Increases in precipitation or humidity generally enhance the carbon sequestration capacity; however, this phenomenon has not been consistent worldwide. In particular, in water-limited arid and semi-arid regions, it remains uncertain whether additional precipitation can offset the soil moisture depletion induced by continuous vegetation greening, and thus sustain carbon sequestration. Using multi-source remote sensing data, we found that along the aridity gradient, interannual precipitation increased at a rate of 7.7 × 10⁻2 mm yr⁻1, whereas the trend of vegetation carbon sequestration initially rose and then declined, with a reversal occurring in the forest–grassland ecotone. This reversal was primarily attributed to the synergistic and tradeoff effects of soil moisture and precipitation. In arid zones, the concurrent increases in soil moisture and precipitation jointly accelerated carbon sequestration, while in semi-arid regions, soil moisture scarcity reduced the water use efficiency (WUE) of forests and grasslands, offsetting 46% and 24% of the precipitation-induced enhancement in carbon sequestration rates, respectively. Notably, vegetation physiological factors such as WUE and leaf area index (LAI) served as key mediators in the indirect regulation of carbon sequestration rates by external water conditions, with their indirect effects exceeding direct effects by 60%. These findings emphasize that, in order to minimize adverse impacts such as groundwater resource depletion caused by vegetation greening, it is crucial to adopt region-specific planting structure optimization strategies.
Li et al. (Tue,) studied this question.