Alterations in microbial-mediated methane, nitrogen, sulfur, and phosphorus cycling within paddy soil induced by...

Rice paddies are crucial ecosystems, supporting dense microbial populations and playing a significant role in global food security. Integrated rice-fish farming has been recognized as an important agricultural production pattern to enhance agro-ecosystem stability and food productivity. Using metagenomic sequencing, we compared the microbial-mediated soil CH₄, N, S, and P cycles in integrated rice-fish farming versus traditional rice monoculture, exploring their potential coupling mechanisms within microbes. Integrated rice-fish farming has significantly impacted these microbial-mediated cycles in paddy soil, altering the overall functional diversity, sum abundance, and microbial host diversity for the CH4, N, S, and P cycling genes. Specifically, it suppressed the denitrification, assimilatory nitrate reduction (ANR), assimilatory sulfate reduction (ASR), thiosulfate oxidation, organic phosphoester hydrolysis, and two-component system pathways and most of their associated functional genes, while enhanced the acetoclastic methanogenesis and the reduction of tetrathionate to thiosulfate processes. Compared to traditional rice monoculture, integrated rice-fish farming resulted in metagenome-assembled genomes (MAGs) with fewer and more isolated biogeochemical cycling genes, lacking potential couplings among multi-element cycles. Additionally, this farming approach increased the soil nutrient levels including the total carbon (TC), total organic carbon (TOC), total nitrogen (TN), total sulfur (TS), and total phosphorus (TP) concentrations, which have been identified as the most crucial factors driving the alterations in microbial functional genes/pathways involved in biogeochemical cycling processes in our study. Overall, integrated rice-fish farming dynamically altered the microbial-mediated CH₄, N, S, and P cycles and their potential couplings within microbes through promoting the soil nutrient levels, which could favor rice growth, thus maintaining food security and providing refined knowledge for maintaining soil sustainability.