Straw return improves soil multifunctionality by altering functional microbial diversity and abundance

Returning straw to the field is widely recognized for its ability to sustain crop productivity and promote the long-term viability of agricultural ecosystems. However, the impact of prolonged straw return on soil functional microbiomes and their relationship with soil multifunctionality (SMF) remain insufficiently understood. This study is based on an 8-year field experiment comprising four treatments: no straw return (N), rice straw return (R), wheat straw return (W), and combined rice and wheat straw return (RW). All straw incorporation methods increased the wheat yield and SMF. Rice straw increased SMF by 69.7 %, while wheat straw enhanced SMF by 52.1 %, with RW exhibiting the most significant long-term positive effect (74.8 %). This enhancement was primarily attributed to elevated available soil nutrient levels and increased enzymatic activities associated with carbon, nitrogen, and phosphorus cycling. Straw return promoted C, N, and P cycling genes following the trend RW > W > R > N. Random forest analysis identified the composition and abundance of functional microbial communities as key determinants of crop productivity. RW markedly diminished the abundance of plant-associated beneficial bacteria and consumers while promoting fungal pathogens in wheat leaves and reducing their prevalence in rhizosphere soil. Potentially beneficial bacteria exhibited a strong predictive capacity for wheat yield, significant associations with soil functionality, and compensatory effects with soil nutrients in their contributions. Structural equation modeling revealed that straw return was significantly positively correlated with enhanced SMF and C-N-P cycling efficiency, ultimately promoting wheat yield. Consequently, these findings suggest that straw return drives microbial community assembly, enhances nutrient cycling, and fosters improved soil fertility and multifunctionality.