Seasonal changes of CO2, CH4 and N2O fluxes in different types of alpine grassland in the Qinghai-Tibetan Plateau of China

Grassland degradation and grassland use type changes are associated with dynamics in soil properties and biogeochemical cycling, with implications for carbon and nitrogen cycling and trace gas fluxes. To examine the influence of grassland degradation and grassland use type changes on gases fluxes, emissions of CO2, CH4 and N2O were measured in three alpine ecosystems (alpine meadow, alpine steppe and alpine desert) with healthy and degraded grasslands on the Qinghai-Tibetan Plateau in May, August and October 2013. The lowest CO2, CH4 and N2O fluxes occurred in alpine deserts, and the highest fluxes occurred in alpine steppe. In general, degraded grasslands had relatively higher gas fluxes than healthy grasslands, except for CH4 dynamics. The temporal variation in gas fluxes indicated that CO2 and N2O fluxes were highest in August and lowest in May, while the lowest fluxes of CH4 were in August. Stepwise linear analysis was employed to explore the key factors for different gas fluxes. In alpine meadow and alpine steppe, the variation in CO2 and N2O fluxes in August could be explained by soil temperature and soil water content, while in May and October, soil physical and chemical properties, including soil pH, clay content and NO3--N, were the key factors. Soil water content and NH4+-N contributed to the CH4 fluxes. However, in alpine desert, soil water content was the key factor affecting gas emissions for different experimental sites. These results indicate that the examined alpine grasslands emitted a large amount of gas emissions especially after the grassland had degraded; therefore, more attention should be paid to protecting grassland degradation in the Qinghai-Tibetan Plateau.