title: Effects of drought on mesophyll conductance and photosynthetic limitations at different tree canopy layers.
abstract: In recent years, many studies have focused on the limiting role of mesophyll conductance (gm ) to photosynthesis (An ) under water stress, but no studies have examined the effect of drought on gm through the forest canopy. We investigated limitations to An on leaves at different heights in a mixed adult stand of sessile oak (Quercus petraea) and beech (Fagus sylvatica) trees during a moderately dry summer. Moderate drought decreased An of top and lowest beech canopy leaves much more than in leaves located in the mid canopy; whereas in oak, An of the lower canopy was decreased more than in sunlit leaves. The decrease of An was probably not due to leaf-level biochemistry given that VCmax was generally unaffected by drought. The reduction in An was instead associated with reduction in stomatal and mesophyll conductances. Drought-induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought-induced increases in mesophyll limitations were largest in leaves from the lowest canopy. Sensitivity analysis highlighted the need to decompose the canopy into different leaf layers and to incorporate the limitation imposed by gm when assessing the impact of drought on the gas exchange of tree canopies.
authors.affiliation: Unidad Docente de Anatomía, Fisiología y Genética Forestal, E.T.S.I. Montes, Universidad Politécnica de Madrid (UPM), Ciudad Universitaria s/n, 28040, Madrid, Spain.
authors.forename: F Javier
authors.initials: FJ
authors.lastname: Cano
authors.forename: David
authors.initials: D
authors.lastname: Sánchez-Gómez
authors.forename: Jesús
authors.initials: J
authors.lastname: Rodríguez-Calcerrada
authors.forename: Charles R
authors.initials: CR
authors.lastname: Warren
authors.forename: Luis
authors.initials: L
authors.lastname: Gil
authors.forename: Ismael
authors.initials: I
authors.lastname: Aranda
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism; D003681:Dehydration; D055864:Droughts; D029964:Fagus / Q000187:drug effects / Q000502:physiology*; D005453:Fluorescence; D058503:Mesophyll Cells / Q000187:drug effects / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology*; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology; D029963:Quercus / Q000187:drug effects / Q000502:physiology*; D011891:Rain; D012044:Regression Analysis; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000187:drug effects / Q000502:physiology*; D055548:Vapor Pressure; D014867:Water
chemical_list: D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D009584:Nitrogen
keywords: beech; chlorophyll fluorescence; drought; process-based models; sensitivity analysis; sessile oak; tree canopy layers; δ13C