Photosynthetic response and tolerance of three willow species to cadmium exposure in hydroponic culture

Three willow species (Salix alba, Salix matsudana and Salix nigra) were exposed to very high cadmium (Cd) concentrations in order to define some physiological traits related to high biomass production. Plants were grown hydroponically under semi-controlled conditions (greenhouse). It was assumed that leaves accumulate different amounts of Cd in relation to their age due to the specific occurrence of symptoms generated by Cd accumulation. The rate of photosynthesis and concentration of photosynthetic pigments in young and old leaves was correlated with biomass production in order to ascertain their significance as indicators of plant performance at sites contaminated with Cd. Changes in the photosynthetic parameters induced by treatments depended on the concentration of Cd in the nutrient solution, the species of willow and leaf age. Fv/Fm ratios were not considerably changed in treated plants, indicating preserved activity of PSII. According to results presented in this work, the Fv/Fm ratio was a less sensitive indicator of Cd stress in willows than the rate of photosynthesis and pigment concentration. High tolerance to applied treatments estimated on the basis of biomass production of S. nigra and S. matsudana irrespective of Cd concentration in the growth substrate might indicate their potential in the reclamation of Cd-contaminated sites.