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

The water potential at turgor loss point (Psi(tlp)) has been suggested as a key functional trait for determining plant drought tolerance, because of its close relationship with stomatal closure. Psi(tlp) may indicate drought tolerance as plants, which maintain gas exchange at lower midday water potentials as soil water availability declines also have lower Psi(tlp). We evaluated 17 species from seasonally dry habitats, representing a range of life-forms, under well-watered and drought conditions, to determine how Psi(tlp) relates to stomatal sensitivity (pre-dawn water potential at stomatal closure: Psi g(s0)) and drought strategy (degree of isohydry or anisohydry; Delta Psi(MD) between well-watered conditions and stomatal closure). Although Psi g(s0) was related to Psi(tlp), Psi g(s0) was better related to drought strategy (Delta Psi(MD)). Drought avoiders (isohydric) closed stomata at water potentials higher than their Psi(tlp); whereas, drought tolerant (anisohydric) species maintained stomatal conductance at lower water potentials than their Psi(tlp) and were more dehydration tolerant. There was no significant relationship between Psi(tlp) and Delta Psi(MD). While Psi(tlp) has been related to biome water availability, we found that Psi(tlp) did not relate strongly to stomatal closure or drought strategy, for either drought avoiders or tolerators. We therefore suggest caution in using Psi(tlp) to predict vulnerability to drought.