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.