Abstract: The carbon and water use efficiency of vegetation are the important variables reflecting ecosystem carbon-water cycle. Analyzing their dynamics and driving factors is of great significance for ecosystem sustainable development in the arid and semi-arid Mongolian Plateau. Using trend analysis, partial correlation analysis, and residual analysis, we analyzed the spatiotemporal variations of vegetation carbon use efficiency (CUE) and water use efficiency (WUE) of the Mongolian Plateau from 2000 to 2019, and examined their relationships with precipitation, temperature, and human activities. The CUE of vegetation in the Mongolian Plateau showed a significant increasing trend during  2000-2019, with a rate of 0.2%·a^-1, while the WUE showed a non-significant decreasing trend. The CUE increased significantly in all ecological divisions except broad-leaved forests, mixed forests, and alpine meadows, while WUE showed an increasing trend only in coniferous forests and desert steppe. The CUE and WUE were positively correlated with precipitation and negatively correlated with temperature in most of the Mongolian Plateau (>60%). Affected by human activities, 62.9% of the plateau area suffered a significantly increased CUE residual, while only 10.6% of the study area showed a significant increasing trend in WUE residual. Our results provide vital information for understanding the impacts of climate change and human activities on carbon-water cycling in the Mongolian Plateau.

Key words: Mongolian Plateau, carbon and water use efficiency, climate change, human activities.