Effects Of Precipitation Exclusion On Soil Microbial Community Structure And Greenhouse Gas Fluxes In A Natural Castanopsis Carlesii Forest In Subtropical China

In forest ecosystems,CO2,CH4 and N2O are the main greenhouse gases those are exchanged in the soil-atmosphere system.They contribute to the greenhouse effect about 56%,20%and 8%,respectively.In the last decades,atmospheric concentrations of CO2 CH4 and N2O have increased,and continue to increase at annual rates of 0.3%,0.6%and 0.5%,respectively.In recent years,global climate change has caused changes of the rainfall pattern.Changes in rainfall will significantly affect the carbon and nitrogen balance in forest ecosystems.However,the effects of rainfall change on soil greenhouse gas fluxes and their mechanisms remain unclear.To investigate the effects of different throughfall exclusion treatments on greenhouse gas fluxes and soil microbial community structure,we conducted a throughfall exclusion experiment in a natural Castanopsis carlesii forest in Sanming Ciry of Fujian Province.There were three treatments,viz.control(no throughfall exclusion,CT),30%reduction in throughfall(A),60%reduction in throughfall(B).The results showed that soil microbial community structure changed after throughfall exclusion.In summer,30%reduction in throughfall significantly increased the amounts of bacteria,fungi,actinomycetes,and total soil microorganisms.In spring and autumn,60%reduction in throughfall significantly reduced the soil gram-positive bacteria,gram-negative bacteria,arbuscular mycorrhiza fungi,and fungi contents.Among all the soil samples,the dominant bacteria on phylum level was Ascomycota and Basidiomycota.However,on genus level unclassified Russulales and Tremellales was dominant bacteria.In addition,a diversity analysis showed that the coverage indices of 18 soil samples were all above 99.9%,and the PC1 and PC2 contribution values of ? diversity analysis were 59.41%and 7.93%,respectively,and the total contribution rate was 67.34%.Two analytical methods all indicated that the results of this sequencing basically represent the real conditions of the microorganisms in the soil samples.During the observation period(April 2016?September 2017),the natural Castanopsis carlesii forest was the sources of CO2 and N2O,but the sink of CH4.From October 2016 to September 2017,CO2 and N2O emissions in treatment of 30%reduction in throughfal increased 14.14%and 7.81%of the control respectively and increased 9.2%of CH4 uptake.The 60%reduction in throughfal resulted in increases of CO2 and N2O emissions by 27.44%and 28.41%respectively and increased CH4 uptake by 15.3%.According to the global warming potential calculated from the cumulative annual emissions of three greenhouse gases from October 2016 to September 2017,the 30%reduction in throughfal and 60%reduction in throughfal increased the global warming potential by 13.38%and 27.02%,respectively.