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

The water potential at turgor loss point (Ψ_tlp ) has been suggested as a key functional trait for determining plant drought tolerance, because of its close relationship with stomatal closure. Ψ_tlp may indicate drought tolerance as plants, which maintain gas exchange at lower midday water potentials as soil water availability declines also have lower Ψ_tlp . We evaluated 17 species from seasonally dry habitats, representing a range of life-forms, under well-watered and drought conditions, to determine how Ψ_tlp relates to stomatal sensitivity (pre-dawn water potential at stomatal closure: Ψg_s0 ) and drought strategy (degree of isohydry or anisohydry; ΔΨ_MD between well-watered conditions and stomatal closure). Although Ψg_s0 was related to Ψ_tlp , Ψg_s0 was better related to drought strategy (ΔΨ_MD ). Drought avoiders (isohydric) closed stomata at water potentials higher than their Ψ_tlp ; whereas, drought tolerant (anisohydric) species maintained stomatal conductance at lower water potentials than their Ψ_tlp and were more dehydration tolerant. There was no significant relationship between Ψ_tlp and ΔΨ_MD . While Ψ_tlp has been related to biome water availability, we found that Ψ_tlp did not relate strongly to stomatal closure or drought strategy, for either drought avoiders or tolerators. We therefore suggest caution in using Ψ_tlp to predict vulnerability to drought.