title: Seasonal variability of foliar photosynthetic and morphological traits and drought impacts in a Mediterranean mixed forest.
abstract: The Mediterranean region is a hot spot of climate change vulnerable to increased droughts and heat waves. Scaling carbon fluxes from leaf to landscape levels is particularly challenging under drought conditions. We aimed to improve the mechanistic understanding of the seasonal acclimation of photosynthesis and morphology in sunlit and shaded leaves of four Mediterranean trees (Quercus ilex L., Pinus halepensis Mill., Arbutus unedo L. and Quercus pubescens Willd.) under natural conditions. Vc,max and Jmax were not constant, and mesophyll conductance was not infinite, as assumed in most terrestrial biosphere models, but varied significantly between seasons, tree species and leaf position. Favourable conditions in winter led to photosynthetic recovery and growth in the evergreens. Under moderate drought, adjustments in the photo/biochemistry and stomatal/mesophyllic diffusion behaviour effectively protected the photosynthetic machineries. Severe drought, however, induced early leaf senescence mostly in A. unedo and Q. pubescens, and significantly increased leaf mass per area in Q. ilex and P. halepensis. Shaded leaves had lower photosynthetic potentials but cushioned negative effects during stress periods. Species-specificity, seasonal variations and leaf position are key factors to explain vegetation responses to abiotic stress and hold great potential to reduce uncertainties in terrestrial biosphere models especially under drought conditions.
authors.affiliation: Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain CREAF, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain dominik@creaf.uab.es.
authors.forename: D
authors.initials: D
authors.lastname: Sperlich
authors.affiliation: Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain CREAF, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain.
authors.forename: C T
authors.initials: CT
authors.lastname: Chang
authors.affiliation: CREAF, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain CSIC, global Ecology Unit CREAF-CSIC-UAB, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Peñuelas
authors.affiliation: Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain CREAF, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Gracia
authors.affiliation: Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain CREAF, Cerdanyola del Vallès, 08193 Barcelona, Catalonia, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Sabaté
mesh_terms: D000064:Acclimatization; D055864:Droughts; D004777:Environment; D029791:Ericaceae / Q000033:anatomy & histology / Q000502:physiology*; D065928:Forests; D010788:Photosynthesis; D028223:Pinus / Q000033:anatomy & histology / Q000502:physiology*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology; D029963:Quercus / Q000033:anatomy & histology / Q000502:physiology*; D012621:Seasons; D013030:Spain; D013045:Species Specificity
keywords: Arbutus unedo; Jmax; Pinus halepensis; Quercus ilex; Quercus pubescens; Vc,max; abiotic stress; leaf position; leaf traits; seasonality