Soil organic carbon accumulation is mainly driven by soil nitrogen in rocky desertified mulberry plantation

Soil organic carbon accumulation is mainly driven by soil nitrogen in rocky desertified mulberry plantation | 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 Soil organic carbon accumulation is mainly driven by soil nitrogen in rocky desertified mulberry plantation yanjin shi, Mei Lu, Junfang Cui, Shiqing Peng, Fang Zhang, Shiyu Han, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7995665/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 Background and Aims Soil organic carbon (SOC), a critical determinant of soil functionality, remains inadequately characterized in its spatiotemporal dynamics and drivers within karst mulberry systems—an ecologically fragile region confronting severe rocky desertification. Methods This study elucidates SOC variability across typical karst landscapes through comparative analysis of mulberry plantations in rocky desertification zones (Rd) versus non-desertification areas (nRd) of central Guizhou, China, focusing on seasonal interactions with macro/micronutrients and biochemical factors. Results Key findings reveal: (1) Changes of SOC content in different soil types and seasons. SOC content in Rd plantations (31.51–39.71 g·kg − 1 ) consistently exceeded nRd counterparts (22.50–28.51 g·kg − 1 ) by 1.28–1.57-fold, with bimodal seasonal peaks in April/November and minima in May–July across both systems. (2) Carbon-nutrient coupling: SOC exhibited significant positive correlations with total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), available potassium (AK), and glomalin-related soil proteins (T-GRSP: Total glomalin-related soil protein; EE-GRSP: Easily extractable glomalin-related soil protein)), contrasting with significant negative associations with available phosphorus (AP). (3) System-specific drivers: Nitrogen-limitation governed SOC dynamics dominantly. However, pH emerged as a key secondary regulator in nRd systems. In addition, soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. Conclusion These findings establish nitrogen management as a critical lever for SOC sequestration optimization in karst mulberry systems while contextualizing landscape-specific edaphic controls. The work provides an empirical foundation for targeted carbon-smart practices in global karst agricultural ecosystems facing desertification pressures. Karst rocky desertification Morus alba cultivation Soil organic carbon dynamics Nitrogen limitation Glomalin-related soil proteins Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Soil organic carbon (SOC) constitutes the largest organic carbon reservoir in terrestrial ecosystems, and its small fluctuations may have a significant impact on atmospheric carbon dioxide levels and global carbon balance (Batlle-Bayer et al., 2010; Bossio et al., 2020; Chen et al., 2008; Zhou et al., 2018 ). It is very important to study the changes and influencing factors of soil organic carbon. The formation and accumulation of SOC result from the interaction between biotic and abiotic factors. Among the biotic factors, vegetation type and development stage are important indicators affecting SOC. Vegetation type influence the carbon supply by altering the quantity and quality of litter input (Julian et al., 2019; Qu et al., 2019). Bai et al.(2020) indicated that, within the 0–20 cm soil layer, the average soil organic carbon stock (SOCS) values exhibited the following order: Zanthoxylum bungeanum forest > round-leaved pine forest > round-bark privet mixed forest > sloping farmland > Zanthoxylum bungeanum-pitaya mixed forest > pitaya forest. During early vegetative stages, plants allocate more carbon belowground, contributing substantially to SOC formation (Yu et al., 2016). As plants mature, the proportion of photosynthetic carbon allocated to SOC decreases, but microbial biomass carbon increases (Shi et al., 2024). Yu et al. (2016) showed that the input of photosynthetic carbon by maize plants into soil organic carbon mainly occurs during the younger growth stages. Different microbial groups dominate carbon incorporation at various growth stages, with saprophytic fungi prevalent during vegetative stages and actinomycetes during reproductive stages (Zhang et al., 2022). Soil microorganism metabolism regulates carbon pool dynamics through the decomposition and transformation of organic matter (Kalbitz et al., 2000; Templer et al., 2004). As a metabolite of microorganisms, the activity of soil enzymes can reflect the availability of soil nutrients. As a protein, it can also directly affect the formation and accumulation of soil SOC. Verma et al. (2017) indicated that soil amendments improve soil organic carbon fractions, with labile fractions better correlated with soil enzyme activity, especially in the rhizosphere. These studies have shown that biological factors play an important role in affecting SOC. Glomalin-related soil protein (GRSP), a unique glycoprotein secreted exclusively by arbuscular mycorrhizal fungi (AMF), is highly stable in the soil environment (Wang et al, 2016). Once released into the soil, GRSP contributes to the accumulation of carbon and nitrogen, thereby enhancing the soil's carbon sequestration capacity (Agnihotri et al., 2021). Banegas et al. (2020) indicated that grazing and nitrogen fertilization of a tropical perennial grass can increase soil carbon through promotion of GRSP in saline environments. Regarding abiotic factors, soil physicochemical properties—such as pH and nutrient factors (eg. N, P, and K) contents levels—indirectly influence SOC content by modulating microbial activity and the soil’s capacity to adsorb organic matter (Huang et al., 2016; Luo et al., 2017). For example, in high pH soils, calcium ions form organic-inorganic complexes with organic matter, thereby reducing the loss of SOC (Tang, 2015). The influence mechanism of nitrogen and phosphorus on SOC is different. The N addition tends to decrease SOC decomposition and increase plant-derived carbon inputs, while P addition primarily enhances plant biomass and carbon inputs (Li et al., 2020; Luo et al., 2023). The impact of P on SOC is strongly mediated by N availability, with greater SOC accumulation observed under high N conditions (Luo et al., 2023). Short-term N and P additions in desert steppes increase SOC levels, particularly in the recalcitrant carbon pool, while decreasing SOC mineralization (Hai et al., 2024). Hai et al. (2024) pointed out that short-term N and P additions in desert steppes increase SOC levels, particularly in the recalcitrant carbon pool, while decreasing SOC mineralization. The results of the Hai et al. (2024) also indicated that these nutrient additions also alter microbial community composition and functional gene abundance, affecting carbon cycling processes. However, whether N and P promote or inhibit SOC accumulation and formation varies depending on soil conditions and nutrient availability. Li et al. (2020) studies have shown that long-term N and P additions may weaken soil carbon storage capacity in some ecosystems, such as alpine meadow. Guizhou, the epicenter of China's karst region, features soils rich in calcium and magnesium with high pH (Cao et al., 2008), creating a harsh environment with scant moisture and nutrients (Zhou et al., 2001; Zhang et al., 2009). Unique geological and climatic conditions, compounded by population pressure and development practices, have led to extensive rocky desertification in southwestern China (Liu ,2009), the region's most severe ecological and geological calamity (Wang, 2003). This has severely degraded soil quality and productivity, heightening concerns over rocky desertification. Mulberry ( Morus alba L.) possesses a well-developed root system and exhibits strong tolerance to cold and drought conditions. It has become an important economic tree species for enhancing the ecological environment and promoting sustainable agricultural development in karst regions (Srivastava et al., 2003). As a key region in the “East Mulberry Westward Expansion” initiative, Guizhou has experienced rapid growth in the sericulture industry, contributing significantly to both regional economic development and ecological restoration. However, in the context of global climate change, the dynamics of soil organic carbon following mulberry cultivation and the underlying mechanisms driving these changes remain poorly understood. Therefore, this study employs a case-based comparative design to assess spatial-temporal SOC dynamics in paired karst agroecosystems—rocky desertification (Rd) and non-desertification (nRd) mulberry plantations—through monthly monitoring of edaphic parameters (SOC, nitrogen, phosphorus, and potassium) and soil biostimulants (Alkaline protease, urease, glomalin-related soil proteins ) across a full growing season. The aim was to explore (1) the temporal variation characteristics of soil organic carbon in mulberry orchards under two different land conditions; (2) the correlation between soil physicochemical indexes and soil enzymes and soil organic carbon; (3) the identification of the dominant factors affecting soil organic carbon in mulberry orchards, and elucidating karst-specific pedogenesis and mitigatory carbon sequestration potential. Materials and methods Study site The study was conducted at the Sericulture Research Institute of the Guizhou Academy of Agricultural Sciences (26°30′2″N, 106°39′12″E), which is located in Guiyang city, Guizhou Province (Fig. 1 ). A field trial has been conducted to examine a long-term mulberry system for its ecological function in the rocky desertified soil zone since 2012. The area is characteristic of a subtropical monsoon humid climate. It has an average annual rainfall of 1178.3 mm, an average temperature of 14.9°C, and an average frost-free period of 246 days (China Meteorological Data Network, 2023, http://data.cma.cn ). The terrain is mainly mountainous and hilly, with an average altitude of 1112 meters (China Meteorological Data Network, 2023, http://data.cma.cn ). The study area is divided into two sites based on soil types. The first study site, named rocky desertification mulberry plantation (Rd), is located on the top and middle of hillslope. Soil in site Rd is classified as Calcisols according to FAO and the soil texture is classified as silty clay (FAO texture class: SC). The topsoil in site Rd is fertile with soil organic matter of 58.62%. The second site, named non-rocky desertification mulberry plantation (nRd), is located at the foot area of the hill. The soil type in site nRd is Ferralsols andthe soil texture is classified as clay loam (FAO texture class: SC), with a higher clay content than site Rd. Soil in site Rd is loose with poor aggregation while soil in site nRd has better aggregation with granular structure. Soils in both sites are developed from limestone parent material (FAO lithology code: Lm) (Guizhou Soil Survey Office, 1994; Guizhou Bureau of Geological and Mineral Exploration and Development, 2016). Soil in site Rd has high rock ratio of approximately 25%, while site nRd has no rocks exposed at all. Mulberry trees (variety ‘Nongsang 14’) were planted in 2012, at a density of approximately 12,000 plants per hectare. Prior to planting, both sites were bared for around 10 years with no farming activities carried out. The soil was ploughed before planting, and both sites have followed the same field management since mulberry planting. The routine management includes urea fertilization (207 kg N per hactare) in spring (at late March or early April) by hole application, in-time weeding in all seasons from spring to autumn, and felling of strips in winter (at early October). Sample Collection and Measurement In this study, soil samples were collected monthly (from April to November) in 2022. In each site, 7 plots (10 m × 10 m) were selected for soil sampling, with 5 sub-plots (2 m × 2 m) set in each plot. Surface litter was removed prior to collecting 0–20 cm depth soil cores using stainless steel augers (Eijkelkamp equipment Co., 5 cm in diameter). 10 soil cores were collected randomly from each sub-plot. Thus, 50 soil cores from each plot were mixed thoroughly into one sample. The collected soil samples were brought back to the laboratory in sealed plastic bags for further laboratory analysis. During the air-drying process of the samples, large soil clods were gently broken for better air-dry. In total, 112 soil samples were collected (2 sites × 7 plots × 8 months) in this study. In the laboratory, all soil samples were air-dried, and plant roots, gravels, and debris were carefully removed. Samples were divided into two proportions. One proportion was sieved through a 2 mm sieve for soil pH measurement. The other proportion was sieved through a 0.15 mm sieve for determination of soil chemical properties. Soil pH was measured using a pH meter (soil-to-water ratio of 1: 2.5). SOC was determined using the potassium dichromate oxidation-external heating method. Total nitrogen (TN) was measured using the semi-micro Kjeldahl method. Total phosphorus (TP) was determined by H 2 SO 4 -HClO 4 digestion and molybdenum-antimony anti-colorimetry. Total potassium (TK) was measured using the NaOH fusion-flame photometry method. Alkali-hydrolyzable nitrogen (AN) was determined by the alkali-hydrolysis diffusion method. Available phosphorus (AP) was measured using 0.5 mol·L − 1 NaHCO 3 extraction and molybdenum-antimony anti-colorimetry. Available potassium (AK) was determined using 1 mol·L − 1 NH 4 OAc extraction and flame photometry. Detailed analysis methods are referenced from the study by Wilke et al. (2005). Easily extractable glomalin-related soil protein (EE-GRSP) and total glomalin-related soil protein (T-GRSP) were measured using sodium citrate extraction and Coomassie brilliant blue G-250 colorimetry (Wright et al., 1998). Soil enzyme activities were measured following methods described by Purev et al. (2014), with soil alkaline protease determined by casein colorimetry and soil urease by phenol-sodium hypochlorite colorimetry. Data Analysis To test the significance of monthly variations of soil properties, one-way ANOVA was performed using IBM SPSS Statistics 25, with multiple comparisons by Duncan's method at P = 0.05 significant level. To analyze the influence of various physicochemical properties on SOC, random forest (RF) regression analysis was conducted using SPSSPRO. The partial least squares structural equation modeling (PLS-SEM) was used to analyze the mechanism of soil type affecting SOC. Figures were created using Origin 2022 and ARCgis 10.2.2. Results Seasonal Dynamics of Soil Organic Carbon (SOC) SOC content in the Rd ranged from 31.51 to 39.71 g·kg − 1 from April to November, whereas it ranged from 22.50 to 28.51 g·kg − 1 in the nRd (Fig. 2 ). The average SOC content during the growing season was 35.09 ± 4.46 g·kg − 1 for the Rd and 25.58 ± 3.62 g·kg − 1 for the nRd. Throughout the growing season, the SOC content in the Rd was consistently higher, reaching 1.28 to 1.57 times that of the nRd. Within the growing season, in the Rd, SOC was much higher in both April and November, reaching 38.18 ± 0.86 g·kg − 1 and 39.71 ± 3.24 g·kg − 1 , respectively, and much lower in May, June, and July, at 31.94 ± 3.08 g·kg − 1 , 31.87 ± 5.58 g·kg − 1 , and 31.51 ± 2.69 g·kg − 1 , respectively. In the nRd, the highest SOC was in November at 28.51 ± 2.82 g·kg − 1 and the lowest in June at 22.50 ± 3.56 g·kg − 1 . In general, SOC showed an “U” pattern (decreased firstly and then increased) throughout the growing season. The fluctuation of SOC content with seasonal changes was slightly larger in the Rd compared to the nRd, with the standard deviations of the monthly averages being 3.10 and 1.95, respectively. The greatest difference in SOC content between the Rd and nRd was in April, with a difference of 13.86 g·kg − 1 , and the smallest difference was shown in July, with a difference of 6.98 g·kg − 1 . Changes of Soil nutrients Analysis of the monthly dynamic data on the physical and chemical properties of the monitored soil revealed a significant spatiotemporal heterogeneity pattern (Table 1 ). In terms of pH value, the Rd group (7.48–7.74) was generally higher than the nRd group (6.41–7.31). Specifically, the pH value of the Rd group reached its peak in August (7.73 ± 0.25) and September (7.74 ± 0.16), while that of the nRd group increased significantly in July (7.16 ± 0.49) and November (7.31 ± 0.21). Additionally, the Rd group maintained a slightly alkaline trend from April to November. TN exhibited prominent spatial and seasonal variations. The Rd group showed a significantly highest TN content in October (5.27 ± 0.58), which was 106.67% higher than that of the nRd group (2.55 ± 0.23) during the same period. In contrast, the TN content of the nRd group reached its peak in November (2.81 ± 0.3). Throughout the entire monitoring period, the average TN content of the Rd group (3.51 g·kg − 1 ) was 53.28% higher than that of the nRd group (2.29 g·kg − 1 ). TP showed slight fluctuations but significant spatial differentiation. The TP content of the Rd group was the highest in August (0.76 ± 0.04 a), while that of the nRd group reached its peak in May (0.82 ± 0.02). There was no significant difference in TP content between the two groups in most months of the growing season (e.g., July: Rd 0.67 ± 0.04 vs. nRd 0.73 ± 0.04). TK exhibited intense seasonal fluctuations. The TK content of the Rd group was extremely high in April (10.45 ± 0.44) but sharply decreased in May (2.7 ± 0.18). In contrast, the TK content of the nRd group was significantly prominent in August (12.59 ± 0.53 vs. Rd 6.67 ± 0.39). AN accumulated significantly in the Rd group during the late stage (July–November), with contents ranging from 0.31 to 0.37 g·kg − 1 (all marked with grade "a"). This was higher than the AN content of the nRd group (0.28–0.35 g/kg) in the same period. However, there was no statistical difference in AN content between the Rd group (0.16–0.24 g·kg − 1 ) and the nRd group (0.16–0.17 g·kg − 1 ) during the early stage (April–June). AP showed that the Rd group reached a significant peak in May (37.39 ± 2.71), which was 94.23% higher than that of the nRd group (19.25 ± 1.89). However, the nRd group surpassed the Rd group in June (29.01 ± 1.16 vs. Rd 23.54 ± 2.58). Additionally, the average AP content of the Rd group during the growing period (April–July) (29.38 mg·kg − 1 ) was higher than that of the nRd group (21.49 mg·kg − 1 ). AK, the content in the Rd group was the highest in October (97.03 ± 9.05), which was 29.65% higher than that in the nRd group (74.84 ± 7.59) during the same period. In contrast, the AK content in the nRd group was slightly better in May and September (74.99 ± 7.56 and 75.1 ± 6.98, respectively). Throughout the entire monitoring period, the average AK content of the Rd group (77.85 mg·kg − 1 ) exceeded that of the nRd group (68.07 mg·kg − 1 ). Collectively, these results indicated that the three soil indicators, namely TN, TK, and AP showed relatively obvious variations across different site conditions and seasons, while the variations of the other indicators were not significant. Table 1 Temporal variation of soil physicochemical properties in mulberry plantations under two different site conditions. Time pH TN(g·kg − 1 ) TP(g·kg − 1 ) TK(g·kg − 1 ) AN(g·kg − 1 ) AP(mg·kg − 1 ) AK(mg·kg − 1 ) Rd nRd Rd nRd Rd nRd Rd nRd Rd nRd Rd nRd Rd nRd April 7.48 ± 0.23c 7.1 ± 0.39a 3.73 ± 0.32bc 2 ± 0.28c 0.68 ± 0.03c 0.76 ± 0.02b 10.45 ± 0.44d 2.69 ± 0.25d 0.24 ± 0.07b 0.17 ± 0.07b 26.22 ± 0.45c 10.34 ± 0.77f 81.59 ± 15.97b 60.99 ± 7.46bc May 7.63 ± 0.15abc 6.71 ± 0.57ab 3 ± 0.32d 1.85 ± 0.08c 0.67 ± 0.02c 0.82 ± 0.02a 2.7 ± 0.18e 5.12 ± 0.29c 0.16 ± 0.01c 0.17 ± 0.05b 37.39 ± 2.71a 19.25 ± 1.89c 60.5 ± 7.37d 74.99 ± 7.56a June 7.54 ± 0.09bc 6.41 ± 0.8b 2.87 ± 0.35d 1.95 ± 0.26c 0.71 ± 0.02bc 0.7 ± 0.03cde 2.63 ± 0.24e 5.09 ± 0.33c 0.18 ± 0.02bc 0.16 ± 0.03b 23.54 ± 2.58d 29.01 ± 1.16a 66.73 ± 6.87cd 58.49 ± 8.97c July 7.7 ± 0.09ab 7.16 ± 0.49a 2.73 ± 0.78d 2.12 ± 0.12c 0.67 ± 0.04c 0.73 ± 0.04bc 7.23 ± 0.42c 5.49 ± 0.21c 0.31 ± 0.05a 0.32 ± 0.04a 30.37 ± 1.6b 27.35 ± 1.32b 76.93 ± 6.43b 68.51 ± 7.93ab August 7.73 ± 0.25a 6.78 ± 0.65ab 3.15 ± 0.82cd 2.57 ± 0.19ab 0.76 ± 0.04a 0.71 ± 0.04cde 6.67 ± 0.39d 12.59 ± 0.53a 0.33 ± 0.07a 0.33 ± 0.09a 23.11 ± 1.51d 16.85 ± 1.15d 82.5 ± 8.78b 61.97 ± 9.19bc Sep. 7.74 ± 0.16a 6.95 ± 0.49ab 3.32 ± 0.05bcd 2.43 ± 0.46b 0.73 ± 0.04ab 0.69 ± 0.02e 8.16 ± 0.42b 5.88 ± 0.35c 0.37 ± 0.08a 0.33 ± 0.08a 14.85 ± 0.66f 15.07 ± 1.83e 73.73 ± 6.22bc 75.1 ± 6.98a October 7.48 ± 0.06c 6.76 ± 0.61ab 5.27 ± 0.58a 2.55 ± 0.23ab 0.69 ± 0.04c 0.69 ± 0.02de 7.47 ± 0.32c 5.88 ± 0.35c 0.37 ± 0.07a 0.35 ± 0.07a 16.89 ± 1.24e 14.97 ± 0.44e 97.03 ± 9.05a 74.84 ± 7.59a Nov. 7.61 ± 0.06abc 7.31 ± 0.21a 3.98 ± 0.95b 2.81 ± 0.3a 0.69 ± 0.03c 0.72 ± 0.04cd 9.07 ± 0.33a 5.96 ± 0.48b 0.37 ± 0.06a 0.28 ± 0.04a 18.03 ± 2.26e 8.16 ± 1.26g 83.77 ± 7.21b 69.63 ± 7.82ab Mean ± SD 7.61 ± 0.11 6.9 ± 0.29 3.51 ± 0.83 2.29 ± 0.35 0.7 ± 0.03 0.73 ± 0.04 6.8 ± 2.81 6.09 ± 2.83 0.29 ± 0.09 0.26 ± 0.08 23.8 ± 7.52 17.63 ± 7.4 77.85 ± 11.22 68.07 ± 6.81 Note: The data in the table are presented as ‘mean ± SD.’. Different lowercase letters in the same column indicate significant differences in the same indicator among different months (P < 0.05). TN: Total nitrogen; TP: Total phosphorus; TK: Total potassium; AN: Alkaline hydrolysis nitrogen; AP: Rapidly available phosphorus; AK: Rapidly available potassium; Rd: Rocky desertification; nRd: Non-desertification. Changes of soil enzyme activity and GRSP content Generally, the soil indicators T-GRSP and Alkaline Protease showed more significant changes between different site conditions and seasons, while changes in other factors were less significant (Table 2 ). The T-GRSP content was higher in the Rd throughout the year compared to the nRd, with the largest difference occurring in April, reaching 2.52 g·kg − 1 . The Alkaline Protease content was slightly higher in the nRd in April, June, August, and November, with the largest difference in November, reaching 1.83 µmol·g·d − 1 , while in the other four months, the content was higher in the Rd. The temporal trends of each indicator were not consistent. Table 2 Temporal variation of GRSP and soil enzyme activity in mulberry plantations under two different site conditions Time EE-GRSP (g·kg − 1 ) T-GRSP (g·kg − 1 ) Alkaline Protease (µmol·g·d − 1 ) Urease (mg·g·d − 1 ) Rd nRd Rd nRd Rd nRd Rd nRd April 0.83 ± 0.1bc 0.61 ± 0.11abc 5 ± 0.84ab 2.48 ± 1.07b 1.88 ± 0.14a 3.45 ± 0.38a 0.47 ± 0.06a 0.3 ± 0.06bc May 0.74 ± 0.17c 0.51 ± 0.11c 4.44 ± 0.41b 2.63 ± 0.34b 1.94 ± 0.2a 0.97 ± 0.09d 0.24 ± 0.05c 0.27 ± 0.05cd June 0.81 ± 0.03bc 0.53 ± 0.13bc 4.39 ± 0.65b 2.94 ± 0.66ab 1.03 ± 0.07c 2.47 ± 0.6b 0.21 ± 0.08cd 0.34 ± 0.06bc July 0.84 ± 0.07bc 0.67 ± 0.07ab 4.66 ± 0.54ab 3.55 ± 0.67a 1.4 ± 0.29b 1.23 ± 0.49cd 0.14 ± 0.04d 0.32 ± 0.07bc August 0.82 ± 0.08bc 0.53 ± 0.11bc 5.19 ± 0.99ab 3.02 ± 0.63ab 1.98 ± 0.52a 2.55 ± 0.59b 0.35 ± 0.08b 0.21 ± 0.03d Sep. 0.94 ± 0.15ab 0.63 ± 0.21abc 4.93 ± 0.66ab 3.6 ± 0.74a 1.85 ± 0.32a 1.65 ± 0.33c 0.18 ± 0.05cd 0.37 ± 0.09b October 0.92 ± 0.13ab 0.62 ± 0.13abc 5.45 ± 1.01a 3.21 ± 0.71ab 1.88 ± 0.32a 1.55 ± 0.5cd 0.24 ± 0.07c 0.32 ± 0.09bc Nov. 0.99 ± 0.1a 0.7 ± 0.09a 5.13 ± 1.02ab 3.19 ± 0.37ab 1.41 ± 0.12b 3.24 ± 0.83a 0.19 ± 0.04cd 0.49 ± 0.08a Mean ± SD 0.86 ± 0.08 0.6 ± 0.07 4.9 ± 0.37 3.08 ± 0.4 1.67 ± 0.35 2.14 ± 0.92 0.25 ± 0.11 0.33 ± 0.08 Note: Data in the table are ‘mean ± SD.’; Different lowercase letters in the same column after the data indicate significant differences in the same study site at different months (P < 0.05). EE-GRSP: Easily extractable glomalin-related soil protein; T-GRSP: Total glomalin-related soil protein. Rd: Rocky desertification; nRd: Non-desertification. Based on the monthly data of GRSP content and enzyme activities in Rd and nRd, the differentiation of ecological functions was revealed. EE-GRSP in the Rd (0.74–0.99 g·kg − 1 ) was significantly higher than that in the nRd (0.51–0.70 g·kg − 1 ), and Rd peaked at November (0.99 ± 0.10), which was 41.43% higher than nRd (0.70 ± 0.09), and Rd was higher than nRd throughout the year. The T-GRSP in the nRd (2.48–3.60 g·kg − 1 ) was lower than that in the Rd (4.39–5.45 g·kg − 1 ). The Rd of October (5.45 ± 1.01) was 69.78% higher than that of nRd (3.21 ± 0.71), and nRd was only close to the lowest level of Rd in July (3.55 ± 0.67) and September (3.60 ± 0.74) but still 21.94% lower. It showed that rocky desertification habitat promotes the accumulation of GRSP and increases soil carbon sink. Alkaline Protease showed significant changes in nRd activity throughout the year (0.97–3.45 mg·g·d − 1 ), while Rd activity was relatively stable (1.03–1.98 mg/g/d), and in April and November, the Alkaline Protease activity of nRd was 83.52% and 129.79% higher than that of Rd, respectively. It showed that organic nitrogen mineralization is stronger in non-rocky desertification area. Urease was high in the early Rd (April: 0.47 ± 0.06), but decreased sharply from July (0.14 ± 0.04), which was 70.21% lower than that in April. The urease activity in the nRd was enhanced in the later period, and the peak value of November (0.49 ± 0.08) was 157.89% higher than that of Rd (0.19 ± 0.04) in the same period, reflecting the habitat timing differentiation of nitrogen metabolism function. In summary, the rocky desertification mulberry field enhances soil carbon sinks by increasing T-GRSP content, but at the expense of inhibiting enzyme activity (Alkaline Protease); the non-rocky desertification mulberry field maintains high-efficiency nitrogen turnover function, and the two form an ecological trade-off pattern of 'carbon fixation in rocky desertification-nitrogen release in non-rocky desertification', which provides a regulatory target for the coordinated management of carbon and nitrogen in the mulberry field system in karst areas. Relationships of Soil Factors with Soil Organic Carbon The relationships of soil various factors with SOC content in both Rd and nRd are shown in the Fig. 3 . SOC showed a significant correlation with most physical and chemical factors. Specifically, SOC was significantly positively correlated with TN, AN, AK, T-GRSP, and EE-GRSP, while it was significantly negatively correlated with AP. There were no significant correlations between SOC and TP, alkaline protease, or urease. In the Rd, SOC had no significant correlation with pH, but in the nRd, SOC was significantly positively correlated with pH, with a correlation coefficient of 0.5253. Additionally, SOC was significantly positively correlated with TK in the Rd but shows no significant correlation in the nRd, with correlation coefficients of 0.1775 and 0.0142, respectively. As shown in Fig. 4 , for the Rd, TN, T-GRSP, and urease had the greatest influence on SOC, with their impact reaching 58.10%, 9%, and 8.9%, respectively. The influence of other factors was relatively minor. In contrast, for the nRd, TN, T-GRSP, and pH were the dominant factors influencing SOC, with their impacts being 25.6%, 18.4%, and 18%, respectively. The influence of other factors did not exceed 15%. In this study, PLS-SEM was used to further reveal the mechanism of SOC accumulation in different soil habitats (Fig. 5 ). PLS-SEM showed that soil type indirectly affected SOC accumulation, specifically, soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. In addition, pH and TN affected SOC accumulation in a direct and positive way, and T-GRSP had similar contributions to SOC accumulation through direct and indirect ways. Discussion Dynamics of SOC in mulberry plantation Rocky desertification is a process of soil degradation. Numerous studies have shown that SOC content decreases with increasing intensity of rocky desertification (Guo et al., 2014; Wang et al., 2021), but gradually increases with positive vegetation succession (Luo et al., 2009; Yang, 2016). However, the results of this study indicated that the SOC content in rocky desertification mulberry plantation is higher than that in non-rocky desertification mulberry plantation. This phenomenon is likely due to differences in microhabitats and soil properties between the two types of mulberry plantation. The results of this study align with previous research. For instance, studies by Huang et al.(2017) in Guizhou, where SOC values ranged from 15.44 to 47.41 g·kg − 1 , and Shao et al.(2022) in Yunnan, with SOC values ranging from 16.22 to 44.23 g·kg − 1 , both showed that karst regions possess higher SOC content. Similarly, Zhong et al. (2020) and Fang et al. (2016) reported that the surface SOC content in the karst areas of Guangxi ranges from 17.23 to 42.52 g·kg − 1 , significantly surpassing the values observed in non-karst areas (13.88–25.99 g·kg − 1 ). Moreover, through field investigations and data collection, Zhu et al.(2022) found that the average SOC content in the southwest karst region was 29.15 g·kg − 1 , which was markedly higher than the corresponding value in non-karst areas (18.40 g·kg − 1 ). Firstly, the higher rock exposure rate in rocky desertification mulberry plantation causes soil to concentrate in low-lying areas between rocks. Consequently, litter, the main source of soil organic matter, also concentrates in the soil, providing relatively richer organic matter sources in rocky desertification soils under the same total litter amount. Fertilization in mulberry plantation mainly concentrates in areas with soil, further increasing the sources of organic matter. This also explained the greater seasonal fluctuations of SOC in rocky desertification mulberry plantation. Secondly, the soil pH in rocky desertification mulberry plantation was generally higher than in non-rocky desertification mulberry plantation (Fig. 3 (a)). In such environmental conditions, Ca²⁺ in the soil (mainly calcareous soil) can combine with humic acid and other organic matter to form more resistant chelates (Tang, 2015). Additionally, the rapid accumulation of macro-aggregates in the soil effectively protects plant-derived carbon, microbe-derived carbon, and particulate carbon (Goebel et al., 2009; Hu et al., 2024), making the organic carbon in the soil more easily preserved compared to non-rocky desertification soils. This extends the turnover time of organic carbon in karst soils (Wang et al., 2018), thereby increasing the SOC content in rocky desertification mulberry plantation. The significant positive correlation between SOC and pH in non-rocky desertification mulberry plantation and the significantly higher soil pH in rocky desertification mulberry plantation supported this view (Fig. 3 (a)). This further proveed the significant application value of mulberry trees in preventing rocky desertification, improving ecology, and developing the economy (Qin et al., 2012). It should be noted that the observed differences in soil organic carbon (SOC) (Rd: 35.09 g·kg − 1 vs. nRd: 25.58 g·kg − 1 ) might occur under the circumstances where the limitations inherent to the pseudo-replication design are taken into account. Although strict site matching was implemented, pre-existing soil differences might confound the plantation effect. For instance, the initial SOC advantage of calcareous soil might amplify the gains caused by the treatments, and this possibility needs to be distinguished through long-term chrono sequence studies. The seasonal variation trend of SOC in rocky desertification mulberry plantation showed more fluctuation compared to non-rocky desertification mulberry plantation. The SOC content in rocky desertification mulberry plantation was higher in April and November and lower in May, June, and July. This is primarily due to the low decomposition rate of organic matter before April due to low temperatures and the accumulation of organic matter from winter fertilization in mulberry plantation. Before November, the increased input of litter in mulberry plantation led to higher SOC content. However, during May, June, and July, the rapid growth of mulberry trees, coupled with increased rainfall and temperature, enhanced soil microbial activity, accelerating SOC decomposition and conversion to water-soluble organic carbon, which resulted in significant SOC loss (Cao et al., 2005). This contrasts with the pattern observed in larch plantation, where SOC content was higher in June, July, and August and lower in May, September, and October (Fan al et., 2018). This difference may be due to the higher latitude environment of larch plantation and the rich sources of organic matter within them. In such environments, increased temperatures in certain months accelerate litter decomposition, supplementing soil organic carbon, while in other months, there may be a depletion of organic carbon. SOC content in 0–30 cm Chinese fir plantation is shown as follows: autumn > summer > spring > winter (Kong, 2019, which is different from the results of this study, indicating that there are differences among different tree species. Influence of soil factors on SOC Soil organic carbon is influenced by various factors, including sources of organic matter, soil properties, climate, and soil carbon fractions ( Huang al et., 2016; Luo al et., 2017). In this study, the differences in climate and sources of organic matter between rocky desertification and non-rocky desertification mulberry plantation were relatively small. Therefore, soil properties may be a significant factor influencing the differences in soil organic carbon content between these two types of mulberry plantation. Owing to inherent limitations in the study design where mulberry were planted into two different soil types, it is impossible to determine for certain, what proportion of the differences in the soil response variables are a result of the Mulberry plantation versus a pre-existing soil condition. However, the more dramatic response observed for more labile forms of nutrients (e.g. AP) suggests that the rocky desertification soils may be responding more rapidly to the mulberry plantation than the rocky desertification soils. The study results showed that soil organic carbon content was significantly affected by soil physicochemical properties. TN, pH, and T-GRSP were the dominant factors influencing SOC in the study area, all of which are significantly positively correlated with SOC. The positive correlation between soil total nitrogen (TN) and soil organic carbon is consistent with previous research findings (Ding al et, 2012; Li al et., 2023; Yan al et., 2011). This strong coupling relationship between soil carbon and nitrogen is primarily driven by the fact that increased soil nitrogen content lowers the carbon-to-nitrogen ratio, which promotes microbial carbon fixation and enhances soil carbon accumulation (Luo al et., 2023). Additionally, nitrogen enrichment in soil inhibits microbial SOC mineralization and reduces soil respiration, further promoting SOC content (Wang al et., 2015). The relationship between soil pH and soil organic carbon showed a significant positive correlation at low pH levels, whereas this correlation was not significant at high pH levels. This could be due to the increasing ability of Ca²⁺ to combine with humic acids and other organic matter to form chelates as pH rises (Tang, 2015). However, once pH increases beyond a certain point, this effect may diminish, possibly even showing a slight negative correlation, similar to the findings of Ding et al. (2012). T-GRSP might contribute to soil organic carbon accumulation by improving soil physical properties, nutrient content, carbon fixation capacity, and microbial activity (Singh al et., 2020). In both rocky desertification and non-rocky desertification mulberry plantation, there was no significant relationship between TP and SOC. However, AP showed a significant negative correlation with SOC, possibly because increased phosphorus content enhances microbial decomposition of soil organic carbon, thereby reducing SOC (Luo al et., 2023). Overall, TN, T-GRSP, and urease were the most influential factors affecting SOC in rocky desertification mulberry plantation, all closely related to nitrogen. In non-rocky desertification mulberry plantation, the three most influential factors were TN, T-GRSP, and pH, with the first two mainly influencing nitrogen and the latter affecting the difficulty of soil organic carbon decomposition. Therefore, it can be inferred that both rocky desertification and non-rocky desertification mulberry plantation are likely nitrogen-limited. This may be due to the significant nitrogen loss from mulberry leaf harvesting, suggesting that appropriate adjustment of nitrogen fertilizer application could increase SOC content. Random forest is a supervised machine learning method constructed through the integration of decision-tree-based learners. While random forest identified TN as the primary SOC driver (58.10% importance in Rd), TN-SOC covariation was moderated by calcium saturation. This suggested ion bridging may enforce C-N coupling in karst soils—a hypothesis warranting nano-scale characterization. PLS-SEM further showed that soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. In addition, pH and TN affected SOC accumulation in a direct and positive way, and T-GRSP had similar contributions to SOC accumulation through direct and indirect ways. GRSP plays a crucial role in SOC sequestration across different ecosystems. Cissé et al. (2023) showed that GRSP content correlates positively with SOC and TN while showing inverse relationships with pH. Cui et al. (2024) showed that during grassland degradation and restoration processes, TN serves as the primary factor explaining variance in GRSP and SOC content, while total phosphorus influences GRSP/SOC ratios. This is consistent with the results of this study. Of course, the relationship between GRSP and SOC is bidirectional. Yang et al. (2024) showed that SOC emerges as the primary positive regulator for GRSP accumulation, with explanatory rates exceeding 80%。 Indication of mulberry plantation on soil carbon accumulation in Karst region This study's findings revealed, throughout the growing season of mulberry trees, the SOC content of rocky desertification mulberry plantation (35.11 ± 3.09 g·kg − 1 ) was significantly higher than that of non-rocky desertification mulberry plantation (25.86 ± 1.57 g·kg − 1 ), and the SOC content of rocky desertification mulberry plantation was 1.28–1.57 times higher than that of the non-rocky desertification, and the average SOC content of mulberry plantation was 30.48 g·kg − 1 , which was much higher than the average SOC content of the soil layer of 0–20 cm of the mulberry plantation in China (10.71 ± 7.01 g·kg − 1 )(Wang al et., 2023)and were also higher than the SOC content in surface soils of cultivated lands (dry and paddy fields) in the karst region of Southwest China(Zhang al et., 2014). The SOC content in rocky desertification mulberry plantation generally exceeded the average SOC content in surface soils of the five main landforms in the karst region of Southwest China (4.62–38.2 g·kg − 1 )(Wang al et., 2021), and was equivalent to the surface SOC content in moderately to severely rocky desertified areas of Guizhou in 2011 and the surface SOC content in slightly to potentially rocky desertified lands in Puding and Libo areas of Guizhou(Wang al et., 2017; Yan al et., 2011). It was also comparable to the average SOC content (38.38 g·kg − 1 ) in the 0–20 cm soil layer of shrubland in Maolan Karst and the SOC content in the surface soil of the succession stages from shrubland to secondary forest in Southwest China (Wang al et., 2017). Additionally, it was equivalent to the surface SOC content in Cunninghamia lanceolata, Cryptomeria fortunei, and Betula platyphylla plantation in western Guizhou around 2012(Ding al et., 2012). On the other hand, the SOC level in non-rocky desertification mulberry plantation was between the SOC content in cultivated lands and shrublands (Wang al et., 2017). Owing to inherent limitations in the study design, we cannot definitively ascertain whether the observed elevation in SOC levels within mulberry plantations and their cross-system disparities stem from post-establishment ecological effects or pre-existing edaphic heterogeneity. To resolve this causal ambiguity, future research must: (1) establish pre-plantation soil carbon baselines through retrospective analysis of land-use history and archived samples, and (2) implement large-scale systematic sampling across heterogeneous karst landscapes (e.g., varying lithology, slope gradients) in Southwest China, ensuring statistical power to delineate plantation-driven SOC dynamics from inherent soil variations. Conclusions This study demonstrated that soil organic carbon and soil total nitrogen have a significant synergistic accumulation relationship, maintaining the dynamic balance of carbon and nitrogen can effectively promote the synergistic expansion of soil organic carbon pool. There are significant differences in the dynamic change characteristics of soil organic carbon between rocky desertification mulberry plantations and non-rocky desertification mulberry plantations. Specifically, the SOC content in rocky desertification mulberry plantations is 1.28–1.57 times that of non-rocky desertification ones. Moreover, in rocky desertification mulberry plantations, SOC content responds more strongly to seasonal variations. Meanwhile, the availability of soil nitrogen is the main regulating factor controlling the accumulation of SOC in the mulberry agricultural ecosystem. Soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. Inter cropping strategically introducing nitrogen-fixing symbiotic species is conducive to enhancing the carbon sink function of artificial forests and provides a theoretical basis for formulating soil carbon sink regulation measures for rocky desertification artificial forests. Declarations Acknowledgements This work was supported by the Guizhou Provincial Science and Technology Program Project (Qiankehe Support [2024] General 076); Guizhou Provincial Science and Technology Program Project (Qiankehe Support [2023] General 011); Guizhou Provincial Science and Technology Program Project (Qiankehe Foundation-ZK[2023]General 161);Ministry of Finance and the Ministry of Agriculture and Rural Affairs: the National Modern Agricultural Industry Technology System(CARS-18-SYZ20);Guizhou Provincial Science and Technology Program Project (Qiankehe Platform KXJZ(2025)028); Guizhou Provincial Science and Technology Program Project (Qiankehe Foundation-ZK[2024]General 550); Guizhou Academy of Agricultural Sciences Youth Fund Project (Qian Nongke Youth Fund [2023] No. 01). Author’s contributions Dan Xing: Conceptualization, Methodology, Writing —review & editing, Supervision, Project administration. 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Plant and Soil 475(1/2):45-59. https://doi.org/10.1007/s11104-021-05220-4 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7995665","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":542538600,"identity":"02533ef3-ac7e-4547-8a9f-f789fa8caf0e","order_by":0,"name":"yanjin 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2","display":"","copyAsset":false,"role":"figure","size":129912,"visible":true,"origin":"","legend":"\u003cp\u003eCharacteristics of temporal changes in soil organic carbon in rocky desertification mulberry plantation (Rd) and non-rocky desertification mulberry plantation (nRd) (n=7).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7995665/v1/d83f3a37805646f6f195ec33.png"},{"id":96269802,"identity":"d857b6c2-494a-43b4-8763-22cd0b18e8ba","added_by":"auto","created_at":"2025-11-19 09:11:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":318307,"visible":true,"origin":"","legend":"\u003cp\u003eRegression analysis of soil organic carbon and related indexes in mulberry plantations under two different site conditions (n=56). TN: total nitrogen; TP: total phosphorus; TK: total potassium; AN: alkaline dissolved nitrogen; AP: quick-acting phosphorus; AK: quick-acting potassium; EE-GRSP: Easily extractable glomalin-related soil protein; T-GRSP: Total glomalin-related soil protein. Rd: Rocky desertification; nRd: Non-desertification.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7995665/v1/ffad7b42c6f711439d08238c.png"},{"id":96363399,"identity":"f16220b9-0cd2-45d0-8720-ba74fa7862f1","added_by":"auto","created_at":"2025-11-20 10:06:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":23498,"visible":true,"origin":"","legend":"\u003cp\u003eImportance ranking of factors affecting soil organic carbon based on random forest analysis(n=56). TN: total nitrogen; TP: total phosphorus; TK: total potassium; AN: alkaline dissolved nitrogen; AP: quick-acting phosphorus; AK: quick-acting potassium; EE-GRSP: Easily extractable glomalin-related soil protein; T-GRSP: Total glomalin-related soil protein. Rd: Rocky desertification; nRd: Non-desertification.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7995665/v1/bce5af56784b8673de27e123.png"},{"id":96269804,"identity":"17c188e6-cd1e-46de-a6cb-57f9f3b83e9e","added_by":"auto","created_at":"2025-11-19 09:11:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":74637,"visible":true,"origin":"","legend":"\u003cp\u003eStructural equation modeling revealing the effects of· different site conditions、Alkaline Protease、pH、T-GRSP、TK and TN on SOC\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7995665/v1/358e195166dcb5fd33fb7647.png"},{"id":98623950,"identity":"7051456f-10ea-4f71-a9aa-62467b64ad13","added_by":"auto","created_at":"2025-12-19 17:07:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2135311,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7995665/v1/6ab9ff9f-3943-4e23-b885-93d3aaad6cd9.pdf"}],"financialInterests":"","formattedTitle":"Soil organic carbon accumulation is mainly driven by soil nitrogen in rocky desertified mulberry plantation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSoil organic carbon (SOC) constitutes the largest organic carbon reservoir in terrestrial ecosystems, and its small fluctuations may have a significant impact on atmospheric carbon dioxide levels and global carbon balance (Batlle-Bayer et al., 2010; Bossio et al., 2020; Chen et al., 2008; Zhou et al., 2018 ). It is very important to study the changes and influencing factors of soil organic carbon. The formation and accumulation of SOC result from the interaction between biotic and abiotic factors. Among the biotic factors, vegetation type and development stage are important indicators affecting SOC. Vegetation type influence the carbon supply by altering the quantity and quality of litter input (Julian et al., 2019; Qu et al., 2019). Bai et al.(2020) indicated that, within the 0\u0026ndash;20 cm soil layer, the average soil organic carbon stock (SOCS) values exhibited the following order: Zanthoxylum bungeanum forest\u0026thinsp;\u0026gt;\u0026thinsp;round-leaved pine forest\u0026thinsp;\u0026gt;\u0026thinsp;round-bark privet mixed forest\u0026thinsp;\u0026gt;\u0026thinsp;sloping farmland\u0026thinsp;\u0026gt;\u0026thinsp;Zanthoxylum bungeanum-pitaya mixed forest\u0026thinsp;\u0026gt;\u0026thinsp;pitaya forest. During early vegetative stages, plants allocate more carbon belowground, contributing substantially to SOC formation (Yu et al., 2016). As plants mature, the proportion of photosynthetic carbon allocated to SOC decreases, but microbial biomass carbon increases (Shi et al., 2024). Yu et al. (2016) showed that the input of photosynthetic carbon by maize plants into soil organic carbon mainly occurs during the younger growth stages. Different microbial groups dominate carbon incorporation at various growth stages, with saprophytic fungi prevalent during vegetative stages and actinomycetes during reproductive stages (Zhang et al., 2022). Soil microorganism metabolism regulates carbon pool dynamics through the decomposition and transformation of organic matter (Kalbitz et al., 2000; Templer et al., 2004). As a metabolite of microorganisms, the activity of soil enzymes can reflect the availability of soil nutrients. As a protein, it can also directly affect the formation and accumulation of soil SOC. Verma et al. (2017) indicated that soil amendments improve soil organic carbon fractions, with labile fractions better correlated with soil enzyme activity, especially in the rhizosphere. These studies have shown that biological factors play an important role in affecting SOC. Glomalin-related soil protein (GRSP), a unique glycoprotein secreted exclusively by arbuscular mycorrhizal fungi (AMF), is highly stable in the soil environment (Wang et al, 2016). Once released into the soil, GRSP contributes to the accumulation of carbon and nitrogen, thereby enhancing the soil's carbon sequestration capacity (Agnihotri et al., 2021). Banegas et al. (2020) indicated that grazing and nitrogen fertilization of a tropical perennial grass can increase soil carbon through promotion of GRSP in saline environments. Regarding abiotic factors, soil physicochemical properties\u0026mdash;such as pH and nutrient factors (eg. N, P, and K) contents levels\u0026mdash;indirectly influence SOC content by modulating microbial activity and the soil\u0026rsquo;s capacity to adsorb organic matter (Huang et al., 2016; Luo et al., 2017). For example, in high pH soils, calcium ions form organic-inorganic complexes with organic matter, thereby reducing the loss of SOC (Tang, 2015). The influence mechanism of nitrogen and phosphorus on SOC is different. The N addition tends to decrease SOC decomposition and increase plant-derived carbon inputs, while P addition primarily enhances plant biomass and carbon inputs (Li et al., 2020; Luo et al., 2023). The impact of P on SOC is strongly mediated by N availability, with greater SOC accumulation observed under high N conditions (Luo et al., 2023). Short-term N and P additions in desert steppes increase SOC levels, particularly in the recalcitrant carbon pool, while decreasing SOC mineralization (Hai et al., 2024). Hai et al. (2024) pointed out that short-term N and P additions in desert steppes increase SOC levels, particularly in the recalcitrant carbon pool, while decreasing SOC mineralization. The results of the Hai et al. (2024) also indicated that these nutrient additions also alter microbial community composition and functional gene abundance, affecting carbon cycling processes. However, whether N and P promote or inhibit SOC accumulation and formation varies depending on soil conditions and nutrient availability. Li et al. (2020) studies have shown that long-term N and P additions may weaken soil carbon storage capacity in some ecosystems, such as alpine meadow.\u003c/p\u003e\u003cp\u003eGuizhou, the epicenter of China's karst region, features soils rich in calcium and magnesium with high pH (Cao et al., 2008), creating a harsh environment with scant moisture and nutrients (Zhou et al., 2001; Zhang et al., 2009). Unique geological and climatic conditions, compounded by population pressure and development practices, have led to extensive rocky desertification in southwestern China (Liu ,2009), the region's most severe ecological and geological calamity (Wang, 2003). This has severely degraded soil quality and productivity, heightening concerns over rocky desertification. Mulberry (\u003cem\u003eMorus alba\u003c/em\u003e L.) possesses a well-developed root system and exhibits strong tolerance to cold and drought conditions. It has become an important economic tree species for enhancing the ecological environment and promoting sustainable agricultural development in karst regions (Srivastava et al., 2003). As a key region in the \u0026ldquo;East Mulberry Westward Expansion\u0026rdquo; initiative, Guizhou has experienced rapid growth in the sericulture industry, contributing significantly to both regional economic development and ecological restoration. However, in the context of global climate change, the dynamics of soil organic carbon following mulberry cultivation and the underlying mechanisms driving these changes remain poorly understood.\u003c/p\u003e\u003cp\u003eTherefore, this study employs a case-based comparative design to assess spatial-temporal SOC dynamics in paired karst agroecosystems\u0026mdash;rocky desertification (Rd) and non-desertification (nRd) mulberry plantations\u0026mdash;through monthly monitoring of edaphic parameters (SOC, nitrogen, phosphorus, and potassium) and soil biostimulants (Alkaline protease, urease, glomalin-related soil proteins ) across a full growing season. The aim was to explore (1) the temporal variation characteristics of soil organic carbon in mulberry orchards under two different land conditions; (2) the correlation between soil physicochemical indexes and soil enzymes and soil organic carbon; (3) the identification of the dominant factors affecting soil organic carbon in mulberry orchards, and elucidating karst-specific pedogenesis and mitigatory carbon sequestration potential.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eStudy site\u003c/h2\u003e\u003cp\u003eThe study was conducted at the Sericulture Research Institute of the Guizhou Academy of Agricultural Sciences (26\u0026deg;30\u0026prime;2\u0026Prime;N, 106\u0026deg;39\u0026prime;12\u0026Prime;E), which is located in Guiyang city, Guizhou Province (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A field trial has been conducted to examine a long-term mulberry system for its ecological function in the rocky desertified soil zone since 2012. The area is characteristic of a subtropical monsoon humid climate. It has an average annual rainfall of 1178.3 mm, an average temperature of 14.9\u0026deg;C, and an average frost-free period of 246 days (China Meteorological Data Network, 2023, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://data.cma.cn\u003c/span\u003e\u003cspan address=\"http://data.cma.cn\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The terrain is mainly mountainous and hilly, with an average altitude of 1112 meters (China Meteorological Data Network, 2023, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://data.cma.cn\u003c/span\u003e\u003cspan address=\"http://data.cma.cn\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe study area is divided into two sites based on soil types. The first study site, named rocky desertification mulberry plantation (Rd), is located on the top and middle of hillslope. Soil in site Rd is classified as Calcisols according to FAO and the soil texture is classified as silty clay (FAO texture class: SC). The topsoil in site Rd is fertile with soil organic matter of 58.62%. The second site, named non-rocky desertification mulberry plantation (nRd), is located at the foot area of the hill. The soil type in site nRd is Ferralsols andthe soil texture is classified as clay loam (FAO texture class: SC), with a higher clay content than site Rd. Soil in site Rd is loose with poor aggregation while soil in site nRd has better aggregation with granular structure. Soils in both sites are developed from limestone parent material (FAO lithology code: Lm) (Guizhou Soil Survey Office, 1994; Guizhou Bureau of Geological and Mineral Exploration and Development, 2016). Soil in site Rd has high rock ratio of approximately 25%, while site nRd has no rocks exposed at all.\u003c/p\u003e\u003cp\u003eMulberry trees (variety \u0026lsquo;Nongsang 14\u0026rsquo;) were planted in 2012, at a density of approximately 12,000 plants per hectare. Prior to planting, both sites were bared for around 10 years with no farming activities carried out. The soil was ploughed before planting, and both sites have followed the same field management since mulberry planting. The routine management includes urea fertilization (207 kg N per hactare) in spring (at late March or early April) by hole application, in-time weeding in all seasons from spring to autumn, and felling of strips in winter (at early October).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eSample Collection and Measurement\u003c/h3\u003e\n\u003cp\u003eIn this study, soil samples were collected monthly (from April to November) in 2022. In each site, 7 plots (10 m \u0026times; 10 m) were selected for soil sampling, with 5 sub-plots (2 m \u0026times; 2 m) set in each plot. Surface litter was removed prior to collecting 0\u0026ndash;20 cm depth soil cores using stainless steel augers (Eijkelkamp equipment Co., 5 cm in diameter). 10 soil cores were collected randomly from each sub-plot. Thus, 50 soil cores from each plot were mixed thoroughly into one sample. The collected soil samples were brought back to the laboratory in sealed plastic bags for further laboratory analysis. During the air-drying process of the samples, large soil clods were gently broken for better air-dry. In total, 112 soil samples were collected (2 sites \u0026times; 7 plots \u0026times; 8 months) in this study.\u003c/p\u003e\u003cp\u003eIn the laboratory, all soil samples were air-dried, and plant roots, gravels, and debris were carefully removed. Samples were divided into two proportions. One proportion was sieved through a 2 mm sieve for soil pH measurement. The other proportion was sieved through a 0.15 mm sieve for determination of soil chemical properties. Soil pH was measured using a pH meter (soil-to-water ratio of 1: 2.5). SOC was determined using the potassium dichromate oxidation-external heating method. Total nitrogen (TN) was measured using the semi-micro Kjeldahl method. Total phosphorus (TP) was determined by H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e-HClO\u003csub\u003e4\u003c/sub\u003e digestion and molybdenum-antimony anti-colorimetry. Total potassium (TK) was measured using the NaOH fusion-flame photometry method. Alkali-hydrolyzable nitrogen (AN) was determined by the alkali-hydrolysis diffusion method. Available phosphorus (AP) was measured using 0.5 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e NaHCO\u003csub\u003e3\u003c/sub\u003e extraction and molybdenum-antimony anti-colorimetry. Available potassium (AK) was determined using 1 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e NH\u003csub\u003e4\u003c/sub\u003eOAc extraction and flame photometry. Detailed analysis methods are referenced from the study by Wilke et al. (2005).\u003c/p\u003e\u003cp\u003eEasily extractable glomalin-related soil protein (EE-GRSP) and total glomalin-related soil protein (T-GRSP) were measured using sodium citrate extraction and Coomassie brilliant blue G-250 colorimetry (Wright et al., 1998). Soil enzyme activities were measured following methods described by Purev et al. (2014), with soil alkaline protease determined by casein colorimetry and soil urease by phenol-sodium hypochlorite colorimetry.\u003c/p\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003eData Analysis\u003c/h2\u003e\u003cp\u003eTo test the significance of monthly variations of soil properties, one-way ANOVA was performed using IBM SPSS Statistics 25, with multiple comparisons by Duncan's method at P\u0026thinsp;=\u0026thinsp;0.05 significant level. To analyze the influence of various physicochemical properties on SOC, random forest (RF) regression analysis was conducted using SPSSPRO. The partial least squares structural equation modeling (PLS-SEM) was used to analyze the mechanism of soil type affecting SOC. Figures were created using Origin 2022 and ARCgis 10.2.2.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eSeasonal Dynamics of Soil Organic Carbon (SOC)\u003c/h2\u003e\u003cp\u003eSOC content in the Rd ranged from 31.51 to 39.71 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e from April to November, whereas it ranged from 22.50 to 28.51 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the nRd (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The average SOC content during the growing season was 35.09\u0026thinsp;\u0026plusmn;\u0026thinsp;4.46 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the Rd and 25.58\u0026thinsp;\u0026plusmn;\u0026thinsp;3.62 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the nRd. Throughout the growing season, the SOC content in the Rd was consistently higher, reaching 1.28 to 1.57 times that of the nRd. Within the growing season, in the Rd, SOC was much higher in both April and November, reaching 38.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 39.71\u0026thinsp;\u0026plusmn;\u0026thinsp;3.24 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively, and much lower in May, June, and July, at 31.94\u0026thinsp;\u0026plusmn;\u0026thinsp;3.08 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 31.87\u0026thinsp;\u0026plusmn;\u0026thinsp;5.58 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 31.51\u0026thinsp;\u0026plusmn;\u0026thinsp;2.69 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. In the nRd, the highest SOC was in November at 28.51\u0026thinsp;\u0026plusmn;\u0026thinsp;2.82 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the lowest in June at 22.50\u0026thinsp;\u0026plusmn;\u0026thinsp;3.56 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. In general, SOC showed an \u0026ldquo;U\u0026rdquo; pattern (decreased firstly and then increased) throughout the growing season. The fluctuation of SOC content with seasonal changes was slightly larger in the Rd compared to the nRd, with the standard deviations of the monthly averages being 3.10 and 1.95, respectively. The greatest difference in SOC content between the Rd and nRd was in April, with a difference of 13.86 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the smallest difference was shown in July, with a difference of 6.98 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eChanges of Soil nutrients\u003c/h2\u003e\u003cp\u003eAnalysis of the monthly dynamic data on the physical and chemical properties of the monitored soil revealed a significant spatiotemporal heterogeneity pattern (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In terms of pH value, the Rd group (7.48\u0026ndash;7.74) was generally higher than the nRd group (6.41\u0026ndash;7.31). Specifically, the pH value of the Rd group reached its peak in August (7.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25) and September (7.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16), while that of the nRd group increased significantly in July (7.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49) and November (7.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21). Additionally, the Rd group maintained a slightly alkaline trend from April to November. TN exhibited prominent spatial and seasonal variations. The Rd group showed a significantly highest TN content in October (5.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58), which was 106.67% higher than that of the nRd group (2.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23) during the same period. In contrast, the TN content of the nRd group reached its peak in November (2.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3). Throughout the entire monitoring period, the average TN content of the Rd group (3.51 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was 53.28% higher than that of the nRd group (2.29 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). TP showed slight fluctuations but significant spatial differentiation. The TP content of the Rd group was the highest in August (0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04 a), while that of the nRd group reached its peak in May (0.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02). There was no significant difference in TP content between the two groups in most months of the growing season (e.g., July: Rd 0.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04 vs. nRd 0.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04). TK exhibited intense seasonal fluctuations. The TK content of the Rd group was extremely high in April (10.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44) but sharply decreased in May (2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18). In contrast, the TK content of the nRd group was significantly prominent in August (12.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53 vs. Rd 6.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39). AN accumulated significantly in the Rd group during the late stage (July\u0026ndash;November), with contents ranging from 0.31 to 0.37 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (all marked with grade \"a\"). This was higher than the AN content of the nRd group (0.28\u0026ndash;0.35 g/kg) in the same period. However, there was no statistical difference in AN content between the Rd group (0.16\u0026ndash;0.24 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and the nRd group (0.16\u0026ndash;0.17 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) during the early stage (April\u0026ndash;June). AP showed that the Rd group reached a significant peak in May (37.39\u0026thinsp;\u0026plusmn;\u0026thinsp;2.71), which was 94.23% higher than that of the nRd group (19.25\u0026thinsp;\u0026plusmn;\u0026thinsp;1.89). However, the nRd group surpassed the Rd group in June (29.01\u0026thinsp;\u0026plusmn;\u0026thinsp;1.16 vs. Rd 23.54\u0026thinsp;\u0026plusmn;\u0026thinsp;2.58). Additionally, the average AP content of the Rd group during the growing period (April\u0026ndash;July) (29.38 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was higher than that of the nRd group (21.49 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). AK, the content in the Rd group was the highest in October (97.03\u0026thinsp;\u0026plusmn;\u0026thinsp;9.05), which was 29.65% higher than that in the nRd group (74.84\u0026thinsp;\u0026plusmn;\u0026thinsp;7.59) during the same period. In contrast, the AK content in the nRd group was slightly better in May and September (74.99\u0026thinsp;\u0026plusmn;\u0026thinsp;7.56 and 75.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.98, respectively). Throughout the entire monitoring period, the average AK content of the Rd group (77.85 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) exceeded that of the nRd group (68.07 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Collectively, these results indicated that the three soil indicators, namely TN, TK, and AP showed relatively obvious variations across different site conditions and seasons, while the variations of the other indicators were not significant.\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\u003eTemporal variation of soil physicochemical properties in mulberry plantations under two different site conditions.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"15\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003epH\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eTN(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eTP(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eTK(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003eAN(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003eAP(mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e\u003cp\u003eAK(mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c14\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c15\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eApril\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e10.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e2.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e26.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e10.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77f\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e81.59\u0026thinsp;\u0026plusmn;\u0026thinsp;15.97b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e60.99\u0026thinsp;\u0026plusmn;\u0026thinsp;7.46bc\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMay\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15abc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e37.39\u0026thinsp;\u0026plusmn;\u0026thinsp;2.71a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e19.25\u0026thinsp;\u0026plusmn;\u0026thinsp;1.89c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e60.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.37d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e74.99\u0026thinsp;\u0026plusmn;\u0026thinsp;7.56a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eJune\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.95\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03cde\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e23.54\u0026thinsp;\u0026plusmn;\u0026thinsp;2.58d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e29.01\u0026thinsp;\u0026plusmn;\u0026thinsp;1.16a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e66.73\u0026thinsp;\u0026plusmn;\u0026thinsp;6.87cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e58.49\u0026thinsp;\u0026plusmn;\u0026thinsp;8.97c\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eJuly\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.78d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" 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colname=\"c11\"\u003e\u003cp\u003e0.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e23.11\u0026thinsp;\u0026plusmn;\u0026thinsp;1.51d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e16.85\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e82.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8.78b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e61.97\u0026thinsp;\u0026plusmn;\u0026thinsp;9.19bc\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSep.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" 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colname=\"c10\"\u003e\u003cp\u003e0.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e14.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66f\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e15.07\u0026thinsp;\u0026plusmn;\u0026thinsp;1.83e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e73.73\u0026thinsp;\u0026plusmn;\u0026thinsp;6.22bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e75.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.98a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOctober\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02de\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e16.89\u0026thinsp;\u0026plusmn;\u0026thinsp;1.24e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e14.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e97.03\u0026thinsp;\u0026plusmn;\u0026thinsp;9.05a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e74.84\u0026thinsp;\u0026plusmn;\u0026thinsp;7.59a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNov.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06abc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.95b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e9.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e18.03\u0026thinsp;\u0026plusmn;\u0026thinsp;2.26e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e8.16\u0026thinsp;\u0026plusmn;\u0026thinsp;1.26g\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e83.77\u0026thinsp;\u0026plusmn;\u0026thinsp;7.21b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e69.63\u0026thinsp;\u0026plusmn;\u0026thinsp;7.82ab\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e6.09\u0026thinsp;\u0026plusmn;\u0026thinsp;2.83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e23.8\u0026thinsp;\u0026plusmn;\u0026thinsp;7.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e17.63\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e77.85\u0026thinsp;\u0026plusmn;\u0026thinsp;11.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c15\"\u003e\u003cp\u003e68.07\u0026thinsp;\u0026plusmn;\u0026thinsp;6.81\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"15\" nameend=\"c15\" namest=\"c1\"\u003e\u003cp\u003eNote: The data in the table are presented as \u0026lsquo;mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD.\u0026rsquo;. Different lowercase letters in the same column indicate significant differences in the same indicator among different months (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). TN: Total nitrogen; TP: Total phosphorus; TK: Total potassium; AN: Alkaline hydrolysis nitrogen; AP: Rapidly available phosphorus; AK: Rapidly available potassium; Rd: Rocky desertification; nRd: Non-desertification.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eChanges of soil enzyme activity and GRSP content\u003c/h3\u003e\n\u003cp\u003eGenerally, the soil indicators T-GRSP and Alkaline Protease showed more significant changes between different site conditions and seasons, while changes in other factors were less significant (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The T-GRSP content was higher in the Rd throughout the year compared to the nRd, with the largest difference occurring in April, reaching 2.52 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The Alkaline Protease content was slightly higher in the nRd in April, June, August, and November, with the largest difference in November, reaching 1.83 \u0026micro;mol\u0026middot;g\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while in the other four months, the content was higher in the Rd. The temporal trends of each indicator were not consistent.\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\u003eTemporal variation of GRSP and soil enzyme activity in mulberry plantations under two different site conditions\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eEE-GRSP\u003c/p\u003e\u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eT-GRSP\u003c/p\u003e\u003cp\u003e(g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eAlkaline Protease\u003c/p\u003e\u003cp\u003e(\u0026micro;mol\u0026middot;g\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eUrease\u003c/p\u003e\u003cp\u003e(mg\u0026middot;g\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eRd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003enRd\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eApril\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11abc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.84ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.48\u0026thinsp;\u0026plusmn;\u0026thinsp;1.07b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06bc\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMay\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05cd\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eJune\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06bc\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eJuly\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07bc\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAugust\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.99ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03d\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSep.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21abc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09b\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOctober\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13abc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.45\u0026thinsp;\u0026plusmn;\u0026thinsp;1.01a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.71ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09bc\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNov.\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.13\u0026thinsp;\u0026plusmn;\u0026thinsp;1.02ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04cd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e3.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"9\"\u003eNote: Data in the table are \u0026lsquo;mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD.\u0026rsquo;; Different lowercase letters in the same column after the data indicate significant differences in the same study site at different months (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). EE-GRSP: Easily extractable glomalin-related soil protein; T-GRSP: Total glomalin-related soil protein. Rd: Rocky desertification; nRd: Non-desertification.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eBased on the monthly data of GRSP content and enzyme activities in Rd and nRd, the differentiation of ecological functions was revealed. EE-GRSP in the Rd (0.74\u0026ndash;0.99 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was significantly higher than that in the nRd (0.51\u0026ndash;0.70 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and Rd peaked at November (0.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10), which was 41.43% higher than nRd (0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09), and Rd was higher than nRd throughout the year. The T-GRSP in the nRd (2.48\u0026ndash;3.60 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was lower than that in the Rd (4.39\u0026ndash;5.45 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The Rd of October (5.45\u0026thinsp;\u0026plusmn;\u0026thinsp;1.01) was 69.78% higher than that of nRd (3.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.71), and nRd was only close to the lowest level of Rd in July (3.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67) and September (3.60\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74) but still 21.94% lower. It showed that rocky desertification habitat promotes the accumulation of GRSP and increases soil carbon sink. Alkaline Protease showed significant changes in nRd activity throughout the year (0.97\u0026ndash;3.45 mg\u0026middot;g\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), while Rd activity was relatively stable (1.03\u0026ndash;1.98 mg/g/d), and in April and November, the Alkaline Protease activity of nRd was 83.52% and 129.79% higher than that of Rd, respectively. It showed that organic nitrogen mineralization is stronger in non-rocky desertification area. Urease was high in the early Rd (April: 0.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06), but decreased sharply from July (0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04), which was 70.21% lower than that in April. The urease activity in the nRd was enhanced in the later period, and the peak value of November (0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08) was 157.89% higher than that of Rd (0.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04) in the same period, reflecting the habitat timing differentiation of nitrogen metabolism function.\u003c/p\u003e\u003cp\u003eIn summary, the rocky desertification mulberry field enhances soil carbon sinks by increasing T-GRSP content, but at the expense of inhibiting enzyme activity (Alkaline Protease); the non-rocky desertification mulberry field maintains high-efficiency nitrogen turnover function, and the two form an ecological trade-off pattern of 'carbon fixation in rocky desertification-nitrogen release in non-rocky desertification', which provides a regulatory target for the coordinated management of carbon and nitrogen in the mulberry field system in karst areas.\u003c/p\u003e\n\u003ch3\u003eRelationships of Soil Factors with Soil Organic Carbon\u003c/h3\u003e\n\u003cp\u003eThe relationships of soil various factors with SOC content in both Rd and nRd are shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. SOC showed a significant correlation with most physical and chemical factors. Specifically, SOC was significantly positively correlated with TN, AN, AK, T-GRSP, and EE-GRSP, while it was significantly negatively correlated with AP. There were no significant correlations between SOC and TP, alkaline protease, or urease. In the Rd, SOC had no significant correlation with pH, but in the nRd, SOC was significantly positively correlated with pH, with a correlation coefficient of 0.5253. Additionally, SOC was significantly positively correlated with TK in the Rd but shows no significant correlation in the nRd, with correlation coefficients of 0.1775 and 0.0142, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, for the Rd, TN, T-GRSP, and urease had the greatest influence on SOC, with their impact reaching 58.10%, 9%, and 8.9%, respectively. The influence of other factors was relatively minor. In contrast, for the nRd, TN, T-GRSP, and pH were the dominant factors influencing SOC, with their impacts being 25.6%, 18.4%, and 18%, respectively. The influence of other factors did not exceed 15%.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn this study, PLS-SEM was used to further reveal the mechanism of SOC accumulation in different soil habitats (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). PLS-SEM showed that soil type indirectly affected SOC accumulation, specifically, soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. In addition, pH and TN affected SOC accumulation in a direct and positive way, and T-GRSP had similar contributions to SOC accumulation through direct and indirect ways.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eDynamics of SOC in mulberry plantation\u003c/h2\u003e\u003cp\u003eRocky desertification is a process of soil degradation. Numerous studies have shown that SOC content decreases with increasing intensity of rocky desertification (Guo et al., 2014; Wang et al., 2021), but gradually increases with positive vegetation succession (Luo et al., 2009; Yang, 2016). However, the results of this study indicated that the SOC content in rocky desertification mulberry plantation is higher than that in non-rocky desertification mulberry plantation. This phenomenon is likely due to differences in microhabitats and soil properties between the two types of mulberry plantation. The results of this study align with previous research. For instance, studies by Huang et al.(2017) in Guizhou, where SOC values ranged from 15.44 to 47.41 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and Shao et al.(2022) in Yunnan, with SOC values ranging from 16.22 to 44.23 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, both showed that karst regions possess higher SOC content. Similarly, Zhong et al. (2020) and Fang et al. (2016) reported that the surface SOC content in the karst areas of Guangxi ranges from 17.23 to 42.52 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, significantly surpassing the values observed in non-karst areas (13.88\u0026ndash;25.99 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Moreover, through field investigations and data collection, Zhu et al.(2022) found that the average SOC content in the southwest karst region was 29.15 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was markedly higher than the corresponding value in non-karst areas (18.40 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e\u003cp\u003eFirstly, the higher rock exposure rate in rocky desertification mulberry plantation causes soil to concentrate in low-lying areas between rocks. Consequently, litter, the main source of soil organic matter, also concentrates in the soil, providing relatively richer organic matter sources in rocky desertification soils under the same total litter amount. Fertilization in mulberry plantation mainly concentrates in areas with soil, further increasing the sources of organic matter. This also explained the greater seasonal fluctuations of SOC in rocky desertification mulberry plantation. Secondly, the soil pH in rocky desertification mulberry plantation was generally higher than in non-rocky desertification mulberry plantation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a)). In such environmental conditions, Ca\u0026sup2;⁺ in the soil (mainly calcareous soil) can combine with humic acid and other organic matter to form more resistant chelates (Tang, 2015). Additionally, the rapid accumulation of macro-aggregates in the soil effectively protects plant-derived carbon, microbe-derived carbon, and particulate carbon (Goebel et al., 2009; Hu et al., 2024), making the organic carbon in the soil more easily preserved compared to non-rocky desertification soils. This extends the turnover time of organic carbon in karst soils (Wang et al., 2018), thereby increasing the SOC content in rocky desertification mulberry plantation. The significant positive correlation between SOC and pH in non-rocky desertification mulberry plantation and the significantly higher soil pH in rocky desertification mulberry plantation supported this view (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a)). This further proveed the significant application value of mulberry trees in preventing rocky desertification, improving ecology, and developing the economy (Qin et al., 2012). It should be noted that the observed differences in soil organic carbon (SOC) (Rd: 35.09 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e vs. nRd: 25.58 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) might occur under the circumstances where the limitations inherent to the pseudo-replication design are taken into account. Although strict site matching was implemented, pre-existing soil differences might confound the plantation effect. For instance, the initial SOC advantage of calcareous soil might amplify the gains caused by the treatments, and this possibility needs to be distinguished through long-term chrono sequence studies.\u003c/p\u003e\u003cp\u003eThe seasonal variation trend of SOC in rocky desertification mulberry plantation showed more fluctuation compared to non-rocky desertification mulberry plantation. The SOC content in rocky desertification mulberry plantation was higher in April and November and lower in May, June, and July. This is primarily due to the low decomposition rate of organic matter before April due to low temperatures and the accumulation of organic matter from winter fertilization in mulberry plantation. Before November, the increased input of litter in mulberry plantation led to higher SOC content. However, during May, June, and July, the rapid growth of mulberry trees, coupled with increased rainfall and temperature, enhanced soil microbial activity, accelerating SOC decomposition and conversion to water-soluble organic carbon, which resulted in significant SOC loss (Cao et al., 2005). This contrasts with the pattern observed in larch plantation, where SOC content was higher in June, July, and August and lower in May, September, and October (Fan al et., 2018). This difference may be due to the higher latitude environment of larch plantation and the rich sources of organic matter within them. In such environments, increased temperatures in certain months accelerate litter decomposition, supplementing soil organic carbon, while in other months, there may be a depletion of organic carbon. SOC content in 0\u0026ndash;30 cm Chinese fir plantation is shown as follows: autumn\u0026thinsp;\u0026gt;\u0026thinsp;summer\u0026thinsp;\u0026gt;\u0026thinsp;spring\u0026thinsp;\u0026gt;\u0026thinsp;winter (Kong, 2019, which is different from the results of this study, indicating that there are differences among different tree species.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eInfluence of soil factors on SOC\u003c/h2\u003e\u003cp\u003eSoil organic carbon is influenced by various factors, including sources of organic matter, soil properties, climate, and soil carbon fractions ( Huang al et., 2016; Luo al et., 2017). In this study, the differences in climate and sources of organic matter between rocky desertification and non-rocky desertification mulberry plantation were relatively small. Therefore, soil properties may be a significant factor influencing the differences in soil organic carbon content between these two types of mulberry plantation. Owing to inherent limitations in the study design where mulberry were planted into two different soil types, it is impossible to determine for certain, what proportion of the differences in the soil response variables are a result of the Mulberry plantation versus a pre-existing soil condition. However, the more dramatic response observed for more labile forms of nutrients (e.g. AP) suggests that the rocky desertification soils may be responding more rapidly to the mulberry plantation than the rocky desertification soils.\u003c/p\u003e\u003cp\u003eThe study results showed that soil organic carbon content was significantly affected by soil physicochemical properties. TN, pH, and T-GRSP were the dominant factors influencing SOC in the study area, all of which are significantly positively correlated with SOC. The positive correlation between soil total nitrogen (TN) and soil organic carbon is consistent with previous research findings (Ding al et, 2012; Li al et., 2023; Yan al et., 2011). This strong coupling relationship between soil carbon and nitrogen is primarily driven by the fact that increased soil nitrogen content lowers the carbon-to-nitrogen ratio, which promotes microbial carbon fixation and enhances soil carbon accumulation (Luo al et., 2023). Additionally, nitrogen enrichment in soil inhibits microbial SOC mineralization and reduces soil respiration, further promoting SOC content (Wang al et., 2015). The relationship between soil pH and soil organic carbon showed a significant positive correlation at low pH levels, whereas this correlation was not significant at high pH levels. This could be due to the increasing ability of Ca\u0026sup2;⁺ to combine with humic acids and other organic matter to form chelates as pH rises (Tang, 2015). However, once pH increases beyond a certain point, this effect may diminish, possibly even showing a slight negative correlation, similar to the findings of Ding et al. (2012). T-GRSP might contribute to soil organic carbon accumulation by improving soil physical properties, nutrient content, carbon fixation capacity, and microbial activity (Singh al et., 2020).\u003c/p\u003e\u003cp\u003eIn both rocky desertification and non-rocky desertification mulberry plantation, there was no significant relationship between TP and SOC. However, AP showed a significant negative correlation with SOC, possibly because increased phosphorus content enhances microbial decomposition of soil organic carbon, thereby reducing SOC (Luo al et., 2023). Overall, TN, T-GRSP, and urease were the most influential factors affecting SOC in rocky desertification mulberry plantation, all closely related to nitrogen. In non-rocky desertification mulberry plantation, the three most influential factors were TN, T-GRSP, and pH, with the first two mainly influencing nitrogen and the latter affecting the difficulty of soil organic carbon decomposition. Therefore, it can be inferred that both rocky desertification and non-rocky desertification mulberry plantation are likely nitrogen-limited. This may be due to the significant nitrogen loss from mulberry leaf harvesting, suggesting that appropriate adjustment of nitrogen fertilizer application could increase SOC content. Random forest is a supervised machine learning method constructed through the integration of decision-tree-based learners. While random forest identified TN as the primary SOC driver (58.10% importance in Rd), TN-SOC covariation was moderated by calcium saturation. This suggested ion bridging may enforce C-N coupling in karst soils\u0026mdash;a hypothesis warranting nano-scale characterization. PLS-SEM further showed that soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. In addition, pH and TN affected SOC accumulation in a direct and positive way, and T-GRSP had similar contributions to SOC accumulation through direct and indirect ways. GRSP plays a crucial role in SOC sequestration across different ecosystems. Ciss\u0026eacute; et al. (2023) showed that GRSP content correlates positively with SOC and TN while showing inverse relationships with pH. Cui et al. (2024) showed that during grassland degradation and restoration processes, TN serves as the primary factor explaining variance in GRSP and SOC content, while total phosphorus influences GRSP/SOC ratios. This is consistent with the results of this study. Of course, the relationship between GRSP and SOC is bidirectional. Yang et al. (2024) showed that SOC emerges as the primary positive regulator for GRSP accumulation, with explanatory rates exceeding 80%。\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eIndication of mulberry plantation on soil carbon accumulation in Karst region\u003c/h2\u003e\u003cp\u003eThis study's findings revealed, throughout the growing season of mulberry trees, the SOC content of rocky desertification mulberry plantation (35.11\u0026thinsp;\u0026plusmn;\u0026thinsp;3.09 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was significantly higher than that of non-rocky desertification mulberry plantation (25.86\u0026thinsp;\u0026plusmn;\u0026thinsp;1.57 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and the SOC content of rocky desertification mulberry plantation was 1.28\u0026ndash;1.57 times higher than that of the non-rocky desertification, and the average SOC content of mulberry plantation was 30.48 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was much higher than the average SOC content of the soil layer of 0\u0026ndash;20 cm of the mulberry plantation in China (10.71\u0026thinsp;\u0026plusmn;\u0026thinsp;7.01 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)(Wang al et., 2023)and were also higher than the SOC content in surface soils of cultivated lands (dry and paddy fields) in the karst region of Southwest China(Zhang al et., 2014). The SOC content in rocky desertification mulberry plantation generally exceeded the average SOC content in surface soils of the five main landforms in the karst region of Southwest China (4.62\u0026ndash;38.2 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)(Wang al et., 2021), and was equivalent to the surface SOC content in moderately to severely rocky desertified areas of Guizhou in 2011 and the surface SOC content in slightly to potentially rocky desertified lands in Puding and Libo areas of Guizhou(Wang al et., 2017; Yan al et., 2011). It was also comparable to the average SOC content (38.38 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in the 0\u0026ndash;20 cm soil layer of shrubland in Maolan Karst and the SOC content in the surface soil of the succession stages from shrubland to secondary forest in Southwest China (Wang al et., 2017). Additionally, it was equivalent to the surface SOC content in Cunninghamia lanceolata, Cryptomeria fortunei, and Betula platyphylla plantation in western Guizhou around 2012(Ding al et., 2012). On the other hand, the SOC level in non-rocky desertification mulberry plantation was between the SOC content in cultivated lands and shrublands (Wang al et., 2017). Owing to inherent limitations in the study design, we cannot definitively ascertain whether the observed elevation in SOC levels within mulberry plantations and their cross-system disparities stem from post-establishment ecological effects or pre-existing edaphic heterogeneity. To resolve this causal ambiguity, future research must: (1) establish pre-plantation soil carbon baselines through retrospective analysis of land-use history and archived samples, and (2) implement large-scale systematic sampling across heterogeneous karst landscapes (e.g., varying lithology, slope gradients) in Southwest China, ensuring statistical power to delineate plantation-driven SOC dynamics from inherent soil variations.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis study demonstrated that soil organic carbon and soil total nitrogen have a significant synergistic accumulation relationship, maintaining the dynamic balance of carbon and nitrogen can effectively promote the synergistic expansion of soil organic carbon pool. There are significant differences in the dynamic change characteristics of soil organic carbon between rocky desertification mulberry plantations and non-rocky desertification mulberry plantations. Specifically, the SOC content in rocky desertification mulberry plantations is 1.28\u0026ndash;1.57 times that of non-rocky desertification ones. Moreover, in rocky desertification mulberry plantations, SOC content responds more strongly to seasonal variations. Meanwhile, the availability of soil nitrogen is the main regulating factor controlling the accumulation of SOC in the mulberry agricultural ecosystem. Soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. Inter cropping strategically introducing nitrogen-fixing symbiotic species is conducive to enhancing the carbon sink function of artificial forests and provides a theoretical basis for formulating soil carbon sink regulation measures for rocky desertification artificial forests.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e This work was supported by the Guizhou Provincial Science and Technology Program Project (Qiankehe Support [2024] General 076); Guizhou Provincial Science and Technology Program Project (Qiankehe Support [2023] General 011); Guizhou Provincial Science and Technology Program Project (Qiankehe Foundation-ZK[2023]General 161);Ministry of Finance and the Ministry of Agriculture and Rural Affairs: the National Modern Agricultural Industry Technology System(CARS-18-SYZ20);Guizhou Provincial Science and Technology Program Project (Qiankehe Platform KXJZ(2025)028); Guizhou Provincial Science and Technology Program Project (Qiankehe Foundation-ZK[2024]General 550); Guizhou Academy of Agricultural Sciences Youth Fund Project (Qian Nongke Youth Fund [2023] No. 01).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor\u0026rsquo;s contributions\u003c/strong\u003e Dan Xing: Conceptualization, Methodology, Writing \u0026mdash;review \u0026amp; editing, Supervision, Project administration. Yanjin Shi: Writing\u0026mdash;original draft, Resources, Data curation, Project administration. Mei Lu: Writing \u0026mdash;review \u0026amp; editing. Junfang Cui: Writing \u0026mdash;review \u0026amp; editing. Shiqing Peng: Resources. Fang Zhang: Formal analysis. Xiaohong Wang: Formal analysis. Zhanfeng Ye: Investigation. Shiyu Han: Methodology.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interest\u003c/strong\u003e The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAgnihotri R, Sharma M P, Prakash A, Ramesh A, Bhattacharjy S, Patra A K, Manna M C, Kurganova I, Kuzyakov Y (2021) Glycoproteins of arbuscular mycorrhiza for soil carbon sequestration: Review of mechanisms and controls. 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Plant and Soil 475(1/2):45-59. https://doi.org/10.1007/s11104-021-05220-4\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":false,"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":"Karst rocky desertification, Morus alba cultivation, Soil organic carbon dynamics, Nitrogen limitation, Glomalin-related soil proteins","lastPublishedDoi":"10.21203/rs.3.rs-7995665/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7995665/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground and Aims\u003c/h2\u003e\u003cp\u003eSoil organic carbon (SOC), a critical determinant of soil functionality, remains inadequately characterized in its spatiotemporal dynamics and drivers within karst mulberry systems\u0026mdash;an ecologically fragile region confronting severe rocky desertification.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eThis study elucidates SOC variability across typical karst landscapes through comparative analysis of mulberry plantations in rocky desertification zones (Rd) versus non-desertification areas (nRd) of central Guizhou, China, focusing on seasonal interactions with macro/micronutrients and biochemical factors.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eKey findings reveal: (1) Changes of SOC content in different soil types and seasons. SOC content in Rd plantations (31.51\u0026ndash;39.71 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) consistently exceeded nRd counterparts (22.50\u0026ndash;28.51 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) by 1.28\u0026ndash;1.57-fold, with bimodal seasonal peaks in April/November and minima in May\u0026ndash;July across both systems. (2) Carbon-nutrient coupling: SOC exhibited significant positive correlations with total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), available potassium (AK), and glomalin-related soil proteins (T-GRSP: Total glomalin-related soil protein; EE-GRSP: Easily extractable glomalin-related soil protein)), contrasting with significant negative associations with available phosphorus (AP). (3) System-specific drivers: Nitrogen-limitation governed SOC dynamics dominantly. However, pH emerged as a key secondary regulator in nRd systems. In addition, soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eThese findings establish nitrogen management as a critical lever for SOC sequestration optimization in karst mulberry systems while contextualizing landscape-specific edaphic controls. The work provides an empirical foundation for targeted carbon-smart practices in global karst agricultural ecosystems facing desertification pressures.\u003c/p\u003e","manuscriptTitle":"Soil organic carbon accumulation is mainly driven by soil nitrogen in rocky desertified mulberry plantation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-19 09:11:53","doi":"10.21203/rs.3.rs-7995665/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":"7507f1f9-3141-48ae-8521-c79b47ea2cc6","owner":[],"postedDate":"November 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-18T05:02:42+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-19 09:11:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7995665","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7995665","identity":"rs-7995665","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}