Low cadmium application increase miscanthus growth and cadmium translocation

Plants of miscanthus were grown in nutrient solution supplied with 0, 0.25, 0.50, and 0.75 mg l−1 cadmium and were harvested after 1 and 3 months of treatment. With cadmium up to 0.50 mg l−1 biomass of secondary culms and roots was increased at both harvests, whereas biomass of the main culm and the rhizome was slightly increased at the first harvest and decreased at the second. With 0.75 mg l−1 Cd biomass of all plant parts except roots was decreased at both harvests. The biomass of the entire plant was always higher than in controls with 0.25 and 0.50 mg l−1 Cd and lower with 0.75 mg l−1 Cd. Relative growth rates (RGRs) showed that the two lower Cd levels stimulated growth only during the first growth period, whereas during the second they reduced growth of the main culm and the rhizome and did not affect that of secondary culms and roots. Root morphology changed with 0.75 mg l−1 Cd: length, surface, and volume drastically decreased, whereas dry weight was not affected and root average diameter increased. All Cd levels decreased specific dry weight increment (SDWI) but did not affect the (net uptake rates) NUR of nitrogen and the N-concentration of different plant parts. Roots showed the highest Cd-concentrations at both harvests and with all Cd levels, and leaves the lowest. The Cd-concentration of aerial plant parts was highest with 0.50 mg l−1 Cd and lowest with 0.75 mg l−1, whereas that of roots increased with Cd supply. Between the first and the second harvest the Cd-concentration of roots, rhizome, and main culm increased only with the highest Cd-level, whereas that of leaves and secondary culms with all levels. The Cd-NUR was linearly related to the concentration of the metal in the nutrient solution during the first month of application and was very low during the following two. Above summarized patterns suggest that cadmium flows passively into roots but the saturation of binding sites limits its uptake. The metal is slowly translocated to the shoot due to mechanisms that restrict internal Cd-transport. This regulation is partially disrupted with 0.75 mg l−1 Cd but translocation to aerial organs is still restricted probably due to reduced transpiration. In this research, the maximum Cd-content achieved by miscanthus was 3.8 mg per plant after a 3-month treatment with 0.75 mg l−1 Cd, but the maximum content of the shoot was 1 mg per plant and was obtained with 0.50 mg l−1 Cd.