Mechanisms of Ecosystem Carbon Exchange in Response to Grazing Rates in Two Hydrologically Contrasting Growing Seasons in a Desert Steppe

Mechanisms of Ecosystem Carbon Exchange in Response to Grazing Rates in Two Hydrologically Contrasting Growing Seasons in a Desert Steppe

Chronic grazing affects grassland soil processes and plant community composition, which may create novel patterns of net ecosystem carbon exchange (NEE) under the mediation of precipitation. Here, we report results from a 14-year field manipulative experiment with four stocking rates in a Stipa breviflora desert steppe in northern China. Ecosystem carbon exchange as well as plant aboveground biomass and composition were measured in the two growing seasons (including a wet and dry growing season). Our results showed a significant interannual variation in CO₂ fluxes, heavy grazing significantly reduced NEE regardless of precipitation. Grazing-induced changes in NEE were largely attributable to differences in plant functional groups under different stocking rates. Perennial forbs was the most important factor influencing ecosystem carbon exchange. These findings provide a scientific basis for the ability of degraded grassland ecosystems to conserve and enhance carbon sinks.