Enhancing soil multifunctionality through restoring erosion environment and microbial functions combined with organic manure and straw mulching

Soil multifunctionality (SMF), the ability of soil to support multiple ecosystem functions, is under severe threat from soil erosion. Organic manure and straw mulching are well-known for mitigating soil erosion. However, the mechanisms by which these organic materials enhance soil multifunctionality during the restoration of erosion-degraded soil remain unclear. To address this, soil multifunctionality in eroded soil was investigated after a decade of continuous organic material application. Four treatments were established: 1) a control group applied only chemical fertilizer (CK); 2) organic manure with 20 % nitrogen substituted (OM); 3) straw mulching with 20 % nitrogen substituted (SW); and 4) a combination of organic manure and straw mulching (1:1) with 20 % nitrogen substituted (OMSW). The findings showed that organic manure, straw mulching, and the combination treatments reduced runoff by 2.12–45.97 % and sediment by 33.54–109.33 %, reduced nutrient loss and increased soil nutrient and water-stable aggregates (WSA) contents, especially in the straw mulching and the combination treatments. The improved soil environment enhanced microbial community stability, increased the microbial functional Shannon index, and enriched carbon (e.g., bcrB/C/D) and nitrogen (e.g., amoB/C, napA, and nirB) cycling genes, thus improving soil multifunctionality. Specifically, organic manure increased soil multifunctionality by 87.88 %, straw mulching by 457.40 %, and their combination by 154.73 %. Soil erosion environment and microbial functions, especially carbon and nitrogen cycling, were key factors influencing soil multifunctionality. Notably, key microbial taxa such as Proteobacteria play pivotal roles in stabilizing community structure and maintaining community function during soil restoration. This study underscores that organic manure application and straw mulching, mainly through reducing soil erosion, improved soil environment, optimized the composition and function of soil microbial communities, and ultimately enhanced soil multifunctionality. This is pivotal for safeguarding the ecological integrity of sloping farmland and fostering sustainable agricultural development.