Paddy soil microbial communities driven by environment- and microbe-microbe interactions: A case study of elevation-resolved microbial communities in a rice terrace.

Rice paddies are a significant source of the greenhouse gas methane, which mainly originates from microbial activity. Methane generation in anaerobic systems involves complex interactions of multiple functional microbial groups. Rice paddies installed in hilly terrain are often terraced, providing multiple quasi-independent plots differing primarily in their elevation up a hillside. This represents an excellent study site to explore the influence of environmental factors on microbial communities and interactions among microbial populations. In this study, we used a combination of geochemical analyses, high-throughput amplicon sequencing, and statistical methods to elucidate these interactions. Sulfate, total nitrogen, total iron, and total organic carbon were determined to be critical factors in steering the ecosystem composition and function. Sulfate-reducing bacteria predominated in the rice terrace microbial communities, and Fe(III)-reducing and methane-oxidizing bacteria were abundant as well. Biotic interactions indicated by co-occurrence network analysis suggest mutualistic interactions among these three functional groups. Paddy-scale methane production may be affected by competition among methanogens and sulfate- and Fe(III)-reducing bacteria, or by direct methane oxidation by methane-oxidizing bacteria. CAPSULE: Microbial communities were characterized in rice terrace. The environment- and microbe-microbe interactions indicated the mitigation of sulfate and Fe on methane production.