title: Season-dependent and independent responses of Mediterranean scrub to light conditions.
abstract: Semi-arid plant species cope with excess of solar radiation with morphological and physiological adaptations that assure their survival when other abiotic stressors interact. At the leaf level, sun and shade plants may differ in the set of traits that regulate environmental stressors. Here, we evaluated if leaf-level physiological seasonal response of Mediterranean scrub species (Myrtus communis, Halimium halimifolium, Rosmarinus officinalis, and Cistus salvifolius) depended on light availability conditions. We aimed to determine which of these responses prevailed independently of the marked seasonality of Mediterranean climate, to define a leaf-level strategy in the scrub community. Thirty six leaf response variables - involving gas exchange, water status, photosystem II photochemical efficiency, photosynthetic pigments and leaf structure - were seasonally measured in sun exposed and shaded plants under field conditions. Physiological responses showed a common pattern throughout the year, in spite of the marked seasonality of the Mediterranean climate and of species-specific differences in the response to light intensity. Variables related to light use, CO2 assimilation, leaf pigment content, and LMA (leaf mass area) presented differences that were consistent throughout the year, although autumn was the season with greater contrast between sun and shade plants. Our data suggest that in Mediterranean scrub shade plants the lutein pool could have an important role in the photoprotection of the photosynthetic tissues. There was a negative linear correlation between the ratio lutein/total chlorophylls and the majority of leaf level variables. The combined effect of abiotic stress factors (light and drought or light and cold) was variable-specific, in some cases enhancing differences between sun and shade plants, while in others leading to unified strategies in all scrub species.
authors.affiliation: Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain. Electronic address: zunzu@us.es.
authors.forename: María
authors.initials: M
authors.lastname: Zunzunegui
authors.affiliation: Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain.
authors.forename: Mari Cruz
authors.initials: MC
authors.lastname: Díaz-Barradas
authors.affiliation: Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Apartado 1095, 41080 Sevilla, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Jáuregui
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad Sevilla y CSIC, Centro de Investigaciones Científicas Isla de la Cartuja, Avenida de Americo Vespucio 49, 41092 Sevilla, Spain.
authors.forename: Herminia
authors.initials: H
authors.lastname: Rodríguez
authors.affiliation: Department of Plant Ecology, University of Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany.
authors.forename: Leonor
authors.initials: L
authors.lastname: Álvarez-Cansino
mesh_terms: D029758:Cistus / Q000254:growth & development*; D008027:Light; D031651:Myrtus / Q000254:growth & development*; D018515:Plant Leaves / Q000378:metabolism*; D027542:Rosmarinus / Q000254:growth & development*; D012621:Seasons
keywords: Chlorophylls; Lutein; Photochemical efficiency; Photosynthesis rate; Xanthophyll cycle