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Geothermal alteration fields are very prohibitive environments, limiting vegetation establishment and growth. In the present study, the ecological specialisation of the pioneer plant Calluna vulgaris (L.) Hull was investigated, assuming that its ability to survive in geothermal habitats derives from a fine regulation of morpho-physiological traits. Mature leaves of C. vulgaris were sampled from plants close to a fumarole (near), and from plants living at a distance of some metres (intermediate) or ~1 km (distant) from a fumarole. Along the sampling sites, a gradient of soil-pH and temperature values occurred, with near plants facing the highest soil temperature and the lowest soil pH. A regulation of constitutive morpho-anatomical and physiological traits in response to different stress levels occurred. A progressive reduction of leaf exposed surface and hair density and mucilages, combined with a gradual increase of oxidative stress levels, of phenols and ascorbate, was observed from distant to near plants. Near plants showed an increase in stomatal density and in lignin and cuticle thickness, and the highest activity of ascorbate peroxidase. Except for high glutathione concentrations, in distant plants antioxidant machinery was consistently less active. The apparent morphological and physiological plasticity demonstrated in the present research contributed to the capability of these plants to tolerate the prohibitive, highly changing environmental conditions of the geothermal field

Cadmium uptake, tissue localization and structural changes induced at cellular level are essential to understand Cd tolerance in plants. In this study we have exposed plants of Pteris vittata to different concentrations of CdCl2 (0, 30, 60, 100 μM) to evaluate the tolerance of the fern to cadmium. Cadmium content determination and its histochemical localization showed that P. vittata not only takes up, but also transports and accumulates cadmium in the aboveground tissues, delocalizing it mainly in the less bioactive tissues of the frond, the trichomes and the scales. Cadmium tolerance in P. vittata was strictly related to morphogenic response induced by the metal itself in the root system. Adaptive response regarded changes of the root apex size, the developmental pattern of root hairs, the differentiation of xylem elements and endodermal suberin lamellae. All the considered parameters suggest that, in our experimental conditions, 60 μM of Cd may represent the highest concentration that P. vittata can tolerate; indeed this Cd level even improves the absorbance features of the root and allows good transport and accumulation of the metal in the fronds. The results of this study can provide useful information for phytoremediation strategies of soils contaminated by Cd, exploiting the established ability of P. vittata to transport, delocalize in the aboveground biomass and accumulate polluting metals.

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