MEA Team

The Micro-Environment and Tree (MEA) team's project aims to study the interactions between tree functioning, its thermal, light and mineral environment, and its architecture. More specifically, the biological functions studied take into account environmental fluctuations as much as possible. They mainly relate to the acquisition and management of carbon and nitrogen resources and their interactions. There are many physical variables that characterise the environment, but the team focuses on temperature, and more specifically on organ temperature as opposed to air temperature. Temperature is one of the main factors affecting metabolic activities and functional responses, and it integrates the various components of the microclimate. It is therefore a key physical variable that effectively links the environment and plant functioning.

To achieve this objective, two areas of research are targeted:

1. The first concerns the characterisation and modelling of functional responses at the organ level in relation to their temperature. The aim is to understand the physical processes (heat balance, phase change) that lead to the occurrence of extreme temperatures (hot or freezing) and to characterise the functional responses (gas exchange, photosynthesis, respiration, water flow, nitrogen acquisition, mobilisation of reserves) of leaves and woody parts under these suboptimal conditions. The occurrence of extreme temperatures is generally linked to (transient) imbalances between energy inputs and losses. Particular attention is therefore paid to characterising short-term processes (sub-hourly) and to the impact of taking these transient states into account, as opposed to only considering steady states, on longer-term physiological responses (day, month, year).

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

In order to link these two axes, a bottom-up approach (from local to global) is favoured, which consists of integrating functional responses at the organ level into the canopy level. In addition to modelling aspects (RATP, RReShar, organ temperature, ice formation models), the work also involves experimental approaches ranging from architectural measurement (digitisation, terrestrial LiDar) to process characterisation (15N labelling, acoustics, biochemical analysis) and environmental characterisation (light, temperature, minerals).

The MEA team focuses its research activities on specific issues relating more specifically to:

- pest management through modification of plant architecture and induction of plant defence systems (PDS), and prediction of their development in a changing climate on well-defined and sufficiently generic pathosystems: Hevea-Corynespora, apple tree/scab, apple tree/marbled leaf miner.

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

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