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.