Contribution of periphytic biofilm of paddy soils to carbon dioxide fixation and methane emissions

Rice paddies are major contributors to anthropogenic greenhouse gas emissions via methane (CH(4)) flux. The accurate quantification of CH(4) emissions from rice paddies remains problematic, in part due to uncertainties and omissions in the contribution of microbial aggregates on the soil surface to carbon fluxes. Herein, we comprehensively evaluated the contribution of one form of microbial aggregates, periphytic biofilm (PB), to carbon dioxide (CO(2)) and CH(4) emissions from paddies distributed across three climatic zones, and quantified the pathways that drive net CH(4) production as well as CO(2) fixation. We found that PB accounted for 7.1%–38.5% of CH(4) emissions and 7.2%–12.7% of CO(2) fixation in the rice paddies. During their growth phase, PB fixed CO(2) and increased the redox potential, which promoted aerobic CH(4) oxidation. During the decay phase, PB degradation reduced redox potential and increased soil organic carbon availability, which promoted methanogenic microbial community growth and metabolism and increased CH(4) emissions. Overall, PB acted as a biotic converter of atmospheric CO(2) to CH(4), and aggravated carbon emissions by up to 2,318 kg CO(2) equiv ha(−1) season(−1). Our results provide proof-of-concept evidence for the discrimination of the contributions of surface microbial aggregates (i.e., PB) from soil microbes, and a profound foundation for the estimation and simulation of carbon fluxes in a potential novel approach to the mitigation of CH(4) emissions by manipulating PB growth.