Leaf physiology does not predict leaf habit; examples from tropical dry forest

Leaf structure and physiology are thought to be closely linked to leaf longevity and leaf habit. Here we com- pare the seasonal variation in leaf hydraulic conductance (kleaf ) and water potential of two evergreen tree species with contrasting leaf life spans, and two species with similar leaf longevity but contrasting leaf habit, one being decidu- ous and the other evergreen. One of the evergreen species, Simarouba glauca, produced relatively short-lived leaves that maintained high hydraulic conductance year round by periodic flushing. The other evergreen species, Quercus oleoides, produced longer-lived leaves with lower kleaf and as a result minimum leaf water potential was much lower than in S. glauca (−2.8 MPa vs −1.6 MPa). Associated with exposure to lower water potentials, Q. oleoides leaves were harder, had a higher modulus of elasticity, and were less vulnerable to cavitation than S. glauca leaves. Both species operate at water potentials capable of inducing 20 (S. glauca) to 50% (Q. oleoides) loss of kleaf during the dry season although no evidence of cumulative losses in kleaf were observed in either species suggesting regular re- pair of embolisms. Leaf longevity in the deciduous species Rhedera trinervis is similar to that of S. glauca, although maximum kleaf was lower. Furthermore, a decline in leaf water potential at the onset of the dry season led to cumu- lative losses in kleaf in R. trinervis that culminated in leaf shedding.