Fiziološki aspekti potencijala vrba (Salix spp.) u asistiranoj fitoremedijaciji kadmijuma upotrebom limunske kiseline [Physiological aspects of willow potential (Salix spp.) in assisted phytoremediation of cadmium using citric acid]

The role of citric acid on morphological, physiological and biochemical characteristics of selected willow clones (Salix spp.) grown in soil with moderately polluted cadmium (Cd) was presented. The aim of this study was to determine the Cd accumulation, translocation and tolerance of different willow clones, as well as the influence of citric acid as a chelator in the assisted phytoremediation process. In order to achieve this goal, plants were grown in semi-controlled conditions for 3 months. The experiment was divided into two phases (two years of research), based on differences in the methodological approach, regarding the application of citric acid. During the first-year experiment, citric acid was added once, while in the second year the application of this chelator was performed in three repetitions. The analyses included: the accumulation and distribution of Cd in soil and various plant organs (root, stem, young and old leaves); influence of Cd and citric acid on morphometric parameters: stem hight and diameter, number of leaves, biomass and area of leaves, biomass and volume of the root; on photosynthetic characteristics: net photosynthetic and transpiration rate, water use efficiency, stomatal conductance, intercellular concentration of CO2, concentration of photosynthetic pigments; on mineral nutrition and distribution of macronutrients in plants (nitrogen, phosphorus and potassium content); on the content of the amino acid proline and cysteine; on the activity of antioxidant enzymes (catalase, ascorbate peroxidase, guaiacol peroxidase), as non-enzymatic components such as reduced glutathione and thiol content. The obtained results indicated the genotypic specificity of the analyzed willow clones in the phytoremediation process, depending on the treatment applied, the Cd dose, and the presence of citric acid. The toxic effect was not evident on the morphological level, while the applied treatments showed a significant influence on the physiologicalbiochemical processes in the willows. The net photosynthetic rate, transpiration rate, as well as, water use eficiency showed decreasing with increasing Cd concentration in plant tissue, while the application of citric acid mitigated the harmful effect of this heavy metal, which was registered on combined treatments. In response to the accumulation of Cd in plant tissue, a change in the activity of anti-oxidant enzymes, as well as nonenzymatic components of the defense system has been established. In addition, the application of citric acid showed the promotion role on the absorption, accumulation and tolerance of willows grown in moderately polluted soil cadmium, which has a practical significance in the improvement of phytoremediation techniques and decontamination of polluted soil.