title: Chronic ozone exposure affects leaf senescence of adult beech trees: a chlorophyll fluorescence approach.
abstract: Accelerated leaf senescence is one of the harmful effects of elevated tropospheric ozone concentrations ([O(3)]) on plants. The number of studies dealing with mature forest trees is scarce however. Therefore, five 66-year-old beech trees (Fagus sylvatica L.) have been exposed to twice-ambient (2xambient) [O(3)] levels by means of a free-air canopy O(3) exposure system. During the sixth year of exposure, the hypothesis of accelerated leaf senescence in 2xambient [O(3)] compared with ambient [O(3)] trees was tested for both sun and shade leaves. Chlorophyll (chl) fluorescence was used to assess the photosynthetic quantum yield, and chl fluorescence images were processed to compare functional leaf homogeneity and the proportion of O(3)-injured leaf area (stipples) under ambient and 2xambient [O(3)] regimes. Based on the analysis of chl fluorescence images, sun leaves of both ambient and 2xambient [O(3)] trees had apparently developed typical necrotic O(3) stipples during high O(3) episodes in summer, while accelerated senescence was only observed with sun leaves of 2xambient [O(3)] trees. This latter effect was indicated along with a faster decrease of photosynthetic quantum yield, but without evidence of changes in non-photochemical quenching. Overall, treatment effects were small and varied among trees. Therefore, compared with ambient [O(3)], the consequence of the observed O(3)-induced accelerated leaf senescence for the carbon budget is likely limited.
authors.affiliation: University of Antwerpen, Campus Drie Eiken, Department of Biology, Research Group of Plant and Vegetation Ecology, Universiteitsplein 1, B-2610 Wilrijk, Belgium. birgit.gielen@ua.ac.be
authors.forename: Birgit
authors.initials: B
authors.lastname: Gielen
authors.forename: Markus
authors.initials: M
authors.lastname: Löw
authors.forename: Gaby
authors.initials: G
authors.lastname: Deckmyn
authors.forename: Ursula
authors.initials: U
authors.lastname: Metzger
authors.forename: Fabrice
authors.initials: F
authors.lastname: Franck
authors.forename: Christian
authors.initials: C
authors.lastname: Heerdt
authors.forename: Rainer
authors.initials: R
authors.lastname: Matyssek
authors.forename: Roland
authors.initials: R
authors.lastname: Valcke
authors.forename: Reinhart
authors.initials: R
authors.lastname: Ceulemans
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects; D002734:Chlorophyll / Q000032:analysis* / Q000378:metabolism; D003624:Darkness; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D029964:Fagus / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D005453:Fluorescence; D010126:Ozone / Q000494:pharmacology*; D017785:Photons; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000187:drug effects / Q000528:radiation effects; D018515:Plant Leaves / Q000187:drug effects* / Q000378:metabolism* / Q000528:radiation effects; D013696:Temperature; D014197:Trees / Q000187:drug effects* / Q000528:radiation effects
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D010126:Ozone