The Effect Of Rainfall On Greenhouse Gas Emissions From Dryland Soil And Its Microbial Mechanisms

The increase of greenhouse gas emissions,resulting in climate warming,has become a great challenge to the world today.Dryland soils are an important source of greenhouse gas emissions.Rainfall changes soil moisture conditions and affects soil carbon and nitrogen cycle processes,which in turn affects the production and emission of greenhouse gases.The study of greenhouse gas emissions from dryland soils and its influence mechanism can provide a theoretical basis for further regulation of greenhouse gas emissions and achieving emission reduction.In this study,we investigated the effects of rainfall on the production and emission of N₂O,CH₄ and CO₂ gases in dryland soils using field experiments,and analyzed the differences in microbial community structure and functional genes using macro-genome sequencing technology;further investigated the effects of different moisture levels on the production and emission of greenhouse gases in dryland soils using indoor simulated incubation experiments;in order to investigate the mechanism of greenhouse gas emission pulse after rainfall in dryland soils.The main results and conclusions are as follows,The main findings and conclusions were as follows:1)Rainfall increases the production of N₂O,CH₄,and CO₂ gases in dryland soil,and emission pulses occur 24 hours after rainfall.The peak concentration of N₂O gas in deep soil lasts for a long time（24h to 48h）,and the N₂O emission flux and profile concentration generated by the first rainfall are significantly higher than those of the second rainfall.From0～24 hours,the NO₃^--N content in each treatment increases,especially in the surface layer,providing sufficient substrate for the production of N₂O gas.NH₄⁺-N rapidly decreased 24hours after the second rainfall,providing a possibility for conversion into NO₃^--N.The MBN of each profile rapidly increased 24 hours after the second rainfall,indicating the activation of microbial activity,leading to peak greenhouse gas emissions.The frequency of rainfall is also the main factor affecting greenhouse gas emissions,with the first rainfall producing significantly higher greenhouse gases than the second rainfall.The greater the rainfall,the more greenhouse gases the soil produces.2)At 48h and 192h after rainfall,Proteobacteria,Acidobacteria and Actinobacteria were the dominant communities of soil microorganisms.Compared to 48 hours,there was no significant difference in the abundance of nitrogen metabolism functional genes between treatments at 192 hours.The changes in soil nitrate nitrogen,ammonium nitrogen,nitrite nitrogen,and microbial biomass carbon and nitrogen are the main factors affecting the structure of soil bacterial communities after rainfall,as well as the factors affecting gene changes in nitrogen metabolism function.3)Compared to 48 hours after rainfall,greenhouse gas emissions stabilized at 192 hours and there was no significant difference between different rainfall levels.At 48 hours,the N₂O emission flux was highly positively correlated with MBC and MBN,and was highly positively correlated with the N₂O concentration in each profile,especially at 10cm,where the correlation between N₂O concentration was the highest.This indicates that the N₂O concentration at 10cm has the strongest contribution to the N₂O emission flux.At 192h,the N₂O emission flux was highly positively correlated with ammonium nitrogen and the N₂O concentration in the profile.The N₂O concentration at each profile level made a significant contribution to the N₂O emission flux.At 48h,N₂O emission flux is positively correlated with nos Z（K00376）,which is a functional gene for denitrification and also controls N₂O reductase synthesis.At 192h,the N₂O emission flux was positively correlated with nas C（K00372）and nar G（K00370）.4)The cumulative N₂O emissions from all treated soils increased with the extension of cultivation time.The accumulated N₂O emissions during flooding treatment from 0 to 48 hours show a rapid increase period,and tend to stabilize after 48 hours;However,other treatments showed a sharp increase from 0 to 96 hours and stabilized after 96 hours.The N₂O emission flux of all treatments reached its peak after 24 hours of cultivation.Under flooding treatment,N₂O gas is mainly produced by denitrification,while under 40%WHC～100%WHC,N₂O gas is mainly produced by nitrification.The mixed kinetic equation can be used to simulate the cumulative emission of N₂O gas from soil during incubation,and can distinguish the proportion of N₂O produced by denitrification and nitrification.In summary,rainfall increases soil moisture,increases the production and concentration of greenhouse gases in soil profiles,and further increases the production and emission of greenhouse gases in dryland soils.Emission pulses occur 24 hours after rainfall.After rainfall,changes in soil nutrients are the main factor affecting the structure of soil bacterial communities and the abundance of nitrogen metabolism functional genes.After a single rainfall,soil N₂O emission in the early stage is mainly affected by the nosZ functional gene of denitrification,and in the later stage,it is mainly affected by the functional gene of the catalytic subunit nasC of assimilating nitrate reductase and the functional gene of nitrate reductase/nitrite oxidoreductase narG.