Light grazing tends to enhance ecosystem carbon sequestration and resource use efficiency in a meadow steppe of northern China

Abstract

Grassland ecosystems are particularly sensitive to human disturbances due to their relatively simple structure and limited resource availability. However, the responses of ecosystem carbon and water exchanges to grazing, the dominant human activity in grasslands, remain insufficiently understood. During growing seasons in 2023 and 2024, a grazing gradient experiment was conducted in a meadow steppe of northern China, incorporating four intensity levels: no grazing (CK), light grazing (LG), moderate grazing (MG), and heavy grazing (HG). Using the static chamber method, we assessed ecosystem carbon fluxes (GPP: gross primary production; ER: ecosystem respiration; NEE: net ecosystem CO₂ exchange; Rh: soil heterotrophic respiration), water exchanges (ET: evapotranspiration; EP: soil evaporation), and resource use efficiencies (CUE: carbon use efficiency; WUE: water use efficiency). Results indicated that light grazing significantly enhanced NEE, CUE, and WUE compared to other treatments. In contrast, increasing grazing intensity markedly reduced carbon and water fluxes in MG and HG plots. Under grazing stress, aboveground biomass (AGB) was the primary determinant of GPP and ET changes, while ER was mainly influenced by soil microclimate and nutrients. GPP emerged as the key driver of NEE, CUE, and WUE variations. These findings highlight the contrasting roles of biotic and abiotic factors in regulating ecosystem functions and provide comprehensive evidence that light grazing could benefit carbon sequestration and resource use efficiency in the meadow steppe. Our study can offer practical and theoretical support for determining appropriate grazing intensity and promoting the sustainable management of grasslands in northern China.