It's about time! Leaf minimum conductance determines time to reach critical thresholds for leaf dehydration in a seasonal tropical forest

Leaf minimum conductance (gmin) is important in determining plant responses to drought. However, we do not understand how gmin is related to drought tolerance, and how important it is in determining the time to reach physiological breakpoints during dehydration. In 18 coexisting tropical species we quantified gmin to test relationships with mild, moderate and severe dehydration thresholds associated with tolerance to turgor loss, structural integrity breakdown, and disruption of Photosystem-II function. We tested the relative importance of gmin and thresholds in determining time to reach physiological breakpoints, quantified other hydraulic and functional traits, and used principal component analyses to identify the major axes of trait variation. The significant variation observed in gmin across species was unrelated to thresholds for mild and severe dehydration, and consistently explained variation in time to reach critical levels of dehydration. gmin was negatively related to maximum stomatal conductance, but unrelated to most other functional and hydraulic traits. These results highlight the importance of avoiding dehydration via minimizing gmin, and suggest that avoidance and tolerance to dehydration represent independent strategies for leaves to cope with drought. Thus, integrating gmin with contemporary threshold-based metrics is essential for a more comprehensive understanding of species vulnerability to drought.