Straw retention combined with phosphorus application improved soil properties, root nitrogen metabolism and optimized the relationship between root and shoot of cotton

Straw retention combined with phosphorus application improved soil properties, root nitrogen metabolism and optimized the relationship between root and shoot of cotton | 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 Straw retention combined with phosphorus application improved soil properties, root nitrogen metabolism and optimized the relationship between root and shoot of cotton Qin Wang, Jiawei Wang, Xiaolin Huang, Wen Jin, Zhitao Liu, Qiang Li, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6218247/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Aims Straw retention combined with phosphorus (P) application has been proven to be an effective method to reduce the P application without decreasing cotton yield, but the related internal physiological mechanism of root is unclear. This study aimed to explore the impact of straw retention combined with different P application rates on soil nutrient content, the yield and quality of fiber, allometric growth relationship between root and shoot, and root nitrogen (N) metabolism. Methods The field experiment was conducted from 2020 to 2021 to study the effects of straw management (removal and retention) combined with different P rates (including 0, 100, and 200 kg P 2 O 5 ha − 1 ) on soil quality, different allocation of biomass, and N uptake and assimilation. Results The results showed that straw retention combined with P application contributed to improving lint yield and fiber quality synergistically. The result due to the fact that straw retention combined with P application increased the soil nutrient contents but decreased the bulk density of soil, creating favorable soil conditions for cotton growth. Compared to straw removal combined with 0 kg P 2 O 5 ha − 1 , improvement of physical and chemical properties of soil markedly increased the activities of nitrate reductase (10.5%-89.2%), glutamine synthetase (8.5%-80.5%), and glutamate synthase (3.0%-45.9%), which enhanced N uptake and assimilation. Additionally, the optimization of root N metabolism enhanced shoot growth of cotton by increasing the leaf area index and affecting cotton biomass allocation, which favored the formation of cotton square and flower, and boll. Conclusions Overall, straw retention combined with P application could improve soil physical and chemical properties and optimize the relationship between root and overground growth, which is conducive to the synergistic improvement of cotton yield and quality. Furthermore, straw retention combined with 100 kg P 2 O 5 ha − 1 was the best choice in the actual field agronomic practice of cotton production. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Highlights • Straw retention combined with phosphorus application improved cotton lint yield and fiber quality. • Straw retention and phosphorus application were more conducive to shoot biomass accumulation than root. • Straw retention and phosphorus application improved nitrogen uptake by cotton. • Root nitrogen metabolism capacity significantly affected lint yield and fiber quality. Introduction Cotton ( Gossypium hirsutum L.), a vital commercial crop in the world, provides raw materials for the textile industry, and its lint yield and fiber quality determine its economic value and textile products quality (Hussain et al., 2022 ; Huang et al., 2024 ). However, soil phosphorus (P) availability is low due to its poor mobility and easy fixation by soil, which seriously reduces the yield and quality of cotton (Huo et al., 2023 ). Applying chemical P fertilizer is considered an effective practice to meet the demand for P in cotton growth and guarantees high yield and quality of cotton (Li et al., 2022b ; Zhang et al., 2023b ). Notably, excessive input of chemical P fertilizer failed to consistently improve cotton yield and fiber quality but would increase the cotton production costs and bring environmental risks (Cordell et al., 2009 ; Xie et al., 2022 ; Li et al., 2023b ). Meanwhile, the non-renewability of the raw material for P fertilizer, phosphate ore, also promotes agricultural producers to explore alternative ways of chemical P fertilizer. Straw retention is considered an environmentally friendly cultivation practice that could affect soil organic P mineralization, improve soil P availability, and interact with chemical P fertilizer to co-promote cotton growth, and ultimately achieve a reduction in chemical P application without reducing cotton yield (Cao et al., 2021 ; Wu et al., 2021 ; Wang et al., 2022a ; Wei et al., 2024 ). However, there are fewer studies on the internal mechanisms of the positive effects on the cotton growth under straw retention combined with P application. Nitrogen (N) metabolism in cotton is closely related to the development of cotton yield and fiber quality as it affects N uptake, photosynthesis, and the transport of nutrients and carbohydrates (Iqbal et al., 2021 ; Hassanzadehdelouei et al., 2022 ). Meanwhile, it should be pointed out that these metabolic processes also require P participation as energy and signaling molecules (Wang et al., 2018 ). Therefore, it is unsurprising that plenty of literature pointed out that there is a significant interaction between P and N in the growth of plants. Krouk and Kiba, ( 2020 ) and Hao et al. ( 2023 ) summarized this phenomenon in detail from the perspective of ecology, agronomy, physiology, and molecular biology by, including the synergistic effects of N and P co-fertilization on crop yield and quality, N and P acquisition and utilization, and the starvation response of N and P. However, until now, the effects of N and P metabolism on crop yield and quality have been considered more separately under different cultivation environments (Liu et al., 2023 ; Zhang et al., 2023b ; Huang et al., 2024 ). Crop root, the organ responsible for nutrient uptake, is the first organ that senses the change of soil nutrient and is sensitive to the changes in environmental factors. Meanwhile, the N required for the formation of crop yield and quality is significantly affected by root N metabolism, which is sensitive to the changes in environmental factors (Oliveira et al., 2013 ; Ding et al., 2023 ). Previous studies reported that optimal irrigation amount and N rate increased N uptake by root and further improved final yield and fiber quality of cotton (Hou et al., 2021 ; Wang et al., 2022b ). He et al. ( 2022 ) also pointed out that the reduction of soil moisture limited root N uptake and changed the N status of cotton, which decreased photosynthetic capacity and yield. Hence, it is of great significance to explore the changes of N metabolism in cotton root to reveal the physiological mechanism of straw retention combined with P fertilizer affecting the formation of cotton yield and quality. N metabolism in roots is controlled by nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT). The absorbed nitrate is reduced to nitrite by NR, and subsequently, nitrite reductase further reduces nitrite to ammonium. GS catalyzes the synthesis of glutamine (Gln) from ammonium and glutamic acid (Glu), while GOGAT catalyzes Gln and α-ketoglutaric acid to form Glu (Liu et al., 2022 ). Part of the absorbed N is assimilated to amino acid preliminarily in the root, which is used for root growth and transferred to the aboveground. Studies in Arabidopsis ( Arabidopsis thaliana ) and soybean ( Glycine max ) showed that P deficiency decreased the activities of NR and GS in roots, limiting N uptake and assimilation and reducing the biomass of plants (Heidari et al., 2011 ; Jiang et al., 2021 ). A previous study on rice ( Oryza sativa L.) reported that straw retention promoted N uptake and accumulation by enhancing root NR activity and oxidative activity, increasing grain yield and quality (Hamoud et al., 2022 ). For cotton, many studies also pointed out that both straw retention and P application could increase N and P accumulation, improving lint yield and fiber quality (Wang et al., 2021 ; Huo et al., 2023 ; Liu et al., 2023 ), but the relevant physiological mechanism is still unclear. Fortunately, it has been proven that high root activities of NR, GS, and GOGAT could increase the uptake, assimilation, and accumulation of N in cotton (Iqbal et al., 2020 ). Therefore, we speculated that straw retention combined with P application might promote the formation of cotton yield and fiber quality by enhancing biomass accumulation and N assimilation affected by NR, GS, and GOGAT in cotton root. It should be noted that the accumulation and distribution of biomass are the basis for the formation of crop yield and quality (Li et al., 2023b ), and an unbalanced relationship between the root and shoot would decrease the crop yield and quality. For example, under abiotic stress conditions (such as nutrient and water limit), the root is preferentially allocated more resources to maintain its growth and function, which would directly limit the aboveground growth and is not conducive to the formation of crop yield and quality (Poorte & Nagel, 2000 ; Robinson, 2023 ). Crop root N metabolism has a significant effect on aboveground photosynthesis and carbon assimilate transport, and this effect would lead to the differences in biomass allocation among different organs (Oliveira et al., 2013 ; Hassanzadehdelouei et al., 2022 ). Hence, it is important to accurately describe the relationship between cotton root and shoot growth under different soil P status to identify the internal mechanism for straw retention combined with P application affecting cotton yield and quality. The allometric biomass partitioning theory model provides a method to achieve this goal (Mccarthy & Equist, 2007; Chen and Weiner, 2024 ). Briefly, straw retention is an environmentally friendly cultivation practice that could partially replace P fertilizer without decreasing seedcotton yield. However, it is not clear how the physiological process of root N metabolism and its relationship with lint yield and fiber quality of cotton respond to straw retention combined with P application. Hence, this study aimed to explore the responses of root N metabolism under different straw management and P application rates to reveal the physiological mechanism of straw retention combined with P application on lint yield and fiber quality. For this purpose, we hypothesized that (1) straw retention combined with P application enhanced root N metabolism in cotton, and (2) the coordinated relationship between root and shoot of cotton improved lint yield and fiber quality synergistically. To verify this hypothesis, we investigated the changes of N metabolism-related substance contents and enzyme activities in roots under different straw managements and P application rates, and their relationship with lint yield and fiber quality. Moreover, due to the indeterminate growth habit of cotton, optimizing the relationship between root and shoot was crucial for its growth and development. Hence, this study also analyzed the dynamic growth relationship between root and shoot. Materials and methods Experimental site The positioning experiment of annual straw retention combined with P fertilizer was conducted from 2016 to 2021 at Dafeng Basic Seed Farm in Yancheng (33°12′N, 120°28′E), China, and the experiment involved in this report was carried out in 2020–2021 (the 5th -6th year of wheat-cotton straw retention to the field). The soil type is sandy loam, and the available P content was 17.3 mg kg − 1 in the soil of 0–20 cm soil layer at the beginning of the positioning experiment, which could not meet the P demand for cotton growth (Cai et al., 2023 ), and the other initial soil properties in 2016 were reported by Cao et al. ( 2021 ), The basic properties of the soil in 0–20 cm soil layer before cotton sowing in 2020 are shown in Table 1 . During the cotton season (May-October), the average temperature was 22.9°C and 23.5°C, and the total precipitation was 865 mm and 633 mm from 2020 to 2021, respectively (Fig. 1 ). Table 1 The physical and chemical properties of soil in 2020 (0–20 cm). Straw management Phosphorus rate (kg P 2 O 5 ha − 1 ) BD (g cm − 3 ) SOM (g kg − 1 ) TN (g kg − 1 ) TP (g kg − 1 ) AN (mg kg − 1 ) AP (mg kg − 1 ) Straw removal 0 1.37 a 10.84 c 0.67 c 0.59 c 8.95b 7.31 d 100 1.30 b 12.14 b 0.74 abc 0.67 b 9.41 b 26.22 c 200 1.28 b 12.26 b 0.73 bc 0.69 ab 9.28 b 34.17 b Straw retention 0 1.23 c 12.29 b 0.72 bc 0.60 c 11.33 a 9.10 d 100 1.21 cd 13.69 a 0.78 ab 0.68 ab 12.12 a 32.02 b 200 1.20 d 14.13 a 0.81 a 0.70 a 11.73 a 39.33 a Values followed by different little letters in the same column are significantly different at P < 0.05 probability level. BD, SOM, TN, TP, AN, and AP represent bulk density, soil organic matter, total nitrogen, total phosphorus, available nitrogen, and available phosphorus, respectively. The data are quoted from (Wang et al., 2024 ). Experimental design The positioning field experiment was designed as a two-factor split plot with three replicates. The main plot was set up with two straw management treatments [straw removal (S 0 ) and straw retention (S 1 )], while the subplot was assigned three P rates [0, 100, and 200 kg P 2 O 5 ha − 1 ]. The cotton cultivar was CCRI 425 and was sown on May 22, 2020 and June 7, 2021 at a density of 90,000 plants ha − 1 , respectively. Every subplot was 13.2 m in length and 6.0 m in width, and the cotton row and plant spacing were 81 cm and 13.7 cm, respectively. The application rate of nitrogen fertilizer (Urea, 46% of N) application rate was 225 kg N ha − 1 , while 40% of the total N fertilizer was input at the seedling stage, and 60% at the initial flowering stage. Potassium (K) fertilizer (Potassium sulfate, 51% of K 2 O, 225 kg K 2 O ha − 1 ) and P fertilizer (Calcium triple superphosphate, 46% of P 2 O 5 ) were input totally at the seedling stage. The wheat cultivar was Yangmai 25 and was sown after harvesting cotton on November 17, 2020 and November 16, 2021 at a seeding rate of 187.5 kg ha − 1 , respectively. The row spacing for wheat was 14 cm, and no chemical fertilizer was input during the wheat seasons. After the wheat or cotton harvest, the crop straw was collected from each plot and cut into 5–8 cm long, respectively. Meanwhile, the treated wheat straw or cotton straw (each 6,000 kg ha − 1 ) were spread evenly to the soil surface of plots corresponding to the straw retention treatment before cotton or wheat sowing. Then, the crop straw was rotated into 0–20 cm soil layer, and the plots of straw removal treatment were also rotated without straw. Other cultivation management was conducted according to local production requirements. Sampling Soil sampling The soil before sowing cotton and after harvesting cotton was collected as follows: Five sites in each plot were selected to measure soil bulk density through the cutting ring method. Simultaneously, soil samples (0–20 cm soil layer) of five sites in each plot were collected randomly and mixed evenly. All the soil samples were removed debris, passed through a 0.85 mm sieve, and divided into two equal parts. One part was used to determine soil available nitrogen contents immediately, and the other was air dried to test the contents of organic matter, total nitrogen, total phosphorus, and available phosphorus in soil. Plant sampling Ten consecutive cotton plants with consistent growth situation in each subplot were marked at the seeding stage, which was used for the statistics of cotton square, flower and boll numbers at the peak squaring stage (PSS), peak flowering stage (PFS), peak boll setting stage (PBS), and boll opening stage (BOS), respectively. Five cotton plants with consistent growth from each subplot were collected at PSS, PFS, PBS, and BOS, respectively. After which these plants were divided into root, stem, leaf, and reproductive organs. The leaf area of 5 plants was measured with a leaf area meter (LI-8100, Li-Cor, Lincoln, USA) to calculate the leaf area index (LAI). Whereafter, all plant samples were separately dried at 105℃ for 30 min and then at 80℃ until a constant weight to measure the biomass, N and P accumulation of cotton per hectare. Three cotton plants were selected randomly from each subplot to collect the root and mix homogeneously at PSS, PFS, PBS, and BOS, respectively. One part of the cotton root sample was frozen with liquid nitrogen and stored at -80℃ for the determination of enzyme activities and soluble protein content in the root; the other part was dried at 105℃ for 30 min and then at 80℃ until a constant weight for the determination of free amino acid content. Soil nutrient content Referring to Lu ( 2000 ), the measurement methods of soil nutrient contents were as follows: Soil organic matter content was determined by the dichromate oxidation method. Total N content was analyzed using the Kjeldahl method. Total P content was assessed through the NaOH fusion and colorimetric method. Available N content was measured utilizing an automated discrete analyzer (CleverChem 380, Dechem-Tech, Germany). Available P content was determined by the molybdenum antimony spectrophotometric method. Lint yield and fiber quality Twenty consecutive cotton plants were selected in each plot to collect all mature opening bolls. After natural air-drying of seedcotton, the fiber was separated from cottonseed and weighted to calculate lint yield. Fiber quality characteristics were measured by using a high-volume instrument (HVI MF100, USTER, Switzerland) according to the specific measurement details in the report of Liu et al. ( 2023 ). The N and P uptake by cotton Samples after drying and weighing biomass were ground and sifted to pass through a 0.5 mm sieve for N and P analysis by the Kjeldahl method and molybdenum antimony spectrophotometric method, respectively according to the specific details in the report of Ma et al. ( 2019 ). The contents of free amino acid and soluble protein Dried cotton root sample (0.3 g) was mixed with 3 mL of 80% (v/v) ethanol and bathed at 80 ℃ for 30 min. Subsequently, the homogenate was centrifuged at 10,000g for 5 min, and the supernatant was transferred into a 10 mL volumetric flask. The above extraction steps were repeated three times, and finally, 80% ethanol was used to dilute the resulting supernatant to 10 mL. The free amino acid content was measured by using the hydrated ninhydrin colorimetric, and the specifical operation was performed following the study of Liu et al. (2010). Fresh root sample (0.3 g) was ground into homogenate with 5 mL phosphate buffer (100 mM, pH 7.5) under aground 4℃. Then, the homogenate was centrifuged at 15,000g for 10 min under 4℃, and the supernatant was collected to measure soluble protein content by coomassie brilliant blue method referring to Bradford ( 1976 ). Enzyme extraction and analysis The activities of nitrate reductase (NR, EC 1.6.6.1), glutamine synthetase (GS, EC 6.3.1.2), and glutamate synthase (GOGAT, EC 1.4.1.14) were measured referring to the method of Lin et al. (1996) and Ding et al. ( 2006 ). Specifically, the extraction solution was prepared as follows: The fresh root sample (0.5 g) was ground into homogenate with 5 mL 0.1 M phosphate buffer (30.10 g Na 2 HPO 4 ·12H 2 O and 2.50 g NaH 2 PO 4 ·2H 2 O, pH 7.5) under 4℃. Then, the homogenate was centrifuged at 15,000g for 15 min under 4℃, and the supernatant was collected to measure NR activity. The NR activity measurement method was as follows: 1 mL prepared extraction solution was mixed evenly with 1.2 mL 0.1 M phosphate buffer and 0.4 mL 2 mg mL − 1 NADH in a tube for 1 h under 25℃. Subsequently, 1 mL of 1% sulfanilamide solution was added to the mixture to terminate the reaction. Then, 1 mL 1% naphthylvinylamine solution was added into the mixture and mixed evenly. After 1 h, the mixture was centrifuged at 15,000 g for 15 min, and the absorbance of supernatant was measured the absorbance at 540 nm to calculate NR activity. The NADH solution was replaced with 0.4 mL 0.1 M phosphate buffer in the control group For GS and GOGAT, fresh root sample (0.5 g) was ground into homogenate with 5 mL 0.1 M Tris-HCl buffer (pH 7.6) under around 4℃. Then, the homogenate was centrifuged at 12,000g for 20 min under 4 ℃, and the supernatant was collected to measure the activities of GS and GOGAT. The GS activity measurement method was as follows: 1.2 mL prepared extraction solution was mixed evenly with reaction solution (including 0.6 mL 0.25 M imidazole-HCl, 0.4 mL 0.3 M sodium glutamate, 0.4 mL 0.03 M ATP-Na, 0.2 mL 0.5 M MgSO 4 , pH 7.0) under a 25 ℃ water bath for 5 min. Subsequently, 0.2 mL 1 M hydroxylamine (including 1 M NaOH and 1 M NH 2 OH-HCl) was combined with the mixture for a 15-min water bath under 25℃. And then, 0.8 mL terminate reaction solution [10% (w/v) FeCl 3 ∙6H 2 O, 50% (v/v) HCl, and 24% (w/v) trichloroacetic acid were mixed in equal volume] was added into the mixture. After 20 min, the mixture was centrifuged at 15,000g for 10 min, and the absorbance of supernatant was measured the absorbance at 540 nm to calculate GS activity. For GOGAT activity, 250 µL prepared extraction solution was mixed evenly with 550 µL reaction solution (including 25 µL 20 mM α-ketoglutaric acid, 50 µL 10 mM KCl, 200 µL 3 mM NADH, 275 µL 0.1 M Tris-HCl buffer, pH 7.6). Then, the reaction was started after adding 200 µL 20 mM L-glutamine, and the change in the absorbance of solution at 340 nm within 5 min was detected to calculate GOGAT activity. Statistical analysis The analysis of experimental data was completed with SPSS 22.0 (IBM, USA) and Microsoft Excel 2019. The least significant difference method (LSD) was used for analyzing the differences in all indicators at P < 0.05 probability level among all treatments. A two-factor analysis of variance was used to explore the effects of straw management, P application, and their interaction effect on all indicators in each year. The partial least squares path analysis was performed by Smart-PLS to analyze the relationships among physical and chemical properties of soil, N-metabolism enzymes, free amino acid, N accumulation with lint yield and fiber quality. All figures were generated by Origin Pro 2023. The relationship between root and aboveground part of cotton was analyzed by the allometric growth model Eq. (1) (Mccarthy and Enquist, 2007 ): lg Y = α lg M + lg β (1) Where α is the scaling exponent, β is the allometric constant. Y and M are the cotton biomass of aboveground part and root in the same stage, respectively. Results Lint yield and fiber quality Both straw management and P application significantly increased lint yield, and there was a significant interaction between straw management and P application on lint yield (Fig. 2 ). Specifically, compared with S 0 , the lint yield under S 1 with 0, 100, and 200 kg P 2 O 5 ha − 1 increased by 8.2%-11.8%, 6.3%-7.3%, and 2.4%-8.8%, respectively. In comparison with 0 kg P 2 O 5 ha − 1 , the lint yield under 100, 200 kg P 2 O 5 ha − 1 increased by 55.6%-72.9%, 74.2%-84.9% for S 0 , and by 54.3%-64.5%, 69.4%-75.2% for S 1 , respectively. Fiber quality also markedly changed under different straw management and P rates (Table 2 ). Straw retention increased fiber length but reduced micronaire (except for fiber length in 2021 and micronaire in 2021), while had no significant effect on fiber strength; P application significantly increased fiber length and strength but reduced micronaire. Straw management and P rate had no significant interaction effect on fiber quality (except for micronaire in 2021). Specifically, compared with S 0 , the fiber length under S 1 with 0, 100, and 200 kg P 2 O 5 ha − 1 increased by 0.5, 0.3, and 0.3 mm in 2020, respectively. In comparison with 0 kg P 2 O 5 ha − 1 , averaged across from 2020 to 2021, the fiber length under 100, 200 kg P 2 O 5 ha − 1 increased 1.7, 2.4 mm for S 0 , by 1.5, 2.1 mm for S 1 ; the fiber strength increased 1.4, 2.0 cN tex − 1 for S 0 , by 1.3, 1.9 cN tex − 1 for S 1 , respectively. The micronaire ranged from 3.9 to 4.5 in each treatment, consistent with high-quality cotton fiber standards (micronaire rank standards: A, 3.7–4.2; B, 3.5–3.6 or 4.3–4.9; C, 3.4 and below or 5.0 and above). Meanwhile, the micronaire value decreased under straw retention and P application, which reached a higher standard in this study. Table 2 Effects of straw management and phosphorus rate on fiber quality from 2020 to 2021. Straw management Phosphorus rate (kg P 2 O 5 ha − 1 ) Fiber length (mm) Fiber strength (cN tex − 1 ) Micronaire 2020 2021 2020 2021 2020 2021 Straw removal 0 28.6 d 28.7 b 29.5 d 28.5 b 4.5 a 4.3 a 100 30.8 c 29.9 a 31.2 c 29.5 a 4.5 a 4.0 bc 200 31.7 ab 30.3 a 32.1 ab 29.9 a 4.2 cd 3.9 c Straw retention 0 29.1 d 29.0 b 29.7 d 28.8 b 4.4 ab 4.1 b 100 31.1 bc 30.0 a 31.6 bc 29.5 a 4.3 bc 4.2 ab 200 32.0 a 30.3 a 32.4 a 29.9 a 4.0 d 4.0 bc Source of variation Straw management (S) * NS NS NS ** NS Phosphorus rate (P) ** ** ** ** ** ** S × P NS NS NS NS NS * Values followed by different little letters in the same column are significantly different at P < 0.05 probability level. *, **, and NS represent significant differences at P < 0.05, P < 0.01, and non-significant at P < 0.05 probability levels, respectively. Each value is the average of 3 replications. Soil nutrient contents and bulk density Straw retention significantly increased the contents of available N (Av-N), available P (Av-P), and organic matter (OM) but decreased bulk density (BD) (Fig. 3 ); P application significantly increased Av-P content but had relatively minor effects on the contents of Av-N, OM, and BD. Specifically, compared with S 0 , the Av-N content under S 1 with 0, 100, 200 kg P 2 O 5 ha − 1 increased by 33.8%-43.6%, 38.4%-39.8%, 16.2%-42.6%; the Av-P content increased by 37.6%-59.4%, 21.7%-24.5%, 16.2%-22.8%; the OM content increased by 16.3%-17.2%, 12.5%-15.8%, 7.8%-16.9%; the BD decreased by 8.6%-8.8%, 7.8%-9.1%, 6.7%-7.1%, respectively. The contents of free amino acid and soluble protein in root The contents of free amino acid and soluble protein in root were significantly affected by straw management, P application, and their interaction at PFS (Fig. 4 ). Specifically, compared with S 0 , the free amino acid content under S 1 with 0, 100, and 200 kg P 2 O 5 ha − 1 increased by 3.0%-6.7%, 9.6%-10.3%, and 6.1%-10.8% (Fig. 4 A); the soluble protein content increased by 14.3%-14.5%, 14.3%-13.7%, and 3.0%-6.4% (Fig. 4 B), respectively. In comparison with 0 kg P 2 O 5 ha − 1 , the free amino acid content under 100, 200 kg P 2 O 5 ha − 1 increased by 9.7%-26.7%, 18.9%-35.2% for S 0 , and by 16.7%-31.6%, 37.8%-40.5% for S 1 (Fig. 4 A); the soluble protein content increased by 25.8%-38.0%, 14.3%-21.8% for S 0 , and by 25.5%-37.3%, 6.9%-9.7% for S 1 (Fig. 4 B) at PFS, respectively. The enzyme activities related to N metabolism in root The nitrate reductase (NR) activity decreased gradually with the growth stage proceeding and peaked at PSS. The activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) increased first and then decreased with the growth stage proceeding and peaked at PFS. Straw management, P application, and their interaction had significant effects on the above enzyme activities at PFS (Fig. 5 ). Specifically, compared with S 0 , the NR activities at PFS under S 1 with 0, 100, and 200 kg P 2 O 5 ha − 1 increased by 10.5%-13.1%, 19.3%-23.6%, and 11.8%-20.0% (Fig. 5 A); the GS activities increased by 8.4%-13.4%, 21.0%-29.6%, and 12.8%-26.6% (Fig. 5 B); the GOGAT activities increased by 7.6%-11.2%, 24.8%-29.2%, and 13.9%-20.2% (Fig. 5 C), respectively. Compared with 0 kg P 2 O 5 ha − 1 , the NR activities at PFS under 100, 200 kg P 2 O 5 ha − 1 increased by 41.0%-50.6%, 57.7%-65.3% for S 0 , and by 52.2%-64.7%, 63.5%-71.2% for S 1 (Fig. 5 A); the GS activities increased by 24.8%-31.0%, 38.5%-42.6% for S 0 , and by 39.2%-49.6%, 44.0%-59.1% for S 1 (Fig. 5 B); the GOGAT activities increased by 39.7%-41.0%, 56.1%-59.4% for S 0 , and by 62.4%-63.5%, 67.8%-68.8% for S 1 (Fig. 5 C), respectively. Nitrogen and phosphorus uptake by cotton The accumulation of N and P in cotton increased gradually with growth stage proceeding and peaked at BOS. Both straw management and P application had a significant positive effect on them (Fig. 6 ), while only the P accumulation was significantly affected by the interacted interaction effect of straw management and P application (except for 2020). Compared with S 0 , straw retention increased the N and P accumulation by 0.6%-12.8% and 3.3%-20.0% from 2020 to 2021 across different P rates, respectively. In comparison with 0 kg P 2 O 5 ha − 1 , the N accumulation under 100, 200 kg P 2 O 5 ha − 1 increased by 38.6%-55.5%, 55.7%-74.1% for S 0 , and by 33.6%-49.0%, 45.4%-61.6% for S 1 ; the P accumulation increased by 72.5%-92.3%, 124.0%-161.2% for S 0 , and by 72.1%-86.9%, 109.6%-126.9% at BOS, respectively. Leaf aera index (LAI) The LAI increased first and then decreased with the growth stage proceeding and reached the highest values at PBS (Fig. 7 ). LAI was significantly influenced by straw management and P application. Compared with S 0 , the LAI increased by 8.2%-13.9%, 5.6%-6.3% for S 1 with 0, 100 kg P 2 O 5 ha − 1 at PBS. Additionally, in comparison with 0 kg P 2 O 5 ha − 1 , the LAI under 100, 200 kg P 2 O 5 ha − 1 increased by 26.1%-32.2%, 45.6%-50.2% for S 0 , and by 23.0%-23.4%, 37.4%-38.8% for S 1 at PBS, respectively. Dynamics of cotton square and flower number and boll number The square and flower number peaked at PFS (maximum was 171 × 10 4 no. ha − 1 ), and the boll number obtained the maximum values at BOS (maximum was 123 × 10 4 no. ha − 1 ); straw retention and P application markedly increased their number (Fig. 8 ). Specifically, Compared with S 0 , the number of square and flower under S 1 with 0, 100, and 200 kg P 2 O 5 ha − 1 increased by 3.7%-4.5%, 7.3%-8.4%, and 1.6%-1.9% at PFS, respectively; the boll number increased by 11.7%-15.4%, 9.0%-9.3%, 1.7%-1.9% at BOS, respectively. In comparison with 0 kg P 2 O 5 ha − 1 , the number of square and flower at PFS under 100, 200 kg P 2 O 5 ha − 1 increased by 11.3%-13.4%, 18.2%-24.0% for S 0 , and by 15.5%-17.3%, 15.7%-21.0% for S 1 , respectively; the boll number at BOS increased by 43.4%-64.8%, 55.7%-88.8% for S 0 , and by 35.7%-61.2%, 37.3%-72.1% for S 1 , respectively. The square and flower number (at PFS) and boll number (at BOS) under S 1 combined with 100 kg P 2 O 5 ha − 1 could reach similar levels under S 0 with 200 kg P 2 O 5 ha − 1 , respectively. Allometric growth relationship between the root and shoot The growth of the root and shoot interacted with each other in an obvious allometric growth relationship, which could be analyzed with the allometric growth model ( R 2 = 0.889**-0.988**, n = 18, R 2 0.01 = 0.348, n = 36, R 2 0.01 = 0.180; Table 3 ). Results showed that the allometric index (α) in each treatment during different growth stages were all over 1.000, indicating that the relative growth rate of shoot was faster than that of the root. Additionally, during PFS to PBS, the value of α in each treatment was the largest, which meant that the relative growth rate of shoot reached the maximum. It could be explained that the formation of reproductive organ was enhanced during this stage. Furthermore, the value of α increased under straw retention and P application which were more conducive to enhancing the shoot growth. Table 3 Effects of straw combined with phosphorus application on cotton parameter of allometric growth equation from 2020 to 2021. Growth stage Straw management Phosphorus rate (kg P 2 O 5 ha − 1 ) allometric indexα allometric constantβ R 2 From PSS to PFS Straw removal 0 1.001 4.764 0.992** 100 1.021 4.519 0.988** 200 1.060 3.819 0.990** Straw retention 0 1.012 4.457 0.997** 100 1.026 4.325 0.994** 200 1.059 3.724 0.992** From PFS to PBS Straw removal 0 1.398 0.428 0.957** 100 1.506 0.219 0.976** 200 1.551 0.176 0.958** Straw retention 0 1.384 0.457 0.975** 100 1.709 0.060 0.938** 200 2.095 0.005 0.933** From PBS to BOS Straw removal 0 1.481 0.254 0.937** 100 1.252 1.222 0.915** 200 1.170 2.366 0.879** Straw retention 0 1.408 0.420 0.836** 100 1.147 2.679 0.898** 200 1.137 2.999 0.884** Full growth stage Straw removal 0 1.102 2.985 0.987** 100 1.134 2.618 0.986** 200 1.173 2.188 0.986** Straw retention 0 1.122 2.679 0.986** 100 1.160 2.259 0.985** 200 1.184 2.014 0.983** n = 12, R 2 0.01 = 0.501 (including the growth stage from PSS to PFS, from PFS to PBS, and from PBS to BOS); n = 24, R 2 0.01 = 0.265 (including the growth stage of full growth stage). ** means the significant differences at P < 0.01 probability level. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively. Relationship among the soil condition, N metabolism, lint yield and fiber quality The partial least squares path analysis was conducted to investigate the relationships among the physical and chemical properties of soil, root N metabolism, and N accumulation with lint yield and fiber quality (Fig. 9 ). The results showed that soil nutrient contents (Av-N, Av-P, and Av-K) had significant positive influences, but BD significantly negatively influenced on the activities of enzymes (NR, GS, and GOGAT) related to N metabolism directly. Furthermore, the enzyme activities related to N metabolism positively influenced N accumulation, which in turn significantly affected lint yield and fiber quality. In addition, the content of free amino acid was directly affected by the enzyme activities related to N metabolism, which could be expressed by linear regression equations: Y free amino acid = 0.055X NR + 0.316X GS − 0.082 X GOGAT + 2.959 ( R 2 = 0.865**, n = 12, R 2 0.05 = 0.604, R 2 0.01 = 0.740). Based on this equation, it is evident that the content of free amino acid was obviously influenced by the activities of NR, GS, and GOGAT in cotton root. Discussion Straw retention combined with P application improved lint yield and fiber quality by optimizing root-shoot allometric growth relationship Straw retention combined with P application significantly improved lint yield in this report (Fig. 2 ; Table 2 ), similar result in seedcotton yield was detected by the research of Cao et al. ( 2021 ), which attributed the increase in seedcotton yield to the increases in the number and weight of cotton boll. Moreover, the results of this study found that straw management, P application, and their interaction had significant influences on lint yield, which could be reflected by the fact that the lint yield under straw retention combined with 100 kg P 2 O 5 ha − 1 was similar to that under straw removal combined with 200 kg P 2 O 5 ha − 1 (Fig. 2 ). Synergistically, straw retention and P application also improved fiber quality. Specifically, P application increased fiber length and strength, and optimized micronaire value. Straw retention mainly increased fiber length and optimized micronaire. Furthermore, the fiber quality (including length, strength, and micronaire) of straw retention combined with 100 kg P 2 O 5 ha − 1 reached a similar level of that under straw removal with 200 kg P 2 O 5 ha − 1 , which reached the highest fiber quality standard statistically in all treatments (Table 2 ). Previous studies also reported that the fiber quality of cotton was not decreased by reducing moderately the amount of N and K fertilizer under straw retention in the field (Qayyum et al., 2020 ; Liu et al., 2023 ). As above, we found that the best lint yield and fiber quality could be achieved by straw retention combined with 100 kg P 2 O 5 ha − 1 in a statistical sense. Biomass is the basis of crop yield and quality formation, but only focusing on the change of biomass cannot improve the yield and quality most effectively. Previous studies pointed out that a coordinated root-shoot relationship guarantees normal growth of plants and formation of yield and quality (Kleyer & Minden, 2015 ; Robinson, 2023 ; Guo et al., 2024 ). Additionally, some studies also have suggested that root dominated the growth balance of cotton (Li et al., 2023b ), and strong root system is essential to supporting shoot growth and promoting the formation of crop yield and quality (Ma et al., 2019 ; Jin et al., 2024 ). Hence, we used allometric growth model to explore the relationship between root and shoot growth of cotton in this study. The result indicated that the relative growth rate of the aboveground was higher than that of root. However, it should be noted that the relatively low growth rate did not mean that root growth was limited. On the contrary, cotton root under straw retention combined with P application obtained higher biomass, indicating that its growth was enhanced (Table 3 ; Table S1). To illustrate the effect of this optimized growth relationship on lint yield and fiber quality, we further evaluated the LAI of the cotton population, which is considered to be an important factor affecting cotton yield and fiber quality (Bange et al., 2022 ; Li et al., 2022a ). Our study found that the yield and quality of fiber, and LAI increased together under straw retention combined with P application. In other words, our results about the allometry relationship between root and shoot demonstrated that straw retention combined with P application tended to enhance the aboveground growth due to better root growth basing on higher LAI (Fig. 7 ; Table 3 ; Table S1). Furthermore, the number of reproductive organs significantly increased under straw retention combined with P application in our study (Fig. 8 ). Previous study also found that P application improved the photosynthesis of cotton leaf, accelerated the formation of cotton boll, and decreased the shedding rate, resulting in higher boll density and lint yield (Li et al., 2022b ). Similarly, Liu et al. ( 2023 ) also reported that maintaining a higher photosynthetic capacity of cotton population contributed to accumulating more biomass and distributing it to the reproductive organs. Meanwhile, for fiber quality, the fiber length and strength of cotton were also positively affected by the photosynthetic capacity of the leaf (Li et al., 2023a ; Huang et al., 2024 ), which was consistent with our result. In conclusion, straw retention had a P reduction effect (Cao et al., 2021 ). A proper amount of P fertilizer reduction under straw retention would not decrease lint yield and fiber quality by achieving a good root-shoot growth relationship. Effects of straw retention combined with P application on root N metabolism In term of soil, a meta-analysis assessed P-application effects on N dynamics, it observed that P application increased soil total N pool, potentially as a result of enhanced plant and microbial immobilization and reduced N losses, with a stronger effect detected under longer duration of P addition (greater than or equal to 5 year) (Wang et al., 2022c ). Moreover, the root, as the main organ of the plant to uptake nutrient, connects the soil and the aboveground part of plant (Robinson, 2023 ). According to a study, the resource allocation between root and aboveground part was also considered potentially related to soil N cycle (An et al., 2025 ). Several reports had shown that root N metabolism capacity had a direct effect on the accumulation and distribution of biomass, thereby affecting yield and quality of crop (Bai et al., 2023 ; Jin et al., 2024 ). In this report, lint yield and fiber quality were positively related to N metabolism capacity of cotton (Fig. 9 ). Similar results were also proved by Chen et al. ( 2016 ) and Bai et al. ( 2023 ) based on different N fertilizer rates and irrigation depth. Analyzing the relevant reasons, straw retention combined with P application increased nutrient availability and regulated the capacity of aeration and infiltration in soil by increasing the contents of Av-N, Av-P, and OM while decreasing BD. Meanwhile, our results indicated that soil properties were mainly affected by OM (Fig. 9 ). Several studies reported that OM was an important factor to improve aggregate fraction, microbial structure and promote nutrients cycling in soil (Bu et al., 2020 ; Qayyum et al., 2020 ; Cao et al., 2021 ). The improvement of soil nutrients and physical conditions alleviated the inhibition of root growth and was conducive to the uptake and assimilation of N in roots (Jin et al., 2024 ). As we know that N assimilation needs to consume adenosine triphosphate (ATP) and nicotine adenine dinucleotide phosphate (NADPH) whose synthesis were regulated by P (Rausch & Bucher, 2002 ; Yanagisawa, 2014 ). Hence, it is not surprising that straw retention combined with P application increased the activities of NR, GS, and GOGAT (Fig. 5 ), leading to a significant increase in free amino acid and soluble protein content (Fig. 4 ). Meanwhile, higher activities of GS and GOGAT contributed to ammonium assimilation, reducing toxic effects of excessive ammonium, which could alleviate premature senescence of root and increase N uptake (Liu et al., 2015 ; Fig. 6 ). Studies in rice ( Oryza sativa L.), cotton ( Gossypium hirsutum L.), soybean ( Glycine max ), and Arabidopsis ( Arabidopsis thaliana ) also showed that both straw retention and P application increased the activity and N metabolism capacity of root (Heidari et al., 2011 ; Jiang et al., 2021 ; Hamoud et al., 2022 ; Jin et al., 2024 ). Moreover, this report also demonstrated that the enhancement in root N metabolism enzymatic activity (NR, GS, and GOGAT) and plant N uptake decreased under per unit of P application as P application rates increased. Meanwhile, the positive effects of straw retention on these indexes also decreased with the increase of P application rate. This also explained from the perspective of N metabolism why the cotton yield of straw retention combined with 100 kg P 2 O 5 ha − 1 had a similar level of that under straw removal with 200 kg P 2 O 5 ha − 1 . In general, the results of partial least squares path model further confirmed that N uptake had significant effects on lint yield and fiber quality (positive with lint yield, fiber length and strength, while negative with micronaire) which also was significantly affected by physical and chemical properties of soil and N-metabolism enzymes (Fig. 9 ). As previously noted, straw retention combined with P application improved chemical properties of soil, N metabolism capacity of root, and N uptake, elucidating the mechanisms driving the change in lint yield and fiber quality. Conclusion Straw retention combined with P application enhanced the N metabolism capacity of root and optimized the relationship between root and shoot, which synergistically improved lint yield and fiber quality. Specifically, straw retention combined with P application improved soil physical and chemical properties (increased the contents of Av-N, Av-P, and OM, but decreased BD), and thus increased the activities of NR, GS, and GOGAT, stimulating the assimilation of N and P. Furthermore, the increased accumulation of N and P in cotton enhanced cotton photosynthetic capacity and regulated the distribution of cotton biomass, which was reflected by the fact that increased LAI provided sufficient carbon assimilates for the formation of cotton reproductive organs, which increased lint yield and improved fiber quality. Cotton under straw retention combined with 100 kg P 2 O 5 ha − 1 obtain a similar level of lint yield and fiber quality to that under straw removal combined with 200 kg P 2 O 5 ha − 1 . 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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-6218247","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":434639877,"identity":"55bcb811-59cf-4ae8-ba4c-f6a4f955a1cf","order_by":0,"name":"Qin Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Qin","middleName":"","lastName":"Wang","suffix":""},{"id":434639878,"identity":"d5e6bb86-07f1-4490-8465-91c0bbf3179f","order_by":1,"name":"Jiawei Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jiawei","middleName":"","lastName":"Wang","suffix":""},{"id":434639879,"identity":"aca9765f-1415-4e1f-a5f0-a5d0738038da","order_by":2,"name":"Xiaolin Huang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Xiaolin","middleName":"","lastName":"Huang","suffix":""},{"id":434639880,"identity":"8b6fc1e1-02c0-4f51-b9df-31794429c520","order_by":3,"name":"Wen Jin","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Wen","middleName":"","lastName":"Jin","suffix":""},{"id":434639881,"identity":"fcd283b0-73ec-4479-a552-4d62764333ad","order_by":4,"name":"Zhitao Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Zhitao","middleName":"","lastName":"Liu","suffix":""},{"id":434639882,"identity":"6e8c9be0-122d-4f68-9b3d-0837360b8ab5","order_by":5,"name":"Qiang Li","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Qiang","middleName":"","lastName":"Li","suffix":""},{"id":434639883,"identity":"7808d45b-95a1-4755-a15c-e9a8e65071b4","order_by":6,"name":"Wei Hu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Hu","suffix":""},{"id":434639884,"identity":"3757059b-f90a-4f68-8aa6-9d4dd14ed287","order_by":7,"name":"Zhiguo Zhou","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Zhiguo","middleName":"","lastName":"Zhou","suffix":""},{"id":434639885,"identity":"e5d66cd0-da3a-46d8-90f8-83ea26dd03f9","order_by":8,"name":"Yali Meng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYNCCAgZmBgbmAwc+/CBaiwFIC1viwZk9JGgBAh7jwxxsRCjWbe89/JrH4A47/4ycD4cZeBjk+cUO4NdiduZcmjWPwTNmiRu5Gw4XWDAYzpydQEDLjRwzYx6Dw8wMIC0zeBgSDG4T0nL/DUSL/I2cB4d52IjRcoPH+DFIi8GNHAYitZzJMWOcA9RieOaZATCQJYjwy/Ezxh/eVBxOljue/PjDhx828vzSBLQAAZsUDwNDMpQjQVA5CDB/BCYTO6KUjoJRMApGwcgEAPWmRzNH5ILFAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-0485-130X","institution":"Nanjing Agricultural University College of Agriculture","correspondingAuthor":true,"prefix":"","firstName":"Yali","middleName":"","lastName":"Meng","suffix":""}],"badges":[],"createdAt":"2025-03-13 09:07:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6218247/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6218247/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80514848,"identity":"abd45373-3951-4cd0-8dfb-2cffb4014225","added_by":"auto","created_at":"2025-04-14 07:53:38","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":79033,"visible":true,"origin":"","legend":"\u003cp\u003eDaily mean, maximum, and minimum air temperature and daily rainfall during cotton growth period (May-October) from 2020 to 2021.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/16575321c919beec3f4199ac.jpg"},{"id":80514418,"identity":"d2634bdd-1ed0-43cc-a198-2434c02f4d6b","added_by":"auto","created_at":"2025-04-14 07:45:37","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":35112,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw management and phosphorus rate on lint yield from 2020 to 2021. *, **, and NS represent significant differences at \u003cem\u003eP\u003c/em\u003e\u0026lt; 0.05, \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01, and non-significant at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 probability levels, respectively. S and P represent straw management and phosphorus rate, respectively. Each value is the average of 3 replications. The data lint yield under straw removal are quoted from Huang et al., 2025\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/f258e7c34b6cb998c94a7a01.jpg"},{"id":80514415,"identity":"781d6b65-f57b-4c69-b5bf-e4a33a7f02b6","added_by":"auto","created_at":"2025-04-14 07:45:37","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":77190,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw management and phosphorus rate on the contents of available nitrogen (A), available phosphorus (B), organic matter (C), and bulk density (D) of soil (0-20 cm) from 2020 to 2021. Values followed by different little letters within the same year are significantly different at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 probability level.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/492267a30628e88b0429bc4d.jpg"},{"id":80514459,"identity":"f14296ab-4f7c-478c-af71-94df9329c280","added_by":"auto","created_at":"2025-04-14 07:45:38","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":85124,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw management and phosphorus rate on the contents of free amino acid (A) and soluble protein (B) in cotton root from 2020 to 2021. *, **, and NS represent significant differences at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05, \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01, and non-significant at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 probability levels, respectively. S and P represent straw management and phosphorus rate, respectively. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively. Each value is the average of 3 replications.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/ab98e1b348fb6442c0013664.jpg"},{"id":80514430,"identity":"ab8a7c91-db61-47d8-be03-5a51754effed","added_by":"auto","created_at":"2025-04-14 07:45:38","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":79851,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw retention and phosphorus rate on the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT)in cotton root from 2020 to 2021. *, **, and NS represent significant differences at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05, \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01, and non-significant at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 probability levels, respectively. S and P represent straw management and phosphorus rate, respectively. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively. Each value is the average of 3 replications.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/297399b5eb3ae560e7d6d0ab.jpg"},{"id":80514420,"identity":"15862531-ab86-488a-8f78-5c3e75fbcde5","added_by":"auto","created_at":"2025-04-14 07:45:37","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":78920,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw management and phosphorus rate on the uptake of nitrogen (A) and phosphorus (B) by cotton from 2020 to 2021. *, **, and NS represent significant differences at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05, \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01, and non-significant at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 probability levels in the boll opening stage, respectively. S and P represent straw management and phosphorus rate, respectively. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively. Each value is the average of 3 replications.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/dd807553793d781cf00a40b3.jpg"},{"id":80514434,"identity":"28837331-1f85-405a-bb93-1c71aafa249a","added_by":"auto","created_at":"2025-04-14 07:45:38","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":39930,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw management and phosphorus rate on the leaf area index from 2020 to 2021. *, ** represent significant differences at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05, \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01, respectively. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively. Each value is the average of 3 replications.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/4dde53f70e2aec50686e810a.jpg"},{"id":80514465,"identity":"13bc5c63-ad0e-4f6e-8531-336a61e488ab","added_by":"auto","created_at":"2025-04-14 07:45:39","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":78278,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of straw management and phosphorus rate on the number of square and flower, and boll from 2020 to 2021. Values followed by different little letters within the same year and stage are significantly different at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 probability level. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively. Each value is the average of 3 replications.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/154d3c0db64315ebccebeecc.jpg"},{"id":80514462,"identity":"b995a002-8210-4768-8114-4c40f9c95d9a","added_by":"auto","created_at":"2025-04-14 07:45:38","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":59283,"visible":true,"origin":"","legend":"\u003cp\u003eThe partial least squares path model for the effects of soil physical and chemical properties, N-metabolism enzymes, free amino acid, N uptake, and lint yield and fiber quality (GOF = 0.791). Physical and chemical properties of soil, N-metabolism enzymes, and fiber quality are latent variables. Physical and chemical properties of soil is indicated by available nitrogen (Av-N), available phosphorus (Av-P), organic matter (OM), and bulk density (BD); N-metabolism enzymes is indicated by the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT); fiber quality is indicated by length, strength, and micronaire. Positive and negative effects are indicated by red and blue line, respectively. ** represent significant differences at \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01 probability levels, respectively.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/45b90a3727f166a817746dcb.jpg"},{"id":80514429,"identity":"fd24b649-7f37-4a1a-85d9-d65b0605b2f2","added_by":"auto","created_at":"2025-04-14 07:45:38","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":63540,"visible":true,"origin":"","legend":"\u003cp\u003eEffects\u003cstrong\u003e \u003c/strong\u003eof straw retention combined with phosphorus application on physical and chemical properties of soil, root N metabolism, the shoot growth, and lint yield and fiber quality. The increased or decreased amplitudes\u003cstrong\u003e \u003c/strong\u003eof substrate contents, enzyme activities, changes of indicators under straw retention combined with phosphorus application were indicated by “↑” with red or “↓” with blue. Av-N: available nitrogen; Av-P: available phosphorus; OM: organic matter; BD: bulk density; NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e: nitrate; NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e: nitrite; NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e: ammonium; Gln: glutamine; Glu: glutamic acid; NR: nitrate reductase; NiR: nitrite reductase; GS: glutamine synthetase; GOGAT: glutamate synthase; FAA: free amino acid; SP: soluble protein; LAI: leaf area index.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/92c3399ca2c5195c72118dbc.jpg"},{"id":90640622,"identity":"2d8a5c65-f5f0-4cde-829d-cbf67b2438e6","added_by":"auto","created_at":"2025-09-05 06:30:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2113604,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/4e7960bc-0b72-47d7-af14-84d16602823a.pdf"},{"id":80514416,"identity":"ce217c96-8793-4665-a9be-087bf031f433","added_by":"auto","created_at":"2025-04-14 07:45:37","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":18664,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaldata.docx","url":"https://assets-eu.researchsquare.com/files/rs-6218247/v1/9823bb7c9583429f76fb5bac.docx"}],"financialInterests":"","formattedTitle":"Straw retention combined with phosphorus application improved soil properties, root nitrogen metabolism and optimized the relationship between root and shoot of cotton","fulltext":[{"header":"Highlights","content":"\u003cp\u003e\u0026bull; Straw retention combined with phosphorus application improved cotton lint yield and fiber quality.\u003c/p\u003e\u003cp\u003e\u0026bull; Straw retention and phosphorus application were more conducive to shoot biomass accumulation than root.\u003c/p\u003e\u003cp\u003e\u0026bull; Straw retention and phosphorus application improved nitrogen uptake by cotton.\u003c/p\u003e\u003cp\u003e\u0026bull; Root nitrogen metabolism capacity significantly affected lint yield and fiber quality.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eCotton (\u003cem\u003eGossypium hirsutum\u003c/em\u003e L.), a vital commercial crop in the world, provides raw materials for the textile industry, and its lint yield and fiber quality determine its economic value and textile products quality (Hussain et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, soil phosphorus (P) availability is low due to its poor mobility and easy fixation by soil, which seriously reduces the yield and quality of cotton (Huo et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Applying chemical P fertilizer is considered an effective practice to meet the demand for P in cotton growth and guarantees high yield and quality of cotton (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e). Notably, excessive input of chemical P fertilizer failed to consistently improve cotton yield and fiber quality but would increase the cotton production costs and bring environmental risks (Cordell et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Xie et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e). Meanwhile, the non-renewability of the raw material for P fertilizer, phosphate ore, also promotes agricultural producers to explore alternative ways of chemical P fertilizer. Straw retention is considered an environmentally friendly cultivation practice that could affect soil organic P mineralization, improve soil P availability, and interact with chemical P fertilizer to co-promote cotton growth, and ultimately achieve a reduction in chemical P application without reducing cotton yield (Cao et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wu et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e; Wei et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, there are fewer studies on the internal mechanisms of the positive effects on the cotton growth under straw retention combined with P application.\u003c/p\u003e \u003cp\u003eNitrogen (N) metabolism in cotton is closely related to the development of cotton yield and fiber quality as it affects N uptake, photosynthesis, and the transport of nutrients and carbohydrates (Iqbal et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Hassanzadehdelouei et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Meanwhile, it should be pointed out that these metabolic processes also require P participation as energy and signaling molecules (Wang et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Therefore, it is unsurprising that plenty of literature pointed out that there is a significant interaction between P and N in the growth of plants. Krouk and Kiba, (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and Hao et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) summarized this phenomenon in detail from the perspective of ecology, agronomy, physiology, and molecular biology by, including the synergistic effects of N and P co-fertilization on crop yield and quality, N and P acquisition and utilization, and the starvation response of N and P. However, until now, the effects of N and P metabolism on crop yield and quality have been considered more separately under different cultivation environments (Liu et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCrop root, the organ responsible for nutrient uptake, is the first organ that senses the change of soil nutrient and is sensitive to the changes in environmental factors. Meanwhile, the N required for the formation of crop yield and quality is significantly affected by root N metabolism, which is sensitive to the changes in environmental factors (Oliveira et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Ding et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Previous studies reported that optimal irrigation amount and N rate increased N uptake by root and further improved final yield and fiber quality of cotton (Hou et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e). He et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) also pointed out that the reduction of soil moisture limited root N uptake and changed the N status of cotton, which decreased photosynthetic capacity and yield. Hence, it is of great significance to explore the changes of N metabolism in cotton root to reveal the physiological mechanism of straw retention combined with P fertilizer affecting the formation of cotton yield and quality.\u003c/p\u003e \u003cp\u003eN metabolism in roots is controlled by nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT). The absorbed nitrate is reduced to nitrite by NR, and subsequently, nitrite reductase further reduces nitrite to ammonium. GS catalyzes the synthesis of glutamine (Gln) from ammonium and glutamic acid (Glu), while GOGAT catalyzes Gln and α-ketoglutaric acid to form Glu (Liu et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Part of the absorbed N is assimilated to amino acid preliminarily in the root, which is used for root growth and transferred to the aboveground. Studies in Arabidopsis (\u003cem\u003eArabidopsis thaliana\u003c/em\u003e) and soybean (\u003cem\u003eGlycine max\u003c/em\u003e) showed that P deficiency decreased the activities of NR and GS in roots, limiting N uptake and assimilation and reducing the biomass of plants (Heidari et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). A previous study on rice (\u003cem\u003eOryza sativa\u003c/em\u003e L.) reported that straw retention promoted N uptake and accumulation by enhancing root NR activity and oxidative activity, increasing grain yield and quality (Hamoud et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For cotton, many studies also pointed out that both straw retention and P application could increase N and P accumulation, improving lint yield and fiber quality (Wang et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Huo et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), but the relevant physiological mechanism is still unclear. Fortunately, it has been proven that high root activities of NR, GS, and GOGAT could increase the uptake, assimilation, and accumulation of N in cotton (Iqbal et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, we speculated that straw retention combined with P application might promote the formation of cotton yield and fiber quality by enhancing biomass accumulation and N assimilation affected by NR, GS, and GOGAT in cotton root.\u003c/p\u003e \u003cp\u003eIt should be noted that the accumulation and distribution of biomass are the basis for the formation of crop yield and quality (Li et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e), and an unbalanced relationship between the root and shoot would decrease the crop yield and quality. For example, under abiotic stress conditions (such as nutrient and water limit), the root is preferentially allocated more resources to maintain its growth and function, which would directly limit the aboveground growth and is not conducive to the formation of crop yield and quality (Poorte \u0026amp; Nagel, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Robinson, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Crop root N metabolism has a significant effect on aboveground photosynthesis and carbon assimilate transport, and this effect would lead to the differences in biomass allocation among different organs (Oliveira et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Hassanzadehdelouei et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Hence, it is important to accurately describe the relationship between cotton root and shoot growth under different soil P status to identify the internal mechanism for straw retention combined with P application affecting cotton yield and quality. The allometric biomass partitioning theory model provides a method to achieve this goal (Mccarthy \u0026amp; Equist, 2007; Chen and Weiner, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBriefly, straw retention is an environmentally friendly cultivation practice that could partially replace P fertilizer without decreasing seedcotton yield. However, it is not clear how the physiological process of root N metabolism and its relationship with lint yield and fiber quality of cotton respond to straw retention combined with P application. Hence, this study aimed to explore the responses of root N metabolism under different straw management and P application rates to reveal the physiological mechanism of straw retention combined with P application on lint yield and fiber quality. For this purpose, we hypothesized that (1) straw retention combined with P application enhanced root N metabolism in cotton, and (2) the coordinated relationship between root and shoot of cotton improved lint yield and fiber quality synergistically. To verify this hypothesis, we investigated the changes of N metabolism-related substance contents and enzyme activities in roots under different straw managements and P application rates, and their relationship with lint yield and fiber quality. Moreover, due to the indeterminate growth habit of cotton, optimizing the relationship between root and shoot was crucial for its growth and development. Hence, this study also analyzed the dynamic growth relationship between root and shoot.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eExperimental site\u003c/h2\u003e \u003cp\u003eThe positioning experiment of annual straw retention combined with P fertilizer was conducted from 2016 to 2021 at Dafeng Basic Seed Farm in Yancheng (33\u0026deg;12\u0026prime;N, 120\u0026deg;28\u0026prime;E), China, and the experiment involved in this report was carried out in 2020\u0026ndash;2021 (the 5th -6th year of wheat-cotton straw retention to the field). The soil type is sandy loam, and the available P content was 17.3 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the soil of 0\u0026ndash;20 cm soil layer at the beginning of the positioning experiment, which could not meet the P demand for cotton growth (Cai et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and the other initial soil properties in 2016 were reported by Cao et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), The basic properties of the soil in 0\u0026ndash;20 cm soil layer before cotton sowing in 2020 are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. During the cotton season (May-October), the average temperature was 22.9\u0026deg;C and 23.5\u0026deg;C, and the total precipitation was 865 mm and 633 mm from 2020 to 2021, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\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\u003eThe physical and chemical properties of soil in 2020 (0\u0026ndash;20 cm).\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=\"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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStraw management\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePhosphorus rate\u003c/p\u003e \u003cp\u003e(kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBD\u003c/p\u003e \u003cp\u003e(g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSOM\u003c/p\u003e \u003cp\u003e(g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTN\u003c/p\u003e \u003cp\u003e(g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTP\u003c/p\u003e \u003cp\u003e(g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAN\u003c/p\u003e \u003cp\u003e(mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAP\u003c/p\u003e \u003cp\u003e(mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\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\u003eStraw removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.37 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.84 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.67 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.59 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e8.95b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e7.31 d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.30 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.14 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.74 abc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.67 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.41 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e26.22 c\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.28 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.26 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.73 bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.69 ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.28 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e34.17 b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStraw retention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.23 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.29 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.72 bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.60 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11.33 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e9.10 d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.21 cd\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.69 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.78 ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.68 ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e12.12 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e32.02 b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.20 d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.13 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.81 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.70 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11.73 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e39.33 a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eValues followed by different little letters in the same column are significantly different at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 probability level. BD, SOM, TN, TP, AN, and AP represent bulk density, soil organic matter, total nitrogen, total phosphorus, available nitrogen, and available phosphorus, respectively. The data are quoted from (Wang et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eExperimental design\u003c/h3\u003e\n\u003cp\u003eThe positioning field experiment was designed as a two-factor split plot with three replicates. The main plot was set up with two straw management treatments [straw removal (S\u003csub\u003e0\u003c/sub\u003e) and straw retention (S\u003csub\u003e1\u003c/sub\u003e)], while the subplot was assigned three P rates [0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]. The cotton cultivar was CCRI 425 and was sown on May 22, 2020 and June 7, 2021 at a density of 90,000 plants ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Every subplot was 13.2 m in length and 6.0 m in width, and the cotton row and plant spacing were 81 cm and 13.7 cm, respectively. The application rate of nitrogen fertilizer (Urea, 46% of N) application rate was 225 kg N ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while 40% of the total N fertilizer was input at the seedling stage, and 60% at the initial flowering stage. Potassium (K) fertilizer (Potassium sulfate, 51% of K\u003csub\u003e2\u003c/sub\u003eO, 225 kg K\u003csub\u003e2\u003c/sub\u003eO ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and P fertilizer (Calcium triple superphosphate, 46% of P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e) were input totally at the seedling stage. The wheat cultivar was Yangmai 25 and was sown after harvesting cotton on November 17, 2020 and November 16, 2021 at a seeding rate of 187.5 kg ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. The row spacing for wheat was 14 cm, and no chemical fertilizer was input during the wheat seasons.\u003c/p\u003e \u003cp\u003eAfter the wheat or cotton harvest, the crop straw was collected from each plot and cut into 5\u0026ndash;8 cm long, respectively. Meanwhile, the treated wheat straw or cotton straw (each 6,000 kg ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were spread evenly to the soil surface of plots corresponding to the straw retention treatment before cotton or wheat sowing. Then, the crop straw was rotated into 0\u0026ndash;20 cm soil layer, and the plots of straw removal treatment were also rotated without straw. Other cultivation management was conducted according to local production requirements.\u003c/p\u003e\n\u003ch3\u003eSampling\u003c/h3\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eSoil sampling\u003c/h2\u003e \u003cp\u003eThe soil before sowing cotton and after harvesting cotton was collected as follows: Five sites in each plot were selected to measure soil bulk density through the cutting ring method. Simultaneously, soil samples (0\u0026ndash;20 cm soil layer) of five sites in each plot were collected randomly and mixed evenly. All the soil samples were removed debris, passed through a 0.85 mm sieve, and divided into two equal parts. One part was used to determine soil available nitrogen contents immediately, and the other was air dried to test the contents of organic matter, total nitrogen, total phosphorus, and available phosphorus in soil.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePlant sampling\u003c/h3\u003e\n\u003cp\u003eTen consecutive cotton plants with consistent growth situation in each subplot were marked at the seeding stage, which was used for the statistics of cotton square, flower and boll numbers at the peak squaring stage (PSS), peak flowering stage (PFS), peak boll setting stage (PBS), and boll opening stage (BOS), respectively.\u003c/p\u003e \u003cp\u003eFive cotton plants with consistent growth from each subplot were collected at PSS, PFS, PBS, and BOS, respectively. After which these plants were divided into root, stem, leaf, and reproductive organs. The leaf area of 5 plants was measured with a leaf area meter (LI-8100, Li-Cor, Lincoln, USA) to calculate the leaf area index (LAI). Whereafter, all plant samples were separately dried at 105℃ for 30 min and then at 80℃ until a constant weight to measure the biomass, N and P accumulation of cotton per hectare.\u003c/p\u003e \u003cp\u003eThree cotton plants were selected randomly from each subplot to collect the root and mix homogeneously at PSS, PFS, PBS, and BOS, respectively. One part of the cotton root sample was frozen with liquid nitrogen and stored at -80℃ for the determination of enzyme activities and soluble protein content in the root; the other part was dried at 105℃ for 30 min and then at 80℃ until a constant weight for the determination of free amino acid content.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSoil nutrient content\u003c/h2\u003e \u003cp\u003eReferring to Lu (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), the measurement methods of soil nutrient contents were as follows: Soil organic matter content was determined by the dichromate oxidation method. Total N content was analyzed using the Kjeldahl method. Total P content was assessed through the NaOH fusion and colorimetric method. Available N content was measured utilizing an automated discrete analyzer (CleverChem 380, Dechem-Tech, Germany). Available P content was determined by the molybdenum antimony spectrophotometric method.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eLint yield and fiber quality\u003c/h3\u003e\n\u003cp\u003eTwenty consecutive cotton plants were selected in each plot to collect all mature opening bolls. After natural air-drying of seedcotton, the fiber was separated from cottonseed and weighted to calculate lint yield. Fiber quality characteristics were measured by using a high-volume instrument (HVI MF100, USTER, Switzerland) according to the specific measurement details in the report of Liu et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eThe N and P uptake by cotton\u003c/h3\u003e\n\u003cp\u003eSamples after drying and weighing biomass were ground and sifted to pass through a 0.5 mm sieve for N and P analysis by the Kjeldahl method and molybdenum antimony spectrophotometric method, respectively according to the specific details in the report of Ma et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eThe contents of free amino acid and soluble protein\u003c/h2\u003e \u003cp\u003eDried cotton root sample (0.3 g) was mixed with 3 mL of 80% (v/v) ethanol and bathed at 80 ℃ for 30 min. Subsequently, the homogenate was centrifuged at 10,000g for 5 min, and the supernatant was transferred into a 10 mL volumetric flask. The above extraction steps were repeated three times, and finally, 80% ethanol was used to dilute the resulting supernatant to 10 mL. The free amino acid content was measured by using the hydrated ninhydrin colorimetric, and the specifical operation was performed following the study of Liu et al. (2010).\u003c/p\u003e \u003cp\u003eFresh root sample (0.3 g) was ground into homogenate with 5 mL phosphate buffer (100 mM, pH 7.5) under aground 4℃. Then, the homogenate was centrifuged at 15,000g for 10 min under 4℃, and the supernatant was collected to measure soluble protein content by coomassie brilliant blue method referring to Bradford (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1976\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eEnzyme extraction and analysis\u003c/h2\u003e \u003cp\u003eThe activities of nitrate reductase (NR, EC 1.6.6.1), glutamine synthetase (GS, EC 6.3.1.2), and glutamate synthase (GOGAT, EC 1.4.1.14) were measured referring to the method of Lin et al. (1996) and Ding et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSpecifically, the extraction solution was prepared as follows: The fresh root sample (0.5 g) was ground into homogenate with 5 mL 0.1 M phosphate buffer (30.10 g Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e\u0026middot;12H\u003csub\u003e2\u003c/sub\u003eO and 2.50 g NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO, pH 7.5) under 4℃. Then, the homogenate was centrifuged at 15,000g for 15 min under 4℃, and the supernatant was collected to measure NR activity. The NR activity measurement method was as follows: 1 mL prepared extraction solution was mixed evenly with 1.2 mL 0.1 M phosphate buffer and 0.4 mL 2 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e NADH in a tube for 1 h under 25℃. Subsequently, 1 mL of 1% sulfanilamide solution was added to the mixture to terminate the reaction. Then, 1 mL 1% naphthylvinylamine solution was added into the mixture and mixed evenly. After 1 h, the mixture was centrifuged at 15,000 g for 15 min, and the absorbance of supernatant was measured the absorbance at 540 nm to calculate NR activity. The NADH solution was replaced with 0.4 mL 0.1 M phosphate buffer in the control group\u003c/p\u003e \u003cp\u003eFor GS and GOGAT, fresh root sample (0.5 g) was ground into homogenate with 5 mL 0.1 M Tris-HCl buffer (pH 7.6) under around 4℃. Then, the homogenate was centrifuged at 12,000g for 20 min under 4 ℃, and the supernatant was collected to measure the activities of GS and GOGAT. The GS activity measurement method was as follows: 1.2 mL prepared extraction solution was mixed evenly with reaction solution (including 0.6 mL 0.25 M imidazole-HCl, 0.4 mL 0.3 M sodium glutamate, 0.4 mL 0.03 M ATP-Na, 0.2 mL 0.5 M MgSO\u003csub\u003e4\u003c/sub\u003e, pH 7.0) under a 25 ℃ water bath for 5 min. Subsequently, 0.2 mL 1 M hydroxylamine (including 1 M NaOH and 1 M NH\u003csub\u003e2\u003c/sub\u003eOH-HCl) was combined with the mixture for a 15-min water bath under 25℃. And then, 0.8 mL terminate reaction solution [10% (w/v) FeCl\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO, 50% (v/v) HCl, and 24% (w/v) trichloroacetic acid were mixed in equal volume] was added into the mixture. After 20 min, the mixture was centrifuged at 15,000g for 10 min, and the absorbance of supernatant was measured the absorbance at 540 nm to calculate GS activity. For GOGAT activity, 250 \u0026micro;L prepared extraction solution was mixed evenly with 550 \u0026micro;L reaction solution (including 25 \u0026micro;L 20 mM α-ketoglutaric acid, 50 \u0026micro;L 10 mM KCl, 200 \u0026micro;L 3 mM NADH, 275 \u0026micro;L 0.1 M Tris-HCl buffer, pH 7.6). Then, the reaction was started after adding 200 \u0026micro;L 20 mM L-glutamine, and the change in the absorbance of solution at 340 nm within 5 min was detected to calculate GOGAT activity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe analysis of experimental data was completed with SPSS 22.0 (IBM, USA) and Microsoft Excel 2019. The least significant difference method (LSD) was used for analyzing the differences in all indicators at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 probability level among all treatments. A two-factor analysis of variance was used to explore the effects of straw management, P application, and their interaction effect on all indicators in each year. The partial least squares path analysis was performed by Smart-PLS to analyze the relationships among physical and chemical properties of soil, N-metabolism enzymes, free amino acid, N accumulation with lint yield and fiber quality. All figures were generated by Origin Pro 2023.\u003c/p\u003e \u003cp\u003eThe relationship between root and aboveground part of cotton was analyzed by the allometric growth model Eq.\u0026nbsp;(1) (Mccarthy and Enquist, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2007\u003c/span\u003e):\u003c/p\u003e \u003cp\u003elg Y\u0026thinsp;=\u0026thinsp;α lg M\u0026thinsp;+\u0026thinsp;lg β (1)\u003c/p\u003e \u003cp\u003eWhere α is the scaling exponent, β is the allometric constant. Y and M are the cotton biomass of aboveground part and root in the same stage, respectively.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eLint yield and fiber quality\u003c/h2\u003e \u003cp\u003eBoth straw management and P application significantly increased lint yield, and there was a significant interaction between straw management and P application on lint yield (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Specifically, compared with S\u003csub\u003e0\u003c/sub\u003e, the lint yield under S\u003csub\u003e1\u003c/sub\u003e with 0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 8.2%-11.8%, 6.3%-7.3%, and 2.4%-8.8%, respectively. In comparison with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the lint yield under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 55.6%-72.9%, 74.2%-84.9% for S\u003csub\u003e0\u003c/sub\u003e, and by 54.3%-64.5%, 69.4%-75.2% for S\u003csub\u003e1\u003c/sub\u003e, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFiber quality also markedly changed under different straw management and P rates (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Straw retention increased fiber length but reduced micronaire (except for fiber length in 2021 and micronaire in 2021), while had no significant effect on fiber strength; P application significantly increased fiber length and strength but reduced micronaire. Straw management and P rate had no significant interaction effect on fiber quality (except for micronaire in 2021). Specifically, compared with S\u003csub\u003e0\u003c/sub\u003e, the fiber length under S\u003csub\u003e1\u003c/sub\u003e with 0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 0.5, 0.3, and 0.3 mm in 2020, respectively. In comparison with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, averaged across from 2020 to 2021, the fiber length under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased 1.7, 2.4 mm for S\u003csub\u003e0\u003c/sub\u003e, by 1.5, 2.1 mm for S\u003csub\u003e1\u003c/sub\u003e; the fiber strength increased 1.4, 2.0 cN tex\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for S\u003csub\u003e0\u003c/sub\u003e, by 1.3, 1.9 cN tex\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for S\u003csub\u003e1\u003c/sub\u003e, respectively. The micronaire ranged from 3.9 to 4.5 in each treatment, consistent with high-quality cotton fiber standards (micronaire rank standards: A, 3.7\u0026ndash;4.2; B, 3.5\u0026ndash;3.6 or 4.3\u0026ndash;4.9; C, 3.4 and below or 5.0 and above). Meanwhile, the micronaire value decreased under straw retention and P application, which reached a higher standard in this study.\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\u003eEffects of straw management and phosphorus rate on fiber quality from 2020 to 2021.\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\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eStraw management\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePhosphorus rate\u003c/p\u003e \u003cp\u003e(kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eFiber length\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eFiber strength\u003c/p\u003e \u003cp\u003e(cN tex\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eMicronaire\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2020\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2021\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2020\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2021\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2020\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e2021\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStraw removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28.6 d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e28.7 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e29.5 d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e28.5 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.5 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.3 a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30.8 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e29.9 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.2 c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.5 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.5 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.0 bc\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.7 ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30.3 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e32.1 ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.9 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.2 cd\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.9 c\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStraw retention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.1 d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e29.0 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e29.7 d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e28.8 b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.4 ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.1 b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.1 bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30.0 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.6 bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.5 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.3 bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.2 ab\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32.0 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30.3 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e32.4 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.9 a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.0 d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.0 bc\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eSource of variation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eStraw management (S)\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\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\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003ePhosphorus rate (P)\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 \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eS \u0026times; P\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\u003e*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eValues followed by different little letters in the same column are significantly different at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 probability level. *, **, and NS represent significant differences at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01, and non-significant at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 probability levels, respectively. Each value is the average of 3 replications.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eSoil nutrient contents and bulk density\u003c/h2\u003e \u003cp\u003eStraw retention significantly increased the contents of available N (Av-N), available P (Av-P), and organic matter (OM) but decreased bulk density (BD) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e); P application significantly increased Av-P content but had relatively minor effects on the contents of Av-N, OM, and BD. Specifically, compared with S\u003csub\u003e0\u003c/sub\u003e, the Av-N content under S\u003csub\u003e1\u003c/sub\u003e with 0, 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 33.8%-43.6%, 38.4%-39.8%, 16.2%-42.6%; the Av-P content increased by 37.6%-59.4%, 21.7%-24.5%, 16.2%-22.8%; the OM content increased by 16.3%-17.2%, 12.5%-15.8%, 7.8%-16.9%; the BD decreased by 8.6%-8.8%, 7.8%-9.1%, 6.7%-7.1%, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eThe contents of free amino acid and soluble protein in root\u003c/h2\u003e \u003cp\u003eThe contents of free amino acid and soluble protein in root were significantly affected by straw management, P application, and their interaction at PFS (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Specifically, compared with S\u003csub\u003e0\u003c/sub\u003e, the free amino acid content under S\u003csub\u003e1\u003c/sub\u003e with 0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 3.0%-6.7%, 9.6%-10.3%, and 6.1%-10.8% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA); the soluble protein content increased by 14.3%-14.5%, 14.3%-13.7%, and 3.0%-6.4% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB), respectively. In comparison with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the free amino acid content under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 9.7%-26.7%, 18.9%-35.2% for S\u003csub\u003e0\u003c/sub\u003e, and by 16.7%-31.6%, 37.8%-40.5% for S\u003csub\u003e1\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA); the soluble protein content increased by 25.8%-38.0%, 14.3%-21.8% for S\u003csub\u003e0\u003c/sub\u003e, and by 25.5%-37.3%, 6.9%-9.7% for S\u003csub\u003e1\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB) at PFS, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eThe enzyme activities related to N metabolism in root\u003c/h2\u003e \u003cp\u003eThe nitrate reductase (NR) activity decreased gradually with the growth stage proceeding and peaked at PSS. The activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) increased first and then decreased with the growth stage proceeding and peaked at PFS. Straw management, P application, and their interaction had significant effects on the above enzyme activities at PFS (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Specifically, compared with S\u003csub\u003e0\u003c/sub\u003e, the NR activities at PFS under S\u003csub\u003e1\u003c/sub\u003e with 0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 10.5%-13.1%, 19.3%-23.6%, and 11.8%-20.0% (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA); the GS activities increased by 8.4%-13.4%, 21.0%-29.6%, and 12.8%-26.6% (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB); the GOGAT activities increased by 7.6%-11.2%, 24.8%-29.2%, and 13.9%-20.2% (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC), respectively. Compared with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the NR activities at PFS under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 41.0%-50.6%, 57.7%-65.3% for S\u003csub\u003e0\u003c/sub\u003e, and by 52.2%-64.7%, 63.5%-71.2% for S\u003csub\u003e1\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA); the GS activities increased by 24.8%-31.0%, 38.5%-42.6% for S\u003csub\u003e0\u003c/sub\u003e, and by 39.2%-49.6%, 44.0%-59.1% for S\u003csub\u003e1\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB); the GOGAT activities increased by 39.7%-41.0%, 56.1%-59.4% for S\u003csub\u003e0\u003c/sub\u003e, and by 62.4%-63.5%, 67.8%-68.8% for S\u003csub\u003e1\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC), respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eNitrogen and phosphorus uptake by cotton\u003c/h2\u003e \u003cp\u003eThe accumulation of N and P in cotton increased gradually with growth stage proceeding and peaked at BOS. Both straw management and P application had a significant positive effect on them (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), while only the P accumulation was significantly affected by the interacted interaction effect of straw management and P application (except for 2020). Compared with S\u003csub\u003e0\u003c/sub\u003e, straw retention increased the N and P accumulation by 0.6%-12.8% and 3.3%-20.0% from 2020 to 2021 across different P rates, respectively. In comparison with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the N accumulation under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 38.6%-55.5%, 55.7%-74.1% for S\u003csub\u003e0\u003c/sub\u003e, and by 33.6%-49.0%, 45.4%-61.6% for S\u003csub\u003e1\u003c/sub\u003e; the P accumulation increased by 72.5%-92.3%, 124.0%-161.2% for S\u003csub\u003e0\u003c/sub\u003e, and by 72.1%-86.9%, 109.6%-126.9% at BOS, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eLeaf aera index (LAI)\u003c/h2\u003e \u003cp\u003eThe LAI increased first and then decreased with the growth stage proceeding and reached the highest values at PBS (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). LAI was significantly influenced by straw management and P application. Compared with S\u003csub\u003e0\u003c/sub\u003e, the LAI increased by 8.2%-13.9%, 5.6%-6.3% for S\u003csub\u003e1\u003c/sub\u003e with 0, 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at PBS. Additionally, in comparison with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the LAI under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 26.1%-32.2%, 45.6%-50.2% for S\u003csub\u003e0\u003c/sub\u003e, and by 23.0%-23.4%, 37.4%-38.8% for S\u003csub\u003e1\u003c/sub\u003e at PBS, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eDynamics of cotton square and flower number and boll number\u003c/h2\u003e \u003cp\u003eThe square and flower number peaked at PFS (maximum was 171 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e no. ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and the boll number obtained the maximum values at BOS (maximum was 123 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e no. ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e); straw retention and P application markedly increased their number (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Specifically, Compared with S\u003csub\u003e0\u003c/sub\u003e, the number of square and flower under S\u003csub\u003e1\u003c/sub\u003e with 0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eincreased by 3.7%-4.5%, 7.3%-8.4%, and 1.6%-1.9% at PFS, respectively; the boll number increased by 11.7%-15.4%, 9.0%-9.3%, 1.7%-1.9% at BOS, respectively. In comparison with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the number of square and flower at PFS under 100, 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased by 11.3%-13.4%, 18.2%-24.0% for S\u003csub\u003e0\u003c/sub\u003e, and by 15.5%-17.3%, 15.7%-21.0% for S\u003csub\u003e1\u003c/sub\u003e, respectively; the boll number at BOS increased by 43.4%-64.8%, 55.7%-88.8% for S\u003csub\u003e0\u003c/sub\u003e, and by 35.7%-61.2%, 37.3%-72.1% for S\u003csub\u003e1\u003c/sub\u003e, respectively. The square and flower number (at PFS) and boll number (at BOS) under S\u003csub\u003e1\u003c/sub\u003e combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e could reach similar levels under S\u003csub\u003e0\u003c/sub\u003e with 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eAllometric growth relationship between the root and shoot\u003c/h2\u003e \u003cp\u003eThe growth of the root and shoot interacted with each other in an obvious allometric growth relationship, which could be analyzed with the allometric growth model (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.889**-0.988**, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;18, \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e0.01\u003c/em\u003e\u003c/sub\u003e = 0.348, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;36, \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e0.01\u003c/em\u003e\u003c/sub\u003e = 0.180; Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Results showed that the allometric index (α) in each treatment during different growth stages were all over 1.000, indicating that the relative growth rate of shoot was faster than that of the root. Additionally, during PFS to PBS, the value of α in each treatment was the largest, which meant that the relative growth rate of shoot reached the maximum. It could be explained that the formation of reproductive organ was enhanced during this stage. Furthermore, the value of α increased under straw retention and P application which were more conducive to enhancing the shoot growth.\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 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of straw combined with phosphorus application on cotton parameter of allometric growth equation from 2020 to 2021.\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 \u003cp\u003eGrowth stage\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw management\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePhosphorus rate\u003c/p\u003e \u003cp\u003e(kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eallometric indexα\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eallometric constantβ\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR\u003csup\u003e2\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\u003eFrom PSS to PFS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.764\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.992**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.021\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.519\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.988**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.060\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.819\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.990**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw retention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.012\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.457\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.997**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.026\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.325\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.994**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.059\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.724\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.992**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFrom PFS to PBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.398\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.428\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.957**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.506\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.976**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.551\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.958**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw retention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.457\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.975**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.709\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.060\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.938**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.095\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.933**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFrom PBS to BOS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.481\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.254\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.937**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.252\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.222\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.915**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.366\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.879**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw retention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.408\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.420\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.836**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.679\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.898**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.137\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.999\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.884**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFull growth stage\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw removal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.985\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.987**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.618\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.986**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.173\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.188\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.986**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStraw retention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.122\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.679\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.986**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.259\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.985**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.184\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.983**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12, \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e0.01\u003c/em\u003e\u003c/sub\u003e = 0.501 (including the growth stage from PSS to PFS, from PFS to PBS, and from PBS to BOS); \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;24, \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e0.01\u003c/em\u003e\u003c/sub\u003e = 0.265 (including the growth stage of full growth stage). ** means the significant differences at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01 probability level. PSS, PFS, PBS, and BOS represent the peak squaring stage, peak flowering stage, peak boll setting stage, and boll opening stage, respectively.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eRelationship among the soil condition, N metabolism, lint yield and fiber quality\u003c/h2\u003e \u003cp\u003eThe partial least squares path analysis was conducted to investigate the relationships among the physical and chemical properties of soil, root N metabolism, and N accumulation with lint yield and fiber quality (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The results showed that soil nutrient contents (Av-N, Av-P, and Av-K) had significant positive influences, but BD significantly negatively influenced on the activities of enzymes (NR, GS, and GOGAT) related to N metabolism directly. Furthermore, the enzyme activities related to N metabolism positively influenced N accumulation, which in turn significantly affected lint yield and fiber quality. In addition, the content of free amino acid was directly affected by the enzyme activities related to N metabolism, which could be expressed by linear regression equations: Y \u003csub\u003e\u003cem\u003efree amino acid\u003c/em\u003e\u003c/sub\u003e = 0.055X \u003csub\u003e\u003cem\u003eNR\u003c/em\u003e\u003c/sub\u003e + 0.316X \u003csub\u003e\u003cem\u003eGS\u003c/em\u003e\u003c/sub\u003e \u0026minus;\u0026thinsp;0.082 X \u003csub\u003e\u003cem\u003eGOGAT\u003c/em\u003e\u003c/sub\u003e + 2.959 (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.865**, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;12, \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e0.05\u003c/em\u003e\u003c/sub\u003e = 0.604, \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003e0.01\u003c/em\u003e\u003c/sub\u003e = 0.740). Based on this equation, it is evident that the content of free amino acid was obviously influenced by the activities of NR, GS, and GOGAT in cotton root.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003e \u003cb\u003eStraw retention combined with P application improved lint yield and fiber quality by optimizing root-shoot allometric growth relationship\u003c/b\u003e \u003c/p\u003e \u003cp\u003eStraw retention combined with P application significantly improved lint yield in this report (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e; Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), similar result in seedcotton yield was detected by the research of Cao et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which attributed the increase in seedcotton yield to the increases in the number and weight of cotton boll. Moreover, the results of this study found that straw management, P application, and their interaction had significant influences on lint yield, which could be reflected by the fact that the lint yield under straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was similar to that under straw removal combined with 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Synergistically, straw retention and P application also improved fiber quality. Specifically, P application increased fiber length and strength, and optimized micronaire value. Straw retention mainly increased fiber length and optimized micronaire. Furthermore, the fiber quality (including length, strength, and micronaire) of straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e reached a similar level of that under straw removal with 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which reached the highest fiber quality standard statistically in all treatments (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Previous studies also reported that the fiber quality of cotton was not decreased by reducing moderately the amount of N and K fertilizer under straw retention in the field (Qayyum et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). As above, we found that the best lint yield and fiber quality could be achieved by straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in a statistical sense.\u003c/p\u003e \u003cp\u003eBiomass is the basis of crop yield and quality formation, but only focusing on the change of biomass cannot improve the yield and quality most effectively. Previous studies pointed out that a coordinated root-shoot relationship guarantees normal growth of plants and formation of yield and quality (Kleyer \u0026amp; Minden, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Robinson, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Guo et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Additionally, some studies also have suggested that root dominated the growth balance of cotton (Li et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e), and strong root system is essential to supporting shoot growth and promoting the formation of crop yield and quality (Ma et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Jin et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Hence, we used allometric growth model to explore the relationship between root and shoot growth of cotton in this study. The result indicated that the relative growth rate of the aboveground was higher than that of root. However, it should be noted that the relatively low growth rate did not mean that root growth was limited. On the contrary, cotton root under straw retention combined with P application obtained higher biomass, indicating that its growth was enhanced (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e; Table S1). To illustrate the effect of this optimized growth relationship on lint yield and fiber quality, we further evaluated the LAI of the cotton population, which is considered to be an important factor affecting cotton yield and fiber quality (Bange et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e). Our study found that the yield and quality of fiber, and LAI increased together under straw retention combined with P application. In other words, our results about the allometry relationship between root and shoot demonstrated that straw retention combined with P application tended to enhance the aboveground growth due to better root growth basing on higher LAI (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e; Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e; Table S1). Furthermore, the number of reproductive organs significantly increased under straw retention combined with P application in our study (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Previous study also found that P application improved the photosynthesis of cotton leaf, accelerated the formation of cotton boll, and decreased the shedding rate, resulting in higher boll density and lint yield (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e). Similarly, Liu et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) also reported that maintaining a higher photosynthetic capacity of cotton population contributed to accumulating more biomass and distributing it to the reproductive organs. Meanwhile, for fiber quality, the fiber length and strength of cotton were also positively affected by the photosynthetic capacity of the leaf (Li et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), which was consistent with our result. In conclusion, straw retention had a P reduction effect (Cao et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). A proper amount of P fertilizer reduction under straw retention would not decrease lint yield and fiber quality by achieving a good root-shoot growth relationship.\u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003eEffects of straw retention combined with P application on root N metabolism\u003c/h2\u003e \u003cp\u003eIn term of soil, a meta-analysis assessed P-application effects on N dynamics, it observed that P application increased soil total N pool, potentially as a result of enhanced plant and microbial immobilization and reduced N losses, with a stronger effect detected under longer duration of P addition (greater than or equal to 5 year) (Wang et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2022c\u003c/span\u003e). Moreover, the root, as the main organ of the plant to uptake nutrient, connects the soil and the aboveground part of plant (Robinson, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). According to a study, the resource allocation between root and aboveground part was also considered potentially related to soil N cycle (An et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Several reports had shown that root N metabolism capacity had a direct effect on the accumulation and distribution of biomass, thereby affecting yield and quality of crop (Bai et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Jin et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In this report, lint yield and fiber quality were positively related to N metabolism capacity of cotton (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). Similar results were also proved by Chen et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and Bai et al. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) based on different N fertilizer rates and irrigation depth. Analyzing the relevant reasons, straw retention combined with P application increased nutrient availability and regulated the capacity of aeration and infiltration in soil by increasing the contents of Av-N, Av-P, and OM while decreasing BD. Meanwhile, our results indicated that soil properties were mainly affected by OM (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). Several studies reported that OM was an important factor to improve aggregate fraction, microbial structure and promote nutrients cycling in soil (Bu et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Qayyum et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Cao et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The improvement of soil nutrients and physical conditions alleviated the inhibition of root growth and was conducive to the uptake and assimilation of N in roots (Jin et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). As we know that N assimilation needs to consume adenosine triphosphate (ATP) and nicotine adenine dinucleotide phosphate (NADPH) whose synthesis were regulated by P (Rausch \u0026amp; Bucher, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Yanagisawa, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Hence, it is not surprising that straw retention combined with P application increased the activities of NR, GS, and GOGAT (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), leading to a significant increase in free amino acid and soluble protein content (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Meanwhile, higher activities of GS and GOGAT contributed to ammonium assimilation, reducing toxic effects of excessive ammonium, which could alleviate premature senescence of root and increase N uptake (Liu et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Studies in rice (\u003cem\u003eOryza sativa\u003c/em\u003e L.), cotton (\u003cem\u003eGossypium hirsutum\u003c/em\u003e L.), soybean (\u003cem\u003eGlycine max\u003c/em\u003e), and Arabidopsis (\u003cem\u003eArabidopsis thaliana\u003c/em\u003e) also showed that both straw retention and P application increased the activity and N metabolism capacity of root (Heidari et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Hamoud et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Jin et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Moreover, this report also demonstrated that the enhancement in root N metabolism enzymatic activity (NR, GS, and GOGAT) and plant N uptake decreased under per unit of P application as P application rates increased. Meanwhile, the positive effects of straw retention on these indexes also decreased with the increase of P application rate. This also explained from the perspective of N metabolism why the cotton yield of straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e had a similar level of that under straw removal with 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn general, the results of partial least squares path model further confirmed that N uptake had significant effects on lint yield and fiber quality (positive with lint yield, fiber length and strength, while negative with micronaire) which also was significantly affected by physical and chemical properties of soil and N-metabolism enzymes (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). As previously noted, straw retention combined with P application improved chemical properties of soil, N metabolism capacity of root, and N uptake, elucidating the mechanisms driving the change in lint yield and fiber quality.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eStraw retention combined with P application enhanced the N metabolism capacity of root and optimized the relationship between root and shoot, which synergistically improved lint yield and fiber quality. Specifically, straw retention combined with P application improved soil physical and chemical properties (increased the contents of Av-N, Av-P, and OM, but decreased BD), and thus increased the activities of NR, GS, and GOGAT, stimulating the assimilation of N and P. Furthermore, the increased accumulation of N and P in cotton enhanced cotton photosynthetic capacity and regulated the distribution of cotton biomass, which was reflected by the fact that increased LAI provided sufficient carbon assimilates for the formation of cotton reproductive organs, which increased lint yield and improved fiber quality. Cotton under straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e obtain a similar level of lint yield and fiber quality to that under straw removal combined with 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Hence, considering lint yield, fiber quality, and ecological environment, straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e should be recommended for cotton production in the wheat-cotton rotation system.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work was supported by the National Natural Science Foundation of China (32071970), Fundamental Research Funds for the Central Universities (XUEKEN2022008), and the China Agriculture Research System (CARS-15-14).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAn Y, Wang L, Zhang MY, Tong SZ, Li YF, Wu HT, Jiang M, Wang X, Guo Y, Jiang L (2025) Synergies and trade-offs between aboveground and belowground traits explain the dynamics of soil organic carbon and nitrogen in wetlands undergoing agricultural management changes in semi-arid regions. 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Agr Ecosyst Environ 344:108301. https://doi.org/10.1016/j.agee.2022.108301.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6218247/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6218247/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cdiv id=\"ASec1\" class=\"AbstractSection\"\u003e \u003cdiv class=\"Heading\"\u003eAims\u003c/div\u003e \u003cp\u003eStraw retention combined with phosphorus (P) application has been proven to be an effective method to reduce the P application without decreasing cotton yield, but the related internal physiological mechanism of root is unclear. This study aimed to explore the impact of straw retention combined with different P application rates on soil nutrient content, the yield and quality of fiber, allometric growth relationship between root and shoot, and root nitrogen (N) metabolism.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"ASec2\" class=\"AbstractSection\"\u003e \u003cdiv class=\"Heading\"\u003eMethods\u003c/div\u003e \u003cp\u003eThe field experiment was conducted from 2020 to 2021 to study the effects of straw management (removal and retention) combined with different P rates (including 0, 100, and 200 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) on soil quality, different allocation of biomass, and N uptake and assimilation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"ASec3\" class=\"AbstractSection\"\u003e \u003cdiv class=\"Heading\"\u003eResults\u003c/div\u003e \u003cp\u003eThe results showed that straw retention combined with P application contributed to improving lint yield and fiber quality synergistically. The result due to the fact that straw retention combined with P application increased the soil nutrient contents but decreased the bulk density of soil, creating favorable soil conditions for cotton growth. Compared to straw removal combined with 0 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, improvement of physical and chemical properties of soil markedly increased the activities of nitrate reductase (10.5%-89.2%), glutamine synthetase (8.5%-80.5%), and glutamate synthase (3.0%-45.9%), which enhanced N uptake and assimilation. Additionally, the optimization of root N metabolism enhanced shoot growth of cotton by increasing the leaf area index and affecting cotton biomass allocation, which favored the formation of cotton square and flower, and boll.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"ASec4\" class=\"AbstractSection\"\u003e \u003cdiv class=\"Heading\"\u003eConclusions\u003c/div\u003e \u003cp\u003eOverall, straw retention combined with P application could improve soil physical and chemical properties and optimize the relationship between root and overground growth, which is conducive to the synergistic improvement of cotton yield and quality. Furthermore, straw retention combined with 100 kg P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was the best choice in the actual field agronomic practice of cotton production.\u003c/p\u003e \u003c/div\u003e","manuscriptTitle":"Straw retention combined with phosphorus application improved soil properties, root nitrogen metabolism and optimized the relationship between root and shoot of cotton","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-14 07:45:32","doi":"10.21203/rs.3.rs-6218247/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"39abe0f5-8154-4fb8-a04b-fd81705979e5","owner":[],"postedDate":"April 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-05T06:21:39+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-14 07:45:32","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6218247","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6218247","identity":"rs-6218247","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}