Soil Fungal Community Dynamics Are More Strongly Influenced by Crop Growth Stage than by Straw Retention Amount Under...

Although soil fungi play a crucial role in straw decomposition, mineralization, nutrient cycling, and soil fertility, soil nitrogen and carbon stoichiometry across crop growth stages under long-term straw retention and wheat-soybean rotation remains poorly understood. We assessed the dynamic changes in soil fungal communities under no straw (NS) retention, half straw (HS) retention, and total straw (TS) retention in winter wheat and summer soybean rotation. Compared with the NS treatment, average total nitrogen (TN) increased by 11.86% and 17.71% and mean soil organic carbon (SOC) increased by 4.10% and 13.08% under the HS and TS treatments, respectively. NO₃^--N/TN and microbial biomass nitrogen (MBN)/TN ratios increased with the increase in straw retention; NH₄⁺-N/TN and dissolved organic carbon/SOC ratios decreased. Microbial biomass carbon (MBC)/SOC increased and subsequently decreased as straw retention increased. The mean soil C:N ratio increased, and the MBC/MBN ratio decreased as straw retention increased. Crop growth stage and straw retention treatments significantly influenced soil fungal diversity and abundance; while they did not induce changes in the dominant species, they affected relative abundance. Soil fungal relative abundance and community dynamics were more sensitive to crop growth than to straw retention treatments. Mantel's r statistic and Pearson correlation coefficient suggest that soil chemical stoichiometric ratios are useful indicators of relationships among the fungal community, soil nutrient status, and crop cultivation. Therefore, straw retention may be suitable for long-term wheat-soybean rotation.