Abstract

ROSA-MANZANO, Edilia de la; ANDRADE, José Luis; ZOTZ, Gerhard  and  REYES-GARCIA, Casandra. Physiological responses to drought of five epiphytic orchid species from two tropical dry forests of the Yucatan Peninsula. Bot. sci [online]. 2014, vol.92, n.4, pp.607-616. ISSN 2007-4476.

Dry forest canopies exhibit drastic changes of light and water availability throughout the year, because most trees drop their leaves during the dry season. Epiphytes that inhabit there show a suit of morphological and physiological traits to tolerate water scarcity and light excess. We studied the physiological responses of five epiphyte orchid species in relation to their vertical microenvironment and the seasonality in a deciduous tropical forest and a semi-deciduous tropical forest, during the wet, early dry and dry seasons. Physiological variation of orchids was mainly seasonal in both forests. Orchids showed different strategies to cope with drought: Encyclia nematocaulon, Cohniella yucatanensis and Laelia rubescens from the deciduous forest maintained their leaf water status constant throughout the year, with reduced photosynthetic rates during the dry season. Although the leaf water status of both, E. nematocaulon and Lophiaris oerstedii from the semi-deciduous forest, diminished during the dry season, photosynthesis did not decline in L. oerstedii. Leaves of Cohniella ascendens did not show significant seasonal physiological variation, arguably due to low stomatal density and tilted leaf orientation, which reduced water loss and exposure to high radiation. The most abundant species, E. nematocaulon, showed small stomata, reduced leaf area and morphological and physiological plasticity to tolerate high radiation and drought in both forests.

Keywords : crassulacean acid metabolism; dry forests; osmotic potential; photoinhibition; relative water content.

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