Land-use change reshapes regional carbon balance and low-carbon spatial optimization in Qinghai's alpine plateau, China.

Alpine plateau regions are highly sensitive to land-use change, yet the regional carbon balance dynamics induced by land-use transitions and low-carbon spatial regulation pathways remain insufficiently quantified for climate mitigation planning. Using Qinghai Province (China) as a case study, this study developed an integrated framework for carbon balance assessment and low-carbon spatial optimization by jointly quantifying ecosystem carbon storage (CST), carbon sink (CSI), carbon emissions (CE), and net carbon emissions (NCE). Regional carbon balance was estimated using multi-source data, the IPCC coefficient method, carbon-balance equation, and InVEST model. The optimal-parameter GeoDetector was used to identify the spatial explanatory power and interactions of natural and socioeconomic factors, while intPLUS and NSGA-III simulated and optimized 2035 land-use patterns under four scenarios. The results showed that (1) Qinghai shifted from a net carbon sink to a net carbon source during 2000-2023; CE increased from 655.80 × 104 t to 3495.75 × 104 t, whereas CSI increased by only 1.26%, and CST followed an "increase then decline" trajectory. Grasslands constituted the dominant carbon pool, and forest and water played an important role in maintaining the stability of regional CSI. (2) High CSI clustered in the Three-River Headwaters region and the Qilian Mountains, whereas carbon sources were concentrated along the eastern towns-transport corridors-resource development belt, revealing a pronounced spatial mismatch between sinks and sources. (3) The spatial differentiation of carbon emissions was associated with N2O emissions and land-use intensity, while GDP, urban land, and their interactions with climatic factors further amplified emission effects. (4) Scenario optimization results indicated that controlling inefficient expansion, stabilizing and moderately expanding grassland, forest, and water, and converting unused land into high-carbon-density ecological land, while meeting reasonable growth demands for construction land, could simultaneously achieve CE reduction and CSI enhancement. These findings provide actionable evidence for low-carbon spatial planning in alpine regions.