Changes in vegetation ecosystem carbon sinks and their response to drought in the karst concentration distribution area of Asia

Changes in net ecosystem productivity (NEP) in karst areas can have a significant impact on terrestrial ecosystem carbon cycling, yet quantifying changes in vegetation NEP and its response to factors such as drought and hydroclimate remains a difficult challenge because of its special climatic and hydrological conditions. We used remote sensing data to estimate vegetation NEP in the Asian karst concentrated distribution area (AKC), analyzed its spatial and temporal variations annually (2000−2020) and during rainy season (May–November), established the drought fluorescence monitoring index (DFMI), and used a ridge regression model to explore the response mechanism of vegetation NEP to dry and wet conditions response mechanism. The results showed the following: (1) Compared with the annual changes, the vegetation NEP changes in the rainy season differed significantly on the karst geographic divisions, in which there was a significant increasing trend in Southwest China (SC) and its karst areas, while a significant decreasing trend in the Indochina Peninsula (IP) and its karst areas. (2) DFMI was the main driver of vegetation NEP change, of which the contributions were 38.05 % and 32.82 % at the annual scale and in the rainy season, respectively, which drove the increase in SC vegetation NEP, and the decrease in IP; note that the increase in vapor pressure deficit (VPD) was the key factor causing the decrease in NEP in the IP karst area during the rainy season. (3) In the lagged effect of drought on vegetation NEP, the time scale of the lag was found to be 1 month. The study revealed differences in the changes in the vegetation carbon sinks in different karst geographic divisions. We obtained a new finding: a significant trend of decreasing vegetation NEP in the IP and its karst area was influenced by the long-term effects of changes in DFMI and VPD. Therefore, the variability of different karst areas, as well as changes in drought and water resources, should be considered in carbon-cycle regulation and vegetation restoration efforts in karst areas.