Straw retention drives microbial community succession to improve soil C/N cycling: insights from a multi-year rice-based system

The soil microbial community plays a crucial role in driving the decomposition and mineralization of plant residues, thereby affecting carbon (C) and nitrogen (N) cycling and storage. Straw retention provides soil with C and N sources, which enhances microbial community composition and nutrient cycling. While long-term straw retention has been shown to improve soil quality and nutrient-use efficiency, the impacts of short-term straw-return treatment on soil quality and the underlying microbiological mechanism of straw in improving soil fertility and nutrient-use efficiency remain unclear. The present study aimed to elucidate the dynamic responses of soil microbial community structure and function to rice straw retention using a multi-year field experiment. The findings revealed that rice straw returned for 3 and 5 consecutive years (S3 and S5, respectively), enhanced soil organic carbon (SOC) and available phosphorous (AP) contents, increased fungal biomass, and stimulated the growth of cellulose-decomposing microbial communities. Furthermore, S3 and S5 treatments increased the activities of C cycling enzymes (β-xylosidase) and N cycling enzymes (N-acetyl-glucosaminidase and urease). These treatments also increased the genes abundance associated with C-cycling (<i>sdimo</i>), nitrification (<i>amoA</i> and <i>amoB</i>), and N fixation (<i>nifH</i>), while enriched genes related to C cycling and N metabolism pathways (nitrification and nitrate reduction). In contrast, the abundance of genes involved in denitrification (<i>nirS</i>) was reduced. However, S3 and S5 treatments led to an increased abundance of the plant pathogens <i>Magnaporthe oryzae</i> and <i>Ustilaginoidea virens</i>. This work demonstrates that short-term straw retention effectively enhances soil microecological environment and microbial functionality and also underscores the need for strategies to mitigate pathogen accumulation for sustainable agricultural practices.