Promotion of Maize Straw Degradation Rate by Altering Microbial Community Structure through the Addition of Soybean Straw

Promotion of Maize Straw Degradation Rate by Altering Microbial Community Structure through the Addition of Soybean Straw | 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 Promotion of Maize Straw Degradation Rate by Altering Microbial Community Structure through the Addition of Soybean Straw Xiaodan Liu, Hongrui Huo, Yuhang Zhang, Huawei Yang, Shumin Li, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4441610/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 The carbon-nitrogen ratio (C/N ratio) of straw significantly influences its mineralization and nutrient release when returned to the soil. This study utilized indoor culture and outdoor pot experiments to investigate the impact of varying straw ratios on straw mineralization, soil property dynamics, soil microbial communities, soil enzyme activities, and maize growth. Design of treatments included: (1) maize straw return (M), (2) soybean straw return (S), (3) 1:1 ratio of maize straw and soybean straw return (MS), (4) 2:1 ratio of maize straw to soybean straw return (2MS), (5) maize straw return combined with nitrogen fertilizer (MF) and (6) no straw return (NS). Compared with M treatment, MS and MF treatment enhanced the straw mineralization rate and nutrient release, thus increasing the biomass of succeeding maize. The MS treatment increased the relative abundance of Chloroflexi, Acidobacteriota, and Proteobacteria by 15.54%, 5.36%, and 14.29%, respectively, compared to the M treatment. Straw return treatments significantly decreased the prevalence of the pathogenic fungus Fusarium compared to the NS approach. Correlation analyses indicated a positive association between soil chemical properties and the presence of Proteobacteria, Firmicutes, Bdellovibrionota, and Nitrospirota. Conversely, these factors showed a negative correlation with Actinobacteriota, Gemmatimonadota, Funneliformis , Trichoderma , and Fusarium . These changes in microbial communities are beneficial for straw degradation and nutrient release. In summary, the combined addition of soybean straw and maize straw in a 1:1 ratio optimizes the microbial community, enhances soil nutrient cycling, improves soil fertility, and positively affects corn biomass and nutrient uptake. Mollisols Residue quality Mixture effect Soil enzyme activity Straw decomposition Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Highlights Incorporating soybean straw with maize straw accelerates straw mineralization. Returning straw to the field reduces the abundance of harmful fungi. Bacteria associated with straw mineralization show increased relative abundance. Different straw C/N ratios and microbial community structures are key mechanisms. 1 Introduction Mollisols in northeastern China are nutrient-rich and have high soil organic carbon (SOC) content. However, these croplands have experienced a reduction in topsoil organic carbon due to extensive farming and increased erosion (Li et al., 2013). Xu et al. ( 2020 ) indicated that after more than 150 years of farming, SOC levels in the northeast region of China have decreased by 46%. Addressing land degradation is crucial for enhancing food security, preserving biodiversity, and effectively mitigating and adapting to climate change (Hossain et al., 2020 ). Tillage management measures notably influence soil quality and have a profound impact on the dynamics of SOC. Returning crop stubble to the soil enhances its physical characteristics, reducing erosion risk while also preserving organic carbon levels, improving biological activity, and promoting soil fertility and productivity. (Li et al., 2022 ). Wang et al. ( 2015 ) analyzed longitudinal experimental data from key agricultural areas in China and found that straw restoration significantly improved crop productivity, SOC, and total nitrogen levels compared to straw removal. Straw decomposition plays a crucial role in SOC balance, organic carbon mineralization, and nutrient release. Factors such as the C/N ratio, temperature, placement depth, and soil moisture significantly influence these processes. However, in northeast China, where temperatures are low, directly returning maize straw with a high C/N ratio to the field can result in competition with crop growth during decomposition, leading to reduced crop yields (Islam et al., 2022 ). Intercropping soybean and maize is a common planting practice in the Northeast region. Previous studies examining soil nutrient utilization efficiency in intercropping have primarily focused on niche differentiation, differences in growth stages, and complementarity in nutrient utilization (Meng et al., 2015 ; Liu et al., 2017 ; Zhang et al., 2020 ). When crops are intercropped, soybean straw with a low C/N ratio and maize straw with a high C/N ratio are typically mixed and decomposed simultaneously in the same soil volume. Understanding the effects of multiple plant cultivation on litter decomposition remains elusive. Early pioneering work (Wardle et al., 1997 ) and subsequent syntheses have highlighted how variable litter diversity influences litter decomposition (Ha¨ttenschwiler et al., 2011; Lecerf et al.,2011). Carbon mineralization of mixed residues is more complex than in single residues. The potential additive effects on carbon mineralization in mixed residues can be attributed to a shift in decay pathways, moving from microbial respiration to mass loss (Li et al., 2013). Handa et al. ( 2014 ) published an article in Nature, highlighting that mixing leaf litter from varied plant functional types accelerates carbon and nitrogen decomposition compared to single plant residue decomposition. This acceleration is believed to result from complementary effects (that is, effects generated by synergistic or antagonistic interactions). Legumes, characterized by a low C/N ratio and high residual nitrogen content, undergo initial decomposition, releasing nutrients. The released nitrogen subsequently reduces the C/N ratio in gramineous crops, thereby enhancing their decomposition and nutrient release. This process could potentially influence the soil's microbiological community (Qiao et al., 2020 ). Straw decomposition is mainly mediated by different soil microorganisms with specific functions. Various microbial communities carry out distinct roles during the breakdown of crop straw. During the later stages of straw decomposition, fungi predominate, primarily breaking down the more complex components. In contrast, bacteria dominate the initial phase, focusing on the degradation of unstable chemical substances (Marschner et al., 2011 ). Fan et al. ( 2014 ) identified Firmicutes, Proteobacteria, and Actinobacteria as significant bacterial phyla in the decomposition of maize residues. Ditch-buried straw return can boost fungal diversity and promote the dominance of plant-beneficial fungi, potentially increasing resistance to soil-borne diseases. The synthesis and release of extracellular enzymes by soil microorganisms play a crucial role in organic matter formation, decomposition, and the regulation of microbial responses to nitrogen and carbon amendments (Tiemann et al., 2011). Soil enzymes such as hydrolases break down non-cellulosic polysaccharides, aiding primary metabolism, while oxidases degrade recalcitrant compounds like lignin (Iqbal et al., 2021 ). These enzymes exhibit varied reactions to different agricultural management practices involving carbon and nitrogen additions (Ortega et al., 2023 ). According to Yang et al. (2020), returning straw to field increased peroxidase activity but decreased β-D-glucosidase activity. Xie et al. ( 2021 ) showed that the addition of N, P and wheat straw enhances the activities of soil β-glucosidase, phosphatase, protease and urease. This increase is possibly due to the exogenous additions expanding the C sources for microbial biomass and diversity, as well as increasing the availability of N and P (Khan et al., 2020 ). Numerous studies have shown that intercropping soybeans and maize can enhance the nitrogen use efficiency of crops in soil, leveraging niche and nutrient use complementarity. Under intercropping conditions, straw returning involves mixing crop residues with varying C/N ratios into the soil. When maize straw with a high C/N ratio and soybean straw with a low C/N ratio were mixed in the soil, the rate of straw decomposition, changes in soil's physical and chemical properties, microbial community structure, enzyme activities, and their interrelations remained unclear. Therefore, we conducted culture and pot experiments to investigate this phenomenon, mainly from the perspective of microbial community composition and straw mixed decomposition effect, to explore the mechanism of adding soybean straw to corn straw to improve maize growth. Our findings offer foundational insights into the microecological theory of soil nutrient utilization and furnish evidence supporting the role of intercropping in enhancing soil fertility. 2 Material and methods 2.1 Experiment materials and experimental design In Harbin, Heilongjiang Province, where maize and soybeans are the principal crops, the Mollisol used in this study was extracted from the tillage layer at a depth of around 20 cm (45°50′N, 126°39′ E). Upon soil collection, visible plant debris, small stones, earthworms, and other large and medium-sized soil organisms were removed and then sieved through a 10-mesh sieve for further processing. The basic physicochemical properties of the soil are as follows: SOC (Soil Organic Carbon) − 25.0 g/kg, TN (Total Nitrogen) − 1.8 g/kg, AN (Ammonium Nitrogen) − 75.4 mg/kg, AP (Available Phosphorus) − 56.8 mg/kg, AK (Available Potassium) − 125.6 mg/kg, and pH − 6.0. Maize and soybean straw utilized in the experiment were obtained from mature plants in the Acheng experimental field of Harbin City, Heilongjiang Province, crushed, and sieved through a 60-mesh sieve prior to use. The incubation experiment and pot experiment consisted of six treatments, each replicated three times. The treatments included: (1) Maize straw incorporated into the soil (M), (2) Soybean straw incorporated into the soil (S), (3) Maize straw and soybean straw incorporated into the soil at a 1:1 ratio by mass (MS), (4) Maize straw and soybean straw incorporated into the soil at a 2:1 ratio by mass (2MS), (5) Maize straw incorporated into the soil with nitrogen fertilizer (MF), and (6) no straw incorporated into the soil (NS). The straw is crushed into a powder before it is mixed into the soil. The total straw input for all straw treatments was 12 g kg − 1 dry soil, and the amount of fertilizer added in treatment MF was determined using a carbon-to-nitrogen ratio of 25:1. Table 1 displays the carbon and nitrogen contents of the additional straw, along with its corresponding C/N ratio for each treatment. Table 1 The carbon and nitrogen content and C/N ratio of added straw in each treatment Treatment C (%) N (%) C/N ratio M 46.83 0.80 58.61 S 38.54 2.38 16.20 MS 42.69 1.59 26.86 2MS 44.07 1.33 33.24 MF 46.83 1.87 25.00 2.2 Incubation experiment and pot experiment To investigate the impact of combined soybean straw and maize straw on straw decomposition rates, a laboratory incubation experiment was conducted under controlled conditions. To restore microbial activity and function, the soil was preincubated at 25°C for seven days before the incubation experiment. Subsequently, the soil moisture level was adjusted to 60% of the field's water capacity. Upon completion of the preincubation period, 200g of soil (dry weight), along with the corresponding straw or fertilizer, was thoroughly mixed in a plastic bottle measuring 5 cm in diameter and 20 cm in height. Each bottle contained a 25 mL glass vial filled with 20 mL of 1 M NaOH as a base trap to collect evolved CO 2 . All bottles were maintained at a constant temperature of 25°C in a dark incubator. Titrations were performed to quantify CO 2 release on specific days: 1, 3, 5, 7, 9, 11, 14, 18, 22, 26, 32, 39, 46, 53, 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150. Throughout the experiment, soil water content was maintained at 65% of the field water capacity through periodic weighing and watering. Precipitation of trapped CO 2 in the NaOH solution was achieved using 0.5 M BaCl 2 solution. Phenolphthalein was used as an indicator, and 0.1 M HCl was employed to neutralize any excess NaOH (Blagodatskaya et al. 2011 ). Following titration, the base trap in each jar was replaced. Cumulative CO 2 -C emission, CO 2 -C emission rate and straw carbon mineralization rate were calculated. The experiment was carried out in the pot farm of Northeast Agricultural University. The maize variety ( Zea mays L. cv.) planted in this experiment was Xianyu 335. The nitrogen fertilizer used was urea (N46%), the phosphate fertilizer was calcium dihydrogen phosphate (P 2 O 5 61.1%), and the potassium fertilizer was potassium sulfate (K 2 O 54%). All treatments were based on the application of phosphate and potassium fertilizers; the amount of calcium dihydrogen phosphate (P 2 O 5 61.1%) was 0.7817 g, and the amount of potassium sulfate (K 2 O 54%) was 0.9815 g.In the MF treatment, 2.80 grams of urea (N 46%) were added to each pot. Each pot was filled with 10 kg of air-dried soil and the corresponding straw or fertilizer into a polyethylene pot with a diameter of 26 cm and a height of 25 cm. The rhizosphere soil was collected on the 13, 43, 83, 103 and 133rd days after planting, and the contents of SOC, TN, NH 4 + -N, NO 3 − -N, AP, AK, MBC, MBN and soil pH were determined. At the time of maize jointing, soil samples were collected to assess soil urease activity (UA), sucrase activity (SA), β-glucosidase (BG), N-acetyl-glucosidase (NAG) and microbial community structure. Plant samples were collected at the mature stage of maize to determine the biomass, N, P and K absorption of maize. 2.3 Analysis of physical and chemical properties of crop and soil The soil's SOC and TN were determined using a CN analyzer (Carlo Erba Nitrogen analyzer 1500, Germany). The contents of ammonium NH 4 + -N and NO 3 − -N were assessed using an automatic flow injection analyzer (FIAstar 5000 Analyzer, Sweden) after extraction with potassium chloride. The analysis of AP and AK content in soil and nitrogen, phosphorus, and potassium content in plants, adhered to Bao's recommended protocol (Bao, 2000). Briefly, AP extraction (0.5 mol L − 1 sodium bicarbonate solution) and AK extraction (1.0 mol L − 1 ammonium acetate solution, pH 7.0) were determined using the molybdenum blue method and measured using a flame photometer (FP6410, Shanghai Jingke, China). Total plant N content was determined by Kjeldahl digestion, while wet digestion with sulfuric acid allowed for the photometric measurement of plant phosphorus content using the molybdenum blue method. Plant potassium content was measured using the same digestion method via flame spectrophotometry. The MBC and MBN of the soil were determined using the direct extraction method of chloroform fumigation (Vance et al., 1987 ). Each 10 g fresh soil sample underwent a 24-hour fumigation with ethanol-free chloroform at 25°C in a vacuum extractor. A control group was set up without fumigation. Subsequently, the soil samples were extracted with 0.5 mol L − 1 K 2 SO 4 , shaken in a shaker for 1 hour, and then filtered. The filtrate was frozen for further analysis. The semi-Kjeldahl and potassium bichromate titrimetric methods were used to measure total N and organic C, respectively. SSoil MBN and MBC were calculated according to the algorithms described by Deng et al. ( 2016 ). A pH meter with glass electrodes (DZS-707, Shanghai, China) was used to measure the pH of the soil. To analyze soil enzyme activity, Guan's technique was followed (Guan 1986 ). Accordingly, 3,5-dinitrosalicylic acid colorimetry was employed to assess SA, while sodium phenol-sodium hypochlorite colorimetry was used to determine UA. BG and NAG were analyzed similarly, involving the homogenization of fresh soil equivalent to 1.0 g dry mass in 100 ml 50 mM acetic acid buffer (pH 8.5). The sample suspension, buffer, 200 µM substrate (7-amino-4-methylocumarin or 4-methylumbelliferone), and 10 µM reference were dispensed into 96-well black microporous plates. Enzyme activity was measured using a microplate fluorometer (Scientific Fluoroskan Ascent FL, Thermo). (DeForest et al., 2009; Zhao et al., 2016). 2.4 Soil DNA extraction and illumina Miseq sequencing For each sample, three replicate samples were analyzed. Initially, soil DNA was extracted, followed by an assessment of its integrity, concentration, and purity. Subsequently, the fungal rRNA gene's ITS1 region and the 16S rRNA gene's V3-V4 region were amplified using primer pairs ITS1F/ITS2R and 338F/806R, respectively. The PCR amplification reaction system contained 1 µl forward and reverse primers, 3 µl 2ng/µl, BSA 5.5 µl ddH 2 O, 10 ng template DNA and 12.5 µl 2xTaq Plus Master Mix. The PCR amplification process involved the following steps: (i) pre-denaturation at 95℃ for 5 minutes; (ii) denaturation at 95°C for 45 seconds, annealing at 55°C for 50 seconds, and extension at 72°C for 45 seconds, repeated for 28 cycles; (iii)final extension at 72°C for 10 minutes, followed by cooling to 4°C. Subsequently, a library was constructed by isolating and purifying the PCR products. Finally, sequencing was performed using the PE250/PE30 sequencing technique (Aoweisen, Beijing) on the Illumina Miseq platform (Illumina, Inc., USA). The raw reads were deposited onto the NCBI Sequence Read Archive (SRA) database with an accession number PRJNA1110815 and PRJNA1111333. 2.5 Statistical analysis The test data were organized using Excel 2020. Statistical analyses, including one-way and two-way ANOVA, were conducted using SPSS 20. R was utilized to compute and plot the α diversity of soil fungi and bacteria. For β diversity, processing and visualization were performed using the "vegan" package in R. Correlation analysis heat maps were generated using the "corrplot" package in R. Additionally, the "plspm" package in R was employed to construct the partial least squares path model. 3 Result 3.1 Mineralization characteristics of organic carbon in straw The cumulative CO 2 -C emission increased in all treatments as the incubation time extended, with the rate of increase gradually decreasing during the later period of incubation (Fig. 1 a). After the end of incubation, the cumulative CO 2 -C emission under M, S, MS, 2MS and MF treatment was 48 times, 62 times, 70 times, 50 times and 69 times higher than that under NS treatment, respectively. In the five straw addition treatments, the cumulative CO 2 -C emission was MS > MF > S > 2MS > M. Consequently, the combined return of maize straw and soybean straw, or nitrogen fertilizer, exhibited an increased potential for the mineralization of organic carbon in straw compared to maize straw returned to the field alone. When different crop straws were added to soil, the CO 2 -C emission rate peaked on the 3rd day of incubation, followed by a gradual decrease with incubation progression, stabilizing after the 42nd day (Fig. 1 b). Soil organic carbon mineralization exhibited similar patterns across different straw decomposition processes. During the early incubation period (0–27 days), the CO 2 -C emission rate varied significantly among treatments, with the MF treatment showing the highest rate, followed by the MS treatment. Conversely, the M treatment had a lower CO 2 -C emission rate compared to other straw addition treatments during this period. Overall, the combination treatment consistently exhibited a higher CO 2 -C emission rate compared to returning maize straw alone. The carbon mineralization rate of added straw C reflects the change trend of conversion of added straw C to CO 2 -C (Fig. 1 c). Carbon mineralization rates increased with the incubation period's extension, with the rate of increase diminishing in the later stages. The carbon mineralization rates of straw treated with MS, 2MS, and MF were 57.16%, 35.73%, and 42.83% higher than those treated with M, respectively. Consequently, combining maize straw with soybean straw or nitrogen fertilizer is more conducive to straw carbon mineralization than using maize straw alone. 3.2 Dry biomass accumulation and nitrogen, phosphorus, and potassium uptake of maize The total biomass of maize in the M and 2MS treatments was significantly lower than in the other four treatments, with the MF treatment exhibiting the highest total biomass. Specifically, the total biomass in the MF treatment increased significantly by 116.53%, 84.46%, and 8.27% compared to the M, 2MS, and NS treatments, respectively ( P < 0.05) (Fig. 2 a). Additionally, potassium, phosphate, and nitrogen uptake in the M and 2MS treatments were significantly lower than in the other four treatments ( P MF > MS, these three treatments exhibited significantly higher uptake compared to the M, 2MS, and NS treatments. In terms of phosphorus uptake, the M and 2MS treatments showed a significant decrease of 42.25% and 28.24%, respectively, compared to the NS treatment. Conversely, the S, MS, and MF treatments displayed significant increases of 29.09%, 26.58%, and 58.39%, respectively, compared to the NS treatment ( P < 0.05). In terms of potassium uptake, the S, MS, and MF treatments indicated significantly higher uptake compared to the M treatment, with increases of 24.16%, 49.01%, and 54.96%, respectively ( P < 0.05). Therefore, the combined application of maize straw with soybean straw or nitrogen fertilizer increased the total biomass of maize and the absorption of N, P and K compared to the sole application of maize straw. 3.3 Dynamic change of soil chemical characters and soil enzyme activity Straw addition significantly affected SOC content, as demonstrated by a two-way ANOVA ( P < 0.001), while the influence of planting time was not significant. However, there was a significant interaction between the two factors ( P < 0.05) (Fig. 3 a). Compared to the NS treatment, SOC content was significantly increased in all straw addition treatments at all planting time points ( P < 0.05). With the extension of planting time, the average SOC content at each time point remained relatively stable, ranging from 24.25 to 25.76 mg/kg. The average SOC content varied significantly among different treatments, with the highest average SOC content observed in the 2MS treatment (26.60 mg/kg) and the lowest in the NS treatment (22.65 mg/kg) (Fig. 3 a). Two-way ANOVA for TN, AP, AK, NH 4 + -N, NO 3 − -N, MBC, MBN, and pH revealed significant effects of straw addition measures and planting time, along with a significant interaction ( P < 0.01) (Fig. 3 b-i). As planting time progressed, soil TN content initially declined and subsequently increased. The average soil TN content was the highest at 133 days of planting (1.86 g/kg), being 1%-7% higher compared to other planting time points. Among treatments, the MF treatment exhibited notably higher average soil TN concentration, while the M treatment showed the lowest, and the NS treatment displayed minimal variation over time ( P < 0.05) (Fig. 3 b). With the extension of planting time, the average soil NH 4 + -N and NO 3 − -N contents initially increased and then decreased, reaching peak values at 43 days of planting (13.27 mg/kg and 46.97 mg/kg, respectively) (Fig. 3 c, Fig. 3 d). At 13 days and 43 days of planting, the contents of NH 4 + -N and NO 3 − -N in MS and 2MS treatment were significantly higher than those in M treatment ( P MS at the early stage of straw addition, while an MF < MS trend at the later stage of straw addition (Fig. 3 c, Fig. 3 d). As planting times were extended, AP exhibited a trend of initially increasing and then decreasing, whereas AK first increased, then decreased, and subsequently increased again. Both AP and AK reached their peak levels at 43 days of planting, measuring 22.09 mg/kg and 174.95 mg/kg, respectively (Fig. 3 e, Fig. 3 f). From the perspective of straw returning measures, the MF treatment had the highest AP content, while the MS treatment had the highest AK content, measuring 24.91 mg/kg and 177.74 mg/kg, respectively (Fig. 3 e, Fig. 3 f). From the perspective of planting time, both MBC and MBN contents exhibited a pattern of initially increasing, then decreasing, and finally increasing again, reaching peak values on day 43 of planting, measuring 230.04 mg/kg and 94.29 mg/kg, respectively. At all planting time points, the MF and MS treatments consistently showed higher MBC and MBN contents compared to other treatments. From the perspective of straw addition measures, the MS and 2MS treatments exhibited significantly higher MBC and MBN contents compared to the M treatment, with MBC contents being 22.35% and 8.16% higher, and MBN contents being 130.69% and 46.64% higher, respectively ( P < 0.05). The results indicated that the addition of soybean straw could significantly increase the MBC and MBN content compared to the sole application of maize straw ( P < 0.05) (Fig. 3 g, Fig. 3 h). The average soil pH at each sampling time point was 6.5. Compared with NS, pH values increased by 1.29%, 2.40%, 2.90%, 1.86%, and 3.02% in the M, S, MS, 2MS, and MF treatments, respectively ( P < 0.05). The planting time of maize had no significant effect on pH (Fig. 3 i). Compared to the NS treatment, the M, S, MS, 2MS, and MF treatments significantly increased UA by 7.57%, 44.66%, 87.06%, 15.14%, and 72.67%, respectively, indicating that the addition of straw can enhance soil urease activity ( P < 0.05). UA in the MS and MF treatments was notably higher than that in the M, 2MS, and NS treatments, suggesting that combining maize straw with soybean straw or nitrogen fertilizer could more effectively boost UA ( P < 0.05) (Fig. 4 a). Except for the S treatment, the soil SA in all straw-added treatments was significantly higher than that in the NS treatment, with increases of 31.76%, 14.87%, 24.93%, and 50.25% in the M, MS, 2MS, and MF treatments, respectively ( P < 0.05). From the perspective of straw addition treatment, SA was higher in the treatment with higher C/N, while SA was lower in the treatment with lower C/N (Fig. 4 b). Compared with NS treatment, straw treatment significantly increased the BG activity ( P < 0.05). BG activity in the high-nitrogen-content S and MS treatments was significantly higher than that in the M treatment ( P < 0.05) (Fig. 4 c). The NAG activities of MS and 2MS were significantly lower than in other treatments ( P MF > S > 2MS > M > NS among all treatments. Compared with NS, the Shannon index of bacteria treated with MS and MF was significantly increased by 2.50% and 1.95% ( P < 0.05) (Fig. 5 a). The Chao1 index indicated that the MS and MF treatments were significantly higher than the M and S treatments, and straw addition treatments were higher than NS (Fig. 5 c). With the exception of the S treatment, the fungal Shannon index of straw addition treatments was lower than that of the treatment with no straw incorporated into the soil (Fig. 5 b). The Shannon index and Chao1 index of fungi under MS treatment and 2MS treatment were significantly lower than those under M and S treatment (Fig. 5 b), indicating that the richness and diversity of fungal community could be significantly reduced by straw incorporated into the soils. Additionally, the richness and diversity of the fungal community under combined maize straw and soybean straw incorporated into the soils could be lower than that under a single addition. The bacterial NMDS analysis stress value was 0.1397, which was generally less than 0.2. A smaller stress function value indicated a more reasonable analysis result. The result indicated that the analysis result is reasonable (Fig. 5 e). Sample points were distributed in each quadrant, with the closest overlap observed between S treatment and MS treatment, as well as between M treatment and 2MS treatment, showing that the bacterial community makeup of S treatment and MS therapy, as well as M treatment and 2MS treatment, was the most similar. Conversely, the distance between the NS treatment and straw addition treatment was relatively long, indicating a significant difference in bacterial community composition between the NS treatment and the other treatments (Fig. 5 e). The results of fungal β diversity showed that PC1 and PC2 accounted for 24.88% and 18.67% of the total variance, respectively. PC1 clearly separated the S, MS, and MF treatments, while PC2 separated the NS and 2MS treatments. Notably, NS treatment and MF treatment were distinctly separated from the other four treatments, suggesting a significant difference in the fungal community composition between NS and MF treatments compared to the other treatments (Fig. 5 f). In the rhizosphere soil of maize, dominant bacterial phyla include Proteobacteria, Actinobacteriota, Acidobacteriota, Bacteroidota, Gemmatimonadota, Chloroflexi and Cyanobacteria, collectively accounting for over 78% of the total abundance (Fig. 6 a). Proteobacteria has the highest relative abundance (33.62%), highlighting its crucial role in maintaining the intricate ecological balance of farmland soil. While the main bacterial groups remained similar across the community, their relative abundances varied significantly (Fig. 6 a). Compared to NS, straw-incorporated groups showed significantly higher levels of Proteobacteria (Fig. S1 a), contrasting with Actinobacteriota and Gemmatimonadota ( P < 0.05) (Fig. S1 b, Fig. S1 c). Notably, the relative abundance of Firmicutes was notably higher in straw addition treatments compared to no-straw treatments, with M, MS, and MF treatments exhibiting 4.06 times, 2.90 times, and 6.16 times higher levels than NS treatment ( P < 0.05) (Fig. S1 d). Furthermore, the relative abundance of Bdellovibrionota was significantly elevated in MS and 2MS treatments compared to M treatments by 15.94% and 5.46% ( P < 0.05) (Fig. S1 e). Additionally, Nitrospirota showed a 115.02% increase in relative abundance in MS treatment compared to M treatment ( P < 0.05) (Fig. S1 f). Therefore, the combination of soybean straw and maize straw incorporation into soils led to increased relative abundances of Gemmatimonadota, Proteobacteria, Bdellovibrionota, and Nitrospirota compared to maize straw alone, while Actinobacteriota and Firmicutes showed reduced abundance. In the maize rhizosphere soil, the dominant bacteria at the genus level include Sphingomona s, RB41 , Sphingobacterium , Ramlibacter , uncultured_ Acidobacteria , metagenome , Altererythrobacter , MND1 , Flavisolibacter , and Gemmatimonas , collectively accounting for more than 20% of the total abundance. Among these, Sphingomonas exhibited the highest relative abundance at 3.78% (Fig. 6 b). Compared with the NS treatment, the relative abundance of Arenimonas , Nitrospira , Phenylobacterium , and the MND1 genus of the Nitrosoomonas family exhibited similar trends, while the M treatment showed no difference, and the MS, 2MS, and MF treatments all displayed increases (Fig. S2b-e). For Brevundimonas , straw addition treatment was significantly lower than no straw incorporated into the soil treatment, but MS and 2MS treatment significantly increased by 120.12% and 42.07% compared with M treatment ( P < 0.05) (Fig. S2f). In the maize rhizosphere soil, the dominant fungal phyla include Ascomycota, Basidiomycota, Chytridiomycota, Rozellomycota, Glomeromycota, Zoopagomycota, and Mortierellomycota, collectively representing more than 94% of the total abundance (Fig. 6 c). Among these, Ascomycota exhibited the highest relative abundance at 53.65%, suggesting its significance in maintaining the complex ecological balance of agricultural soil. Although the main phyla in the community were similar, the relative abundance varied significantly. The relative abundance of Ascomycota in the straw addition treatment group was significantly higher compared to NS, whereas Chytridiomycota and Glomeromycota displayed the opposite trend. Compared with M treatment, the relative abundance of Chytridiomycota increased significantly by 3.79 times in MS treatment ( P < 0.05) (Fig. S3c), whereas Glomeromycota decreased by 49.66% in the MS treatment (Fig. S3d). Moreover, the relative abundance of Basidiomycota treated with MS was 8.55 times higher than that treated with M and 34.49% higher than that treated with S ( P < 0.05) (Fig. S3b). Therefore, the incorporation of soybean straw and maize straw into the soils led to enhancements in the relative abundance of Ascomycota, Basidiomycota, and Chytridiomycota, while reducing the relative abundance of Glomeromycota. In the maize rhizosphere soil, the dominant fungal genera include Zopfiella , Conocybe , Acremonium , Cercophora and Ascobolus , collectively representing more than 30% of the relative abundance (Fig. 6 d). Compared with NS treatment, the dominant fungi genera of M, S, MS, 2MS and MF treatments significantly decreased by 89.58%, 59.47%, 49.36%, 96.76% and 92.76%, respectively ( P < 0.05) (Fig. S4). For Trichoderma , relative abundances in M, MS, 2MS, and MF treatments decreased significantly by 75.47%, 66.04%, 98.11%, and 88.68%, respectively, compared with NS treatments ( P < 0.05) (Fig. S4b). The relative abundance of Chaetomium treated with M, S and MF was significantly higher than that treated with MS, 2MS and NS ( P < 0.05) (Fig. S4c). The relative abundance of Funneliformis in treatments with straw addition was significantly lower than in treatments without straw incorporation into soils, with no significant differences observed among various straw addition treatments (Fig. S4d). 3.5 Relationship among soil microbial community, environmental factors and maize growth quality indexes The α diversity index of bacteria (Shannon and Chao1) was positively correlated with NH 4 + -N, AP, AK, MBC, MBN, pH, UA and BG ( P < 0.001) (Fig. 7 a). Proteobacteria, a eutrophic bacterium, thrives in nutrient-rich environments and displayed a significant positive correlation with MBC ( P < 0.05). However, Actinobacteriota has a significant negative correlation with UA, BG, MBC, MBN, pH, AP, AK and NH 4 + -N ( P < 0.05). Straw organic carbon serves as a metabolic substrate for Gemmatimonadota. With the exception of TN, SOC, NO 3 − -N, AK and NAG, Gemmatimonadota exhibited negative correlations with all other assessed soil chemical factors ( P < 0.05) (Fig. 7 a). Firmicutes bacteria produce glyco-based hydrolases, enzymes crucial for cellulose breakdown. This study found that Firmicutes had a significant positive correlation with available AP, MBC, pH, SA and Chao1 ( P < 0.05). Bdellovibrionota correlations were significant with all soil chemical factors except TN, SOC, NO 3 − -N, AK and SA ( P < 0.05) (Fig. 7 a). Bacteria from the Nitrospirota phylum convert nitrites into nitrates, which serve as readily absorbable nitrogen nutrients for plants and other microorganisms. Nitrospirota had strong positive correlations with Shannon, TN, AP, and Chao1. In general, Actinobacteriota, Gemmatimonadota, Firmicutes, Bdellovibrionota and Nitrospirota were significantly influenced by soil chemical factors. NH 4 + -N, MBC, MBN, pH, UA and BG are the main chemical factors affecting the dominant phyla. All soil chemical factors, except for TN, BG, and NAG, demonstrated a negative correlation with the fungal α diversity index (Shannon and Chao1), with NAG showing a significant positive correlation with the Shannon index ( P < 0.05) and an extremely positive correlation with the Chao1 index ( P < 0.001) (Fig. 7 b). In this study, Fusarium exhibited a negative correlation with all soil chemical properties, notably with AK and pH at significant levels. Trichoderma was negatively correlated with AK, NO 3 − -N and SA ( P < 0.05). Besides TN and NAG, Funneliformis showed negative correlations with other soil chemical properties (Fig. 7 b). In general, soil chemistry had a substantial negative impact on Trichoderma , Funneliformis and Fusarium . All soil chemical factors variably influenced the dominant fungi, AK and NO 3 − -N were the most impactful. A partial least squares path model (PLS-PM) was developed to comprehensively analyze the complex interactions among different straw types, crop growth, soil characteristics, microbial populations, and soil enzyme activities (Fig. 8 ). Bacterial communities, in contrast to fungal communities, exerted significant direct effects on soil enzyme activity (a combination of BG and UA) and soil properties (a combination of TN, NH 4 + -N, NO 3 − -N and pH) (0.14 and 0.78). The Straw C/N ratio negatively influenced soil enzyme activity and bacterial and fungal communities, with the bacterial community experiencing the most substantial impact (-0.70). In terms of plant growth factors (a combination of PN, PP, PK and biomass), soil properties had the greatest effect (0.47), followed by soil enzyme activity (0.41). While the type of straw did not fully account for variations in plant growth, it directly affected microbial communities (-0.70 and − 2.00), enzyme activity (0.53) and soil properties (0.13), thereby influencing plant growth. Principal component analysis (PCA) was employed to assess the impact of various straw returning methods on soil properties, soil enzyme activities, and microbial diversity. The first principal component (PC1) and the second principal component (PC2) effectively captured the essence of soil-related indicators across six straw returning methods, accounting for 71.8% and 12.8% of the total variance, respectively (Fig. 9 a). Significant contributors to PC1 included SOC, NO 3 − -N, MBN, AP, AK, BG, and B-Chao1. In contrast, except for the fungal Shannon index, Chao1 index, and NAG, other indices notably influenced PC2 (Fig. 9 b). PC1 significantly separated the 2MS treatment, and PC2 significantly separated the NS, M, and MS treatments, demonstrating significant variations among the straw returning methods (Fig. 9 c). The random forest plots showed that different straw returning methods significantly influenced the fungal diversity index (F-Shannon), bacterial richness index (B-Chao1) and fungal richness index (B-Chao1). As for soil enzyme activities, BG, SA, NAG and UA were affected by the straw returning mode. For soil property indexes, NH 4 + -N, MBC, MBN, AP, AK, NO 3 − -N, pH and TN were sequentially influenced by the straw returning approaches (Fig. 9 d). 4 Discussion 4.1 Characteristics of carbon mineralization in straw Upon incorporation into soil, straw mineralization unfolds in three distinct phases: an initial rapid mineralization stage, followed by a gradual deceleration, and culminating in a relatively stable phase (Fig. 1 b). This progression is linked to the chemical composition of the straw. The organic carbon in the straw breaks down into readily degradable components (such as starch and glucose) and more resistant components (such as lignin). Soybean straw contains more easily degradable parts, whereas maize straw has more resistant components (Surigaoge et al., 2023 ). During the early stages of incubation, readily decomposable crop residues were broken down first, boosting soil microbial growth, releasing substantial nutrients, and significantly enhancing CO 2 emission (Gezahegn et al., 2019). As the incubation progresses, the consumption of decomposable components slows down, and CO 2 release gradually decreases, ultimately achieving a state of equilibrium (Gezahegn et al., 2019). This pattern of straw mineralization was observed in our study as well. Furthermore, the dynamics of ammonium nitrogen, nitrate nitrogen, and MBN in the soil were consistent with the characteristics of straw mineralization, exhibiting an initial increase, followed by a decrease, and eventually stabilizing (Fig. 3 ), with peak levels observed on the 43rd day of incubation. In this study, compared to the sole application of maize straw (M), integrating soybean straw or nitrogen fertilizer with maize straw (MF and MS treatments) led to an increase in soil cumulative CO 2 release (Fig. 1 a) and enhanced soil fertility (Fig. 3 ), indicating that soybean straw or nitrogen fertilizer plays a positive regulating role in the decomposition of maize straw. These findings align with Lin's research. Throughout the incubation, the exclusive use of maize straw demonstrated that maize straw competed with the succeeding crops in soil nitrogen. Conversely, the amalgamation of soybean straw and nitrogen fertilizer with maize straw improved the soil inorganic nitrogen content and accelerated straw mineralization, thereby mitigating this competition (Lin et al., 2014 ). Schwendener et al. (2005) identified a "mixed decomposition effect" occurring when leaf litter with a high carbon-to-nitrogen ratio was mixed and decomposed with leaf litter with a low ratio. In this process, high-quality straw decomposes first, providing nutrients for the decomposition of lower-quality straw. During the final phase of maize cultivation, SOC content of MS and 2MS treatment was higher than that of M and MF treatment (Fig. 3 b), indicating that soybean straw combined with maize straw treatment increased soil organic carbon content. Therefore, incorporating soybean straw into maize straw not only accelerates the straw mineralization rate but also positively impacts soil organic carbon storage without any detrimental effects. 4.2 Soil chemical properties and enzyme activities In our study, the combined application of soybean straw with maize straw, as opposed to the combination of nitrogen fertilizer with maize straw, delayed nitrogen release initially and prolonged nitrogen availability later (Fig. 3 ). This approach aligns the nitrogen release with crop demand, resonating with the findings of Li et al. ( 2016 ). Although the C/N ratio of MF and MS is about 25:1, the organic nitrogen in soybean straw causes a slower nitrogen release in the MS treatment compared to the MF treatment, extending nitrogen availability. The content of available nutrients (NH 4 + -N, NO 3 − -N, AP, AK) of maize straw added with soybean straw was higher than that of maize straw applied alone (Fig. 3 ). The alteration in nutrient dynamics and straw decomposition rate due to combined straw returning is attributed to the interaction of the straws affecting the physical, chemical, and biological processes in the straw decomposition microenvironment. This interaction alters the community structure and activity of microorganisms, subsequently impacting the straw decomposition rate (Gartner et al., 2004; Chapman et al., 2010). Maize root exudates and residues play a crucial role in influencing soil microbial activity and enzyme levels (Hao et al., 2022 ). In this study, in the early growth stage of maize (vegetative growth stage), both MBC and MBN showed an increasing trend with maize growth and straw mineralization (Fig. 3 ). During the vegetative growth period of maize, root exudates serve as substantial energy sources for soil microbes, and the roots offer a habitat that enhances the living conditions for these organisms, thus fostering microbial metabolic activities and increasing soil microbial biomass (Zuber et al., 2016). In this study, MBC increased continuously and then decreased at the later stage of maize growth. MBN initially increased, then decreased, and experienced a slight uptick towards the end of the maize growth period (Fig. 3 h). As maize matures and senesces, maize litter is introduced into the soil. The addition of organic materials from maize leaf litter and stump roots enriches the soil. The presence of abundant oxygen in the soil facilitates decomposition, aiding in nitrogen retention and leading to a minor increase in MBN content, which is consistent with the research results of Yang et al. ( 2017 ). Bolinder et al. ( 1999 ) posited that soil microbial activity, particularly enzyme activity, was more indicative of changes in soil quality than SOC. Therefore, soil MBC, MBN and enzyme activities serve as effective indicators of the impact of straw returning practices on the microecology of black soil regions. Consistent with the findings of Zhao et al. (2016), our study confirmed that straw returning treatments enhanced soil MBC, MBN, and enzyme activities, demonstrating the beneficial effects of these practices on soil microbial dynamics. Urease facilitates the transformation of soil nitrogen, while sucrase primarily catalyzes the decomposition of soil organic matter (Pamidipati et al., 2019). BG is responsible for the degradation of cellulose to obtain C, and NAG plays a crucial role in nitrogen cycling (Zhao et al., 2016). Soil C and N levels can regulate soil enzyme activity. In this study, the activities of UA, SA and BG were enhanced following the application of fertilizers and the return of straw to the field (Fig. 4 ). This increase is attributed to soil microbes producing more enzymes to decompose SOM for carbon acquisition, especially when soil nitrogen levels are high, thereby meeting the carbon demands for microbial growth. These observations align with Zhao et al. (2016). Both UA and BG activities were significantly positively correlated with mineral nitrogen (Fig. 7 b), indicating the positive influence of soil enzyme activities on soil nitrogen dynamics. The response of NAG to single straw application (M and S treatment) was significantly higher than that of combined maize and soybean straw application (MS and 2MS treatment), and the response of combined straw application was significantly lower than that of NS treatment. Consistent with our findings (Fig. 7 b), Chung et al. ( 2007 ) reported that fungal communities predominantly drive NAG activity and highlighted a strong positive link between fungal abundance and NAG activity. Hence, soil enzyme activity is influenced by the levels of soil carbon and nitrogen. The inclusion of soybean straw modifies the mineral nitrogen content, which, in turn, impacts the activities of enzymes associated with carbon and nitrogen cycling. 4.3 Nutrient accumulation in succeeding maize Returning straw to the field is a pivotal practice for enhancing soil fertility. Decomposing straw releases various mineral elements, improving soil nutrient accumulation and boosting crop yields (Latifmanesh et al., 2020 ). However, introducing straw with a high C/N ratio can impede crop nitrogen availability due to microbial immobilization during decomposition, consequently diminishing crop yield and nutrient uptake (Zhu et al., 2017 ). In this study, the total biomass and nutrient uptake of M treatment and 2MS treatment were significantly lower than NS treatment, a disparity linked to their elevated C/N ratios. Some studies have indicated that returning maize straw to the field can reduce wheat biomass and grain yield (Dai et al., 2013 ). In this study, the total biomass of MS treatment and MF treatment was significantly higher than that of M treatment and 2MS treatment. This enhancement is likely due to soybean straw, and nitrogen fertilizer can accelerate the decomposition of maize straw by reducing the C/N ratio of the substrate and stimulating the microbial community growth, thereby releasing straw nutrients and improving crop yield and nutrient absorption (Yang et al., 2019 ). Zhang et al. ( 2023 ) also showed that the mixing of the plant litter could improve the fertility of the soil and improve the productivity of the crops. Therefore, the inclusion of soybean straw or nitrogen fertilizer resulted in superior nutrient accumulation and biomass in the succeeding maize compared to treatments using maize straw alone. 4.4 Soil microbiota Incorporating straw into soil significantly influences the bacterial community structure, with the degradation of straw primarily initiated by rapidly proliferating bacteria. This study observed a notable increase in the bacterial Chao1 and Shannon indices following straw addition treatments (Fig. 5 a and Fig. 5 c). According to Zhang et al.'s research, the addition of straw straw addition supplies organic materials, fostering bacterial growth and reducing competition among bacterial communities, thereby enhancing soil bacterial diversity (Zhang et al. 2020 ). The dominant bacterial phyla identified were Proteobacteria, Actinobacteriota, and Acidobacteriota (Fig. 6 a), which are prevalent in agricultural soils. Proteobacteria include numerous nitrogen-fixing bacterial species that play a crucial role in the biochemical cycling of soil mineral carbon, nitrogen, and other nutrients. Their activity is beneficial for plant development and the maintenance of soil fertility. Firmicutes are involved in the expression of glycosyl hydrolases that break down cellulose (Wegner and Liesack, 2016). In this study, the application of straw to soil, specifically in the MS and 2MS treatments, led to an increased relative abundance of Firmicutes and Proteobacteria compared to the NS treatment, aligning with findings by Yuan et al. ( 2023 ). Proteobacteria abundance in MS and 2MS treatments was significantly higher than in M and S treatments (Fig. S1 a), indicating a more nutrient-rich soil environment conducive to Proteobacteria growth. Correlation analysis revealed a positive association between the abundance of Proteobacteria and Firmicutes and soil nutrient indexes (Fig. 7 a). Glycosyl hydrolases, enzymes crucial for hemicellulose decomposition, were predominantly expressed by Acidobacteriota and Chloroflexi (Liu et al., 2020). Chloroflexi, primarily consisting of anaerobic microorganisms, play a vital role in decomposing sugars and polysaccharides into organic acids and hydrogen, thereby accelerating the breakdown and assimilation of organic matter in the soil. In this research, Acidobacteriota and Chloroflexi exhibited higher relative abundances in soil treated with MS and 2MS than in soil treated with M (Fig. 6 a), which is consistent with the results of urease activity and β-glucosidase activity (Fig. 4 a, Fig. 4 c). Yu et al. ( 2018 ) observed a significant increase in the relative abundance of Chloroflexi in soils subjected to straw return for six consecutive years compared to soils without straw application. Rhodanobacter, part of the denitrifying community, plays a crucial role in nitrate reduction (Cao et al., 2021 ). Nitrate, an essential nitrogenous nutrient easily assimilated by plants and other microorganisms, is produced from nitrite through the metabolic activities of the Nitrospirota (Holland-Moritz et al., 2021 ). Compared with the M and S treatments, the relative abundance of Rhodanobacter treated with MS and 2MS decreased, while the relative abundance of Nitrospirota increased (Fig. S2a, Fig. S2d), indicating that the combined application of maize and soybean straw could reduce the biological denitrification of soil, improve the transformation of nitrites, and increase the soil nitrogen content (Fig. 3 ). Additionally, correlation analysis revealed a strong positive correlation between TN and AP and the relative abundance of Nitrospirota (Fig. 7 a). The richness and diversity of the bacterial community significantly increased when soybean straw or nitrogen fertilizer was applied in conjunction with maize straw, in contrast to using maize straw or soybean straw alone. Conversely, the richness and diversity of the fungal community showed a decline with these combined applications (Fig. 5 ). Ascomycota and Basidiomycota dominate the fungal community (Fig. 6 c). Ascomycota functioning as saprophytes that produce cellulase to decompose soil and straw organic matter, such as cellulose and lignin, thereby releasing nutrients (Zhang et al., 2023 ). White rot fungi in Basidiomycota possess a distinctive capability to break down lignin and lignocellulosic complexes (Zhao et al., 2019 ). Consistent with the findings of this study, Ma et al. ( 2024 ) examined the impact of straw on soil physicochemical properties and fungal community diversity. Their investigation demonstrated an increase in the relative abundance of Ascomycota following the application of straw. Compared with M treatment, the relative abundance of Basidiomycota increased in MS treatment and decreased in Ascomycota, while Ascomycota increased in 2MS treatment without a significant change in Basidiomycota, indicating that the decomposition roles of different fungi vary with the proportion of straw returned to the field. Fusarium , a soil-borne pathogenic fungus responsible for wheat scab, plant blight, and root rot (Clemmensen et al., 2015 ), experienced a reduction in relative abundance with straw returning to the field, negatively correlating with soil nutrient indexes (Fig. 7 b). Compared to the M treatment, the relative abundance of Fusarium was decreased in the 2MS treatment (Fig. S4a). Therefore, straw returning to the field can increase soil nutrient content and reduce the relative abundance of pathogens, with soybean straw further reducing pathogen abundance compared to maize straw alone. Consistent with our findings, Tang et al. ( 2020 ) demonstrated that the addition of wheat straw reduced the relative abundance of Fusarium . Trichoderma , known to enhance plant development by antagonizing plant pathogenic fungi (Alwadai et al., 2022 ), exhibited increased relative abundance with MS compared to M treatment, with the opposite trend observed in the 2MS treatment (Fig. S4b). Chaetomium is a saprophytic fungus involved in the degradation of organic matter (Zhang et al., 2023 ). M, S, and MF significantly increased the relative abundance of Chaetomium , while MS and 2MS decreased compared with M and S treatments (Fig. S4c). The partial least squares path model (PLS-PM) indicated that straw with different C/N ratios impacted microbial α diversity and enzyme activity, thus affecting soil nutrients and plant growth (Fig. 8 ). These findings indicated that combined straw returning alters soil microorganism composition, enhances organic matter transformation, and promotes succeeding maize growth. 5 Conclusion Our findings demonstrated that the combined incorporation of maize and soybean straw enhances the mineralization rate and nutrient release of straw. Application of soybean straw or nitrogen fertilizer can effectively alleviate the competition for soil nitrogen between maize straw and subsequent crops compared to using maize straw alone. Furthermore, the combined use of both straw types alters soil microbial community structure, expediting soil organic matter transformation and straw nutrient release, thereby fostering later maize growth. In summary, the synergistic decomposition effect of soybean straw and maize straw elucidates the mechanism of intercropping for enhancing nutrient utilization efficiency from a different perspective. Declarations CRediT authorship contribution statement Xiaodan Liu：Data curation, Writing – original draft. Hongrui Huo: Data curation. Yuhang Zhang: Writing – review & editing. Huawei Yang: Data curation. Shumin Li: Writing – review & editing, Conceptualization, Supervision, Funding acquisition. Lingbo Meng：Writing- Reviewing and Editing. Declaration of interests 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. 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Oikos 1997: 247–258. https://doi.org/10.2307/3546010 Xie W, Zhang Y, Li J et al (2021) Straw application coupled with N and P supply enhanced microbial biomass, enzymatic activity, and carbon use efficiency in saline soil. Appl Soil Ecol 168:104128. https://doi.org/10.1016/j.apsoil.2021.104128 Xu X, Pei J, Xu Y et al (2020) Soil organic carbon depletion in global Mollisols regions and restoration by management practices: A review. J Soils Sediments 20:1173–1181. https://doi.org/10.1007/s11368-019-02557-3 Yang L, Zhang L, Yu C et al (2017) Nitrogen fertilizer and straw applications affect uptake of 13C, 15N-glycine by soil microorganisms in wheat growth stages. PLoS ONE 12(1):e0169016. https://doi.org/10.1371/journal.pone.0169016 Yang L, Zhou X, Liao Y et al (2019) Co-incorporation of rice straw and green manure benefits rice yield and nutrient uptake. Crop Sci 59(2):749–759. https://doi.org/10.2135/cropsci2018.07.0427 Yu D, Wen Z, Li X et al (2018) Effects of straw return on bacterial communities in a wheat-maize rotation system in the North China Plain. PLoS ONE 13(6):e0198087. https://doi.org/10.1371/journal.pone.0198087 Yuan L, Gao Y, Mei Y et al (2023) Effects of continuous straw returning on bacterial community structure and enzyme activities in rape-rice soil aggregates. Sci Rep 13(1):2357. https://doi.org/10.1038/s41598-023-28747-1 Zhang L, Li J, Zhang M (2020) Effect of rice-rice-rape rotation on physicochemical property and bacterial community of rhizosphere soil. Oil Crop Sci 5(3):149–155. https://doi.org/10.1016/j.ocsci.2020.08.003 Zhang R, Meng L, Li Y et al (2021) Yield and nutrient uptake dissected through complementarity and selection effects in the maize/soybean intercropping. Food Energy Secur 10(2):379–393. https://doi.org/10.1002/fes3.282 Zhang S, Li M, Cui X et al (2023) Effect of different straw retention techniques on soil microbial community structure in wheat–maize rotation system. Front Microbiol 13:1069458. https://doi.org/10.3389/fmicb.2022.1069458 Zhang W, Fornara D, Yang H et al (2023) Plant litter strengthens positive biodiversity–ecosystem functioning relationships over time. Trends Ecol Evol 38(5):473–484. https://doi.org/10.1016/j.tree.2022.12.008 Zhao S, Li K, Zhou W et al (2015) Changes in soil microbial community, enzyme activities and organic matter fractions under long-term straw return in north-central China. Agric Ecosyst Environ 216:82–88. https://doi.org/10.1016/j.agee.2015.09.028 Zhao S, Qiu S, Xu X et al (2019) Change in straw decomposition rate and soil microbial community composition after straw addition in different long-term fertilization soils. Appl Soil Ecol 138:123–133. https://doi.org/10.1016/j.apsoil.2019.02.018 Zhu L, Xiao Q, Shen Y et al (2017) Effects of biochar and maize straw on the short-term carbon and nitrogen dynamics in a cultivated silty loam in China. Environ Sci Pollut Res 24:1019–1029. https://doi.org/10.1007/s11356-016-7829-0 Zuber SM, Villamil MB (2016) Meta-analysis approach to assess effect of tillage on microbial biomass and enzyme activities. Soil Biol Biochem 97:176–187. https://doi.org/10.1016/j.soilbio.2016.03.011 Supplementary Files Supplementarymaterials.docx 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4441610","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":311345619,"identity":"1b835bfe-e5b9-47d0-b717-c7c50ef3557c","order_by":0,"name":"Xiaodan Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Xiaodan","middleName":"","lastName":"Liu","suffix":""},{"id":311345620,"identity":"faff9194-b182-4f24-abc9-7d129df72f0c","order_by":1,"name":"Hongrui Huo","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Hongrui","middleName":"","lastName":"Huo","suffix":""},{"id":311345621,"identity":"55c49217-542e-4173-89a7-8b8c311577c5","order_by":2,"name":"Yuhang Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yuhang","middleName":"","lastName":"Zhang","suffix":""},{"id":311345622,"identity":"19cf8501-8485-4f6c-8557-ef19b43a3e9e","order_by":3,"name":"Huawei Yang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Huawei","middleName":"","lastName":"Yang","suffix":""},{"id":311345623,"identity":"a4d130cc-b3ef-4341-85e4-f0e36d10f4a1","order_by":4,"name":"Shumin Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyUlEQVRIiWNgGAWjYBACPmYGNiAlwcDGzH7wQUKFDWEtbDAtfOw8yQYPzqQRoQWMgECOn8FM8mHbISK0sLM/e8ybY5EHtC6tIoHtAAN/e3cCAYfxmBvzbpMoZmNmPHYjgecOg8SZsxsIaWGTBmpJbAPaciNB4hmDgUQuIS3sz2BazAoSDA4To4XBDK6FISGBKC08ZpJzwVp4kiUSDqTxEPQLP//xZxJvt9Ulzu8/fvDjz382cvztvfi1YAAe0pSPglEwCkbBKMAKAP7TOxecnDBuAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-9251-0686","institution":"Northeast Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"Shumin","middleName":"","lastName":"Li","suffix":""},{"id":311345624,"identity":"5f170dbb-60e2-4a78-b6d6-a5fdd7bd2b72","order_by":5,"name":"Lingbo Meng","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Lingbo","middleName":"","lastName":"Meng","suffix":""}],"badges":[],"createdAt":"2024-05-18 15:25:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4441610/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4441610/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":58712440,"identity":"d02aa6c0-f74c-4ced-b040-c204f813a7c6","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":328144,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCumulative CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-C emission (a), CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-C emission rate (b) and added C mineralization (c) under different treatments. M: maize straw, S: soybean straw, MS: mixture maize and soybean straw 1:1, 2MS: mixture maize and soybean straw 2:1, MF: maize straw and N fertilizer incorporated into the soils and NS: no straw incorporated into the soils, the same below.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/33d8ac49cb373dbf03f9ed10.png"},{"id":58712438,"identity":"2782a0de-4871-4ff2-bdf5-364630f03e41","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":137142,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffects of different treatments on total biomass (a), nitrogen uptake (b), phosphorus uptake (c) and potassium uptake (d) of maize. Standard deviation is represented by error bars. Significant variations between the straw addition treatments are represented by different lowercase letters (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eP\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e\u0026lt;0.05). The same notation applies below.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/257fbd243324d25f506519c2.png"},{"id":58712437,"identity":"8580eba0-e979-4058-bba7-5233e0044555","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":404205,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDynamic changes of soil chemical factors under different treatments. (a): Soil organic carbon (SOC); (b): Total nitrogen (TN); (c): ammonium nitrogen (NH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e-N); (d): nitrate nitrogen (NO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003csup\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e-N); (e): available phosphorus (AP); (f): available potassium (AK); (g): microbial biomass carbon (MBC); (h): microbial biomass nitrogen (MBN); (i): pH. The results of two-way analysis of variance on the effects of planting time (Time), straw addition treatment (Treatment), and their interaction (Time×Treatment) on SOC, TN, NH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e-N, NO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003csup\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e-N, AP, AK, MBC, MBN and pH are also shown in the figure. *\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eP\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e\u0026lt;0.05; **\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eP\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e\u0026lt;0.01; ***\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eP\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e\u0026lt;0.001; “ns”, not significant at the 5% level. Significant variations between the straw addition treatments are represented by different lowercase letters (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eP\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e\u0026lt;0.05).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/af8128e7565cefdfaa7d4ca0.png"},{"id":58712442,"identity":"b2f15580-2765-4e1c-93d3-3bcd63dbb708","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":115492,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffects of different treatments on soil enzymatic activities. (a): urease activity; (b): Sucrase activity; (c): β-glucosidase (BG) activity; (d): N-acetyl-glucosaminidase (NAG) activity.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/7386c36b960e424635bfbfe5.png"},{"id":58713006,"identity":"ac35f031-ac03-49f3-af9a-a9b1bd09b75e","added_by":"auto","created_at":"2024-06-20 07:01:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":260359,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffects of different straw returning measures onα diversity index and β diversity index of bacteria and fungi. (a): Bacteria shannon index; (b): Bacteria chao1 index; (c): Fungi shannon index; (d): Fungi chao1 index; (e): NMDS analysis of bacterial community structure; (f): PCA analysis of fungal community structure.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/900b6ea5867fa251784b46b8.png"},{"id":58712444,"identity":"e5c2dfff-1ee1-42c6-b0fa-f057de2a1cdd","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":729035,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRelative abundance of phylum level and genus level for bacterial and fungal communities in different treatments. (a): Phylum level of bacteria; (b): Genus level of bacteria; (c): Phylum level of fungi; (d): Genus level of fungi.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/60a9649ce1355453fb8461eb.png"},{"id":58712441,"identity":"4dabe6bf-4444-4147-91c3-44a918a016c9","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":362366,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCorrelation analysis of soil chemical properties with bacterial dominant phyla (a) and fungal dominant genus (b).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/d5833084211dad36ea19b091.png"},{"id":58712446,"identity":"b971fb26-660b-4a0e-9faa-2230acf59120","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":180501,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDirected graph of the partial least squares path model (PLS-PM). a: inner model. b: outer model. Each box represents an observed variable (i.e., measured) or latent variable (i.e., constructs). The numbers listed by the arrows in Figure a are standardized path coefficients, which are reflected in the width of the arrows in dark blue and red to indicate positive and negative effects, respectively. The values in Figure b represent the loading values between the observed and latent variables. The model was assessed using goodness of fit (GoF) statistics, and the GoF value was 0.68. BC, Bacterial community; FC, Fungal community; PG, Plant growth. PN, PP and PK represent plant nitrogen, phosphorus, and potassium uptake.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/33cec37b9df917ba4b682524.png"},{"id":58712445,"identity":"fb5cd1c1-f82d-4a2a-978a-0c94ee714d28","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":326644,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePrincipal component analysis (PCA) and random forest analysis of soil properties, soil enzyme activity and microbial diversity under different straw returning methods. (a): Factor loading matrix diagram of soil-related indexes retaining principal components under different treatment conditions. (b): Loading of PCl and PC2 by soil properties, soil enzyme activity and microbial diversity index. PCl, the first principal component; PC2, the second principal component. (c): PCA was used to analyze the changes of soil related indexes under different treatments. (d): Random Forest analysis of soil-related indicators under different straw returning methods. B-Shannon, Bacterial diversity index; B-Chao1, Bacterial richness index; F-Shannon, Fungal diversity index; F-Chao1, Fungal richness index.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/e28bf39cdd73a0acea3edc6d.png"},{"id":62795644,"identity":"bb61a669-aad9-4d23-990f-44328febc6b3","added_by":"auto","created_at":"2024-08-19 15:10:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4241732,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/c4376af3-66fa-4b19-850c-18614d1fbbea.pdf"},{"id":58712447,"identity":"59880880-57c2-41ad-afb7-2c7c24b687da","added_by":"auto","created_at":"2024-06-20 06:53:52","extension":"docx","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":1907647,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterials.docx","url":"https://assets-eu.researchsquare.com/files/rs-4441610/v1/b0cd2679a7916c045cb03278.docx"}],"financialInterests":"","formattedTitle":"Promotion of Maize Straw Degradation Rate by Altering Microbial Community Structure through the Addition of Soybean Straw","fulltext":[{"header":"Highlights","content":"\u003col\u003e\n\u003cli\u003eIncorporating soybean straw with maize straw accelerates straw mineralization.\u003c/li\u003e\n\u003cli\u003eReturning straw to the field reduces the abundance of harmful fungi.\u003c/li\u003e\n\u003cli\u003eBacteria associated with straw mineralization show increased relative abundance.\u003c/li\u003e\n\u003cli\u003eDifferent straw C/N ratios and microbial community structures are key mechanisms.\u003c/li\u003e\n\u003c/ol\u003e\n"},{"header":"1 Introduction","content":"\u003cp\u003eMollisols in northeastern China are nutrient-rich and have high soil organic carbon (SOC) content. However, these croplands have experienced a reduction in topsoil organic carbon due to extensive farming and increased erosion (Li et al., 2013). Xu et al. (\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) indicated that after more than 150 years of farming, SOC levels in the northeast region of China have decreased by 46%. Addressing land degradation is crucial for enhancing food security, preserving biodiversity, and effectively mitigating and adapting to climate change (Hossain et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Tillage management measures notably influence soil quality and have a profound impact on the dynamics of SOC.\u003c/p\u003e \u003cp\u003eReturning crop stubble to the soil enhances its physical characteristics, reducing erosion risk while also preserving organic carbon levels, improving biological activity, and promoting soil fertility and productivity. (Li et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Wang et al. (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) analyzed longitudinal experimental data from key agricultural areas in China and found that straw restoration significantly improved crop productivity, SOC, and total nitrogen levels compared to straw removal. Straw decomposition plays a crucial role in SOC balance, organic carbon mineralization, and nutrient release. Factors such as the C/N ratio, temperature, placement depth, and soil moisture significantly influence these processes. However, in northeast China, where temperatures are low, directly returning maize straw with a high C/N ratio to the field can result in competition with crop growth during decomposition, leading to reduced crop yields (Islam et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIntercropping soybean and maize is a common planting practice in the Northeast region. Previous studies examining soil nutrient utilization efficiency in intercropping have primarily focused on niche differentiation, differences in growth stages, and complementarity in nutrient utilization (Meng et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). When crops are intercropped, soybean straw with a low C/N ratio and maize straw with a high C/N ratio are typically mixed and decomposed simultaneously in the same soil volume. Understanding the effects of multiple plant cultivation on litter decomposition remains elusive. Early pioneering work (Wardle et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) and subsequent syntheses have highlighted how variable litter diversity influences litter decomposition (Ha\u0026uml;ttenschwiler et al., 2011; Lecerf et al.,2011). Carbon mineralization of mixed residues is more complex than in single residues. The potential additive effects on carbon mineralization in mixed residues can be attributed to a shift in decay pathways, moving from microbial respiration to mass loss (Li et al., 2013). Handa et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) published an article in Nature, highlighting that mixing leaf litter from varied plant functional types accelerates carbon and nitrogen decomposition compared to single plant residue decomposition. This acceleration is believed to result from complementary effects (that is, effects generated by synergistic or antagonistic interactions). Legumes, characterized by a low C/N ratio and high residual nitrogen content, undergo initial decomposition, releasing nutrients. The released nitrogen subsequently reduces the C/N ratio in gramineous crops, thereby enhancing their decomposition and nutrient release. This process could potentially influence the soil's microbiological community (Qiao et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eStraw decomposition is mainly mediated by different soil microorganisms with specific functions. Various microbial communities carry out distinct roles during the breakdown of crop straw. During the later stages of straw decomposition, fungi predominate, primarily breaking down the more complex components. In contrast, bacteria dominate the initial phase, focusing on the degradation of unstable chemical substances (Marschner et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Fan et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) identified Firmicutes, Proteobacteria, and Actinobacteria as significant bacterial phyla in the decomposition of maize residues. Ditch-buried straw return can boost fungal diversity and promote the dominance of plant-beneficial fungi, potentially increasing resistance to soil-borne diseases.\u003c/p\u003e \u003cp\u003eThe synthesis and release of extracellular enzymes by soil microorganisms play a crucial role in organic matter formation, decomposition, and the regulation of microbial responses to nitrogen and carbon amendments (Tiemann et al., 2011). Soil enzymes such as hydrolases break down non-cellulosic polysaccharides, aiding primary metabolism, while oxidases degrade recalcitrant compounds like lignin (Iqbal et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These enzymes exhibit varied reactions to different agricultural management practices involving carbon and nitrogen additions (Ortega et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). According to Yang et al. (2020), returning straw to field increased peroxidase activity but decreased β-D-glucosidase activity. Xie et al. (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) showed that the addition of N, P and wheat straw enhances the activities of soil β-glucosidase, phosphatase, protease and urease. This increase is possibly due to the exogenous additions expanding the C sources for microbial biomass and diversity, as well as increasing the availability of N and P (Khan et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNumerous studies have shown that intercropping soybeans and maize can enhance the nitrogen use efficiency of crops in soil, leveraging niche and nutrient use complementarity. Under intercropping conditions, straw returning involves mixing crop residues with varying C/N ratios into the soil. When maize straw with a high C/N ratio and soybean straw with a low C/N ratio were mixed in the soil, the rate of straw decomposition, changes in soil's physical and chemical properties, microbial community structure, enzyme activities, and their interrelations remained unclear. Therefore, we conducted culture and pot experiments to investigate this phenomenon, mainly from the perspective of microbial community composition and straw mixed decomposition effect, to explore the mechanism of adding soybean straw to corn straw to improve maize growth. Our findings offer foundational insights into the microecological theory of soil nutrient utilization and furnish evidence supporting the role of intercropping in enhancing soil fertility.\u003c/p\u003e"},{"header":"2 Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Experiment materials and experimental design\u003c/h2\u003e \u003cp\u003eIn Harbin, Heilongjiang Province, where maize and soybeans are the principal crops, the Mollisol used in this study was extracted from the tillage layer at a depth of around 20 cm (45\u0026deg;50\u0026prime;N, 126\u0026deg;39\u0026prime; E). Upon soil collection, visible plant debris, small stones, earthworms, and other large and medium-sized soil organisms were removed and then sieved through a 10-mesh sieve for further processing. The basic physicochemical properties of the soil are as follows: SOC (Soil Organic Carbon) \u0026minus;\u0026thinsp;25.0 g/kg, TN (Total Nitrogen) \u0026minus;\u0026thinsp;1.8 g/kg, AN (Ammonium Nitrogen) \u0026minus;\u0026thinsp;75.4 mg/kg, AP (Available Phosphorus) \u0026minus;\u0026thinsp;56.8 mg/kg, AK (Available Potassium) \u0026minus;\u0026thinsp;125.6 mg/kg, and pH \u0026minus;\u0026thinsp;6.0. Maize and soybean straw utilized in the experiment were obtained from mature plants in the Acheng experimental field of Harbin City, Heilongjiang Province, crushed, and sieved through a 60-mesh sieve prior to use.\u003c/p\u003e \u003cp\u003eThe incubation experiment and pot experiment consisted of six treatments, each replicated three times. The treatments included: (1) Maize straw incorporated into the soil (M), (2) Soybean straw incorporated into the soil (S), (3) Maize straw and soybean straw incorporated into the soil at a 1:1 ratio by mass (MS), (4) Maize straw and soybean straw incorporated into the soil at a 2:1 ratio by mass (2MS), (5) Maize straw incorporated into the soil with nitrogen fertilizer (MF), and (6) no straw incorporated into the soil (NS). The straw is crushed into a powder before it is mixed into the soil. The total straw input for all straw treatments was 12 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e dry soil, and the amount of fertilizer added in treatment MF was determined using a carbon-to-nitrogen ratio of 25:1. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e displays the carbon and nitrogen contents of the additional straw, along with its corresponding C/N ratio for each treatment.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe carbon and nitrogen content and C/N ratio of added straw in each treatment\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eN (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eC/N ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e46.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e58.61\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e16.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2MS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e44.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e33.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e46.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e25.00\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 \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Incubation experiment and pot experiment\u003c/h2\u003e \u003cp\u003eTo investigate the impact of combined soybean straw and maize straw on straw decomposition rates, a laboratory incubation experiment was conducted under controlled conditions. To restore microbial activity and function, the soil was preincubated at 25\u0026deg;C for seven days before the incubation experiment. Subsequently, the soil moisture level was adjusted to 60% of the field's water capacity. Upon completion of the preincubation period, 200g of soil (dry weight), along with the corresponding straw or fertilizer, was thoroughly mixed in a plastic bottle measuring 5 cm in diameter and 20 cm in height. Each bottle contained a 25 mL glass vial filled with 20 mL of 1 M NaOH as a base trap to collect evolved CO\u003csub\u003e2\u003c/sub\u003e. All bottles were maintained at a constant temperature of 25\u0026deg;C in a dark incubator. Titrations were performed to quantify CO\u003csub\u003e2\u003c/sub\u003e release on specific days: 1, 3, 5, 7, 9, 11, 14, 18, 22, 26, 32, 39, 46, 53, 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150. Throughout the experiment, soil water content was maintained at 65% of the field water capacity through periodic weighing and watering. Precipitation of trapped CO\u003csub\u003e2\u003c/sub\u003e in the NaOH solution was achieved using 0.5 M BaCl\u003csub\u003e2\u003c/sub\u003e solution. Phenolphthalein was used as an indicator, and 0.1 M HCl was employed to neutralize any excess NaOH (Blagodatskaya et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Following titration, the base trap in each jar was replaced. Cumulative CO\u003csub\u003e2\u003c/sub\u003e-C emission, CO\u003csub\u003e2\u003c/sub\u003e-C emission rate and straw carbon mineralization rate were calculated.\u003c/p\u003e \u003cp\u003eThe experiment was carried out in the pot farm of Northeast Agricultural University. The maize variety (\u003cem\u003eZea mays\u003c/em\u003e L. cv.) planted in this experiment was Xianyu 335. The nitrogen fertilizer used was urea (N46%), the phosphate fertilizer was calcium dihydrogen phosphate (P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e 61.1%), and the potassium fertilizer was potassium sulfate (K\u003csub\u003e2\u003c/sub\u003eO 54%). All treatments were based on the application of phosphate and potassium fertilizers; the amount of calcium dihydrogen phosphate (P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e 61.1%) was 0.7817 g, and the amount of potassium sulfate (K\u003csub\u003e2\u003c/sub\u003eO 54%) was 0.9815 g.In the MF treatment, 2.80 grams of urea (N 46%) were added to each pot. Each pot was filled with 10 kg of air-dried soil and the corresponding straw or fertilizer into a polyethylene pot with a diameter of 26 cm and a height of 25 cm. The rhizosphere soil was collected on the 13, 43, 83, 103 and 133rd days after planting, and the contents of SOC, TN, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, AP, AK, MBC, MBN and soil pH were determined. At the time of maize jointing, soil samples were collected to assess soil urease activity (UA), sucrase activity (SA), β-glucosidase (BG), N-acetyl-glucosidase (NAG) and microbial community structure. Plant samples were collected at the mature stage of maize to determine the biomass, N, P and K absorption of maize.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Analysis of physical and chemical properties of crop and soil\u003c/h2\u003e \u003cp\u003eThe soil's SOC and TN were determined using a CN analyzer (Carlo Erba Nitrogen analyzer 1500, Germany). The contents of ammonium NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N were assessed using an automatic flow injection analyzer (FIAstar 5000 Analyzer, Sweden) after extraction with potassium chloride. The analysis of AP and AK content in soil and nitrogen, phosphorus, and potassium content in plants, adhered to Bao's recommended protocol (Bao, 2000). Briefly, AP extraction (0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e sodium bicarbonate solution) and AK extraction (1.0 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e ammonium acetate solution, pH 7.0) were determined using the molybdenum blue method and measured using a flame photometer (FP6410, Shanghai Jingke, China). Total plant N content was determined by Kjeldahl digestion, while wet digestion with sulfuric acid allowed for the photometric measurement of plant phosphorus content using the molybdenum blue method. Plant potassium content was measured using the same digestion method via flame spectrophotometry.\u003c/p\u003e \u003cp\u003eThe MBC and MBN of the soil were determined using the direct extraction method of chloroform fumigation (Vance et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1987\u003c/span\u003e). Each 10 g fresh soil sample underwent a 24-hour fumigation with ethanol-free chloroform at 25\u0026deg;C in a vacuum extractor. A control group was set up without fumigation. Subsequently, the soil samples were extracted with 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, shaken in a shaker for 1 hour, and then filtered. The filtrate was frozen for further analysis. The semi-Kjeldahl and potassium bichromate titrimetric methods were used to measure total N and organic C, respectively. SSoil MBN and MBC were calculated according to the algorithms described by Deng et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eA pH meter with glass electrodes (DZS-707, Shanghai, China) was used to measure the pH of the soil. To analyze soil enzyme activity, Guan's technique was followed (Guan \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Accordingly, 3,5-dinitrosalicylic acid colorimetry was employed to assess SA, while sodium phenol-sodium hypochlorite colorimetry was used to determine UA. BG and NAG were analyzed similarly, involving the homogenization of fresh soil equivalent to 1.0 g dry mass in 100 ml 50 mM acetic acid buffer (pH 8.5). The sample suspension, buffer, 200 \u0026micro;M substrate (7-amino-4-methylocumarin or 4-methylumbelliferone), and 10 \u0026micro;M reference were dispensed into 96-well black microporous plates. Enzyme activity was measured using a microplate fluorometer (Scientific Fluoroskan Ascent FL, Thermo). (DeForest et al., 2009; Zhao et al., 2016).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Soil DNA extraction and illumina Miseq sequencing\u003c/h2\u003e \u003cp\u003eFor each sample, three replicate samples were analyzed. Initially, soil DNA was extracted, followed by an assessment of its integrity, concentration, and purity. Subsequently, the fungal rRNA gene's ITS1 region and the 16S rRNA gene's V3-V4 region were amplified using primer pairs ITS1F/ITS2R and 338F/806R, respectively. The PCR amplification reaction system contained 1 \u0026micro;l forward and reverse primers, 3 \u0026micro;l 2ng/\u0026micro;l, BSA 5.5 \u0026micro;l ddH\u003csub\u003e2\u003c/sub\u003eO, 10 ng template DNA and 12.5 \u0026micro;l 2xTaq Plus Master Mix. The PCR amplification process involved the following steps: (i) pre-denaturation at 95℃ for 5 minutes; (ii) denaturation at 95\u0026deg;C for 45 seconds, annealing at 55\u0026deg;C for 50 seconds, and extension at 72\u0026deg;C for 45 seconds, repeated for 28 cycles; (iii)final extension at 72\u0026deg;C for 10 minutes, followed by cooling to 4\u0026deg;C. Subsequently, a library was constructed by isolating and purifying the PCR products. Finally, sequencing was performed using the PE250/PE30 sequencing technique (Aoweisen, Beijing) on the Illumina Miseq platform (Illumina, Inc., USA). The raw reads were deposited onto the NCBI Sequence Read Archive (SRA) database with an accession number PRJNA1110815 and PRJNA1111333.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eThe test data were organized using Excel 2020. Statistical analyses, including one-way and two-way ANOVA, were conducted using SPSS 20. R was utilized to compute and plot the α diversity of soil fungi and bacteria. For β diversity, processing and visualization were performed using the \"vegan\" package in R. Correlation analysis heat maps were generated using the \"corrplot\" package in R. Additionally, the \"plspm\" package in R was employed to construct the partial least squares path model.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Result","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Mineralization characteristics of organic carbon in straw\u003c/h2\u003e \u003cp\u003eThe cumulative CO\u003csub\u003e2\u003c/sub\u003e-C emission increased in all treatments as the incubation time extended, with the rate of increase gradually decreasing during the later period of incubation (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). After the end of incubation, the cumulative CO\u003csub\u003e2\u003c/sub\u003e-C emission under M, S, MS, 2MS and MF treatment was 48 times, 62 times, 70 times, 50 times and 69 times higher than that under NS treatment, respectively. In the five straw addition treatments, the cumulative CO\u003csub\u003e2\u003c/sub\u003e-C emission was MS\u0026thinsp;\u0026gt;\u0026thinsp;MF\u0026thinsp;\u0026gt;\u0026thinsp;S\u0026thinsp;\u0026gt;\u0026thinsp;2MS\u0026thinsp;\u0026gt;\u0026thinsp;M. Consequently, the combined return of maize straw and soybean straw, or nitrogen fertilizer, exhibited an increased potential for the mineralization of organic carbon in straw compared to maize straw returned to the field alone.\u003c/p\u003e \u003cp\u003eWhen different crop straws were added to soil, the CO\u003csub\u003e2\u003c/sub\u003e-C emission rate peaked on the 3rd day of incubation, followed by a gradual decrease with incubation progression, stabilizing after the 42nd day (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Soil organic carbon mineralization exhibited similar patterns across different straw decomposition processes. During the early incubation period (0\u0026ndash;27 days), the CO\u003csub\u003e2\u003c/sub\u003e-C emission rate varied significantly among treatments, with the MF treatment showing the highest rate, followed by the MS treatment. Conversely, the M treatment had a lower CO\u003csub\u003e2\u003c/sub\u003e-C emission rate compared to other straw addition treatments during this period. Overall, the combination treatment consistently exhibited a higher CO\u003csub\u003e2\u003c/sub\u003e-C emission rate compared to returning maize straw alone.\u003c/p\u003e \u003cp\u003eThe carbon mineralization rate of added straw C reflects the change trend of conversion of added straw C to CO\u003csub\u003e2\u003c/sub\u003e-C (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Carbon mineralization rates increased with the incubation period's extension, with the rate of increase diminishing in the later stages. The carbon mineralization rates of straw treated with MS, 2MS, and MF were 57.16%, 35.73%, and 42.83% higher than those treated with M, respectively. Consequently, combining maize straw with soybean straw or nitrogen fertilizer is more conducive to straw carbon mineralization than using maize straw alone.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Dry biomass accumulation and nitrogen, phosphorus, and potassium uptake of maize\u003c/h2\u003e \u003cp\u003eThe total biomass of maize in the M and 2MS treatments was significantly lower than in the other four treatments, with the MF treatment exhibiting the highest total biomass. Specifically, the total biomass in the MF treatment increased significantly by 116.53%, 84.46%, and 8.27% compared to the M, 2MS, and NS treatments, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Additionally, potassium, phosphate, and nitrogen uptake in the M and 2MS treatments were significantly lower than in the other four treatments (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb-d). For nitrogen uptake, S\u0026thinsp;\u0026gt;\u0026thinsp;MF\u0026thinsp;\u0026gt;\u0026thinsp;MS, these three treatments exhibited significantly higher uptake compared to the M, 2MS, and NS treatments. In terms of phosphorus uptake, the M and 2MS treatments showed a significant decrease of 42.25% and 28.24%, respectively, compared to the NS treatment. Conversely, the S, MS, and MF treatments displayed significant increases of 29.09%, 26.58%, and 58.39%, respectively, compared to the NS treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In terms of potassium uptake, the S, MS, and MF treatments indicated significantly higher uptake compared to the M treatment, with increases of 24.16%, 49.01%, and 54.96%, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Therefore, the combined application of maize straw with soybean straw or nitrogen fertilizer increased the total biomass of maize and the absorption of N, P and K compared to the sole application of maize straw.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Dynamic change of soil chemical characters and soil enzyme activity\u003c/h2\u003e \u003cp\u003eStraw addition significantly affected SOC content, as demonstrated by a two-way ANOVA (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), while the influence of planting time was not significant. However, there was a significant interaction between the two factors (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Compared to the NS treatment, SOC content was significantly increased in all straw addition treatments at all planting time points (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). With the extension of planting time, the average SOC content at each time point remained relatively stable, ranging from 24.25 to 25.76 mg/kg. The average SOC content varied significantly among different treatments, with the highest average SOC content observed in the 2MS treatment (26.60 mg/kg) and the lowest in the NS treatment (22.65 mg/kg) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eTwo-way ANOVA for TN, AP, AK, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, MBC, MBN, and pH revealed significant effects of straw addition measures and planting time, along with a significant interaction (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb-i). As planting time progressed, soil TN content initially declined and subsequently increased. The average soil TN content was the highest at 133 days of planting (1.86 g/kg), being 1%-7% higher compared to other planting time points. Among treatments, the MF treatment exhibited notably higher average soil TN concentration, while the M treatment showed the lowest, and the NS treatment displayed minimal variation over time (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). With the extension of planting time, the average soil NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N contents initially increased and then decreased, reaching peak values at 43 days of planting (13.27 mg/kg and 46.97 mg/kg, respectively) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). At 13 days and 43 days of planting, the contents of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N in MS and 2MS treatment were significantly higher than those in M treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), indicating that soybean straw addition could alleviate early-stage nitrogen deficiency in maize after straw incorporation. The contents of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N in soil showed MF\u0026thinsp;\u0026gt;\u0026thinsp;MS at the early stage of straw addition, while an MF\u0026thinsp;\u0026lt;\u0026thinsp;MS trend at the later stage of straw addition (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). As planting times were extended, AP exhibited a trend of initially increasing and then decreasing, whereas AK first increased, then decreased, and subsequently increased again. Both AP and AK reached their peak levels at 43 days of planting, measuring 22.09 mg/kg and 174.95 mg/kg, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). From the perspective of straw returning measures, the MF treatment had the highest AP content, while the MS treatment had the highest AK content, measuring 24.91 mg/kg and 177.74 mg/kg, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003eFrom the perspective of planting time, both MBC and MBN contents exhibited a pattern of initially increasing, then decreasing, and finally increasing again, reaching peak values on day 43 of planting, measuring 230.04 mg/kg and 94.29 mg/kg, respectively. At all planting time points, the MF and MS treatments consistently showed higher MBC and MBN contents compared to other treatments. From the perspective of straw addition measures, the MS and 2MS treatments exhibited significantly higher MBC and MBN contents compared to the M treatment, with MBC contents being 22.35% and 8.16% higher, and MBN contents being 130.69% and 46.64% higher, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The results indicated that the addition of soybean straw could significantly increase the MBC and MBN content compared to the sole application of maize straw (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). The average soil pH at each sampling time point was 6.5. Compared with NS, pH values increased by 1.29%, 2.40%, 2.90%, 1.86%, and 3.02% in the M, S, MS, 2MS, and MF treatments, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The planting time of maize had no significant effect on pH (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCompared to the NS treatment, the M, S, MS, 2MS, and MF treatments significantly increased UA by 7.57%, 44.66%, 87.06%, 15.14%, and 72.67%, respectively, indicating that the addition of straw can enhance soil urease activity (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). UA in the MS and MF treatments was notably higher than that in the M, 2MS, and NS treatments, suggesting that combining maize straw with soybean straw or nitrogen fertilizer could more effectively boost UA (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Except for the S treatment, the soil SA in all straw-added treatments was significantly higher than that in the NS treatment, with increases of 31.76%, 14.87%, 24.93%, and 50.25% in the M, MS, 2MS, and MF treatments, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). From the perspective of straw addition treatment, SA was higher in the treatment with higher C/N, while SA was lower in the treatment with lower C/N (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Compared with NS treatment, straw treatment significantly increased the BG activity (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). BG activity in the high-nitrogen-content S and MS treatments was significantly higher than that in the M treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). The NAG activities of MS and 2MS were significantly lower than in other treatments (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Soil microbial community structure\u003c/h2\u003e \u003cp\u003eThe Shannon index of bacteria exhibited the following trend: MS\u0026thinsp;\u0026gt;\u0026thinsp;MF\u0026thinsp;\u0026gt;\u0026thinsp;S\u0026thinsp;\u0026gt;\u0026thinsp;2MS\u0026thinsp;\u0026gt;\u0026thinsp;M\u0026thinsp;\u0026gt;\u0026thinsp;NS among all treatments. Compared with NS, the Shannon index of bacteria treated with MS and MF was significantly increased by 2.50% and 1.95% (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The Chao1 index indicated that the MS and MF treatments were significantly higher than the M and S treatments, and straw addition treatments were higher than NS (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). With the exception of the S treatment, the fungal Shannon index of straw addition treatments was lower than that of the treatment with no straw incorporated into the soil (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). The Shannon index and Chao1 index of fungi under MS treatment and 2MS treatment were significantly lower than those under M and S treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), indicating that the richness and diversity of fungal community could be significantly reduced by straw incorporated into the soils. Additionally, the richness and diversity of the fungal community under combined maize straw and soybean straw incorporated into the soils could be lower than that under a single addition.\u003c/p\u003e \u003cp\u003eThe bacterial NMDS analysis stress value was 0.1397, which was generally less than 0.2. A smaller stress function value indicated a more reasonable analysis result. The result indicated that the analysis result is reasonable (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). Sample points were distributed in each quadrant, with the closest overlap observed between S treatment and MS treatment, as well as between M treatment and 2MS treatment, showing that the bacterial community makeup of S treatment and MS therapy, as well as M treatment and 2MS treatment, was the most similar. Conversely, the distance between the NS treatment and straw addition treatment was relatively long, indicating a significant difference in bacterial community composition between the NS treatment and the other treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003eThe results of fungal β diversity showed that PC1 and PC2 accounted for 24.88% and 18.67% of the total variance, respectively. PC1 clearly separated the S, MS, and MF treatments, while PC2 separated the NS and 2MS treatments. Notably, NS treatment and MF treatment were distinctly separated from the other four treatments, suggesting a significant difference in the fungal community composition between NS and MF treatments compared to the other treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the rhizosphere soil of maize, dominant bacterial phyla include Proteobacteria, Actinobacteriota, Acidobacteriota, Bacteroidota, Gemmatimonadota, Chloroflexi and Cyanobacteria, collectively accounting for over 78% of the total abundance (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). Proteobacteria has the highest relative abundance (33.62%), highlighting its crucial role in maintaining the intricate ecological balance of farmland soil. While the main bacterial groups remained similar across the community, their relative abundances varied significantly (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). Compared to NS, straw-incorporated groups showed significantly higher levels of Proteobacteria (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ea), contrasting with Actinobacteriota and Gemmatimonadota (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eb, Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ec). Notably, the relative abundance of Firmicutes was notably higher in straw addition treatments compared to no-straw treatments, with M, MS, and MF treatments exhibiting 4.06 times, 2.90 times, and 6.16 times higher levels than NS treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ed). Furthermore, the relative abundance of Bdellovibrionota was significantly elevated in MS and 2MS treatments compared to M treatments by 15.94% and 5.46% (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ee). Additionally, Nitrospirota showed a 115.02% increase in relative abundance in MS treatment compared to M treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ef). Therefore, the combination of soybean straw and maize straw incorporation into soils led to increased relative abundances of Gemmatimonadota, Proteobacteria, Bdellovibrionota, and Nitrospirota compared to maize straw alone, while Actinobacteriota and Firmicutes showed reduced abundance.\u003c/p\u003e \u003cp\u003eIn the maize rhizosphere soil, the dominant bacteria at the genus level include \u003cem\u003eSphingomona\u003c/em\u003es, \u003cem\u003eRB41\u003c/em\u003e, \u003cem\u003eSphingobacterium\u003c/em\u003e, \u003cem\u003eRamlibacter\u003c/em\u003e, uncultured_\u003cem\u003eAcidobacteria\u003c/em\u003e, \u003cem\u003emetagenome\u003c/em\u003e, \u003cem\u003eAltererythrobacter\u003c/em\u003e, \u003cem\u003eMND1\u003c/em\u003e, \u003cem\u003eFlavisolibacter\u003c/em\u003e, and \u003cem\u003eGemmatimonas\u003c/em\u003e, collectively accounting for more than 20% of the total abundance. Among these, Sphingomonas exhibited the highest relative abundance at 3.78% (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). Compared with the NS treatment, the relative abundance of \u003cem\u003eArenimonas\u003c/em\u003e, \u003cem\u003eNitrospira\u003c/em\u003e, \u003cem\u003ePhenylobacterium\u003c/em\u003e, and the \u003cem\u003eMND1\u003c/em\u003e genus of the Nitrosoomonas family exhibited similar trends, while the M treatment showed no difference, and the MS, 2MS, and MF treatments all displayed increases (Fig. S2b-e). For \u003cem\u003eBrevundimonas\u003c/em\u003e, straw addition treatment was significantly lower than no straw incorporated into the soil treatment, but MS and 2MS treatment significantly increased by 120.12% and 42.07% compared with M treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. S2f).\u003c/p\u003e \u003cp\u003eIn the maize rhizosphere soil, the dominant fungal phyla include Ascomycota, Basidiomycota, Chytridiomycota, Rozellomycota, Glomeromycota, Zoopagomycota, and Mortierellomycota, collectively representing more than 94% of the total abundance (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). Among these, Ascomycota exhibited the highest relative abundance at 53.65%, suggesting its significance in maintaining the complex ecological balance of agricultural soil. Although the main phyla in the community were similar, the relative abundance varied significantly. The relative abundance of Ascomycota in the straw addition treatment group was significantly higher compared to NS, whereas Chytridiomycota and Glomeromycota displayed the opposite trend. Compared with M treatment, the relative abundance of Chytridiomycota increased significantly by 3.79 times in MS treatment (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. S3c), whereas Glomeromycota decreased by 49.66% in the MS treatment (Fig. S3d). Moreover, the relative abundance of Basidiomycota treated with MS was 8.55 times higher than that treated with M and 34.49% higher than that treated with S (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. S3b). Therefore, the incorporation of soybean straw and maize straw into the soils led to enhancements in the relative abundance of Ascomycota, Basidiomycota, and Chytridiomycota, while reducing the relative abundance of Glomeromycota.\u003c/p\u003e \u003cp\u003eIn the maize rhizosphere soil, the dominant fungal genera include \u003cem\u003eZopfiella\u003c/em\u003e, \u003cem\u003eConocybe\u003c/em\u003e, \u003cem\u003eAcremonium\u003c/em\u003e, \u003cem\u003eCercophora\u003c/em\u003e and \u003cem\u003eAscobolus\u003c/em\u003e, collectively representing more than 30% of the relative abundance (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). Compared with NS treatment, the dominant fungi genera of M, S, MS, 2MS and MF treatments significantly decreased by 89.58%, 59.47%, 49.36%, 96.76% and 92.76%, respectively (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. S4). For \u003cem\u003eTrichoderma\u003c/em\u003e, relative abundances in M, MS, 2MS, and MF treatments decreased significantly by 75.47%, 66.04%, 98.11%, and 88.68%, respectively, compared with NS treatments (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. S4b). The relative abundance of \u003cem\u003eChaetomium\u003c/em\u003e treated with M, S and MF was significantly higher than that treated with MS, 2MS and NS (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig. S4c). The relative abundance of \u003cem\u003eFunneliformis\u003c/em\u003e in treatments with straw addition was significantly lower than in treatments without straw incorporation into soils, with no significant differences observed among various straw addition treatments (Fig. S4d).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Relationship among soil microbial community, environmental factors and maize growth quality indexes\u003c/h2\u003e \u003cp\u003eThe α diversity index of bacteria (Shannon and Chao1) was positively correlated with NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, AP, AK, MBC, MBN, pH, UA and BG (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Proteobacteria, a eutrophic bacterium, thrives in nutrient-rich environments and displayed a significant positive correlation with MBC (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). However, Actinobacteriota has a significant negative correlation with UA, BG, MBC, MBN, pH, AP, AK and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Straw organic carbon serves as a metabolic substrate for Gemmatimonadota. With the exception of TN, SOC, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, AK and NAG, Gemmatimonadota exhibited negative correlations with all other assessed soil chemical factors (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Firmicutes bacteria produce glyco-based hydrolases, enzymes crucial for cellulose breakdown. This study found that Firmicutes had a significant positive correlation with available AP, MBC, pH, SA and Chao1 (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Bdellovibrionota correlations were significant with all soil chemical factors except TN, SOC, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, AK and SA (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Bacteria from the Nitrospirota phylum convert nitrites into nitrates, which serve as readily absorbable nitrogen nutrients for plants and other microorganisms. Nitrospirota had strong positive correlations with Shannon, TN, AP, and Chao1. In general, Actinobacteriota, Gemmatimonadota, Firmicutes, Bdellovibrionota and Nitrospirota were significantly influenced by soil chemical factors. NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, MBC, MBN, pH, UA and BG are the main chemical factors affecting the dominant phyla.\u003c/p\u003e \u003cp\u003eAll soil chemical factors, except for TN, BG, and NAG, demonstrated a negative correlation with the fungal α diversity index (Shannon and Chao1), with NAG showing a significant positive correlation with the Shannon index (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and an extremely positive correlation with the Chao1 index (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb). In this study, \u003cem\u003eFusarium\u003c/em\u003e exhibited a negative correlation with all soil chemical properties, notably with AK and pH at significant levels. \u003cem\u003eTrichoderma\u003c/em\u003e was negatively correlated with AK, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N and SA (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Besides TN and NAG, \u003cem\u003eFunneliformis\u003c/em\u003e showed negative correlations with other soil chemical properties (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb). In general, soil chemistry had a substantial negative impact on \u003cem\u003eTrichoderma\u003c/em\u003e, \u003cem\u003eFunneliformis\u003c/em\u003e and \u003cem\u003eFusarium\u003c/em\u003e. All soil chemical factors variably influenced the dominant fungi, AK and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N were the most impactful.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA partial least squares path model (PLS-PM) was developed to comprehensively analyze the complex interactions among different straw types, crop growth, soil characteristics, microbial populations, and soil enzyme activities (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Bacterial communities, in contrast to fungal communities, exerted significant direct effects on soil enzyme activity (a combination of BG and UA) and soil properties (a combination of TN, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N and pH) (0.14 and 0.78). The Straw C/N ratio negatively influenced soil enzyme activity and bacterial and fungal communities, with the bacterial community experiencing the most substantial impact (-0.70). In terms of plant growth factors (a combination of PN, PP, PK and biomass), soil properties had the greatest effect (0.47), followed by soil enzyme activity (0.41). While the type of straw did not fully account for variations in plant growth, it directly affected microbial communities (-0.70 and \u0026minus;\u0026thinsp;2.00), enzyme activity (0.53) and soil properties (0.13), thereby influencing plant growth.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePrincipal component analysis (PCA) was employed to assess the impact of various straw returning methods on soil properties, soil enzyme activities, and microbial diversity. The first principal component (PC1) and the second principal component (PC2) effectively captured the essence of soil-related indicators across six straw returning methods, accounting for 71.8% and 12.8% of the total variance, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea). Significant contributors to PC1 included SOC, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, MBN, AP, AK, BG, and B-Chao1. In contrast, except for the fungal Shannon index, Chao1 index, and NAG, other indices notably influenced PC2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb). PC1 significantly separated the 2MS treatment, and PC2 significantly separated the NS, M, and MS treatments, demonstrating significant variations among the straw returning methods (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec). The random forest plots showed that different straw returning methods significantly influenced the fungal diversity index (F-Shannon), bacterial richness index (B-Chao1) and fungal richness index (B-Chao1). As for soil enzyme activities, BG, SA, NAG and UA were affected by the straw returning mode. For soil property indexes, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, MBC, MBN, AP, AK, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, pH and TN were sequentially influenced by the straw returning approaches (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Characteristics of carbon mineralization in straw\u003c/h2\u003e \u003cp\u003eUpon incorporation into soil, straw mineralization unfolds in three distinct phases: an initial rapid mineralization stage, followed by a gradual deceleration, and culminating in a relatively stable phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). This progression is linked to the chemical composition of the straw. The organic carbon in the straw breaks down into readily degradable components (such as starch and glucose) and more resistant components (such as lignin). Soybean straw contains more easily degradable parts, whereas maize straw has more resistant components (Surigaoge et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). During the early stages of incubation, readily decomposable crop residues were broken down first, boosting soil microbial growth, releasing substantial nutrients, and significantly enhancing CO\u003csub\u003e2\u003c/sub\u003e emission (Gezahegn et al., 2019). As the incubation progresses, the consumption of decomposable components slows down, and CO\u003csub\u003e2\u003c/sub\u003e release gradually decreases, ultimately achieving a state of equilibrium (Gezahegn et al., 2019). This pattern of straw mineralization was observed in our study as well. Furthermore, the dynamics of ammonium nitrogen, nitrate nitrogen, and MBN in the soil were consistent with the characteristics of straw mineralization, exhibiting an initial increase, followed by a decrease, and eventually stabilizing (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), with peak levels observed on the 43rd day of incubation.\u003c/p\u003e \u003cp\u003eIn this study, compared to the sole application of maize straw (M), integrating soybean straw or nitrogen fertilizer with maize straw (MF and MS treatments) led to an increase in soil cumulative CO\u003csub\u003e2\u003c/sub\u003e release (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) and enhanced soil fertility (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), indicating that soybean straw or nitrogen fertilizer plays a positive regulating role in the decomposition of maize straw. These findings align with Lin's research. Throughout the incubation, the exclusive use of maize straw demonstrated that maize straw competed with the succeeding crops in soil nitrogen. Conversely, the amalgamation of soybean straw and nitrogen fertilizer with maize straw improved the soil inorganic nitrogen content and accelerated straw mineralization, thereby mitigating this competition (Lin et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Schwendener et al. (2005) identified a \"mixed decomposition effect\" occurring when leaf litter with a high carbon-to-nitrogen ratio was mixed and decomposed with leaf litter with a low ratio. In this process, high-quality straw decomposes first, providing nutrients for the decomposition of lower-quality straw.\u003c/p\u003e \u003cp\u003eDuring the final phase of maize cultivation, SOC content of MS and 2MS treatment was higher than that of M and MF treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), indicating that soybean straw combined with maize straw treatment increased soil organic carbon content. Therefore, incorporating soybean straw into maize straw not only accelerates the straw mineralization rate but also positively impacts soil organic carbon storage without any detrimental effects.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Soil chemical properties and enzyme activities\u003c/h2\u003e \u003cp\u003eIn our study, the combined application of soybean straw with maize straw, as opposed to the combination of nitrogen fertilizer with maize straw, delayed nitrogen release initially and prolonged nitrogen availability later (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This approach aligns the nitrogen release with crop demand, resonating with the findings of Li et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Although the C/N ratio of MF and MS is about 25:1, the organic nitrogen in soybean straw causes a slower nitrogen release in the MS treatment compared to the MF treatment, extending nitrogen availability. The content of available nutrients (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N, AP, AK) of maize straw added with soybean straw was higher than that of maize straw applied alone (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The alteration in nutrient dynamics and straw decomposition rate due to combined straw returning is attributed to the interaction of the straws affecting the physical, chemical, and biological processes in the straw decomposition microenvironment. This interaction alters the community structure and activity of microorganisms, subsequently impacting the straw decomposition rate (Gartner et al., 2004; Chapman et al., 2010).\u003c/p\u003e \u003cp\u003eMaize root exudates and residues play a crucial role in influencing soil microbial activity and enzyme levels (Hao et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this study, in the early growth stage of maize (vegetative growth stage), both MBC and MBN showed an increasing trend with maize growth and straw mineralization (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). During the vegetative growth period of maize, root exudates serve as substantial energy sources for soil microbes, and the roots offer a habitat that enhances the living conditions for these organisms, thus fostering microbial metabolic activities and increasing soil microbial biomass (Zuber et al., 2016). In this study, MBC increased continuously and then decreased at the later stage of maize growth. MBN initially increased, then decreased, and experienced a slight uptick towards the end of the maize growth period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). As maize matures and senesces, maize litter is introduced into the soil. The addition of organic materials from maize leaf litter and stump roots enriches the soil. The presence of abundant oxygen in the soil facilitates decomposition, aiding in nitrogen retention and leading to a minor increase in MBN content, which is consistent with the research results of Yang et al. (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Bolinder et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) posited that soil microbial activity, particularly enzyme activity, was more indicative of changes in soil quality than SOC. Therefore, soil MBC, MBN and enzyme activities serve as effective indicators of the impact of straw returning practices on the microecology of black soil regions. Consistent with the findings of Zhao et al. (2016), our study confirmed that straw returning treatments enhanced soil MBC, MBN, and enzyme activities, demonstrating the beneficial effects of these practices on soil microbial dynamics.\u003c/p\u003e \u003cp\u003eUrease facilitates the transformation of soil nitrogen, while sucrase primarily catalyzes the decomposition of soil organic matter (Pamidipati et al., 2019). BG is responsible for the degradation of cellulose to obtain C, and NAG plays a crucial role in nitrogen cycling (Zhao et al., 2016). Soil C and N levels can regulate soil enzyme activity. In this study, the activities of UA, SA and BG were enhanced following the application of fertilizers and the return of straw to the field (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This increase is attributed to soil microbes producing more enzymes to decompose SOM for carbon acquisition, especially when soil nitrogen levels are high, thereby meeting the carbon demands for microbial growth. These observations align with Zhao et al. (2016). Both UA and BG activities were significantly positively correlated with mineral nitrogen (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb), indicating the positive influence of soil enzyme activities on soil nitrogen dynamics. The response of NAG to single straw application (M and S treatment) was significantly higher than that of combined maize and soybean straw application (MS and 2MS treatment), and the response of combined straw application was significantly lower than that of NS treatment. Consistent with our findings (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb), Chung et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) reported that fungal communities predominantly drive NAG activity and highlighted a strong positive link between fungal abundance and NAG activity. Hence, soil enzyme activity is influenced by the levels of soil carbon and nitrogen. The inclusion of soybean straw modifies the mineral nitrogen content, which, in turn, impacts the activities of enzymes associated with carbon and nitrogen cycling.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Nutrient accumulation in succeeding maize\u003c/h2\u003e \u003cp\u003eReturning straw to the field is a pivotal practice for enhancing soil fertility. Decomposing straw releases various mineral elements, improving soil nutrient accumulation and boosting crop yields (Latifmanesh et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, introducing straw with a high C/N ratio can impede crop nitrogen availability due to microbial immobilization during decomposition, consequently diminishing crop yield and nutrient uptake (Zhu et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In this study, the total biomass and nutrient uptake of M treatment and 2MS treatment were significantly lower than NS treatment, a disparity linked to their elevated C/N ratios. Some studies have indicated that returning maize straw to the field can reduce wheat biomass and grain yield (Dai et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In this study, the total biomass of MS treatment and MF treatment was significantly higher than that of M treatment and 2MS treatment. This enhancement is likely due to soybean straw, and nitrogen fertilizer can accelerate the decomposition of maize straw by reducing the C/N ratio of the substrate and stimulating the microbial community growth, thereby releasing straw nutrients and improving crop yield and nutrient absorption (Yang et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Zhang et al. (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) also showed that the mixing of the plant litter could improve the fertility of the soil and improve the productivity of the crops. Therefore, the inclusion of soybean straw or nitrogen fertilizer resulted in superior nutrient accumulation and biomass in the succeeding maize compared to treatments using maize straw alone.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Soil microbiota\u003c/h2\u003e \u003cp\u003eIncorporating straw into soil significantly influences the bacterial community structure, with the degradation of straw primarily initiated by rapidly proliferating bacteria. This study observed a notable increase in the bacterial Chao1 and Shannon indices following straw addition treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). According to Zhang et al.'s research, the addition of straw straw addition supplies organic materials, fostering bacterial growth and reducing competition among bacterial communities, thereby enhancing soil bacterial diversity (Zhang et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The dominant bacterial phyla identified were Proteobacteria, Actinobacteriota, and Acidobacteriota (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), which are prevalent in agricultural soils. Proteobacteria include numerous nitrogen-fixing bacterial species that play a crucial role in the biochemical cycling of soil mineral carbon, nitrogen, and other nutrients. Their activity is beneficial for plant development and the maintenance of soil fertility. Firmicutes are involved in the expression of glycosyl hydrolases that break down cellulose (Wegner and Liesack, 2016). In this study, the application of straw to soil, specifically in the MS and 2MS treatments, led to an increased relative abundance of Firmicutes and Proteobacteria compared to the NS treatment, aligning with findings by Yuan et al. (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Proteobacteria abundance in MS and 2MS treatments was significantly higher than in M and S treatments (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ea), indicating a more nutrient-rich soil environment conducive to Proteobacteria growth. Correlation analysis revealed a positive association between the abundance of Proteobacteria and Firmicutes and soil nutrient indexes (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Glycosyl hydrolases, enzymes crucial for hemicellulose decomposition, were predominantly expressed by Acidobacteriota and Chloroflexi (Liu et al., 2020). Chloroflexi, primarily consisting of anaerobic microorganisms, play a vital role in decomposing sugars and polysaccharides into organic acids and hydrogen, thereby accelerating the breakdown and assimilation of organic matter in the soil. In this research, Acidobacteriota and Chloroflexi exhibited higher relative abundances in soil treated with MS and 2MS than in soil treated with M (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), which is consistent with the results of urease activity and β-glucosidase activity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). Yu et al. (\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) observed a significant increase in the relative abundance of Chloroflexi in soils subjected to straw return for six consecutive years compared to soils without straw application. Rhodanobacter, part of the denitrifying community, plays a crucial role in nitrate reduction (Cao et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Nitrate, an essential nitrogenous nutrient easily assimilated by plants and other microorganisms, is produced from nitrite through the metabolic activities of the \u003cem\u003eNitrospirota\u003c/em\u003e (Holland-Moritz et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Compared with the M and S treatments, the relative abundance of \u003cem\u003eRhodanobacter\u003c/em\u003e treated with MS and 2MS decreased, while the relative abundance of \u003cem\u003eNitrospirota\u003c/em\u003e increased (Fig. S2a, Fig. S2d), indicating that the combined application of maize and soybean straw could reduce the biological denitrification of soil, improve the transformation of nitrites, and increase the soil nitrogen content (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Additionally, correlation analysis revealed a strong positive correlation between TN and AP and the relative abundance of \u003cem\u003eNitrospirota\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eThe richness and diversity of the bacterial community significantly increased when soybean straw or nitrogen fertilizer was applied in conjunction with maize straw, in contrast to using maize straw or soybean straw alone. Conversely, the richness and diversity of the fungal community showed a decline with these combined applications (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Ascomycota and Basidiomycota dominate the fungal community (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). Ascomycota functioning as saprophytes that produce cellulase to decompose soil and straw organic matter, such as cellulose and lignin, thereby releasing nutrients (Zhang et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). White rot fungi in Basidiomycota possess a distinctive capability to break down lignin and lignocellulosic complexes (Zhao et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Consistent with the findings of this study, Ma et al. (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) examined the impact of straw on soil physicochemical properties and fungal community diversity. Their investigation demonstrated an increase in the relative abundance of Ascomycota following the application of straw. Compared with M treatment, the relative abundance of Basidiomycota increased in MS treatment and decreased in Ascomycota, while Ascomycota increased in 2MS treatment without a significant change in Basidiomycota, indicating that the decomposition roles of different fungi vary with the proportion of straw returned to the field. \u003cem\u003eFusarium\u003c/em\u003e, a soil-borne pathogenic fungus responsible for wheat scab, plant blight, and root rot (Clemmensen et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), experienced a reduction in relative abundance with straw returning to the field, negatively correlating with soil nutrient indexes (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb). Compared to the M treatment, the relative abundance of \u003cem\u003eFusarium\u003c/em\u003e was decreased in the 2MS treatment (Fig. S4a). Therefore, straw returning to the field can increase soil nutrient content and reduce the relative abundance of pathogens, with soybean straw further reducing pathogen abundance compared to maize straw alone. Consistent with our findings, Tang et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) demonstrated that the addition of wheat straw reduced the relative abundance of \u003cem\u003eFusarium\u003c/em\u003e. \u003cem\u003eTrichoderma\u003c/em\u003e, known to enhance plant development by antagonizing plant pathogenic fungi (Alwadai et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), exhibited increased relative abundance with MS compared to M treatment, with the opposite trend observed in the 2MS treatment (Fig. S4b). \u003cem\u003eChaetomium\u003c/em\u003e is a saprophytic fungus involved in the degradation of organic matter (Zhang et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). M, S, and MF significantly increased the relative abundance of \u003cem\u003eChaetomium\u003c/em\u003e, while MS and 2MS decreased compared with M and S treatments (Fig. S4c). The partial least squares path model (PLS-PM) indicated that straw with different C/N ratios impacted microbial α diversity and enzyme activity, thus affecting soil nutrients and plant growth (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). These findings indicated that combined straw returning alters soil microorganism composition, enhances organic matter transformation, and promotes succeeding maize growth.\u003c/p\u003e \u003c/div\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eOur findings demonstrated that the combined incorporation of maize and soybean straw enhances the mineralization rate and nutrient release of straw. Application of soybean straw or nitrogen fertilizer can effectively alleviate the competition for soil nitrogen between maize straw and subsequent crops compared to using maize straw alone. Furthermore, the combined use of both straw types alters soil microbial community structure, expediting soil organic matter transformation and straw nutrient release, thereby fostering later maize growth. In summary, the synergistic decomposition effect of soybean straw and maize straw elucidates the mechanism of intercropping for enhancing nutrient utilization efficiency from a different perspective.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXiaodan Liu：Data curation, Writing \u0026ndash; original draft. Hongrui Huo: Data curation. Yuhang Zhang: Writing \u0026ndash; review \u0026amp; editing. Huawei Yang: Data curation. Shumin Li: Writing \u0026ndash; review \u0026amp; editing, Conceptualization, Supervision, Funding acquisition. Lingbo Meng：Writing- Reviewing and Editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe 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\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by National Natural Science Foundation of China (32171547).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data that support the findings of this study are included within the article (and any supplementary information files).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlwadai AS, Perveen K, Alwahaibi M (2022) The isolation and characterization of antagonist Trichoderma spp. from the soil of Abha, Saudi arabia. 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Soil Biol Biochem 97:176\u0026ndash;187. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.soilbio.2016.03.011\u003c/span\u003e\u003cspan address=\"10.1016/j.soilbio.2016.03.011\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":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":"Mollisols, Residue quality, Mixture effect, Soil enzyme activity, Straw decomposition","lastPublishedDoi":"10.21203/rs.3.rs-4441610/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4441610/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe carbon-nitrogen ratio (C/N ratio) of straw significantly influences its mineralization and nutrient release when returned to the soil. This study utilized indoor culture and outdoor pot experiments to investigate the impact of varying straw ratios on straw mineralization, soil property dynamics, soil microbial communities, soil enzyme activities, and maize growth. Design of treatments included: (1) maize straw return (M), (2) soybean straw return (S), (3) 1:1 ratio of maize straw and soybean straw return (MS), (4) 2:1 ratio of maize straw to soybean straw return (2MS), (5) maize straw return combined with nitrogen fertilizer (MF) and (6) no straw return (NS). Compared with M treatment, MS and MF treatment enhanced the straw mineralization rate and nutrient release, thus increasing the biomass of succeeding maize. The MS treatment increased the relative abundance of Chloroflexi, Acidobacteriota, and Proteobacteria by 15.54%, 5.36%, and 14.29%, respectively, compared to the M treatment. Straw return treatments significantly decreased the prevalence of the pathogenic fungus \u003cem\u003eFusarium\u003c/em\u003ecompared to the NS approach. Correlation analyses indicated a positive association between soil chemical properties and the presence of Proteobacteria, Firmicutes, Bdellovibrionota, and Nitrospirota. Conversely, these factors showed a negative correlation with Actinobacteriota, Gemmatimonadota, \u003cem\u003eFunneliformis\u003c/em\u003e, \u003cem\u003eTrichoderma\u003c/em\u003e, and \u003cem\u003eFusarium\u003c/em\u003e. These changes in microbial communities are beneficial for straw degradation and nutrient release. In summary, the combined addition of soybean straw and maize straw in a 1:1 ratio optimizes the microbial community, enhances soil nutrient cycling, improves soil fertility, and positively affects corn biomass and nutrient uptake.\u003c/p\u003e","manuscriptTitle":"Promotion of Maize Straw Degradation Rate by Altering Microbial Community Structure through the Addition of Soybean Straw","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-20 06:53:47","doi":"10.21203/rs.3.rs-4441610/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":"da386b8d-cb8c-4edd-8557-0aec9e443c41","owner":[],"postedDate":"June 20th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-08-19T15:01:51+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-20 06:53:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4441610","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4441610","identity":"rs-4441610","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}