title: Photoprotection related to xanthophyll cycle pigments in epiphytic orchids acclimated at different light microenvironments in two tropical dry forests of the Yucatan Peninsula, Mexico.
abstract: Epiphytic orchids from dry forests of Yucatán show considerable photoprotective plasticity during the dry season, which depends on leaf morphology and host tree deciduousness. Nocturnal retention of antheraxanthin and zeaxanthin was detected for the first time in epiphytic orchids. In tropical dry forests, epiphytes experience dramatic changes in light intensity: photosynthetic photon flux density may be up to an order of magnitude higher in the dry season compared to the wet season. To address the seasonal changes of xanthophyll cycle (XC) pigments and photosynthesis that occur throughout the year, leaves of five epiphytic orchid species were studied during the early dry, dry and wet seasons in a deciduous and a semi-deciduous tropical forests at two vertical strata on the host trees (3.5 and 1.5 m height). Differences in XC pigment concentrations and photosynthesis (maximum quantum efficiency of photosystem II; F v/F m) were larger among seasons than between vertical strata in both forests. Antheraxanthin and zeaxanthin retention reflected the stressful conditions of the epiphytic microhabitat, and it is described here in epiphytes for the first time. During the dry season, both XC pigment concentrations and photosystem II heat dissipation of absorbed energy increased in orchids in the deciduous forest, while F v/F m and nocturnal acidification (ΔH(+)) decreased, clearly as a response to excessive light and drought. Concentrations of XC pigments were higher than those in orchids with similar leaf shape in semi-deciduous forest. There, only Encyclia nematocaulon and Lophiaris oerstedii showed somewhat reduced F v/F m. No changes in ΔH(+) and F v/F m were detected in Cohniella ascendens throughout the year. This species, which commonly grows in forests with less open canopies, showed leaf tilting that diminished light interception. Light conditions in the uppermost parts of the canopy probably limit the distribution of epiphytic orchids and the retention of zeaxanthin can help to cope with light and drought stress in these forests during the dry season.
authors: Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A. C., Calle 43 Núm. 130, Colonia Chuburná de Hidalgo, 97200, Mérida, Yucatán, Mexico.|Instituto de Ecología Aplicada, Universidad Autónoma de Tamaulipas, Av. División del Golfo Núm. 356, Colonia Libertad, 87091, Ciudad Victoria, Tamaulipas, Mexico.
authors: Edilia
authors: E
authors: de la Rosa-Manzano
authors: Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A. C., Calle 43 Núm. 130, Colonia Chuburná de Hidalgo, 97200, Mérida, Yucatán, Mexico. andrade@cicy.mx.
authors: José Luis
authors: http://orcid.org/0000-0002-4991-5020
authors: JL
authors: Andrade
authors: Departamento de Oceanografía Biológica, Centro de Investigación Científica y de Educación Superior de Ensenada, Km. 107 Carretera Tijuana-Ensenada, 22860, Ensenada, Baja California, Mexico.
authors: Ernesto
authors: E
authors: García-Mendoza
authors: Functional Ecology Group, Institute of Biology and Environmental Sciences, University of Oldenburg, Box 2503, 26111, Oldenburg, Germany.
authors: Gerhard
authors: G
authors: Zotz
authors: Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, A. C., Calle 43 Núm. 130, Colonia Chuburná de Hidalgo, 97200, Mérida, Yucatán, Mexico.
authors: Casandra
authors: C
authors: Reyes-García
mesh_terms: D065928:Forests; D008027:Light; D008800:Mexico; D029595:Orchidaceae / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000528:radiation effects; D018515:Plant Leaves / Q000033:anatomy & histology / Q000378:metabolism* / Q000528:radiation effects; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D024341:Xanthophylls
keywords: Carotenoids; Leaf morphology; Photoinhibition; Photosynthesis; Photosystem II heat dissipation; Xanthophyll cycle