Abstract: Land-use patterns in the wetlands of northwest Yunnan Plateau have undergone changes due to climate change and human activities. However, the impacts and mechanisms of these land-use changes on soil carbon and nitrogen stocks in the wetlands remain unclear. In this study, we analyzed the changes in soil organic carbon (TOC) and total nitrogen (TN) contents and stocks under different land-use types (wetlands, meadows, and croplands) of Napahai. Our aims were to elucidate the relationship between soil carbon and nitrogen stocks, plant biomass, and soil physicochemical properties under different land-use types, and to clarify the influencing mechanisms of land-use types on soil carbon and nitrogen stocks and main controlling factors. The results showed that soil moisture, TOC, TN content, aboveground biomass, and belowground biomass were significantly higher in wetlands than in croplands and meadows (P<0.05), while bulk density was significantly lower in wetlands (P<0.05). Soil carbon and nitrogen stocks in wetlands, croplands, and meadows decreased with increasing soil depth (0-100 cm). Carbon and nitrogen stocks were the highest in wetland soil, and the lowest in meadow soil. Soil organic carbon stocks showed a significant positive correlation with TOC content, carbon-nitrogen ratio, and aboveground biomass (P<0.01). Soil total nitrogen stocks were positively correlated with soil moisture, TOC and TN contents, and aboveground biomass (P<0.01), while negatively correlated with bulk density and carbon-nitrogen ratio (P<0.05). Land-use type, soil moisture, bulk density, and TOC content directly affected soil carbon stocks, while soil depth, land-use type, carbon-nitrogen ratio, and TN content directly affected soil nitrogen stocks. In summary, bulk density, soil moisture, carbon-nitrogen ratio, aboveground biomass, and belowground biomass were identified as the main factors affecting soil carbon and nitrogen stocks in Napahai wetlands. The carbon and nitrogen stocks in the soil of Napahai wetlands were highest in wetlands, followed by croplands and meadows, indicating that drainage of wetlands into meadows or conversion of wetlands into croplands will result in carbon and nitrogen losses in the soil of Napahai wetlands.

Key words: land-use type, soil carbon stock, soil nitrogen stock, Napahai wetland