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Drought constraints on leaf gas exchange by Miconia ciliata (Melastomataceae) in the understory of an eastern Amazonian regrowth forest stand¹

²School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, P.O. Box 110760, Gainesville, Florida 32611-0760 USA; ³Department of Botany, College of Liberal Arts and Sciences, University of Florida, P.O. Box 118526, Gainesville, Florida 34002-8526 USA; ⁴Laboratório de Ecofitologia e Propagação de Plantas, Empresa Brasileira de Pesquisa Agropecuária-Amazônia Oriental, Trav. Dr. Enéas Pinheiro S/N-Marco, CX.POSTAL 48, Belém, Pará CEP-66095-100, Brazil

Analyses of the effects of drought stress on Amazonian regrowth stands are lacking. We measured leaf gas exchange and leaf water potential of Miconia ciliata (Melastomataceae) in a dry-season irrigation experiment in 14-yr-old regrowth. In the dry season, irrigated plants maintained significantly higher leaf water potentials, photosynthetic capacity at light saturation (A_max), stomatal conductance (g_s), internal CO₂ concentration (C_i), and lower A_max/g_s than control plants. The degree of dry-season down-regulation of control plant A_max, along with its fast recovery following rain, reveals the importance of occasional dry-season rains to the carbon budget of M. ciliata. During the wet season, we observed higher A_max for control plants than for plants that had been irrigated during the dry season. We hypothesize that reduced drought constraints on photosynthesis of irrigated plants advanced the flowering and fruiting phenology of irrigated plants into the dry season. Flowers and fruits of control plants developed later, during the wet season, potentially stimulating a compensatory reproductive photosynthesis response in nearby leaves. The relative drought intolerance of M. ciliata may be a deciding factor in its ability to survive through the dynamic successional development of the regrowth stand studied.

Key Words: Amazon • compensatory (reproductive) photosynthesis • dry-season irrigation • leaf water potential • Melastomataceae • Miconia ciliata • phenology • secondary forest • tropical forests

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				D. V. Aragao, L. B. Fortini, S. S. Mulkey, D. J. Zarin, M. M. Araujo, and C. J. R. de Carvalho Correlation but no causation between leaf nitrogen and maximum assimilation: the role of drought and reproduction in gas exchange in an understory tropical plant Miconia ciliata (Melastomataceae) Am. J. Botany, March 1, 2005; 92(3): 456 - 461. [Abstract] [Full Text] [PDF]