Microbial Mechanisms of Nitrogen Reduction Effects on SOC Pools Under Straw Return in Paddy Soils

This study identified a critical threshold of 20% synthetic nitrogen reduction (80%NR) with full straw return in rice-wheat rotations. The 80%NR treatment maintained grain yield while significantly improving soil carbon dynamics: increasing labile soil organic carbon (36% higher readily oxidizable carbon, 37% more microbial biomass carbon) and enhancing macroaggregate stability. Microbial analysis revealed 28% greater abundance of cellulolytic Firmicutes and Actinobacteria, along with suppressed methanogen populations. Metagenomic data demonstrated upregulation of CO2 fixation genes through the reductive TCA cycle and reduced methane production potential. These findings provide a scientifically validated approach to maintain productivity while enhancing soil carbon sequestration in intensive rice-wheat systems.