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Leaf Structure and Patterns of Photoinhibition in Two Neotropical Palms in Clearings and Forest Understory During the Dry Season

Jose L. Araus and Kevin P. Hogan
American Journal of Botany
Vol. 81, No. 6 (Jun., 1994), pp. 726-738
Stable URL: http://www.jstor.org/stable/2445651
Page Count: 13
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Leaf Structure and Patterns of Photoinhibition in Two Neotropical Palms in Clearings and Forest Understory During the Dry Season
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Abstract

We studied the leaf structural, water status, and fast fluorescence responses of two palms, Socratea exorrhiza and Scheelea zonensis, under natural dry season conditions in a clearing (high light [HL] palms) and the forest understory (low light [LL] palms) on Barro Colorado Island, Panama. HL-Socratea leaves were more shade-adapted, less xeromorphic, and more strongly affected by drought than HL-Scheelea. Fv/Fm (the ratio of variable to maximum chlorophyll fluorescence) and tfrac12 (the half-rise time of Fm) was lower in HL-leaves of both species, indicating photoinhibition. In HL-Scheelea, the light-induced reduction of Fv/Fm was much less than in HL-Socratea, and Fv/Fm recovered completely overnight. Patterns of relative water content, specific leaf dry weight, stable carbon isotope composition, and leaf conductance suggest that increased drought resistance in Scheelea reduces susceptibility to photoinhibition. An increase in F0 indicated the inactivation of PSII reaction centers in HL-Socratea. The very low chlorophyll a/b ratio and alterations in chloroplast ultrastructure in HL-Socratea are consistent with photoinhibition. Under LL, the species showed no appreciable interspecific differences in chlorophyll fluorescence. Excess light leads to low values of Fv/Fm in HL-plants relative to LL-plants on both leaf surfaces, particularly on the lower surface, due to a decrease of Fm in both surfaces and an increase in F0 of lower surface. For both species, F0 for the lower surfaces of HL-plants was higher and tfrac12 was markedly lower than for the upper surface, as is typical for shade-adapted leaves. Xeromorphic leaf structure may reduce susceptibility to photoinhibition during the dry season. Drought-enhanced photoinhibition could limit the ability of some species to exploit treefall gaps.

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