Overgrazing leads to decoupling of precipitation patterns and ecosystem carbon exchange in the desert steppe through changing community composition

Background and aims Understanding the effects of grazing and precipitation pattern on ecosystem carbon (C) exchange, and their interactions is crucial to predict the transformation of carbon sources and sinks in long-term grazed grassland under climate change. Methods We continuously measured net ecosystem CO 2 exchange (NEE), gross primary production (GPP) and ecosystem respiration (ER) under different grazing intensity treatments (i.e., control (CK), light grazing (LG), moderate grazing (MG), and heavy grazing (HG)) during the growing seasons from 2011 to 2013 in a desert steppe on the Mongolian Plateau. Results Our results showed that all grazing treatments (irrespective of intensity) significantly reduced ecosystem C fluxes relative to no grazing in all experimental years. With increasing grazing intensity, NEE was suppressed (less negative) by 13–26%, 38–63% and 41–65% in LG, MG and HG plots, respectively. Changes in vegetation coverage, aboveground biomass and soil moisture induced by grazing intensity mainly caused decreases in ecosystem C fluxes in grazed grasslands. However, the interannual variabilities of NEE may be determined by precipitation evenness during the growing season in this arid desert steppe, and there was significant interaction between grazing intensity and precipitation patterns on NEE in our experiment. Conclusions Our results highlight the importance of grazing intensity and precipitation patterns in altering ecosystem C exchange, and indicate that overgrazing may lead to the decoupling of precipitation patterns and NEE through changing community composition in desert steppe ecosystems.