Straw return is an important approach to improving soil quality and crop yield stability. However, the comprehensive effects of different straw return modes on soil quality, stable organic carbon saturation, and crop yield stability were not well studied in the wheat-cotton double cropping system. To address this gap, a 10‑year field experiment was conducted in East China, which included four straw return modes: straw removal (CK), single-season cotton straw return (RC), single-season wheat straw return (RW), and annual wheat and cotton straw return (RCW). The effects of these modes on soil quality, soil organic carbon (SOC) fractions, apparent stable carbon saturation, and seedcotton yield stability were evaluated. The results showed that straw return increased soil quality index (SQI) compared with CK, with RCW being the best. Straw return increased crop yield, and RCW and RW significantly reduced the variation coefficient and increased the sustainable yield index of seedcotton yield. Meantime, straw return promoted the contents of particulate organic carbon (POC) and mineral-associated organic carbon (MOC) fractions, and increased the contribution of unprotected POC to SOC, but reduced the contribution of MOC to SOC. Nevertheless, straw return increased the apparent saturation capacity and saturation deficit (CSD) of MOC, indicating a larger remaining capacity for stable carbon sequestration. Furthermore, SQI was positively correlated with CSD and seedcotton yield. SQI and CSD also positively correlated with the sustainable yield index while negatively correlated with the variation coefficient of seedcotton yield. Therefore, annual straw return mode can effectively improve soil quality, enhance stable SOC sequestration, and increase seedcotton yield stability for sustainable cotton farming in East China.

To investigate the regulatory effects and physiological mechanisms of different K+/Na+ ratios on floral bud differentiation, silique formation, and yield in rapeseed (Brassica napus L.) under salt stress and to identify the optimal K+/Na+ ratio under different salt concentrations. Three total salt levels were established: 0.15% (S1), 0.30% (S2), and 0.45% (S3), with different K+/Na+ ratios applied at each concentration. Developmental progression, yield components, and leaf physiological parameters were dynamically monitored. (1) Under salt stress, floral bud differentiation exhibited “early initiation yet delayed development,” with moderate and high salinity (S2, S3) prolonging the emergence-to-flowering interval and total growth duration. (2) Salinity elevated leaf Na+ and reduced the K+/Na+ ratio; optimal K+/Na+ ratios restored ionic homeostasis. (3) The optimal K+/Na+ ratio upregulated zeatin riboside (ZR) and gibberellins (GAs), downregulated abscisic acid (ABA), increased osmolyte (soluble protein, free amino acid, and soluble sugar) contents and antioxidant enzyme (superoxide dismutase, peroxidase, and catalase) activities, and reduced malondialdehyde (MDA) accumulation. (4) Salt stress reduced yield primarily by decreasing the number of siliques. The optimal K+/Na+ ratio improved floral bud-to-open flower and open flower-to-silique conversion efficiency—low and moderate salinity favored the former, and high salinity favored the latter—thereby significantly increasing yield. (5) PLSPM revealed that K+/Na+ homeostasis indirectly promoted silique formation and yield by positively regulating carbon–nitrogen metabolism while negatively modulating hormone and antioxidant metabolism. In conclusion, an appropriate K+/Na+ ratio enhances conversion efficiency and yield by reestablishing ionic homeostasis, optimizing hormonal balance, and strengthening carbon–nitrogen metabolism and antioxidant capacity. The optimal ratios under low, moderate, and high salinity were 1/7, 1/13, and 1/15, respectively, providing a theoretical basis for zone-specific potassium-mediated salt mitigation in rapeseed cultivation on salinealkali land.

Boron deficiency is a major yield-limiting factor in intensive cotton (Gossypium hirsutum L.) production. However, the physiological mechanisms and the critical periods for boron regulation of cotton seed kernel biomass remain unclear, hindering precise nutrient management. This study aimed to (i) identify the key boron-regulated window for cottonseed kernel biomass accumulation, (ii) establish the critical kernel boron concentration during this period, and (iii) elucidate the underlying sucrose metabolic mechanisms. A three-year field experiment was conducted on two contrasting soils with three boron application rates. Dynamics of kernel biomass, tissue boron concentration, carbohydrate profiles, as well as the activities and gene expression of key enzymes involved in sucrose metabolism and glycolysis were monitored during kernel development. The results identified a critical boron-regulation window at 11.7-24.4 days post-anthesis, during which boron supply modulated yield primarily by affecting the accumulation rate. The critical kernel boron concentrations for optimal biomass were 53.5-80.5 mg & sdot;kg- 1. Adequate boron supply improved sucrose transport, optimized sucrose metabolism, and stimulated glycolytic flux, thereby directing carbon toward storage compounds and increasing kernel biomass. These findings provide a physiology-informed strategy for precision boron management to improve cottonseed yield and supporting sustainable production.

Drought negatively impacts photosynthesis and water transport in plants, so new technologies to enhance drought tolerance are urgently needed. Here, a hydroponic experiment revealed that foliar application of polyacrylic acid-coated nanoceria (PNC, 100 mg L−1) to cotton leaves under drought stress (DS, 5% (w/v) polyethylene glycol 6000, 5 d) significantly improved the growth performance and biomass accumulation. Compared with the DS control, foliar application of PNC under DS conditions (DP) significantly improved leaf hydraulic conductance (Kleaf) and mesophyll conductance (gm) by 73.4% and 34.9%, respectively, thereby leading to 42.2% higher net photosynthetic rate (A). Moreover, compared with the DS control, the DP treatment considerably increased the volume fraction of intercellular airspace and the surface area of mesophyll cells exposed to intercellular airspace by 24.5% and 56.3%, respectively, which contributed to the simultaneous improvements in gm and outside-xylem hydraulic conductance (Kox). Furthermore, relative to the DS control, the DP treatment considerably decreased hydrogen peroxide and superoxide anion levels by 45.2% and 65.4%, respectively, which largely explained the variations in above mentioned leaf anatomy. Additionally, compared with the DS control, enhancement in Kox under the DP treatment was also ascribed to the increased leaf vein density. Therefore, these findings indicated that foliar application of nanoceria could improve both Kleaf and gm by modifying leaf anatomy, thereby improving the A of drought-stressed cotton seedlings.

Global warming has resulted in an increasing frequency of high-temperature (HT) stress during the critical growth stages of cotton. cotton. However, systematic investigations into its effects during the seedling and aquaring stages remain limited. In this study, the cotton cultivar 'CCRI425 as subjected to HT treatments at both stages to evaluate the impacts on floral bud differentiation, young square development, and associated metabolic regulation. HT stress during the seedling stage delayed floral bud differentiation, reduced bud number, and induced morphological abnormalities. These changes were linked to hormonal imbalances, specifically increased levels of auxin (IAA) and cytokinin (CTKz) and decreased levels of abecizic acid (ABA) and jasmonic acid (JA) in the apical meristems. Concurrently, disrupted sugar and antioxidant metabolizm further impaired reproductive development, ultimately leading to a 56.7 56 reduction in seed cotton yield. In contrast, HT during the squaring stage exerted more severe inhibitory effects on young square development, disturbing sugar metabolism and ROS scavenging in both stamens and pirtils. This disturbance resulted in decreased pollen viability and stigma receptivity, culminating a 78.1 56 yield loss. By revealing stage-specific metabolic disruptions in cotton reproductive development under HT stress, this study provides critical insights into the mechanisma limiting yield and offers a theoretical basis for breeding heat-tolerant varieties and mitigating high-temperature damage.

Drought stress has been reported to impair chemotropism of pollen tube growth in the pistil, yet the physiological mechanisms underlying this phenomenon remain unexplored in G. hirsutum. This study hypothesized that drought-induced nitric oxide (NO) changes in ovules may inhibit pollen tube directional growth. To test the above hypothesis, pools experiments were conducted using two cotton (Gossypium hirsutum L.) cultivars Yuzaomian 9110 (drought-sensitive) and Dexiamian 1 (drought-tolerant) under water stress. Results demonstrated that drought stress inhibited the directional growth of pollen tube to the embryo sac and simultaneously reduced fertilization rate, the number of cotton seeds per boll as well as the single boll weight. Moreover, correlation analyses showed that NO content in the ovules had significantly negative correlation with the fertilization rate, implying that NO changes in ovules might inhibit pollen tube directional growth and subsequent yield component formation. Further analyses showed that drought stress elevated nitrate reductase (NR) activity in the ovules of both cultivars, facilitating the conversion of nitrite (NO2-) to NO. This process was accompanied by the up-regulation of NR gene (GhNIAD) expressions in the drought-affected ovules of both cultivars, further promoting NO synthesis. The reduction in S-nitrosoglutathione reductase (GSNOR) activity under drought conditions was correlated with an accumulation of S-nitrosoglutathione (GSNO), suggesting that the compromised removal of NO contributed to the higher NO levels in the ovules. Additionally, elevated NO levels may, as part of a regulatory mechanism, further inhibit the activity of GSNOR in the ovules of both cultivars under drought stress. Thus, these findings revealed that drought leads to the accumulation of NO in the cotton ovules, which may be a factor inhibiting pollen tube growth. Of course, this causal relationship requires more evidence to be confirmed in future research. These results provide novel insights into the molecular-physiological mechanisms by which water deficit triggers reproductive failure in cotton.

Abstract Background Boron (B) constitutes a critical yield constraint in global cotton production. Although B application plays a vital role in cotton yield, research gaps persist regarding cultivar-specific B requirements, vertical canopy dynamics, and precision management protocols in B-deficient agroecosystems. Results In this study, we investigated the effects of B application rates on yield variation and spatial variation across two varieties at three locations. In Yancheng, applying 2.5 kg·hm−2 of boron resulted in yield increases of 14.7%–25.9%, and in Xinghua, applying 2.0 kg·hm−2 of boron achieved yield increases of 17.30%–20.58%. The optimal B application rates determined by quadratic function fitting were 1.90–2.36 kg·hm−2 of boron for CCRI 425 and 2.05–2.36 kg·hm−2 for Siza 3. Vertical canopy analysis revealed that the middle canopy (FB5–8), contributing 48.2% of total yield, responded significantly to B application rates. Conclusions Cultivar-tailored B application within 1.90–2.36 kg·hm−2 reconciles yield maximization. The boll number, especially those in the middle canopy, responded significantly to B application rates and was the main factor contributing to differences in yield formation. These findings underscore the necessity of location- and cultivar-specific B management.

Stomatal anatomical traits are known to influence stomatal movements and water use efficiency (WUE). However, it is unclear how strongly stomatal distribution regulates stomatal kinetics and WUE. In this study, we examined gas exchange parameters and stomatal traits in 5 cereal and 5 dicotyledonous C3 crops to study the relationship between stomatal distribution and stomatal kinetics. Using modeling and experimental validation, we further assessed the impacts of stomatal distribution on WUE in cereals and dicots, represented by rye and cotton, respectively. Results showed that stomatal kinetics were specifically correlated with the ratio of adaxial to abaxial stomatal density (SR) across these C3 crops. Moreover, increased SR could reduce water loss by accelerating stomatal closure when transitioning from light to darkness, thereby significantly improving leaf intrinsic WUE and reducing whole-plant water consumption under well-watered and drought conditions. In addition, the higher SR observed in cereals than dicots contributed to the former's faster stomatal kinetics and enhanced WUE. These findings highlight the critical function of stomatal distribution on stomatal kinetics and WUE in C3 crops, and its differential regulation between cereals and dicots, providing a feasible approach for breeding drought-tolerant crops in future water-saving agriculture.

Boron is an essential trace element for sustaining normal growth and development in cotton. Appropriate boron application promotes fiber length, but its underlying mechanism remains unclear. To explore this, a soil column experiment with three boron fertilizer rates (0 kg B ha-1, as a control; 2.3 kg B ha-1, optimal boron quantity; 4.6 kg B ha-1, boron excess) was conducted. Results indicated that compared with the control, optimal boron application increased the maximum fiber elongation velocity, thereby promoting fiber elongation. More specifically, optimal boron application enhanced cellulose synthase (CesA) activity as well as the expression of GhCesA3/6, GhGAUT1/8/10, and GhXXT1/2, which facilitated the biosynthesis of cellulose, pectin, and hemicellulose in the primary cell wall, respectively, thereby promoting fiber elongation. Meanwhile, optimal boron application increased the accumulation of sucrose, hexose, and K+, consequently promoting cell turgor pressure and fiber elongation. Moreover, optimal boron application augmented exo-beta-1,4-glucanase activity to accelerate cellulose hydrolysis, increased pectin methylesterase (PME) activity and GhPME1/2 expression to promote pectin de-esterification, and upregulated GhXTH6/7/8 expression to mediate hemicellulose cleavage during the process of primary cell wall loosening and remodeling. Simultaneously, optimal boron application upregulated the expression of GhEXPA1/2/4 encoding expansins. These changes facilitated fiber primary cell wall loosening and remodeling to promote fiber length. This study is the first to uncover the physiological mechanisms of boron regulating fiber length, laying a foundation for efficient boron utilization in cotton production.

Purpose. This study aimed to explore the impact of straw retention combined with different phosphorus (P) rate on soil nutrient content, the yield and quality of fiber, the allometric growth relationship between root and shoot, and root nitrogen (N) metabolism. Methods. The field experiment was conducted from 2020 to 2021 to study the effects of straw management (removal and retention) and P rate (0, 44, and 88 kg P ha− 1) on soil quality, biomass allocation, and N uptake and assimilation. Results. Straw retention combined with P application contributed to improving lint yield and fiber quality synergistically. This result was due to it improved physical and chemical properties of soil (increasing the contents of available nitrogen, available P, and organic matter, but decreased the bulk density), thereby increasing the activities of nitrate reductase (10.5

Context: Boron (B) deficiency is a critical yield-limiting factor in global cotton cultivation. Effective B management is complicated by a narrow sufficiency range between deficiency and toxicity, and site-specific studies lack broader agroecological applicability. Objective: This study aimed to quantitatively assess cotton yield responses to B fertilization across diverse soil and climatic conditions, and to establish evidence-based, precision B management strategies for major cultivation areas. Methods: A meta-analytical was conducted, synthesizing data from 234 experimental observations in 31 field studies across five continents. Hierarchical mixed-effects models evaluated interactions with soil properties, climate, and agronomic practices. Optimal B application rates at maximum yield increase were simulated using quadratic and logistic models under varying soil available B levels. Results: B fertilization increased cotton yields by an average of 12.27 %. The greatest yield improvements occurred under suitable conditions: in medium-to-fine textures soils with low soil available B content (< 0.2 mg kg(-1)), slightly acidic pH (< 6), moderate organic matter content (10-20 g kg(-1)), average temperatures (25-30 degrees C), and planting densities below 4 plant m(-2). Operational guidelines propose soil application (3.00 kg B ha(-1)) for suitable conditions in cotton cultivation areas. Otherwise, foliar fertilization (2.07 kg B ha(-1)) is recommended for marginal environments. Conclusions: This work provided the first global evidence-based decision framework for precision B management in cotton. It enabled site-specific optimization of fertilizer inputs to concurrently maximize yield potential across diverse cultivation systems.

Heat stress (HT) severely impairs the physiological activity of the leaf subtending to cotton boll (LSCB), causing severe yield loss. Although 1-methylcyclopropene (1-MCP) is known to potentially enhance heat tolerance in cotton, its physiological mechanisms involved remain unclear. To investigate this, a two-year pot experiment was conducted under normal temperature (NT, 32/24 degrees C) and high temperature (HT, 42/34 degrees C) conditions, during the flowering and boll forming stages, and LSCB were sprayed with distilled water or a 400 mu mol L-1 concentration of 1-MCP. HT severely reduced seed cotton yield by 77.5-79.9% and increased the boll abscission rate compared to NT. The foliar application of 1-MCP effectively alleviated HT-induced yield loss, resulting in increases of 101.4-141.7% and a decrease in the boll abscission rate relative to HT. However, the final yield, boll weight, and boll number in the HT+ 1-MCP treatment group remained significantly lower than those in the NT group. Physiological analyses revealed that 1-MCP mitigated HT-induced photoinhibition in LSCB, enhanced photosynthetic efficiency by increasing Fv/Fm, Phi PSII, and the electron transport rate (ETR), and reduced non-stomatal limitations to photosynthesis. Additionally, 1-MCP improved carbon partitioning by promoting sucrose accumulation. Furthermore, HT+ 1-MCP enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), reduced oxidative damage, and modulated hormone homeostasis, notably suppressing the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) while elevating abscisic acid (ABA) and salicylic acid (SA) levels. Structural equation modeling indicated that 1-MCP enhanced yield by both directly and indirectly improving LSCB function, by which facilitating through osmotic adjustment, antioxidant activity, and hormone homeostasis. Consequently, antioxidant-mediated optimization could support sucrose accumulation and carbohydrate allocation to the cotton bolls. These findings elucidate how 1-MCP sustains the LSCB functions and carbohydrate supply under HT, providing a physiological basis for its application as a field strategy to enhance cotton's heat tolerance.

The objective of this study was to identify a boron (B) application strategy maximizing cotton yield. In a two-year experiment across two soil types with three B application rates, B availability significantly regulated boll biomass accumulation rate in a 12u201319-d post-anthesis window; B concentrations of 41u201374 mg B kgu22121 in leaves subtending bolls maximized boll weight; and moderate B application increased sourceu2013sink carbon flux by increasing net photosynthetic rate, sucrose biosynthesis, and phloem loading efficiency. Integrating these three findings will increase photoassimilate partitioning to reproductive sinks, boosting cotton yield and B-use efficiency.

Studies on drought stress physiology have primarily focused on the newest fully expanded leaves, in which drought reduces cytokinin (CTK) content, thereby disrupting water balance and photosynthesis. Mature (old) leaves usually exhibit greater sensitivity to drought than the newest fully expanded ones. However, the impact of higher endogenous CTK levels on photosynthetic rate (AN) and water use efficiency (WUE) in drought-stressed mature leaves remains underexplored. To address this, a drought experiment was performed using wild-type (WT) cotton and two CYTOKININ DEHYDROGENASE (GhCKX) suppression lines with elevated CTK levels. Here, suppressing GhCKX optimized the trade-off between AN and intrinsic WUE (iWUE) in mature leaves during drought, since not only higher AN but also higher iWUE were observed in transgenic lines than the WT under drought. This optimization was driven by shifts in the relationships of mesophyll conductance (gm) and maximum carboxylation rate (Vcmax) to stomatal conductance (gs), specifically higher gm/gs and Vcmax/gs ratios, resulting from larger enhancements in gm and Vcmax than in gs, caused by up-regulated CTK. Moreover, higher gm in drought-stressed transgenic lines than drought-stressed WT resulted from thinner cell wall, shorter distance between adjacent chloroplasts, and larger ratio of chloroplast area to mesophyll area facing the intercellular airspace; and their superior Vcmax was attributed to increased Rubisco content and initial Rubisco activity. This study reveals that promoting endogenous CTK simultaneously enhances AN and iWUE in mature leaves under drought via the coordination of photosynthetic constraints, offering a sustainable strategy to improve the drought resistance of crops.

The beneficial impacts of biochar and straw amendments on soil fertility and crop productivity were welldocumented. However, the legacy effects of these practices on crop productivity, nutrient utilization, and arbuscular mycorrhizal fungal (AMF) symbiosis under subsequent straw return remain insufficiently understood. To address this knowledge gap, a split-plot field experiment was conducted to evaluate the legacy effects on seedcotton yield, nutrient use efficiency, AMF functional traits (root colonization rate, colonization intensity, spore density, and hyphal density), and AMF community structure in a cotton-rapeseed double-cropping system (2023-2024). The main plots were previous four-year fertilization treatments: chemical fertilization only (F), straw amendment with F (SF), and biochar amendment with F (BF). The subplots were subsequent cottonrapeseed straw removal and straw return. Overall, compared to F, SF and BF treatments not only enhanced soil nitrogen (N) and phosphorus (P) availability, enzyme activities, nutrient use efficiencies, and seedcotton yield, but also positively influenced AMF functional traits and diversity. Among these, BF proved to be better than SF. Furthermore, subsequent straw return could further improve nutrient use efficiencies and seedcotton yield under previous fertilization treatments. Notably, compared to straw removal, the incremental benefit of yield and N and P agronomy efficiencies under straw return in BF were less than SF. Conversely, the increment benefit of N and P recovery efficiencies under straw return in BF were greater than SF. Furthermore, AMF functional traits served as a vital link among soil N- and P-related enzymes, nutrient mobilization, and seedcotton formation. Collectively, this study revealed that the legacy effects of historical fertilization management, especially BF, profoundly influenced the synergy benefits of subsequent straw return on AMF symbiosis, nutrient utilization, and cotton productivity.

Cottonseed is a major source of edible oil and plant protein, yet its development is highly sensitive to drought. Short-term droughts frequently occur during cotton reproductive growth, but how nitrogen supply regulates root-leaf nitrogen metabolic coordination and post-drought kernel recovery remains poorly understood. Using a controlled pot experiment, we examined the effects of short-term drought and nitrogen application on nitrogen metabolism in cotton root and the leaf subtending the cotton boll (LSCB), as well as on cottonseed kernel nutrient accumulation after re-watering. Short-term drought suppressed nitrate assimilation and nitrogen transport in both root and LSCB by inhibiting key nitrogen-assimilating enzymes, resulting in reduced 15N allocation to the developing kernel. Nitrogen application alleviated these constraints by enhancing nitrate reduction, restoring enzymatic activity, and promoting nitrogen translocation. Under moderate drought, optimal nitrogen supply (150 kg N ha-1) enabled rapid nitrogen metabolic recovery after re-watering and fully restored cottonseed kernel yield and nutrient production, whereas severe drought caused sustained inhibition. Integrative analyses indicated that LSCB nitrogen metabolism acts as an important metabolic hub linking root nitrogen processes with kernel nutrient accumulation, with nitrate reductase and glutamate synthase emerging as key regulatory components. Overall, these results demonstrate that an appropriate nitrogen fertilization of 150 kg N ha-1 can reestablish root-LSCB nitrogen metabolic coordination under moderate short-term drought, thereby sustaining cottonseed kernel development. This study provides physiological guidance for optimizing water-nitrogen management in cotton production under transient drought conditions.

The objective of this study was to identify a boron (B) application strategy maximizing cotton yield. In a two-year experiment across two soil types with three B application rates, B availability significantly reg- ulated boll biomass accumulation rate in a 12-19-d post-anthesis window; B concentrations of 41-74 mg B kg' in leaves subtending bolls maximized boll weight; and moderate B application increased source- sink carbon flux by increasing net photosynthetic rate, sucrose biosynthesis, and phloem loading effi- ciency. Integrating these three findings will increase photoassimilate partitioning to reproductive sinks, boosting cotton yield and B-use efficiency. (c) 2026 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC- ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

BackgroundSaline-alkali soils commonly face the dual challenges of low stock and activity in soil organic carbon (SOC), and long-term excessive nitrogen (N) fertilizer application further exacerbates soil quality degradation. Acid-modified biochar offers a promising approach for improving the fertility of saline-alkali soils, yet the effects of its combined application with N fertilizer on SOC fractions and soil quality remain insufficiently studies.MethodsTherefore, we conducted a two-year field experiment to comprehensively assess the effects of acid-modified biochar combined with N fertilizer application on soil quality index (SQI), microbial nutrient limitation and microbial carbon use efficiency (CUE), SOC fractions and yield. A randomized complete block experiment with five treatments was established: no chemical N fertilizer and no acid-modified biochar (CK), 300 kg N ha−1 (N1), 450 kg N ha−1 (Recommended N application rate, N2), 300 kg N ha−1 + acid-modified biochar (BN1), and 450 kg N ha−1 + acid-modified biochar (BN2).ResultsThe BN1 and BN2 treatments effectively lowered soil pH by 3.7%–5.6% and increased the contents of available phosphorus (Av-P), available potassium (Av-K), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and microbial biomass nitrogen (MBN). These improvements collectively resulted in a SQI that was 4.0–5.1 times higher than that in the N1 and N2 treatments. Furthermore, the BN1 and BN2 treatments reversed the suppression of soil enzyme activities induced by sole N application, enhanced microbial CUE by 71.7%–105.2%, and mitigated microbial C limitation. Compared with N2, BN1 and BN2 treatments increased SOC by 35.5%–51.2%, easily oxidizable carbon (EOC) by 1.2–2.7 folds, and microbial biomass carbon (MBC) by 34.4%–46.1%. The cotton yield under BN treatments exceeded that of N2 by 10.1%–15.5% in two years. No significant differences were observed between BN1 and BN2 in terms of SQI, microbial CUE, and yield. Path analysis confirmed that fertilization-induced alterations in soil properties indirectly promoted soil enzyme activities and microbial CUE, which not only facilitated SOC accumulation but also directly boosted yield.ConclusionOverall, 20% reduction of conventional N fertilizer combined with acid-modified biochar was more effective at improving soil quality and reducing microbial C limitation, enhance microbial CUE, and foster the accumulation of SOC, providing guidance for sustainable development in saline-alkali soil.

Soil carbon sequestration is intricately linked to microbial metabolism. However, the impacts of straw management combined with potassium (K) fertilization on soil organic carbon (SOC) pool and microbial metabolic limitation remains poorly understood in a wheat-cotton cropping system. An eight-year (2015–2022) field experiment was conducted to investigate the effects of four types of straw management, including straw removal (CK), cotton straw returning (SC), wheat straw returning (SW), and cotton and wheat straw double returning (SCW), with three K rates (0, 150, and 225 kg K2O ha− 1) on SOC functional fraction, SOC stability (the ratio of mineral-associated organic carbon to particulate organic carbon), and microbial metabolic limitation using vector modeling in sandy loam topsoil (0–20 cm). Straw returning significantly increased SOC and its fractions while reducing SOC stability. K rate primarily altered unprotected SOC fractions, but having no significant effect on SOC stability. Straw returning, rather than K rate, alleviated microbial carbon and phosphorus limitations, with the order of mitigative effect being SCW > SW > SC. Meanwhile, microbial carbon and phosphorus limitations were key predictors of SOC fractions and stability. This study revealed that dual regulatory mechanisms of straw management rather than K fertilizer to promote SOC sequestration via directly increasing the content of SOC fractions and indirectly mitigating soil microbial metabolic limitation to regulate SOC stability. Cotton and wheat straw double returning was most beneficial to improve SOC sequestration and alleviate microbial metabolic limitation. However, K fertilization has almost no effect on the wheat-cotton fields.