Soil Carbon Pool Destabilization via Distinct Pathways Induced by Warming and Nitrogen Deposition Enhances Wetland Soil Respiration

Abstract

Changes in temperature and nitrogen deposition associated with altered climatic conditions are likely to significantly alter rates of soil organic matter decomposition. However, our current knowledge about how warming and nitrogen deposition interactively alter mineralization of soil organic carbon is largely limited. Therefore, we selected a herbaceous marsh in the Funiu Mountain for a field simulation experiment of warming and nitrogen deposition. We found that, in the topsoil layer, nitrogen deposition significantly decreased the carbon pool management index (CPMI) and increased soil respiration flux, whereas neither warming nor its interaction with nitrogen deposition significantly affected either of these two indicators. Partial least squares path modeling (PLS‐PM) analysis revealed that nitrogen deposition accelerates soil carbon decomposition by increasing cellobiohydrolase activity and decreasing microbial carbon use efficiency (CUE), whereas warming reduces soil labile carbon content. Both of these processes contribute to a decrease in the soil CPMI, which ultimately promotes the enhancement of soil respiration. This study revealed a significant interactive effect of warming and nitrogen deposition on wetland soil respiration. Specifically, nitrogen deposition accelerates soil carbon release by activating microbial carbon‐acquiring enzymes and decreasing microbial CUE, whereas warming indirectly promotes respiration by reducing labile carbon content. Our findings provided key parameters for the development of climate‐carbon cycle feedback models and offered a theoretical basis for formulating protection strategies for wetland carbon sink functions.