Multi-scale dynamic changes of Net Ecosystem Productivity in Inner Mongolia Autonomous Region and its impact factors

Climate warming intensifies the carbon cycle process. Net Ecosystem Productivity (NEP) serves as a vital indicator for evaluating the carbon sink strength of the Inner Mongolia Autonomous Region (IMAR). Yet, a comprehensive understanding of its spatiotemporal evolution and the precise roles played by meteorological, topographical, and anthropogenic factors remains elusive. Accordingly, this study leveraged the Carnegie-Ames-Stanford Approach (CASA) model and a soil respiration equation to investigate the multi-scale dynamic changes in NEP for IMAR over the period 1982-2022. To elucidate the underlying impact mechanisms, we employed a suite of statistical methods, including partial correlation analysis, ridge regression analysis, and geographic detector analysis. The findings of this study reveal that: (1) The average annual Net Ecosystem Productivity (NEP) of the Inner Mongolia Autonomous Region (IMAR) exhibited an increasing trend at a rate of 0.283 g C m^-2 yr^-1. The year 2012 was identified as a significant mutation point, with a mutation probability of 99.46%. Spatially, NEP demonstrated a pattern of higher values in the southeastern regions and lower values in the northwest, with pronounced high-value areas localized in Hulunbuir City and Hinggan League. (2) Summer constitutes the primary contributor to the annual NEP, displaying a growth rate of 0.174 g C m^-2 yr^-1, which markedly surpasses that observed in spring and autumn. Among different land cover types, cropland showed the highest NEP growth rate (0.718 g C m^-2 yr^-1), albeit with considerable seasonal variability. In contrast, forests experienced a decline in growth rate exceeding 50% during summer and autumn, while barren areas consistently functioned as carbon sources. (3) Actual evapotranspiration (Aet) emerged as the most influential positive factor, with an average partial correlation coefficient of 0.279. Potential evapotranspiration (Pet) and temperature (Temp) jointly accounted for 44.118% of the observed NEP variations across IMAR. Meanwhile, the explanatory power of nighttime lights (Ntl) increased by 48.700% over the 41-year study period, underscoring the growing impact of urbanization. (4) The implementation of the Grain for Green Project has resulted in a net forest gain of 14166.890 km²; however, concurrent grassland degradation and the expansion of impervious surfaces have partially offset these gains, thereby weakening the overall regional carbon sequestration potential. The findings of this study establish a scientific foundation for optimizing IMAR's ecological barrier function and its pathway to carbon neutrality.