Species-specific cadmium and lead tolerance in four Eucalyptus seedlings: implications for phytoremediation of metal-contaminated soils
Introduction Phytoremediation using fast-growing tree species has emerged as a sustainable approach for restoring metal-contaminated soils. However, comparative information on species-specific responses to metal stress tolerance remains limited. Methods This study evaluated chlorophyll content, growth performance, and biomass allocation, including metal tolerance efficiency, of four Eucalyptus species (i.e., E. tereticornis, E. camaldulensis, E. globulus, and E. citriodora) under varying concentrations of Cadmium (Cd, 25, 50, and 100 mg kg⁻¹) and Lead (Pb, 100, 125, and 250 mg kg⁻¹). A factorial, completely randomized pot experiment was conducted under controlled conditions, using sterilized red soil as the medium for 120 days. Plant growth performance and metal tolerance efficiency were measured and analyzed using ANOVA followed by post hoc comparison. Results Cd exhibited significantly greater phytotoxicity than Pb across species and parameters studied. Marked species-specific differences in metal tolerance were observed in Eucalyptus citriodora, outperforming other species in maintaining superior growth performance and metal tolerance even at the highest metal concentrations (Cd 100 mg kg⁻¹). However, E. camaldulensis was the species most sensitive to Cd stress. Hierarchical clustering rank based on superior tolerance characteristics of species was: E. citriodora > E. camaldulensis > E. tereticornis > E. globulus. Discussion It was concluded that Eucalyptus citriodora was the most promising candidate for future phytoremediation studies of Cd- and Pb-contaminated soils due to its superior metal tolerance ability as reflected by sustained growth performance and chlorophyll retention of the species. The species can be recommended for restoration programs and sustainable management of metal-polluted areas based on performance at the initial phase.