MEA (Impact of climate changes on tree winter survival and geographical distribution)

Leader : Dr. Philippe MALAGOLI

Staff

The project of the "Micro-Environment and Tree" (MEA) team aims to study the interactions between the tree physiology, its thermal, luminous or mineral environment and its architecture. More specifically, the targeted biological functions are studied by taking into account as much as possible the fluctuations of the environment. They mainly relate to the acquisition and management of carbon and nitrogen resources and their interactions. The physical variables characterizing the environment are numerous but the team focuses on temperature and more specifically on organ temperature as opposed to air temperature. Indeed, temperature is one of the main factors affecting metabolic activities and functional responses, and integrates the different components of the microclimate. It is therefore a key physical variable that links the environment and the functioning of the plant well.

To achieve this objective, two research axes are targeted:

1. The first concerns the characterization and modeling of functional responses at the scale of organs in relation to their temperature. The aim is to understand the physical processes (heat balance, phase change) that lead to the appearance of extreme temperatures (hot or freezing) and to characterize in these sub-optimal conditions the functional responses (gas exchanges, respiration , nitrogen acquisition, reserve mobilization) of leaves and woody parts. The occurrence of extreme temperatures is generally linked to (transient) unbalances between energy inputs and losses. Particular attention is therefore paid to the characterization of processes in short time (sub-hour) and to the impact of taking into account these transient states, compared to only taking into account stationary states, on physiological responses in the longer term (day, month, year).

2. The second axis aims to explain the spatio-temporal dynamics of these responses in relation to the spatial variability (3D architecture) of the tree and the fluctuations of the environment. More specifically, the objective is to characterize the interactions between functional architecture: resource acquisition (photosynthetic assimilation, nitrogen absorption); resource allocation (growth, reserves, respiration) combining long-distance transport (coupled water/carbon flows); and microclimate at the organ level.

                In order to link these 2 axes, a bottom-up approach (from local to global) which consists in integrating at the scale of the canopy the functional responses at the scale of the organs is privileged. In addition to modelling aspects (RATP, RReShar, organ temperature, ice formation models), the work is also addressed through experimental approaches ranging from architecture measurement (digitizing, terrestrial LiDar) to process (15N labeling, acoustics, biochemical analysis) and environmental (light, temperature, minerals) characterization.

The MEA team addresses its research actions on targeted issues related more specifically to:

-       management of pests and diseases by modifying the architecture and induction of the plant defense system  and predicting their development under a changing climate on well-defined and sufficiently generic pathosystems: Hevea-Corynespora, apple/tavelure, apple/marbled miner.

-       the vulnerability of tree systems to climate change, phenotyping and explanation of tree response mechanisms to extreme temperatures are also targeted, particularly on the cold acclimatization of trees, where we contribute to varietal selection to adapt our production systems to the risk of frost (fall frosts and spring frosts).

-       the vulnerability of cities to climate change (urban heat island) and adaptation levers are addressed through the study of the role of trees according to their physiological states and management (e. g. architectural pipes and types of planting (shading vs. transpiration) on urban thermal climate.