Respuestas fisiológicas a la sequía, de cinco especies de orquídeas epífitas, en dos selvas secas de la península de Yucatán

Abstract

4Autor para la correspondencia: andrade@cicy.mxResumen: El dosel de las selvas secas presenta cambios anuales drásticos de luz y disponibilidad de agua, debido a que la mayoría de los árboles pierde sus hojas durante la temporada de sequía. Las epífi tas que ahí habitan presentan una morfología y fi siología adecuadas para tolerar la escasez de agua y el exceso de luz. Se estudiaron las respuestas fi siológicas de cinco especies de orquí-deas epífi tas en relación con la variación vertical del microambiente y a la estacionalidad en una selva baja caducifolia y en una selva mediana subcaducifolia, durante las temporadas de lluvias, nortes y sequía. Los cambios fi siológicos en las orquídeas fueron debido al efecto de los cambios estacionales en ambas selvas. Las orquídeas mostraron diferentes estrategias de tolerancia a la sequía: las hojas de Encyclia nematocaulon, Cohniella yucatanensis y Laelia rubescens, de la selva baja, mantuvieron su estado hídrico constante durante el año, pero disminuyeron su tasas de fotosíntesis durante la sequía. Aunque el estado hídrico foliar de E. nematocaulon y Lophiaris oerstedii, de la selva mediana, disminuyó durante las sequía, la fotosíntesis no disminuyó en L. oerstedii. Cohniella ascendens no mostró variación fi siológica estacional en sus hojas; se sugiere que esto fue debido a su baja densidad estomática y a la inclinación de las mismas, porque ello evita la perdida de agua y la exposición directa a la radiación. La especie más abundante, E. nematocaulon, mostró reducción foliar y estomas pequeños, lo que le confi rió gran plasticidad morfológica y fi siológica para tolerar la alta radiación y la sequía en ambas selvas. Palabras clave: contenido relativo de agua, fotoinhibición, metabolismo ácido de las crasuláceas, potencial osmótico, selvas secas.Abstract: 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 fi ve 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 signifi cant seasonal physiological variation, arguably due to low stomatal density and tilted leaf orientation, which ...

High-Temperature Tolerance by the Endangered Mexican Mayflower Orchid, Laelia Speciosa

“…Similarly, the quantum yield is reduced for epiphytic orchids from the Yucatán Peninsula during the time of year when the air temperatures are highest [18]. In contrast, high quantum yields can be indicative of growth for some orchids [26].…”

“…The quantum yield (Fv/Fm) was relatively stable for the Mayflower, except for the in-vitro propagated individuals incubated under the highest temperature treatment, which had a substantial reduction in variable fluorescence. Similarly, the quantum yield is reduced for epiphytic orchids from the Yucatán Peninsula during the time of year when the air temperatures are highest [18]. In contrast, high quantum yields can be indicative of growth for some orchids [26].…”

“…On the one hand, the oak forests of central Mexico, to which L. speciosa is restricted, are among the most endangered ecosystems in the country under various climate change scenarios [3,[13][14][15][16]. On the other hand, epiphytes such as the Mayflower are especially exposed to changing environmental factors, such as insolation, changes in temperature, severe and frequent droughts, and even atmospheric pollution [11,12,[17][18][19]. Higher exposure leads to increased risk unless a species is tolerant of stress, but studies of environmental stress tolerance are scant for non-timber species from oak forests.…”

“…Higher exposure leads to increased risk unless a species is tolerant of stress, but studies of environmental stress tolerance are scant for non-timber species from oak forests. Moreover, besides broad biogeographical and morpho-physiological patterns, high-temperature tolerance is unknown for orchids in general [18,20].…”

“…High quantum yields can be indicative of growth for orchids [26]. In contrast, the quantum yield (Fv/Fm) shrinks by half for epiphytic orchids from the Yucatán Peninsula during the dry season, when air temperatures are the highest [18].…”