Vegetation carbon use efficiency response to drought in the Manas River Basin of Xinjiang

Carbon Use Efficiency (CUE), quantified as the ratio of net primary production to gross primary production (NPP/GPP), serves as a crucial indicator of ecosystem carbon sequestration capacity. However, understanding of its spatiotemporal dynamics and drought response mechanisms in arid inland basins remains limited. This study investigates the CUE characteristics in the Manas River Basin, a representative arid endorheic basin in Xinjiang, China, using MODIS satellite data (2001-2020). Results demonstrate that the multi-year mean CUE of the basin was 0.50 (±0.12), with coniferous forests exhibiting the highest values and croplands the lowest. Seasonal analysis revealed CUE in spring and autumn significantly exceeded that in winter (p<0.01). Spatially, 57.99% of the basin displayed low CUE fluctuation, primarily distributed in grassland and woodland areas. Future trend projections indicate divergent persistence patterns between plain and desert grasslands. Drought response analysis identified a dominant 3-month lag effect, with forests showing greater drought resistance and longer response lags compared to croplands (1.2 months longer, p=0.03). The ecosystem maintains high resilience, regulated by the interactive effects of vegetation type, irrigation practices, and climate gradients. These findings establish a mechanistic framework for understanding carbon cycling processes in arid lands under climate stress, providing scientific basis for global dryland ecosystem management.