Comparison of Cr(III) accumulation and distribution between two willow species and effects on photosynthesis-related parameters.

Species of the genus Salix are fast growing short-rotation plants and high yielding biomass producers, with a greatly developed root apparatus. They are suitable for phytoremediation, a low cost and large-scale clean-up technology that may be exploited for the removal of pollutants from soils, waters and sediments. Among inorganic environmental contaminants, chromium (Cr) is regarded as one of the most harmful. In the last decades, its extensive utilization in several industrial processes has led to a significant increase of Cr pollution worldwide. In this contest, to establish the Cr phytoremediation potential of willows, the capacity of two Salix species (S. fragilis and S. matsudana) to accumulate chromium, as well as the variation of photosynthesis-related parameters, were analysed in the present study. Plants obtained from cuttings of each species were exposed for 4h, 24 h and 15 d to 100 M or 300 M chromium chloride (CrCl3), and the content of Cr in leaves and roots, of total chlorophyll and carotenois, the photosynthetic activity, the transpiration and the stomatal conductance were determined. Both Salix species accumulated chromium more in roots than in leaves, with higher values recorded in S. fragilis than in S. matsudana. Leaf Cr accumulation was higher when plants were supplied with 300 M Cr3+ than with 100 M Cr3+, especially in S. fragilis. A similar trend of Cr accumulation was observed in roots. Chlorophyll a, b and carotenoids were reduced after 15 d of plant exposure to Cr. In particular, in S. fragilis such reduction was more pronounced at 300 M Cr. Values of photosynthetic activity, transpiration and stomatal conductance were lower in plants treated with Cr compared to the control. In S. matsudana plants, this effect was not observed at time 24 h when they were cultivated in the presence of 100 M Cr. In conclusion, S. fragilis and S. matsudana plants could be considered for the reclaiming of Cr-contaminated soil, as they accumulate appreciable amount of Cr in their tissues. However, the level of Cr exposure should be carefully evaluated since high chromium concentrations could exert a number of phytotoxic effects.