Does the turgor loss point characterize drought response in dryland plants?

Abstract

The water potential at turgor loss point (Ψ ) has been suggested as a key functional trait for determining plant drought tolerance, because of its close relationship with stomatal closure. Ψ may indicate drought tolerance as plants, which maintain gas exchange at lower midday water potentials as soil water availability declines also have lower Ψ . We evaluated 17 species from seasonally dry habitats, representing a range of life-forms, under well-watered and drought conditions, to determine how Ψ relates to stomatal sensitivity (pre-dawn water potential at stomatal closure: Ψg ) and drought strategy (degree of isohydry or anisohydry; ΔΨ between well-watered conditions and stomatal closure). Although Ψg was related to Ψ , Ψg was better related to drought strategy (ΔΨ ). Drought avoiders (isohydric) closed stomata at water potentials higher than their Ψ ; whereas, drought tolerant (anisohydric) species maintained stomatal conductance at lower water potentials than their Ψ and were more dehydration tolerant. There was no significant relationship between Ψ and ΔΨ . While Ψ has been related to biome water availability, we found that Ψ did not relate strongly to stomatal closure or drought strategy, for either drought avoiders or tolerators. We therefore suggest caution in using Ψ to predict vulnerability to drought.

Tree hydraulic traits are coordinated and strongly linked to climate‐of‐origin across a rainfall gradient

“…However, in the current study, although TLP and P gs90 were significantly correlated, P gs90 was consistently lower than TLP, indicating that stomata remained open even after bulk leaf turgor was lost. A similar observation has been reported for some tree and shrub species (Brodribb et al, ; Farrell et al, ) and is interpreted as a decoupling between guard cell and bulk leaf water potential (Mott & Franks, ). Indeed, stomatal behaviour is governed by numerous biophysical and biochemical (i.e., abscisic acid) factors (Brodribb & Holbrook, ; Brodribb & McAdam, ; Salleo et al, ).…”

Drought survival is positively associated with high turgor loss points in temperate perennial grassland species

“…First, turgor loss can trigger the biosynthesis of abscisic acid, which leads to stomatal closure even at high leaf water potentials (McAdam & Brodribb, ). Positive correlations between π tlp and stomatal closure in woody species (Bartlett, Klein, Jansen, Choat, & Sack, ) as well as in herbaceous species (re‐analysed from Farrell et al, ) support this mechanistic linkage, and indeed the correlation also emerged in our focal species (Sun, Engelbrecht, unpubl. data).…”

“…Turgor loss point measured with traditional P – V curve methods ( π tlp‐ P – V ) was significantly related to osmotic water potential at full turgor assessed with an osmometer ( π o‐osmo ) across all 14 grassland species, and separately within the forbs and grasses measured in our study. Additionally, relations are shown for C 3 and C 4 grasses, grasses and forbs, and herbaceous and woody species combined from this and previous studies (Bartlett, Scoffoni, Ardy, et al, ; Bartlett, Scoffoni, & Sack, ; Griffin‐Nolan et al, ; Gotsch et al, ; Ocheltree et al, ; Farrell et al, ; Májeková et al, ). Relations were significant within each of the species groups (all p < .05, see legend for r 2 values) and slopes did not differ between grasses versus forbs (this study nor combined), C 3 versus C 4 , nor herbaceous versus woody species (all p > .1).…”

“…For example, in C 4 perennial grasses, species with high leaf resistance to hydraulic failure exhibited low π tlp , consistent with woody species (Ocheltree et al, ), but species from drier habitats had higher π tlp than those from wetter habitats, which is opposite to the trend in woody species (re‐analysed from Liu & Osborne, ). In most studies focusing on herbaceous species, π tlp was unrelated to their distributional association with the dryness of habitats (Farrell, Szota, & Arndt, ; Griffin‐Nolan et al, ; Májeková et al, ; Ocheltree et al, ) or biomes (re‐analysed only for herbaceous species from Bartlett, Scoffoni, & Sack, ). In a recent study, π tlp was instead positively correlated with the wet extremes of species distributions (Griffin‐Nolan et al, ), which was attributed to competition from more acquisitive (high‐ π tlp ) species limiting the distribution of low‐ π tlp species into wetter habitats.…”

Climatic limits of temperate rainforest tree species are explained by xylem embolism resistance among angiosperms but not among conifers

“…Given that the climate measures only reflect the average dryness of a region, P50 may perform even better as a predictor of species range limits if local drought measures such as soil water potential could be used instead. Stem P50 consistently exhibits strong relationships with climatic niches of trees (Larter et al , ), but Farrell, Szota, & Arndt () urged caution in using leaf TLP to predict vulnerability to drought. We measured leaf TLP on rehydrated samples from the field and so implicitly treat leaf TLP as a fixed trait.…”