Rooting for water: Bridging Plant Hydraulics and Ecohydrology to Predict Drought Stress
Forests regulate climate and sustain biodiversity, but their resilience is increasingly threatened by drought-induced hydraulic failure, when xylem water transport is impaired by embolism. A critical but poorly constrained determinant of this risk largely due to limited observations of deep root water uptake is the amount of root-accessible (sub)soil water storage (SR), which governs…
Forests play a crucial role in regulating climate and maintaining biodiversity, but their resilience is increasingly at risk due to drought-induced hydraulic failure. This occurs when xylem water transport is disrupted by embolism within the plant's vascular system. A key factor influencing this risk is the amount of root-accessible soil water storage (SR) in the subsoil, which influences the exchange of water between the land and atmosphere during extended dry periods.
Ecohydrological theory has postulated a delicate equilibrium between soil water storage in the rooting zone, vegetation growth, and drought tolerance, yet this idea has not yet been incorporated into models predicting hydraulic failure. A new, process-based inversion framework has been developed that combines ecohydrological optimality theory with plant hydraulic principles to estimate SR. By utilizing the SurEau plant hydraulic model, researchers have determined the SR value that strikes a balance between the costs associated with soil exploration and the need to avoid hydraulic damage caused by drought.
This methodology was initially applied to a well-monitored Mediterranean Quercus ilex forest, where the inferred SR closely matched independent measurements obtained from neutron probes and eddy covariance systems, and successfully replicated observed drought responses, including changes in leaf water potential and sap flow dynamics.
To further test the approach, it was then scaled up to cover European forests using remotely-sensed data, allowing for the estimation of spatially explicit SR values and associated hydraulic failure risk. Across more than 20 species and sites, the inferred SR and drought stress metrics aligned with field observations and surpassed estimates derived from traditional soil databases or models solely based on remote sensing.
By integrating plant physiology and ecohydrological theory into a scalable inversion framework, this new approach enhances predictions of forest drought risk in the context of climate change.
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