title: Repeated Summer Drought and Re-watering during the First Growing Year of Oak (Quercus petraea) Delay Autumn Senescence and Bud Burst in the Following Spring.
abstract: Climate change predicts harsher summer droughts for mid-latitudes in Europe. To enhance our understanding of the putative impacts on forest regeneration, we studied the response of oak seedlings (Quercus petraea) to water deficit. Potted seedlings originating from three locally sourced provenances were subjected to two successive drought periods during the first growing season each followed by a plentiful re-watering. Here, we describe survival and phenological responses after the second drought treatment, applying general linear mixed modeling. From the 441 drought treated seedlings 189 subsisted with higher chances of survival among smaller plants and among single plants per pot compared to doubles. Remarkably, survival was independent of the provenance, although relatively more plants had died off in two provenances compared to the third one with mean plant height being higher in one provenance and standard deviation of plant height being higher in the other. Timing of leaf senescence was clearly delayed after the severe drought treatment followed by re-watering, with two seedlings per pot showing a lesser retardation compared to single plants. This delay can be interpreted as a compensation time in which plants recover before entering the subsequent developmental process of leaf senescence, although it renders seedlings more vulnerable to early autumn frosts because of the delayed hardening of the shoots. Onset of bud flush in the subsequent spring still showed a significant but small delay in the drought treated group, independent of the number of seedlings per pot, and can be considered as an after effect of the delayed senescence. In both phenological models significant differences among the three provenances were detected independent from the treatment. The only provenance that is believed to be local of origin, displayed the earliest leaf senescence and the latest flushing, suggesting an adaptation to the local maritime climate. This provenance also displayed the highest standard deviation of plant height, which can be interpreted as an adaptation to variable and unpredictable weather conditions, favoring smaller plants in drought-prone summers and higher plants in more normal growing seasons.
authors.affiliation: Department of Forest Genetic Resources, Research Institute for Nature and Forest Geraardsbergen, Belgium.
authors.forename: Kristine
authors.initials: K
authors.lastname: Vander Mijnsbrugge
authors.affiliation: Department of Forest Genetic Resources, Research Institute for Nature and ForestGeraardsbergen, Belgium; Department of Biometrics and Agricultural Informatics, Corvinus University of BudapestBudapest, Hungary; Department of Forest Reproductive Material and Plantation Management, Institute of Silviculture and Forest Protection, West-Hungarian UniversitySopron, Hungary.
authors.forename: Arion
authors.initials: A
authors.lastname: Turcsán
authors.affiliation: Department of Agro- and Biotechnology, School of Technology, Odisee University College Sint-Niklaas, Belgium.
authors.forename: Jorne
authors.initials: J
authors.lastname: Maes
authors.affiliation: Department of Agro- and Biotechnology, School of Technology, Odisee University College Sint-Niklaas, Belgium.
authors.forename: Nils
authors.initials: N
authors.lastname: Duchêne
authors.affiliation: Department of Agro- and Biotechnology, School of Technology, Odisee University College Sint-Niklaas, Belgium.
authors.forename: Steven
authors.initials: S
authors.lastname: Meeus
authors.affiliation: Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University Ghent, Belgium.
authors.forename: Kathy
authors.initials: K
authors.lastname: Steppe
authors.affiliation: Department of Forest Genetic Resources, Research Institute for Nature and Forest Geraardsbergen, Belgium.
authors.forename: Marijke
authors.initials: M
authors.lastname: Steenackers
keywords: bud burst; drought; general linear mixed models; leaf senescence; oak provenance; re-watering; seedling; survival