Abstract: Drought influences carbon fixation by plants. Therefore, elucidating its impact on carbon fluxes in plants at the ecosystem level is crucial for assessing their role in mitigating climate change. Using carbon fluxes and environmental factor data from FLUXNET sites, we analyzed the influence of drought on carbon fluxes, their drivers, time-lag effects, and recovery times across various climatic regions and seasons. Results showed drought significantly decreased gross primary production (GPP), ecosystem respiration, and net ecosystem productivity in arid regions but slightly increased carbon sequestration in humid regions. Summer droughts negatively affected vegetation carbon fluxes, partly offset by the positive impact of spring droughts. Nonforest carbon fluxes were more susceptible to drought effects than forest fluxes. Soil water content (SWC) was the main influence on changes in arid regions, whereas vapor pressure deficit (VPD) dominated humid regions. Decreased SWC and increased VPD reduced carbon sequestration in arid regions but increased it in humid regions. Increased VPD reduced GPP, leading to forest carbon loss, whereas decreased SWC reduced GPP, leading to nonforest carbon loss. The lag time of the drought effects on carbon fluxes was longer in humid regions (19.44 d) than in arid regions (14.71 d). Compared to nonforest areas (16.74 d and 57 d for drought lag and recovery time, respectively), forest areas had a longer lag (18.81 d) and recovery time (92 d). The findings revealed discrepancies in the main factors regulating vegetation carbon fluxes during droughts between arid and humid regions and between forest and nonforest ecosystems. These insights provide a new perspective on understanding and simulating carbon–climate feedback. Enhancing ecosystem diversity is a feasible measure to increase drought resistance.

Key words: Carbon sequestration, Regulatory factor, Drought lag time, Recovery time, Climatic regions