Vegetation productivity responses to increased atmospheric vapor pressure deficit across the globe

Atmospheric vapor pressure deficit (VPD) has been identified as a key factor influencing vegetation productivity, with spatially divergent positive and negative effects observed across global ecosystems. However, the mechanisms underlying these heterogeneous responses remain insufficiently understood.

Here, we integrated long-term global satellite observations with multiple statistical approaches to investigate the drivers of divergent vegetation responses to VPD. We examined the responses of leaf area index (LAI) and evapotranspiration (ET) to VPD along spatial gradients of soil and atmospheric water availability, and further explored the roles of plant water-use strategies and atmospheric moisture conditions using mediation analyses.

Our results showed that vegetation responses of LAI and ET to VPD varied significantly along gradients of soil water content (SWC) and relative humidity (RH). When SWC and RH increased beyond critical thresholds, vegetation responses to VPD shifted from negative to positive for both LAI and ET. These transition patterns were closely associated with spatial variations in plant water-use strategies. Mediation analyses further revealed that changes in ET responses to VPD, jointly regulated by SWC and plant water-use strategies, were associated with variations in atmospheric moisture conditions, which in turn influenced vegetation responses to VPD. Specifically, in water-limited regions, conservative plant water-use strategies and low soil moisture were associated with reduced ET responses under increasing VPD, potentially contributing to lower atmospheric humidity and constrained vegetation productivity. In contrast, in water-rich regions, higher soil moisture and more water-intensive strategies were associated with positive ET responses to VPD, which may help maintain relatively humid atmospheric conditions and less constrained vegetation productivity.

Overall, we propose an integrated observational framework to reconcile spatially divergent vegetation responses to VPD, highlighting the importance of soil water availability, atmospheric moisture conditions, and plant water-use strategies in regulating vegetation-climate interactions. These findings may improve our understanding of ecosystem responses to ongoing climate change.