Southern forests are at the highest ozone (O3) risk in Europe where ground-level O3is a pressing sanitary problem for ecosystem health. Exposure-based standards for protecting vegetation are not representative of actual field conditions. A biologically-sound stomatal flux-based standard has been proposed, although critical levels for protection still need to be validated. This innovative epidemiological assessment of forest responses to O3was carried out in 54 plots in Southeastern France and Northwestern Italy in 2012 and 2013. Three O3indices, namely the accumulated exposure AOT40, and the accumulated stomatal flux with and without an hourly threshold of uptake (POD1 and POD0) were compared. Stomatal O3fluxes were modeled (DO3SE) and correlated to measured forest-response indicators, i.e. crown defoliation, crown discoloration and visible foliar O3injury. Soil water content, a key variable affecting the severity of visible foliar O3injury, was included in DO3SE. Based on flux-effect relationships, we developed species-specific flux-based critical levels (CLef) for forest protection against visible O3injury. For O3sensitive conifers, CLef of 19mmolm-2for Pinus cembra (high O3sensitivity) and 32mmolm-2for Pinus halepensis (moderate O3sensitivity) were calculated. For broadleaved species, we obtained a CLef of 25mmolm-2for Fagus sylvatica (moderate O3sensitivity) and of 19mmolm-2for Fraxinus excelsior (high O3sensitivity). We showed that an assessment based on PODY and on real plant symptoms is more appropriated than the concentration-based method. Indeed, POD0 was better correlated with visible foliar O3injury than AOT40, whereas AOT40 was better correlated with crown discoloration and defoliation (aspecific indicators). To avoid an underestimation of the real O3uptake, we recommend the use of POD0 calculated for hours with a non-null global radiation over the 24-h O3accumulation window.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Environmental Chemistry
- Waste Management and Disposal
Sicard, P., De Marco, A., Dalstein-Richier, L., Tagliaferro, F., Renou, C., & Paoletti, E. (2016). An epidemiological assessment of stomatal ozone flux-based critical levels for visible ozone injury in Southern European forests. Science of the Total Environment, 541, 729 - 741. https://doi.org/10.1016/j.scitotenv.2015.09.113