Response of Quercus pubescens leaves exposed to geothermal pollutant input in southern Tuscany (Italy)

The paper reports a case of evident and widespread leaf damage on trees in southern Tuscany (Central Italy) attributed to the input of pollutants produced in a geothermal area. The main potentially phytotoxic substances are boron and hydrogen sulphide. Trees affected are conifers as well as both evergreen and deciduous broadleaves. In the present study the possible impact of geothermal pollutants on Quercus pubescens leaves has been considered. Leaf samples coming from three sampling locations (S1 inside the geothermal area; S2 on the margins; S3 outside) and three consecutive dates (June, July and August) were analyzed for the following parameters: sulphur and boron concentration; leaf area; leaf mass per area; chlorophyll fluorescence (Fv/Fm); chlorophyll a, chlorophyll b and carotenoid concentrations. Anatomical and ultrastructural observations were also performed. In all sampling location sulphur and boron concentrations are greater than the background values recorded in southern Tuscany in a previous survey. The sulphur concentration in leaves was higher in S1 than S2 and S3, but did not increase throughout the survey period. Boron reached the greatest concentrations in S2 and showed a continuous increase over the study period. Leaves subjected to a higher load of pollutants were smaller in size (in terms of leaf area), but were more sclerophyllous. Damaged chloroplasts and reduced Fv/Fm values were observed at S1 and S2, but chlorophyll concentration values were higher at S1. Such an apparent anomaly can possibly be explained by the onset of compensation and recovery mechanisms. Foliar injuries appeared to be related to boron concentration.