Ozone effort, a five-year study on ozone exposure, flux and effects on vegetation in Trentino (Northern Italy): a synthesis

The project Ozone EFFORT (Ozone EFfects on FORests in Trentino) was carried out in the province of Trento, northern Italy (6207 km2) over the 2007-2011 period to provide explicit answers to three main questions: (i) is there a potential risk placed by ozone to vegetation? (ii) Are there specific ozone symptoms on plants, and are they related to ozone levels? (iii) Are there ozone-related effects on forest health and growth? Different methods and techniques (field sample survey for ozone levels, injury, and chlorophyll-related measurements; modeling for spatialization, ozone flux, and effect assessment) and vegetation targets (ad hoc introduced and spontaneous bioindicators, forest trees) were adopted. As for question (i), mapped ozone exposure (AOT40) after measurements by passive sampling and conventional monitors revealed exceedance of risk thresholds (both EU Directive 50/2008 and UNECE) for >90% of the investigated area (Gottardini et al., 2010, Atmos. Environ., 44, 147-152; Ferretti et al., 2012, J. Environ. Monit., 14, 2238–2244; Cristofori et al., 2014, Ann. For. Sci., DOI 10.1007/s13595-014-0440-y). As for question (ii), although ozone levels were significantly related to foliar symptoms and height increment of introduced Nicotiana tabacum L. Bel-W3 plants, other factors (site, time, air temperature, relative humidity) resulted equally or even more important (Cristofolini et al., 2011, Ecol. Ind., 11, 1065–1073). Foliar symptoms on the spontaneous, ozone-sensitive Viburnum lantana L. were significantly (but not proportionally) related to ozone exposure both in time (Gottardini et al., 2010, J. Environ. Monit., 12, 2237–2243) and space (Gottardini et al., 2014, Sci. Tot. Environ., 493, 954–960). In the former case, results were corroborated by chlorophyll content and stress signals (chlorophyll a fluorescence transient analysis) (Gottardini et al., 2014, Ecol. Ind., 39, 65–74). Finally [question (iii)], statistical analyses on forest health (in terms of defoliation) and growth (in terms of basal area increment) measured at 15 ICP Forests Level I plots revealed scarce relationship with ozone exposure. Instead, damage due to biotic and abiotic causes and foliar nutrition were consistently identified as the main drivers. Ozone flux estimated for one intensive Picea abies (L.) Karst. site over the 1996-2009 period exceeds frequently and largely the recommended POD1 8 mmol m−2 (CLRTAP, 2014). Yet, no relationship was found with health and growth, nor foliar symptoms were reported (Ferretti et al., in prep.). In conclusion, the potential risk for vegetation in terms of ozone exposure and flux is very high in Trentino. Evidence of effects, however, are limited, and decreases when moving from specific bioindicator plants to forest trees, and from foliar symptoms to forest health and growth.