Microbial Enzyme Activities Drive CO2 and CH4 Emissions During Freeze–Thaw Cycles in Peatlands

Climate change is projected to intensify freeze–thaw cycles (FTCs) in the peatlands of Changbai Mountain, influencing soil biogeochemistry and carbon cycling. In order to elucidate microbial regulation of carbon emissions during FTCs, we performed controlled laboratory simulations using soils from a peatland in the Changbai Mountains, Northeast China. Our findings indicate that after 15 FTCs with small (−5°C to 5°C) and large amplitudes (−10°C to 10°C), the carbon dioxide (CO₂) emission rates from surface soils declined by 63.8% and 64.2%, respectively, compared to the constant-temperature control; in deeper soils, the respective declines were 27.5% and 50.9%. We found that oxidase activities were negatively correlated with CO₂ emissions during FTCs and served as the primary driver of these emissions. Methane (CH₄) was oxidized during FTCs, with oxidation rates inversely related to FTC amplitude and greater under small amplitude than large amplitude conditions. Soil hydrolase activities were negatively correlated with CH₄ oxidation rates, functioning as the primary regulators of methane oxidation. The carbon emissions were subsequently influenced by microbial phospholipid fatty acids, which modulated enzyme activities. This investigation comprehensively explores the interactive effects of soil enzymes, organic carbon fractions, and microbial community composition on carbon emissions. The results underscore the central role of soil enzymes in mediating these processes. Collectively, these findings provide novel insights into the microbial mechanisms governing greenhouse gas emissions from peatlands during FTCs.