Regolith water storage patterns determine vegetation productivity in global karst regions

Although the distribution of vegetation productivity is largely determined by temperature and precipitation variations, the influence of the substrate condition still requires further exploration, especially in karst regions characterized by extremely shallow soil underlain by weathered bedrock. In this study, we find that the regolith in karst landscapes can behave much like soil layer in many other terrestrial landscapes and the contribution of bedrock lithology to GPP by affecting water availability is significant, but dominant chemical elements have inconsistent impacts across the selected karst regions worldwide. In karst landscapes with tropical (Savannah, Aw) and temperate (without dry season, Cf) climates, more than 80% of the grids show a significant positive correlation between available water for plants and precipitation supply, and calcium-rich areas with lower average root length tend to form higher GPP. Conversely, in karst landscapes with arid (Steppe, Bs) and temperate (Dry winter, Cw) climates, more than 70% of the grids show decoupled water availability for plants from variability of precipitation, and silicon-rich regions with deeper average root lengths contribute to higher vegetation productivity. Instead of climate regimes, the effect of bedrock lithology on vegetation productivity is mediated by how precipitation is stored and released to plants. Our results highlight that the critical role of bedrock lithology-related water storage should not be ignored in the Earth system models.

Automated summary

Although temperature and precipitation variations largely determine the distribution of vegetation productivity, the influence of substrate condition, especially in karst regions, still needs further exploration. The regolith in karst landscapes behaves similarly to soil layer in other terrestrial landscapes and bedrock lithology significantly affects water availability, but the impacts of dominant chemical elements vary across karst regions worldwide. The effect of bedrock lithology on vegetation productivity is mediated by water storage and release to plants, not solely determined by climate regimes. Understanding the critical role of bedrock lithology-related water storage is important for Earth system models.