Spatiotemporal dynamics and driving mechanisms of vegetation carbon sources and sinks in the Heihe River Basin

Net ecosystem productivity (NEP) is a key indicator of ecosystem carbon balance and vegetation carbon source–sink dynamics. The Heihe River Basin (HRB), a representative arid and semi-arid inland basin in northwestern China, provides an ideal natural laboratory for long-term carbon dynamics research. Despite its ecological significance, few studies have systematically quantified long-term, large-scale patterns of net primary productivity (NPP) and NEP in this basin. Using an improved Carnegie–Ames–Stanford Approach (CASA) model and a soil respiration model, we quantified NPP and NEP in 2000, 2005, 2010, 2015 and 2022. Results show that the HRB functioned overall as a carbon source, while NEP increased from −113.10 to −96.33 g C·m⁻²·a⁻¹. NEP exhibited pronounced seasonality, peaking in July and reaching a minimum in January. Spatially, higher NEP occurred in the south and east, with Qilian and Minle counties acting as carbon sinks. Temperature, precipitation and altitude are dominant drivers, with strong temperature‒precipitation interactions.