Asymmetric response of vegetation NPP to extreme climate over a vulnerable karst Region in Southwest China

Understanding how vegetation in ecologically fragile karst regions responds to extreme climate events is critical for global change adaptation. However, the response of net primary productivity (NPP) to extreme climate indices, rather than to mean climatic conditions, has not been systematically investigated across large, contiguous karst areas. To address this gap, this study used MODIS NPP data and 12 ETCCDI extreme climate indices calculated from daily meteorological records (2000-2018) to investigate the spatiotemporal evolution of NPP and its asymmetric response to extreme temperature and precipitation events across Guizhou Province, Southwest China. Pixel-level Pearson correlation and Theil-Sen trend analyses were applied, with false discovery rate (FDR) correction for multiple comparisons. The results show that: (1) annual mean NPP increased significantly at a rate of approximately 3.8 g C m-2 yr-1, with a west-high, east-low spatial pattern; (2) climate trends showed asymmetric warming (nighttime warming three to four times faster than daytime) and intensified total precipitation but reduced persistence; and (3) NPP exhibited strong, spatially extensive positive correlations with extreme temperature indices (especially warm night frequency and annual minimum temperature), whereas correlations with extreme precipitation indices were weak and highly heterogeneous. Thermal conditions, particularly nighttime warming, appear to be the primary driver of vegetation dynamics in this humid karst region, while the unique dualistic hydrological structure likely decouples precipitation from plant water availability. Future karst ecosystem management should prioritize extreme temperature events and adopt spatially differentiated strategies.