How is carbon storage in plateau–plain transition zone influenced? Evidence from Minjiang River Basin, China

Topographic transition zones are vital for global carbon storage and are sensitive to climate change, playing a key role in achieving global carbon neutrality goals. However, previous studies have not adequately addressed the characteristics of these zones from a comprehensive macroscopic perspective. To fill this gap, this study examines the Minjiang River Basin (MRB), which exemplifies a typical plateau–plain transition zone, dividing it into three areas: upstream, midstream, and downstream. Carbon density values were estimated based on land use and soil attribute data from 2000 to 2020, and the spatiotemporal distribution and changes in carbon storage were analyzed using the Integrated Valuation of Ecosystem Services and Trade-offs model along with Standard Deviation Ellipse Analysis. Sixteen natural economic indicators from 52 districts and counties were selected to construct a geographically and temporally weighted regression model, exploring the spatiotemporal heterogeneity of influencing factors across the basin. The results revealed the following: (1) From 2000 to 2020, total carbon storage in the MRB decreased by 5.563×10⁶ t, with the midstream region accounting for 83.93% of this decline. (2) The dominant factors influencing carbon storage were nighttime light (NL) and relative humidity, with average influence intensities of -0.181 and 0.111, respectively. (3) Influencing factors exhibited significant spatiotemporal heterogeneity; the upstream area was most adversely affected by NL, with a maximum regression coefficient of -3.29. In contrast, the midstream and downstream areas experienced relatively weak influences, primarily from the positive effects of annual production value in the primary industry and soil pH, which had maximum regression coefficients of 0.437 and 0.747, respectively. These findings provide robust data for assessing regional carbon sequestration capacity in the MRB and offer a theoretical basis for conducting ecological protection and managing human activities in areas with complex terrain.