Nitrogen Mineralisation Processes in High-Altitude Wet Meadow Soils Along a Vegetation Degradation Gradient and Their Sensitivity to Temperature and Humidity

Abstract. Nitrogen (N) cycling in alpine wetlands plays a crucial role in global nitrogen cycling and its balance. Although the mechanisms underlying the net nitrogen mineralization rate (Rmin) in degraded soils of alpine wetlands have been extensively studied, research on the effects of temperature and humidity on the Rmin process under different vegetation degradation gradients remains limited. Alpine wet meadows with different vegetation degradation conditions (i.e. undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD) were selected to examine effects of temperature, soil moisture, and their interactions on soil net N mineralization. The results indicated that vegetation degradation significantly inhibited the Rmin process, with its rate remaining constant or gradually decreasing as degradation severity increased. Soil moisture significantly affects Rmin. Within the moisture range of 20%–60% FC, Rmin increases with increasing humidity, but decreases gradually beyond 60% FC. Additionally, reduced moisture significantly affects Rmin in soils with different degrees of vegetation degradation. Temperature also significantly affects Rmin. The Q10 values for the four levels of degraded soil are 1.73–2.37 (UD), 0.82–2.98 (LD), 0.93–2.30 (MD), and 1.12–2.10 (HD), respectively. The growth rate of Rmin at all moisture levels decreases with increasing temperature, and the soil nitrogen mineralization process is most sensitive in the 15°C–25°C temperature range. Temperature changes have a greater impact on nitrogen mineralization in MD sites than in UD, LD, and HD sites. Overall, temperature and moisture exhibit synergistic and antagonistic effects on soil nitrogen mineralization, with temperature effects being more pronounced. The optimal temperature for Rmin among the four degradation levels is 20.50–25.00°C, and the optimal moisture condition is 50.00–69.52% FC.  These findings provide crucial scientific evidence for understanding soil nitrogen dynamics on the Tibetan Plateau and formulating targeted management measures.