layout of the root system within the soil profile significantly influenced the absorption of soil water and nutrients, thereby impacting crop productivity and resource-use efficiency (Xu et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The architecture and distribution pattern of the root system can exhibit considerable plasticity and may be regulated by changes in soil water, nutrients, and numerous other factors (Jing and Shi \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In the present study, W2 elevated the proportion of root length within the surface soil layer (0\u0026ndash;20 cm) could be related to the formation of adventitious roots caused by waterlogging (Qiu et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The interaction among these strategies\u0026mdash;quiescence securing survival during flooding, escape offering temporary relief, and compensatory aiding recovery\u0026mdash;discloses a hierarchical trade-off in adaptation (Zhang et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Alternatively, maize focused on hormonal regulation via ZmEREB180, increasing the mRNA levels of genes related to endogenous hormones, thus triggering adventitious root development through auxin and ethylene signaling to aid in the formation of escape structures (Reynoso et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Moreover, the root system of maize is mainly concentrated in the topsoil layer (0\u0026ndash;40 cm), indicating that appropriate soil water and nitrogen availability in the upper layer rather than the deep layer (60\u0026ndash;100 cm) contributed to maintaining an extensive root system (Qi and Hu \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Therefore, it is of great importance to balance root growth and distribution through adjusting water and nitrogen supply for enhancing resource use efficiency and crop yield (Xu et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Notably, when compared with other nitrogen treatments, under waterlogging conditions, only the N5 treatment resulted in the highest RLD within the 0\u0026ndash;40 cm soil depth, suggesting that a high nitrogen application rate predominantly facilitated root recovery growth in the topsoil stratum.\u003c/p\u003e \u003cp\u003eThe root-shoot ratio acts as a sign of biomass distribution between aboveground and belowground parts of plants, showing the redundancy and functional condition of root growth (Wang et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, harmonizing root and shoot development is crucial for crop output and resource utilization. A high level of water and nitrogen fertilizer supply led to a reduced root-to-shoot ratio in wheat (Wang et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In the current study, waterlogging led to a reduction in the relative root-to-shoot ratio (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), suggesting that waterlogging inhibit root growth to a greater extent than shoot growth. Soil oxygen deficiency can directly restrict plant growth and final yield by changing root metabolism (Ghobadi et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). On the other hand, the suppression of root recovery growth caused by insufficient oxygen is a primary limiting factor for plant growth after waterlogging (Manghwar et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Moreover, increasing nitrogen application rate boosted recovery growth of shoot more than its of root after waterlogging, as indicated by the reduced relative root-to-shoot ratios for the W2N5 treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Roots serve as the primary storage for assimilates and require twice the photosynthesis to produce dry matter compared to shoots (Passioura \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1983\u003c/span\u003e). This indicates that crops with a lower root-to-shoot ratio can direct more carbohydrates to shoots (Xu et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Qi and Hu \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), enhancing shoot growth and nitrogen use efficiency. In line with this reasoning, the W2N5 achieved a relatively high grain yield (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). However, the W2N1 treatment, despite had a low relative root-to-shoot ratio, exhibited the smallest grain yield. Given that the combined stress of waterlogging and nitrogen deficiency significantly diminished shoot biomass accumulation and its distribution to grain components, along with the \u003cem\u003eSPAD\u003c/em\u003e value, the net photosynthetic rate, and the leaf area index, it also accelerated leaf senescence (Tian et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Qi and Pan, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRoot dry weight, volume, length, surface area, ROA, Z\u0026thinsp;+\u0026thinsp;ZR, and IAA contents showed a significant and positive correlation with rice yield and NUE (Xu et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Chu et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Similarly, our research discovered that root morphological and physiological parameters at the VT, R2, and R6 stages are closely associated with maize yield and NUE (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This connection might be associated with the boosted root development during the middle and late growth phases, which enhances the leaf size (Qi et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e), aiding in prolonged photosynthesis (Jing et al., 2025). This established a firm groundwork for improvement of crop production (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). At the same time, the improvement of root system showed an increased demand for nutrients and water to support shoot growth (Xu et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), enhancing the nitrogen nutrition status of rice plants (Qi et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, the connection among grain yield, NUE, and the oxidation activity, Z\u0026thinsp;+\u0026thinsp;ZR levels, and IAA levels in roots were stronger than their connection with root morphological traits. This indicated that physiological factors of root are more closely related to grain yield and nitrogen utilization in maize plants.\u003c/p\u003e \u003cp\u003eOne limitation of this study is that the changes in soil redox and the processes of toxin accumulation during and after waterlogging were not determined. Moreover, root growth at the end of waterlogging was not observed timely. These confine the understanding mechanism underlying root recover growth in maize with varying nitrogen application rates after waterlogging, which merits a further study. Additionally, increasing the nitrogen application rate to mitigate stress damage would also increase the probability of nitrogen loss from agricultural land, thus leading to the waste of limited agricultural resources and ecological deterioration (Ju et al. 2009). Therefore, accurately quantifying the amount of nitrogen loss from maize fields via ammonia generation, denitrification, deep leaching, and surface runoff is essential for enhancing the NUE of crops under different nitrogen application rates and waterlogging conditions. Besides, in the future, the underlying mechanisms by which nitrogen fertilization contributes to a relatively high grain yield of waterlogged maize should be investigated from the perspective of soil microbial community structure.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eAt the early (sixth leaf) stage, 6 days of waterlogging limited the roots' length, dry weight, surface area, volume, oxidation activity, zeatin\u0026thinsp;+\u0026thinsp;zeatin riboside and indole-3 -acetic acid contents of maize, suggesting that it is infeasible for the roots to fully recover their growth when subjected to waterlogging at the early stage. The inhibited root growth was responsible for low grain yield and nitrogen use efficiency under waterlogging. Nevertheless, increasing the nitrogen fertilization rates could partially compensate for grain yield loss caused by early-stage waterlogging by boosting both root morphological and physiological traits. The enhanced root growth was associated with the increased soil nitrogen availability due to a high nitrogen rate under waterlogged conditions. Therefore, we concluded that appropriate increases in the nitrogen application rate (up to 360 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) could stimulate root recover growth, resulting in high grain yield in maize after early-stage waterlogging. The results also reveal the physiological mechanisms underlying the responses of grain yield and nitrogen use efficiency to nitrogen application rates from the perspective of root recovery growth under excessive soil water conditions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgement\u003c/h2\u003e \u003cp\u003eWe are grateful to Scientific Research Foundation of Zhejiang University of Water Resources and Electric Power (Grant No. JBGS2025005) and Open-ended Found of Agricultural Environmental Science Observation Experiment Stations of Shangqiu, CAAS (FIRI2018-07-01).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBashar KK (2018) Hormone dependent survival mechanisms of plants during postwaterlogging stress. 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Am J Plant Sci 3:721\u0026ndash;730. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4236/ajps.2012.36087\u003c/span\u003e\u003cspan address=\"10.4236/ajps.2012.36087\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"plant-and-soil","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"plso","sideBox":"Learn more about [Plant and Soil](https://www.springer.com/journal/11104)","snPcode":"11104","submissionUrl":"https://submission.nature.com/new-submission/11104/3","title":"Plant and Soil","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Root length density, Root distribution, Economic yield, Nitrogen uptake, Zea mays","lastPublishedDoi":"10.21203/rs.3.rs-8598554/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8598554/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Aims The growth and development of the root system are of critical significance for crop yield and nutrient utilization. Nitrogen fertilization is frequently utilized to modulate and augment plants' tolerance to abiotic stresses. This study aimed to investigate the effects of nitrogen fertilization on the recovery growth of maize (Zea mays L.) roots and their correlations with grain yield and nitrogen use efficiency after waterlogging stress. \nMethods A two-year experiment was conducted to examine effects of nitrogen fertilizer application rates (0, 90, 180, 270, and 360 kg N ha-1, designated as N1, N2, N3, N4 and N5, respectively) on root morphological and physiological characteristics under well-watered (W1) conditions across the maize grown season and waterlogging for 6 days at the sixth leaf (V6) growth stage (W2). \nResults In comparison to W1, W2 significantly decreased length, dry weight, surface area, volume, oxidation activity, zeatin + zeatin riboside, and indole-3-acetic acid contents in roots at the tasselling, filling, and maturity stages regardless of nitrogen rates. Furthermore, these parameters increased with the increase in nitrogen rates (up to N5) under W2, indicating that a high nitrogen rate (such as N5) could enhance the root recovery growth of maize after early(V6)-stage waterlogging. Moreover, the N5 led to a more developed root system, contributing to the improved nitrogen use efficiency under the W2 condition.\nConclusion Collectively, a high nitrogen application rate (N5) promoted root recovery growth after waterlogging at the V6 stage, and thus obtained relatively high grain yield and nitrogen use efficiency in maize.","manuscriptTitle":"Effects of nitrogen application rates on root recover growth of maize after waterlogging","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-05 09:43:17","doi":"10.21203/rs.3.rs-8598554/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revisions","date":"2026-02-26T10:58:24+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2026-02-04T11:42:26+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-03T13:34:50+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Plant and Soil","date":"2026-02-01T10:06:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-01T09:34:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Plant and Soil","date":"2026-01-26T20:03:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"plant-and-soil","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"plso","sideBox":"Learn more about [Plant and Soil](https://www.springer.com/journal/11104)","snPcode":"11104","submissionUrl":"https://submission.nature.com/new-submission/11104/3","title":"Plant and Soil","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b2e5e6a7-3567-4e85-8438-3f526f6a01c6","owner":[],"postedDate":"February 5th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-25T11:22:27+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-05 09:43:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8598554","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8598554","identity":"rs-8598554","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}