Differential Soil Dissolved Organic Matter Responses to Grazing Restoration in Meadow and Peat Wetlands of the Qinghai‐Tibetan Plateau

Dissolved organic matter (DOM) is the predominant form of aqueous carbon export from wetland soils. However, in restored alpine wetlands, the hydrological control over DOM composition, specifically how restoration‐induced moisture changes differentially reshape fluorescent signatures in meadow versus peat wetlands, remains unresolved. Here, we collected 0–20 cm soil samples from two typical wetlands (meadow and peat wetlands) subjected to both grazing and restoration treatments (through micro‐dam construction) in the Zoige area. Dissolved organic carbon (DOC) concentrations and DOM fluorescent components were analyzed to explore whether restoration has a consistent impact on DOM. The results demonstrated that the DOC concentration in the meadow wetland was significantly (p < 0.05) decreased by 29%, and that in the peat wetland showed a non‐significant increase after restoration from grazing. Nevertheless, both meadow and peat wetland restoration from grazing had the potential to promote DOM lability, as evidenced by increased protein‐like components and decreased humic‐like components. Compared to grazing meadow wetlands, the increased moisture content sharply decreased the nitrate concentration by 58 times after restoration, which elevated the nitrogen limitation because restoration increased the ratio of microbial biomass carbon to nitrogen (MBC/MBN ratio) by 20 times, ultimately leading to DOM depletion and protein‐like component accumulation. Moreover, the stronger nitrogen limitation (much higher MBC/MBN ratio) experienced by peat wetland microbial communities resulted in a lower increase in the protein‐like component compared to meadow wetlands. The increased lability and rapid turnover of DOM with lower content in meadow wetlands after restoration from grazing probably result in a rise in potential for DOM degradation.