Sacrificing growth and maintaining a dynamic carbohydrate storage are key processes for promoting beech survival under prolonged drought conditions
In case of a prolonged drought, the stored carbohydrates in trees were remobilized to fuel survival functions until their nearly depletion at death stage.
Dynamic global vegetation models project forest tree mortality in response to the recurrent severe droughts likely in the future. However, these models should better take into account the physiological processes involved in tree mortality. Faced with severe drought, the Fagus sylvatica L. tree strongly limits its cambial growth. This suggests that readjustments in carbon (C) allocation among sink functions are taking place in response to the lack of water and this could allow tree’s survival. For 3 years, we induced a water shortage on 8-year-old beech trees in a rain exclusion system. During this period, we analysed the consequences of severe drought on survival rate, growth, and non-structural carbohydrate (NSC) dynamics in the aboveground and belowground compartments of control, water-stressed living, and dead trees. The survival rate after 3 years of drought was 87%, while primary and secondary growth was strongly reduced. The first 2 years, NSC concentrations increased in all tree compartments (stem, branches, and roots) in response to drought. However, during the third year, starch dropped markedly in water-stressed trees, while soluble sugar concentrations remained similar to control trees. All the compartments in dead trees were virtually empty of starch and soluble sugars. Maintaining an active C storage function at the expense of growth was certainly key to F. sylvatica survival under prolonged extreme drought conditions. Process-based models predicting mortality should better take into account C storage and remobilization processes in forest trees.
KeywordsCarbon allocation Carbon starvation Fagus sylvatica L. Mortality Non-structural carbohydrates (NSC) Storage
PA Chuste received a PhD grant from the Laboratory of Excellence ARBRE. The experiment and operating costs were funded by the French National Research Agency (ANR), (“Investissements d’Avenir” program [ANR-11-LABX-0002-01, Laboratory of Excellence ARBRE] within the framework of the Mepib-Death multidisciplinary project) and the Lorraine Region Project [Survival, contract n°12000453]. The authors thank Thierry Paul for the oversight of the roof construction and his help in growth measurements, François Gérémia for his help with sampling and measurements, Lynda Si Ouali and Elisé Bonkoungou for their help in the NSC analysis. The authors thank Bastien Gérard SILVATECH, ISC from UMR 1434 SILVA, 1136 IAM, 1138 BEF, 4370 EA LERMAB research center INRA Nancy-Lorraine for its contribution to NSC analyses and for the welcome and training of students. SILVATECH facility is supported by the French National Research Agency through the Laboratory of Excellence ARBRE (ANR-11-LABX-0002-01).
Author contribution statement
This project was conceived by CM, PM, and NB, principal investigator of the project. Sampling and analyses were designed and carried out by PAC with help from CM, PM, ET, RW, and JL with guidance from CM and PM, and with contributions from NB. CM, PAC, PM, and NB led the manuscript writing. All co-authors contributed ideas and helped edit the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interests.
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