Summary

In the past several decades, field studies have shown that woody plants can access substantial volumes of water from the pores and fractures of bedrock. If, like soil moisture, bedrock water storage serves as an important source of plant-available water, then conceptual paradigms regarding water and carbon cycling may need to be revised to incorporate bedrock properties and processes. Here we present a lower-bound estimate of the contribution of bedrock water storage to transpiration across the continental United States (CONUS) using distributed, publicly available datasets. We find:

• Temporal and spatial patterns of bedrock water use across the CONUS indicate that woody plants extensively access bedrock water for transpiration.
• Plants across diverse climates and biomes access bedrock water routinely and not just during extreme drought conditions.
• On an annual basis in California, the volumes of bedrock water transpiration exceed the volumes of water stored in human-made reservoirs, and woody vegetation that accesses bedrock water accounts for over 50% of the aboveground carbon stocks in the state.
• Plants commonly access rock moisture, as opposed to groundwater, from bedrock and that like soil moisture, rock moisture is a critical component of terrestrial water and carbon cycling.