Critical soil moisture thresholds of plant water stress in terrestrial ecosystems.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 36332021.
- Also identified by DOI 10.1126/sciadv.abq7827 and PMC identifier 9635832.
- Licence recorded as CC BY-NC.
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Abstract
Plant water stress occurs at the point when soil moisture (SM) limits transpiration, defining a critical SM threshold (θ<sub>crit</sub>). Knowledge of the spatial distribution of θ<sub>crit</sub> is crucial for future projections of climate and water resources. Here, we use global eddy covariance observations to quantify θ<sub>crit</sub> and evaporative fraction (EF) regimes. Three canonical variables describe how EF is controlled by SM: the maximum EF (EF<sub>max</sub>), θ<sub>crit</sub>, and slope (S) between EF and SM. We find systematic differences of these three variables across biomes. Variation in θ<sub>crit</sub>, S, and EF<sub>max</sub> is mostly explained by soil texture, vapor pressure deficit, and precipitation, respectively, as well as vegetation structure. Dryland ecosystems tend to operate at low θ<sub>crit</sub> and show adaptation to water deficits. The negative relationship between θ<sub>crit</sub> and S indicates that dryland ecosystems minimize θ<sub>crit</sub> through mechanisms of sustained SM extraction and transport by xylem. Our results further suggest an optimal adaptation of local EF-SM response that maximizes growing-season evapotranspiration and photosynthesis.