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.

Epidemiological derivation of fl ux-based critical levels for visible ozone injury in European forests

The European MOTTLES project set-up a newgeneration network for ozone(O 3)monitoring in 17 plots in France,Italy and Romania.These monitoring stations allowed:(1)estimating the accumulated exposure AOT40 and stomatal O 3 fl uxes(PODY)with an hourly threshold of uptake(Y)to represent the detoxifi cation capacity of trees(POD1,with Y=1 nmol O 3 m^−2 s^−1 per leaf area);and(2)collecting data of forest-response indicators,i.e.crown defoliation and visible foliar O 3-like injury over the time period 2017–2019.The soil water content was the most important parameter aff ecting crown defoliation and was a key factor aff ecting the severity of visible foliar O 3-like injury on the dominant tree species in a plot.The soil water content is thus an essential parameter in the PODY estimation,particularly for water-limited environments.An assessment based on stomatal fl ux-based standard and on real plant symptoms is more appropriated than the exposure-based method for protecting vegetation.From fl ux-eff ect relationships,we derived fl ux-based critical levels(CLef)for forest protection against visible foliar O 3-like injury.We recommend CLef of 5 and 12 mmol m^−2 POD1 for broadleaved species and conifers,respectively.Before using PODY as legislative standard in Europe,we recommend using the CLec for≥25%of crown defoliation in a plot:17,000 and 19,000 nmol mol^−1 h AOT40 for conifers and broadleaved species,respectively.

Correction To: Epidemiological derivation of flux-based critical levels for visible ozone injury in European forests

Correction to:J.For.Res.https://doi.org/10.1007/s11676-020-01191-x In the Original publication of the article,the authors found an error in the text“We recommend CLef of 5 and 12 mmol m−2 POD1 for broadleaved species and conifers,respectively”under the section abstract and conclusion.

Protecting the photosynthetic performance of snap bean under free air ozone exposure

Tropospheric ozone（O3） is a major air pollutant and causes serious injury to vegetation. To protect sensitive plants from O3 damage, several agrochemicals have been assessed,including cytokinin（e.g., kinetin, KIN） and ethylenediurea（EDU） with cytokinin-like activity.In higher plant, leaves are primarily injured by O3 and protective agrochemicals are often applied by leaf spraying. To our knowledge, the mitigating abilities of EDU and KIN have not been compared directly in a realistic setup. In the present research, impacts of elevated O3（2 × ambient O3, 24 hr per day, for 8 days） on an O3 sensitive line（S156） of snap bean（Phaseolus vulgaris）, which is often used for biomonitoring O3 pollution, were studied in a free air controlled exposure system. The day before starting the O3 exposure, plants were sprayed with a solution of EDU（300 ppm）, KIN（1 mmol/L） or distilled water, to compare their protective abilities. The results demonstrated that 2 × ambient O3 inhibited net photosynthetic rate and stomatal conductance, increased the minimal fluorescence yield of the dark-adapted state, decreased the maximal quantum yield of PSII photochemistry, and led to visible injury. KIN and EDU alleviated the reduction of the photosynthetic performance, and visible injury under O3 fumigation. The plants sprayed with EDU showed greater ability to mitigate the O3 damage than those sprayed with KIN. Chlorophyll fluorescence imaging may have detected more precisely the differences in O3 response across the leaf than the conventional fluorometer.

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.