Wetland soil carbon dioxide emission dynamics with external dissolved organic matter in mid–high-latitude forested watershed

Long-term low temperatures in mid–high-latitude forested watersheds can slow litter decomposition during freeze–thaw periods, and release more nutrients from the surface layer during rainy seasons. Hydrologically dissolved organic matter (DOM) is transported to downstream wetlands and influences soil CO2 emissions. In this study, multiscale approaches were used to further understand soil CO2 emissions in the mid−high-latitude forested wetland watershed. First, the in situ soil CO2 emission rate measurements and microbial abundances during freeze–thaw period and rainy season were compared to analyze their occurrences. Wetland soil could emit large amounts of CO2 during rainy season, which was strongly stimulated by genus of Vicinamibacterales and Basidiomycota. Second, the in situ micrometeorology, water quality measurement, and model simulation methods were adopted to reveal the factors influencing wetland soil CO2 emission efflux during rainy season. Dissolved organic carbon concentrations strongly correlated with wetland soil CO2 emission efflux, and their magnitudes were controlled by DOM components in the upstream river. Furthermore, hydrological DOM flow paths were influenced by rainfall patterns, and more low-molecular-weight compounds released from upland forests under increasing frequency of heavy rainfall events. Finally, we simulated watershed soil CO2 emission effluxes using the denitrification and decomposition model, and globally analyzed the effects of latitude on soil CO2 emission effluxes. Wetland soil CO2 emissions in mid−high-latitude forested watershed should not be ignored and efficient mitigation measures needed to be further investigated for enhancing carbon sequestration potential.