Response of carbon emissions and the bacterial community to freeze thaw cycles in a permafrost affected forest wetland ecotone in Northeast China

Climate warming can affect freeze thaw cycles (FTCs) patterns in northern high-latitude regions and might affect permafrost carbon emissions. The response of carbon release and microbial communities to FTCs has not been well characterized. Here, we conducted laboratory incubation experiments to investigate the relationships among carbon emissions, bacterial community, and soil variables in a permafrost-affected forest wetland ecotone in Northeast China. The emission rates of CO2 and CH4 increased during the FTCs. FTC amplitude, FTC frequency, and patch type had significant effects on carbon emissions. FTCs increased the contents of soil DOC, NH4+-N, and NO3--N but reduced bacterial alpha diversity (Chao and Shannon indices). CO2 emissions were mainly affected by bacterial alpha diversity and composition, and the inorganic nitrogen content was the most important factor affecting CH4 emissions. Our findings indicated that FTCs could significantly regulate CO2 and CH4 emissions by reducing bacterial community diversity and increasing the concentration of available soil substrates, and increases in CO2 emissions and decreases in CH4 emissions were related to declines in bacterial alpha diversity. Our findings shed new light on the microorganism-substrate mechanisms regulating the response patterns of soil carbon cycle to FTCs in permafrost regions.