Leaf age and the timing of leaf abscission in two tropical dry forest trees |
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Authors: | Marco V Gutiérrez-Soto Adriana Pacheco N Michele Holbrook |
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Institution: | (1) Estación Experimental Fabio Baudrit, Universidad de Costa Rica, Apartado, 183-4050 Alajuela, Costa Rica;(2) Department of Environmental Engineering, University of Florida, Gainesville, FL 32601, USA;(3) Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA |
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Abstract: | We used experimental defoliations to examine the effect of leaf age on the timing of leaf shedding in two tropical dry forest
trees. Trees of the deciduous Bombacopsis quinata (bombacaceae, a.k.a. Pachira quinata) and the brevi-deciduous Astronium graveolens (anacardiaceae) were manually defoliated for three times during the rainy season. All trees started to produce a new crown
of leaves 2 weeks after defoliation, and continued expanding leaves throughout the rainy season. At the transition to the
dry season, the experimental groups consisted of trees with known differences in maximum leaf age. Defoliations resulted in
declines in stem growth but did not affect the mineral content or water relations of the leaves subsequently produced. There
was no effect of leaf age on the timing of leaf abscission in B. quinata. In A. graveolens, the initiation of leaf shedding followed in rank order, the maximum leaf age of the four treatments, but there was substantial
coherence among treatments in the major period of leaf abscission such that trees completed leaf shedding at the same time.
In the two species, leaf water potential (ΨL) and stomatal conducantce (g
S) declined with the onset of the dry season, reaching minimum values of –0.9 MPa in P. quinata and <–2.0 MPa in A. graveolens. Within each species, leaves of different age exhibited similar ΨL and g
S at the onset of drought, and then decreased at a similar rate as the dry season progressed. Overall, our study suggests that
the environmental factors were more important than leaf age in controlling the timing of leaf shedding. |
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Keywords: | Astronium graveolens Bombacopsis quinata Phenology Tropical dry forest Water relations |
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