Tree Species Interactions under Soil Drought Conditions
PI : Damien Bonal (UR 1137 Joint Research Unit for Forest Ecology and Ecophysiology — EEF)
Co-applicants : M. Schaub (Forest, Snow and Landscape Research — WSL, Switzerland)
MB. Bogeat-Triboulot, N. Angeli, D. Epron, A. Fruleux (PhD student) — EEF
B. Moser, A. Gessler, L. Schönbeck (PhD student) — WSL
Context — Extreme events induced by climate change will have drastic consequences on forest functions and services and may lead to more drought-induced die-off events. It is well known that biodiversity can promote forest ecosystem productivity and resistance to insect pests and diseases, both being expected to increase with climate change. Furthermore, depending on local environmental conditions and species composition, it has been demonstrated that mixed species forests can be, but are not necessarily, more resistant to drought stress than pure stands.
Objectives — In this project, we propose to further develop the collaboration between WSL and INRA [A. Gessler and D. Bonal] and to establish an extended framework for a longer-term collaboration between WSL, INRA, and University of Lorraine on tree ecophysiology, forest ecology and tree species interactions under soil drought conditions. The main objective of the present project is to characterize the soil water uptake dynamics and carbon allocation patterns of tree seedlings growing under different species interaction conditions and different soil water regimes (drought vs. well-watered) thus strongly extending and complementing on-going work at INRA and WSL.
Approaches — To address the mechanisms leading to diversity and interaction effects, we plan to assess above- and be-low-ground biomass allocation, characterize photosynthetic activity and water use efficiency on Pine and Oak seedlings to be grown in mesocosms under controlled greenhouse conditions at INRA in 2015-2016. Moreover, we will conduct a double labelling experiment (13C in ambient CO2 and 2H for water) to assess the ability of plants to partition new assimilates and exploit soil water resources when exposed to varying water availability and interaction. Complementing the main experiment in Nancy, C-allocation (13C pulse labelling) will be characterised under different drought intensities (gradient of soil water content) in Pine and Oak monocultures in an experimental set-up at WSL.
Expected results and impacts — Such experiments under controlled conditions in mesocosms are essential for characterising mechanisms for biodiversity effects previously observed in the field, to assessing tipping points for carbon allocation in drought intensity gradients, and will constitute a solid basis for the next step, i.e. a joint ANR/SNF project, to transfer the respective mechanisms to field settings in Switzerland and France (mature plantations or forests).