Dynamics Of Methane Emission And Microbial Community In Flooded Rice Paddy Soil Amended With Modified Biochar

Methane（CH₄）is a potent greenhouse gas,and reducing methane emissions from farmland is an important direction to alleviate the greenhouse effect.In order to further improve its ability to inhibit methane emissions,the modification of biochar was chosen to improve its environmental benefits.In this research,two different modified biochars were prepared（nitric acid modified biochar（NBC）and hydrogen peroxide modified biochar（OBC））and water-washed biochar（WBC）was used as the experimental control.The chemical composition and microscopic morphology of different modified biochars were characterized by SEM,FTIR,XPS,EA,BET and electrochemistry.Meanwhile,four groups of different treatments were designed on the flooded anaerobic paddy soil,namely blank group（paddy soil without biochar addition）,and paddy soil with water washed biochar,paddy soil with nitric acid modified biochar and paddy soil with hydrogen peroxide modified biochar.Biochemical indicators such as iron reduction,concentration of short-chain fatty acids,pH,CH₄,CO₂ and H₂ emissions,community changes of bacteria and archaea during cultivation,as well as microbial relative abundance and environmental factors were explored under different treatments.correlation.The main findings are as follows:After modification,the surface of biochar became rough,the pore volume decreased.Both modifiers increased the oxygen-containing functional groups on the biochar surface.The nitric acid modifier also introduced NO₂ functional groups on the biochar surface.Electrochemical analysis found that nitric acid modification increased the electron charge and discharge ability of biochar,while hydrogen peroxide decreased the electron charge and discharge ability of biochar.The three kinds of biochars all reduced the accumulation of CH₄ in paddy soil,and the modification of biochar could improve the inhibition of CH₄ emission.The ability of biochar to inhibit CH₄ emission from strong to weak was NBC>OBC>WBC,while NBC would increase the CO₂ emission of paddy soil.The addition of three biochars reduced the maximum accumulation of H₂.The addition of biochar promoted the iron reduction process of paddy soil to a certain extent.However,NBC treatment had an inhibitory effect on the iron reduction process of paddy soil at the beginning of the experiment（Days 0-1）,but showed a promoting effect on Day 70.NBC had a significant inhibitory effect on the accumulation of short-chain fatty acids in paddy soil.NBC lowered paddy soil pH at the end of the experiment.For the bacterial community of paddy soil,at the end of the experiment,the bacterialα-diversity of paddy soil treated with three biochars increased compared with the blank group.In the early stage of the experiment（Days 0-12）,the relative abundance of Clostridium＿sensu＿stricto series species in the biochar treatment group was lower than that in the blank group,especially in the NBC treatment.Fonticella,Clostridium＿sensu＿strictos＿10 and Clostridium＿sensu＿strictos＿12 showed a significant negative correlation with NBC,while Geobacter showed a significant positive correlation with NBC.For the archaeal community in paddy soil,theα-diversity of the archaeal community was increased in three types of biochars just added to the paddy soil.On Day 12,WBC and OBC reduced the archaealα-diversity in paddy soil,while NBC had the opposite effect.At the end of the experiment（Day 70）,the addition of the three biochars moderated the reduction inα-diversity of the archaeal community.NBC was beneficial to maintain the biodiversity of paddy soil archaeal communities throughout the experiment.The modified biochars inhibited the relative abundance of methanogenic archaea,the growth of Methanobacterium and Methanocella of the hydrogenotrophic methanogens were inhibited by OBC,while the growth of Methanosaeta and Methanosarcina were mainly inhibited by NBC.Furthermore,the modified biochars could stimulate the increase of the relative abundance of anaerobic methanotroph Candidatus＿Methanoperedens.This research found that the modification of biochar can further improve the ability of regulating methane emissions from rice fields,which has extremely important ecological significance.In addition,the effects of modified biochar on bacterial and archaea communities in paddy soil were revealed,and the correlation between microbial community succession and soil biochemical indexes was evaluated,which provided a theoretical basis for modified biochar to regulate microbial succession in paddy soil and influence biochemical reactions in paddy soil.