How do severe drought and defoliation alter nitrogen cycle in beech trees?
PI : Catherine Massonnet (UMR 1137 Forest Ecology and Ecophysiology — EEF)
Co-applicants : Bernd Zeller (UR Forest Ecosystem Biogeochemistry — BEF), Pascale Maillard (UMR EEF), Pierre Antoine Chuste (doctorant, UMR EEF), Christian Hossann (PTEF, UMR EEF)
_________________________________________________________________________
Context — The lack of nitrogen can be particularly limiting for growth of forest trees. The future more frequent drought predicted by climatic models suggests difficulties to access water and nutrients in the soil by roots. In this context, the storage of nitrogen in the tree and its remobilization (internal cycle of nitrogen) will be essential for growth and survival.
Objectives — The project aims to characterize the dynamics of the internal cycle of nitrogen during the growing season in various beech populations of Lorraine grown in common garden and subjected to a drastic drought or repeated defoliation. In particular, we will address the following specific objectives: i) Is there a nitrogen threshold in the tree from which survival is questioned; ii) Is there a critical plant water potential threshold for 15N translocation capacity? iii) Will the treatment influence the nitrogen allocation scheme in beech. iv) How will responses to the previous questions vary across beech populations of Lorraine?
Approaches — The dynamics of absorption, assimilation and translocation of nitrogen in beech trees will be investigated and compared between three treatments (control, drought, defoliation) during the growing season (4 dates: May, June, July, September) through stable isotope labelling method using 15N urea applied on the foliage. The last labeling in September will allow following the use of reserves at the following spring in all compartments of the tree (leaves, branches, trunk and fine roots). Genetic variability of dynamic responses to treatments will also be studied by comparing various beech populations of Lorraine grown in common garden.
Expected results and impacts — The results of NitroBeech will improve our understanding of nitrogen cycle under extreme drought and nutrient deficiency and its role in the death of trees. This project will allow also a better knowledge of beech populations performance in Lorraine in response to constraints.
