Dynamics Of Methane Emission And Microbial Community In Rice Paddy Soil Amended With Different Types Of Biochar

Methane(CH₄),a powerful greenhouse gas naturally formed in various environments,has drawn great environmental and social concerns.Rice paddy fields are one of the major sources of worldwide CH₄ emissions,because the anaerobic environment in flooded paddy soil is favor for the production of CH₄.Biochar is a porous and carbon-rich solid with properties of stability and eco-friendliness,and vast industrial or agricultural wastes in China provide considerable quantity of feedstocks for biochar preparation.Therefore,application of biochar to environment could be an effective strategy which reuses industrial or agricultural wastes as well as reduces CH₄ emission.Previous researches have demonstrated that biochar addition influenced microbial community and physicochemical properties of paddy soil.However,studies about whether different types of biochar amendment would have effects on Fe(III)reduction and SCFAs profile were rarely reported.Besides,the response of CH₄ emission and succession of bacterial and archaeal community in paddy soil to different types of biochar remained controversial.In our study,three biochars derived from rice straw(RB),orange peel(OB)and bamboo powder(BB)were added to paddy soil respectively and incubated anaerobically in laboratory for 90 days.We characterized the chemical composition and properties of three biochars,and investigated the influence of biochars amendment on variation of Fe(III)reduction,six SCFAs(acetate,propionate,butyrate,isobutyrate,valerate and isovalerate)and emissions of CH₄,CO₂ and H₂ in rice paddy soil during the incubation.Furthermore,the diversity and succession of bacterial and archaeal community,and the correlation between microbial taxa and biochemical parameters were explored by high-throughput sequencing and bioinformatics analysis.The main results are listed as follows:(1)Three biochars pyrolysed from different agricultural or forestry wastes under same pyrolysis condition harbored similar carbon and oxygen functional groups but differed in content.(2)After 90 days incubation of paddy soil,RB,OB and BB decreased CH₄accumulation by 20.9%?17.3%and 15.9%;increased Fe(II)concentration by 49.8%?25.7%and 5.6%;averagely decreased 9.3%?12.7%and 21.2%of the total SCFAs accumulation at eight sampling dates.(3)The?-diversity of bacterial and archaeal community all significantly decreased at the end of incubation,and three biochars intensified the loss of bacterial?-diversity but mitigated the loss of archaeal?-diversity.Besides,bacterial and archaeal community had obviously succession during the incubation,but biochar additions had no significant effect on the succession of microbial community.(4)Fe(III)-reducing bacteria such as Bacillus,Clostridium and Thiobacillus were significantly correlated with Fe(III)reduction,and biochar additions i ncreased the total relative abundance of Fe(III)-reducing bacteria most by 15.1%?28.4%and17.4%.Syntrophus,Syntrophobacter,Sporotomaculum,Geobacter,Defluviicoccus,Desulfatiglans and methanogens were active in the production and consumption of SCFAs.The inhibited SCFAs accumulation by biochar additions might be due to the fact that the promotion of Fe(III)reduction accelerated the consumption of SCFAs.(5)Methanosaeta,Methanosarcina,Methanocellales and Methanobacterium were mainly responsible for CH₄ production.Three types of biochar almost had no significant effect on the relative abundance of methanogens,so the inhibition of CH₄accumulation by biochars might be due to the increased relative abundance of methanotrophs,especially for Candidatus?Methanoperedens.This study is conducive to comprehensively understand the effect of biochar addition to biochemical reactions in paddy soil,as well as the overall assess ment to succession of microbial community and correlation b etween microorganism and biochemical parameters,which provides fundamental information for developing future strategies of biochar generation from various types of green waste and biochar amendment in regulating CH₄ emission in rice cropping ecosystem,having important ecological significance.