The effect of ozone on pine forests in South-Eastern France from 2017 to 2019

In South-Eastern forests of France,risks linked to the effects of tropospheric ozone(O_(3))are real;its annual impact has been observed specifically near the coastline and in high altitude mountains during the period 2017-2019.In this study,the risk assessment of O_(3)pollutant was carried out using two approaches based on forest response indicators such as O_(3)specific foliar visible injury and by stomatal O_(3)flux.Phytotoxic O_(3)dose values(POD_(0))were obtained by the DO_(3)SE model.The model requires hourly O_(3)concentration for POD_(0)calculation.A modified approach that uses measurements from passive samplers(monthly average O_(3)concentration)was tested for the calculation of POD_(0)and test results showed good agreement with the POD_(0)calculated using hourly O_(3)data.In the model input file,the average O_(3)concentration is used for POD_(0),and this could be useful for POD_(0)calculation when the active monitor is limited.In this study,a flux-based assessment provided better correlation with O_(3)specific leaf injury,which is also species-specific.Foliar visible injury in response to O_(3)indicates that Pinus cembra and Pinus halepensis are more affected and therefore more sensitive than Pinus sylvestris.The POD_(0)and stomatal conductance(Gsto)seem to be induced by environmental factors,primarily rainfall and the soil water potential(fSWP).The correlation between the O_(3)flux metric and environmental variables with forest response indicators by Spearman rank test confirms P.cembra as one of the most sensitive species to O_(3).

Testing visible ozone injury within a Light Exposed Sampling Site as a proxy for ozone risk assessment for European forests

Biologically meaningful and cost-effective indicators are needed for assessing and monitoring the impacts of tropospheric ozone(0_(3)) on vegetation and are required in Europe by the National Emission Ceilings Directive(2016).However,a clear understanding on the best suited indicators is missing.The MOTTLES(MOnitoring ozone injury for seTTing new critical LEvelS) project set up a new generation network for 0_(3) monitoring in forest plots in order to:1) estimate the stomatal 0_(3) fluxes(Phytotoxic Ozone Dose above a threshold Y of uptake,PODY);and 2) collect visible foliar 0_(3) injury,both within the forest plot(ITP) and along the Light Exposed Sampling Site(LESS) along the forest edge.Nine forest sites at high 0_(3) risk were selected across Italy over 2017-2019 and significant correlations(p <0.05) were found between the percentage of symptomatic plant species within the LESS,and POD1(PODY,with Y=1 nmol 0_(3) m^(-2) s^(-1)) calculated for mixed forest species(r=0.53)and with the occurrence and severity of visible foliar 0_(3) injury on the dominant species in the plots(r=0.65).A generic flux-based critical level for mixed forest species was derived within the LESS and it was recommended using11 mmol m^(-2) POD1 as the critical level for forest protection against 0_(3) injury,similar to the critical level obtained in the ITP(12 mmol m^(-2) POD1).It was concluded that the frequency of symptomatic plant species within a LESS is a suitable and effective plant-response indicator of phytotoxic 0_(3) levels in forest monitoring.LESS is a non-destructive,less complex and less time-consuming approach compared to the ITP for monitoring foliar 0_(3) injury in the long term.Assessing visible foliar 0_(3) injury in the ITP might only underestimate the 0_(3) risk assessment at individual sites.These results are biologically meaningful and useful to monitoring experts and environmental policy makers.