title: Leaf physiological responses to extreme droughts in Mediterranean Quercus ilex forest.
abstract: Global climate change is expected to result in more frequent and intense droughts in the Mediterranean region. To understand forest response to severe drought, we used a mobile rainfall shelter to examine the impact of spring and autumn rainfall exclusion on stomatal (S(L) ) and non-stomatal (NS(L) ) limitations of photosynthesis in a Quercus ilex ecosystem. Spring rainfall exclusion, carried out during increasing atmospheric demand and leaf development, had a larger impact on photosynthesis than autumn exclusion, conducted at a time of mature foliage and decreasing vapour pressure deficit. The relative importance of NS(L) increased with drought intensity. S(L) and NS(L) were equal once total limitation (T(L) ) reached 60%, but NS(L) greatly exceeded S(L) during severe drought, with 76% NS(L) partitioned equally between mesophyll conductance (MC(L) ) and biochemical (B(L) ) limitations when T(L) reached 100%. Rainfall exclusion altered the relationship between leaf water potential and photosynthesis. In response to severe mid-summer drought stress, A(n) and V(cmax) were 75% and 72% lower in the spring exclusion plot than in the control plot at the same pre-dawn leaf water potential. Our results revealed changes in the relationship between photosynthetic parameters and water stress that are not currently included in drought parameterizations for modelling applications.
authors.affiliation: DREAM, CEFE, CNRS, UMR 5175, 1919 route de Mende, F-34293 Montpellier, Cedex 5, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Misson
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Limousin
authors.forename: Raquel
authors.initials: R
authors.lastname: Rodriguez
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Letts
mesh_terms: D055864:Droughts; D017753:Ecosystem; D005602:France; D019083:Mediterranean Region; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology*; D054046:Plant Stomata / Q000502:physiology; D029963:Quercus / Q000502:physiology*; D012621:Seasons; D014197:Trees / Q000502:physiology; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water