Soil Hydraulic Constraints on Stomatal Regulation of Plant Gas Exchange

Terrestrial water fluxes are dominated by transpiration, with stomata exerting an important control by regulating transpirational water loss. Transpiration and stomatal conductance are in turn constrained by the hydraulic properties of the soil-plant-atmosphere continuum, thus providing a link between the physics of water flow (soil-plant hydraulics) and the gas exchange between vegetation and atmosphere (via stomatal regulation). In this article, we review the principles of water flow in soil and plants and the links to stomatal responses to decreasing soil water availability. We make use of a soil-plant hydraulic framework to define the physical constraints on transpiration and predict stomatal responses. We then discuss the role of soil-plant hydraulics for different plant water use strategies (i.e. degree of iso/anisohydry) with changing soil hydraulic properties, root hydraulic distribution and xylem vulnerability.