Bridging experimental and monitoring research for visible foliar injury as bio-indicator of ozone impacts on forests

Tropospheric ozone(O_(3))is a phytotoxic air pollutant and the O_(3)-induced visible foliar injury(O_(3)VFI)is a biomarker.A recently developed Free-air O_(3)eXposure(FO_(3)X)is a promising facility to verify field-observed“O_(3)-like”VFIs and to establish a flux-based threshold for the O_(3)VFI onset.The present study compared O_(3)-like VFI registered in the southern European forest sites with actual O_(3)VFI observed in a FO_(3)X experiment.The O_(3)-like VFIs were evaluated by eye in forests and thus it was subjective.According to the imaging analysis,we firstly demonstrated that major parts of the colors were similar in the field and the FO_(3)X.The color pallets for O_(3)VFI was species-specific and considered a advanced tool for the O_(3)VFI diagnosis.In addition,we calculated a flux-based threshold for the O_(3)VFI onset at the FO_(3)X based on a Phytotoxic Ozone Dose(POD_(1)),which ranged from 4.9 to 18.1 mmol m^(-2)POD1.This FO_(3)X-derived threshold partly explained but did not necessarily match with the observation for several tree species in actual forests.The multivariate analysis showed that O_(3)VFI was decreased by the presence of various species and suggested the importance of continuous monitoring activities in the field for the further analysis.

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).