Presentation
The urban vegetation is often considered for its ecosystem benefits alone. However, it is a potential source of pollutants due to its emissions of biogenic volatile organic compounds (BVOCs). Their complex regulation, especially in response to water stress, remains poorly understood in urban environments.
The project sTREEt funded by the French ANR (Oct. 2019-Apr. 2024) combined experimentations and modelling with the aim to (i) analyse interactions between abiotic urban factors, plant physiology and BVOC emissions, (ii) model how urban tree work, and (iii) integrate those results into air quality modelling.
Young plane trees (Platanus x hispanica) in pots in a urban environment (Vitry-sur-Seine, in the southern surburbs of Paris), submitted or not to dryness, have been studied at the leave and/or branch scale. Environmental and ecophysiological parameters, biochemical stress indicators, and BVOC emissions have been characterised in spring-summer from 2020 to 2022. During summer 2022, the gazeous and particulate phases of urban air have been monitored in situ at the Jardin des Combattants de la Nueve (Hôtel de Ville, Paris), a site under the joint influence of a summer source of BVOCs and of an intense urban traffic.
These experimental data, among others, allowed us to test and develop a model of the hydric functioning of the urban tree, as well as air quality models at the regional and the street scales.
Major Results
Isoprene emissions of the plane tree present an important variability, both seasonal and intra-branch. During drought, they are not related to CO2 assimilation, but rather to the management of the light energy. Plane tree beneficial services (e.g. shading, transpiration) decrease after a severe drought, together with isoprene emissions.
A model experiment shows that during a heat wave in Paris, the presence of trees contributes to an increase of 2.4% in ozone, and 5.4% in urban secondary organic aerosols.
Coordination
Juliette Leymarie, UMR 7618, Institut d’écologie et des sciences de l’environnement de Paris (IESS), Université Paris Est Créteil Val-de-Marne – Paris 12
Partnership
- UMR 1402, Ecologie fonctionnelle et écotoxicologie des agroécosystèmes (EcoSys), INRAE
- UMR 8212, Laboratoire des Sciences du Climat et de l’Environnement (LSCE), CNRS
- Centre d’Enseignement et de Recherche en Environnement Atmosphérique (CEREA), Ecole Nationale des Ponts et Chaussées
- Mairie de Paris – Direction des Espaces Verts et de l’Environnement
Contact CAE : Christophe Boissard