Several recent studies have focused on quantifying the degree to which plants regulate their leaf water potential as soil water potential declines and/or vapor pressure deficit increases. The end points of the continuum of the regulatory responses are referred to as iso- and anisohydry. Isohydric species maintain their midday leaf water potentials at relatively constant minimum values regardless of soil or atmospheric water status. In contrast, anisohydric species exhibit much less stomatal regulation of leaf water potential. Although considerable progress has been made in characterizing species’ operating ranges along this continuum, previous approaches have required intensive monitoring of leaf water potential and stomatal conductance during prolonged soil drying and can produce inconsistent rankings along the continuum among species. We evaluated and compared several new and previously developed metrics of stomatal regulation of water potential in eight greenhouse-grown woody species representative of a range of vegetation types that include riparian, forest, oak woodland, chaparral and sagebrush scrub. We also evaluated whether easily determined leaf pressure-volume traits such as water potential at turgor loss (TLP) and the osmotic potential at full turgor could serve as useful proxies for stomatal regulation of plant water potential in drying soil.
Results/Conclusions
Two metrics of stomatal control of water potential were strongly correlated (p< 0.004) with TLP and the osmotic potential at full turgor. The first is the slope of the daily range of leaf water potential vs the predawn water potential as the latter declined during increased water stress. The second is a so-called “hydroscape,” which incorporates the range of predawn and daily minimum water potential over which stomata effectively controlled water potential. The area defined by a plant’s hydroscape correlated strongly with the first metric (the slope; p=0.0006), indicating that they would result in similar rankings of species along the continuum of stomatal regulation. The links between the relatively simple to assess metrics described here, stomatal regulation of gas exchange, and the suite of other traits that imparts overall drought tolerance may provide a priori insights into relative roles of mechanisms contributing to drought-induced mortality.