Do ecosystem services have a biological cost? Ozone and climate regulation by Norway spruce forests along an Alpine altitudinal transect in Trentino, northern Italy

Regulating air pollution and climate are important ecosystem services provided by forests. Among air pollution, ozone is particularly important because its high values and wide distribution in remote forest areas. Forests may help in reducing ozone concentration because stomatal and non-stomatal deposition. Ozone, however, can potentially affect the vegetation, leading to a reduction of photosynthesis with consequences, from plant to ecosystem level. In a cost-benefit approach, this may be considered as a biological cost. To assess the size of ozone and climate regulating services provided by Alpine forests, a fully randomized study was established along an altitudinal gradient (900 - 1500 m a.s.l.) in Trentino, northern Italy. Environmental variables (O3, NO2, T, RH, LAI) were measured between May and August 2013. Tree response variables (crown condition, needle weight, shoot length, chlorophyll fluorescence, C and O isotopes) were also investigated on mature Norway spruce trees. Ozone concentration increased with altitude, both inside and outside forests. Significant (P<0.001; Wilcoxon test) lower ozone concentrations, however, were observed within the forest (64.8 g m-3) with respect to open areas (71.3 g m-3). Effect of forests on temperature was particularly marked for maximum daily values. As for response indicators, a distinct elevation pattern with concurrent increase of crown transparency and decrease of shoot growth, needle weight and photosynthetic activity potential was obvious. Nested within such a superimposed effect, the various response indicators were related to each other. Estimates of ozone removal in terms of AOT40, relationship between exposure to ozone, ozone removal and tree- and plot-related variables will be presented and discussed. This will allow (i) the evaluation of possible biological costs of removing air pollutants and (ii) the functional interpretation of monitoring data. All together, this will help understanding the role of tree health on the regulating services provided by forests and vice versa.