Greenhouse assessment of citric acid-assisted phytoremediation of cadmium by willows (Salix spp.) - effect on photosynthetic performances and metal tolerance

Abstract

The aim of this study was to define effects of cadmium (Cd) applied alone and in combination with citric acid, on the plant tolerance, accumulation, translocation and photosynthesis in willows (Salix viminalis, S. matsudana and S. alba). Low metal bioavailability in soil is often the limiting factor for phytoextraction, thus citric acid was used as a chelating agent aiming to improve metal solubility and therefore accelerates phytoextraction. Willows were grown by soil culture method in semi-controlled conditions (greenhouse) with two different Cd concentrations (3 and 6 ppm), applied separately and in combination with citric acid (20 mM/kg of dry soil), followed by control plants. The reduction of plant growth, biomass, photosynthesis parameters, chlorophyll and carotenoids were induced by Cd supplied. The addition of citric acid showed beneficial effects on different morpho-physiological levels through alleviate stress conditions as well as enhancing overall phytoextraction. Citric acid (CA) has increased transport of the accumulated Cd from the roots to aerial part in S.viminalis and S.alba in comparison with same treatments without CA, as well as tolerance of analyzed clones. Significant depressive effect on photosynthetic CO₂ assimilation was evident in plants grown in soil with Cd applied. A significant negative correlation between biomass production, leaf area, and photosynthesis due to the presence of Cd in plant tissue was observed in S. viminalis. Bioaccumulation factor among selected willow clones was higher than 1, reliably suggesting good potential of selected genotypes for phytoextraction.

Key words: willows, cadmium, citric acid, soil phytoextraction, photosynthesis, accumulation, translocation, tolerance