title: Xylem adjustment of sessile oak at its southern distribution limits.
abstract: Drought is a key limiting factor for tree growth in the Mediterranean Basin. However, the variability in acclimation via xylem traits is largely unknown. We studied tree growth and vessel features of Quercus petraea (Matt.) Lieb. in five marginal stands across southern Europe. Tree-ring width (TRW), mean earlywood vessel area (MVA) and number of earlywood vessels (NV) as well as theoretical hydraulic conductivity (Kh) chronologies were developed for the period 1963-2012. Summer drought signals were consistent among TRW chronologies; however, climatic responses of vessel features differed considerably among sites. At the three xeric sites, previous year's summer drought had a negative effect on MVA and a positive effect on NV. In contrast, at the two mesic sites, current year's spring drought negatively affected NV, while exerting a positive influence on MVA. In both cases, Kh was not altered by this xylem adjustment. All variables revealed identical east-west geographical patterns in growth and anatomical features. Sessile oak copes with drought in different ways: at xeric sites and after unfavourable previous summer conditions more but smaller vessels are built, lowering vulnerability to cavitation, whereas at mesic sites, dry springs partly lead to tree-rings with wider but fewer vessels. The variability of vessel-related features displays a similar geographical dipole in the Mediterranean Basin previously described for tree growth by other studies.
authors.affiliation: Ecoclimatology, Department of Ecology and Ecosystem Management, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising, Germany.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Martínez-Sancho
authors.affiliation: Ecoclimatology, Department of Ecology and Ecosystem Management, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising, Germany.|Departamento de Silvicultura y Gestión de los Sistemas Forestales, CIFOR-INIA, Carretera de la Coruña Km 7,5, 28040, Madrid, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Dorado-Liñán
authors.affiliation: Department 5 Geoarchives, GFZ - German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Heinrich
authors.affiliation: Section 5.2 Climate Dynamics and Landscape Evolution, GFZ - German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Helle
authors.affiliation: Ecoclimatology, Department of Ecology and Ecosystem Management, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising, Germany.|Institute for Advanced Study, Technische Universität München, Lichtenbergstraße 2a, 85748 Garching, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Menzel
mesh_terms: D000064:Acclimatization; D002980:Climate; D055864:Droughts; D005060:Europe; D029963:Quercus / Q000502:physiology*; D052584:Xylem / Q000502:physiology*
keywords: Mediterranean Basin; Quercus petraea; dendroecology; earlywood vessels; quantitative wood anatomy; tree-ring