Impacts of experimental warming and moderate grazing on ecosystem carbon exchange and its compositions in an alpine meadow on the eastern Qinghai-Tibetan Plateau
How net ecosystem carbon exchange and its composition respond to warming and grazing in the alpine meadow ecosystem is considerably uncertain. We used open top chambers (OTCs) and clipping plus dung application to simulate the effects of warming and moderate grazing on ecosystem carbon exchange, including net ecosystem exchange, ecosystem respiration, gross ecosystem photosynthesis, and soil respiration. Our findings suggested that warming and moderate grazing significantly affected net ecosystem carbon exchange and its compositions, which varied with time. Warming significantly increased the net ecosystem carbon exchange and gross ecosystem photosynthesis, as well as the net carbon fixation. Moderate grazing decreased the ecosystem respiration and soil respiration. The effects of moderate grazing on net ecosystem exchange and gross ecosystem photosynthesis varied with seasonal dynamics: grazing significantly reduced net ecosystem exchange and gross ecosystem photosynthesis in early August; as the growing season continued, they increased in the late growing season and became higher than those in the control. No significant interaction was noted between warming and grazing. Warming with grazing increased the seasonal average net ecosystem exchange and seasonal average gross ecosystem photosynthesis, but no significant impact on seasonal average ecosystem respiration was noted. Interaction of carbon exchange with warming and moderate grazing showed a time-dependent change. Our findings suggest that carbon sequestration might enhance under the future climate warming and moderate grazing in the alpine meadow.