High-Altitude CO2 Flux in Cropland and Grassland of Eastern Qilian Mountains, China: Variation and Driving Factors

Abstract

Understanding soil carbon dynamics in climate-sensitive alpine ecosystems is critical for addressing global warming challenges. This study systematically investigated CO₂ flux patterns and drivers in cropland and grassland ecosystems (2000–2020) across China's eastern Qilian Mountains through integrated field monitoring, remote sensing and modeling. Results revealed rapid vertical CO₂ flux intensification at − 10 to − 20 cm depths, with cropland and grassland soils exhibiting 623–1,252 ppm and 690–1,133 ppm respectively, which is 4–5 times higher than atmospheric levels, driven by microbial activity and pore structure transitions. Principal Component Analysis identified soil nutrient interactions explaining 69.6% of soil biogeochemical variance, where subsequent altitude-nutrient interaction analysis revealed elevation-driven soil organic carbon (SOC, R² = 0.7253, p < 0.05) and total nitrogen (TN, R² = 0.6841, p < 0.01) correlations in cropland and total phosphorus (TP, R² = 0.4278, p < 0.01) correlation in grassland. Over two decades, 99.53% of the study area exhibited rising net primary productivity (NPP), with 72.62% showing extremely significant increases, synergistically enhanced by climate drivers (90.9% of the area) and human activities (99.5% of the area). Land-use change significantly influenced carbon storage in last two decades with an overall decrease in 0.100 Mt of C, which suggested increasing pressure on the ecosystem from human activities and climate changes. This study provides a reference for carbon cycle process and ecological protection in high-altitude regions, highlighting the need for further innovation in policies that integrate altitude-specific nutrient management with adaptive land-use planning, with methodological frameworks transferable to global mountain systems facing similar climate and anthropogenic challenges.