Changes with Leaf Age in Stomatal Function and Water Status of Several Tropical Tree Species

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Abstract
Changes with leaf age in diffusive resistance (r1) and xylem pressure potential (Pp) were monitored in leaves of five tropical tree species. In all species, very young, expanding leaves had high r1 and Pp in situ and wilted soon after being excised. Among fully expanded leaves, stomatal control declined with increasing age, especially in the deciduous species. In Tabebuia rosea, intact older leaves had lower r1 and greater water deficits than younger leaves. In T. rosea and Cordia glabra, excised older leaves had higher transpiration rates and wilted sooner than younger leaves. Also, old T. rosea (but not C. glabra) leaves had lower r1 at night than younger leaves. In Licania arborea, Anacardium excelsium, and Mangifera indica, intact older leaves had higher r1 and a smaller range of r1 than younger leaves and displayed less stomatal closure following excision. The observed differences in water relations between species were related to their ecological characteristics. M. indica and L. arborea leaves had the most sensitive stomatal response and the best control of water loss, even when detached. Trees of these two species remained evergreen and continued to grow even during seasonal drought. In contrast, stomatal control of water loss was poorest in T. rosea, which is leafless 4 to 6 months each year. Considering the generally long life span of tropical tree leaves, age-related changes in stomatal behavior and differences between species could have importance ecological implications.

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