Response of vegetation carbon use efficiency to drought: A case study of the Manas River Basin in Xinjiang

Carbon Use Efficiency (CUE) – defined as the ratio of net to gross primary production (NPP/GPP) – is a critical regulator of ecosystem carbon sequestration. Focusing on the Manas River Basin (Xinjiang, China), a typical arid endorheic basin, we analyzed CUE dynamics across four ecosystems (coniferous forest, broadleaf forest, grassland, cropland) during 2001–2020 using MODIS-derived products. Key findings: (1) Basin-scale CUE averaged 0.50 (± 0.12), peaking in coniferous forests (highest) and croplands (lowest), with strong seasonality (spring/autumn > winter, *p*<0.01); (2) Spatiotemporal stability revealed low-fluctuation zones (57.99% of the basin, primarily grasslands/woodlands) and divergent future persistence trends between plain/desert grasslands; (3) Drought response showed 3-month lag dominance, with forests exhibiting greater drought resistance (lag > croplands by 1.2 months, *p*=0.03); (4) Ecosystem resilience was generally high, modulated by interactions between vegetation type, irrigation, and climate gradients. This study establishes a mechanistic framework for predicting arid-land carbon cycling under climate stress, with implications for global dryland management.