Ecology Letters (2012) 15: 393–405
Increasing drought is one of the most critical challenges facing species and ecosystems worldwide, and improved theory and practices are needed for quantification of species tolerances. Leaf water potential at turgor loss, or wilting (πtlp), is classically recognised as a major physiological determinant of plant water stress response. However, the cellular basis of πtlp and its importance for predicting ecological drought tolerance have been controversial. A meta-analysis of 317 species from 72 studies showed that πtlp was strongly correlated with water availability within and across biomes, indicating power for anticipating drought responses. We derived new equations giving both πtlp and relative water content at turgor loss point (RWCtlp) as explicit functions of osmotic potential at full turgor (πo) and bulk modulus of elasticity (ε). Sensitivity analyses and meta-analyses showed that πo is the major driver of πtlp. In contrast, ε plays no direct role in driving drought tolerance within or across species, but sclerophylly and elastic adjustments act to maintain RWCtlp, preventing cell dehydration, and additionally protect against nutrient, mechanical and herbivory stresses independent of drought tolerance. These findings clarify biogeographic trends and the underlying basis of drought tolerance parameters with applications in comparative assessments of species and ecosystems worldwide.