Contrasting Effects of Atmospheric and Soil Compound Extreme Events on NPP, RH, and NEE in the Dongting Lake Eco-Economic Zone Under Different Land Use Types

Compound extreme climate events have become increasingly frequent under climate change and may alter terrestrial carbon cycling through different atmospheric and soil pathways. Focusing on the Dongting Lake Eco-Economic Zone, this study identified three types of compound extreme events during 2003–2024: atmospheric compound hot–dry events (ACHDs), soil compound hot–dry events (SCHDs), and drought-to-rewetting events (DRWs). We then examined their associations with monthly anomalies of net primary production (NPP), heterotrophic respiration (RH), and net ecosystem exchange (NEE) under different land cover backgrounds. The results showed that ACHDs and SCHDs both increased significantly, whereas DRWs exhibited a slight decreasing trend and a more scattered spatial distribution. During the same period, regional NPP increased significantly, RH decreased slightly, and NEE became more negative, indicating an overall strengthening of net carbon uptake. Different event types were associated with contrasting carbon flux response pathways: ACHDs were mainly associated with reduced NPP and slightly increased RH, thereby shifting NEE toward more positive values and weakening regional net carbon uptake, whereas SCHDs and DRWs were more strongly associated with reduced RH and more negative NEE. In addition, the event–carbon relationships differed among land cover types, with cropland, built-up land, and sparsely vegetated surfaces showing higher sensitivity to ACHDs, whereas the responses to SCHDs and DRWs varied markedly among forest, grassland, wetland, and open water classes. These results highlight that compound atmospheric and soil extremes influence regional carbon cycling through distinct component-specific pathways, and that land use background is an important factor associated with differences in carbon flux sensitivity in humid lake–floodplain systems.