Effects of cadmium toxicity on the physiology and growth of a halophytic plant, Tamarix usneoides (E. Mey. ex Bunge).

Heavy metal polluted soils can be remediated using plants, a process called phytoremediation. However, high concentrations of heavy metals can negatively affect plant physiology and growth. We experimentally evaluated the effects of cadmium (Cd) on the growth, (i.e. height, shoot and biomass) and physiology (i.e. leaf chlorophyll and relative water contents) of Tamarix usneoides. In a greenhouse experiment, T. usneoides clones were subjected to a once off treatment of 100 mmol/l NaCl with three different Cd concentrations (6, 12, and 18 mg/kg) applied 3 times/week for eight weeks. We predicted that plant health would decrease with an increase in Cd concentration. Results revealed a 35.9% reduction in chlorophyll content between the 18 mg/kg Cd treated plants and the control, suggesting that T. usneoides experienced a reduction in photosynthetic rate, which in turn influenced the growth and relative water content (RWC) of the plant. Although T. usneoides' growth and physiology were significantly decreased at 12 and 18 mg/kg Cd concentrations, the plants tolerated up to 6 mg/kg Cd concentration, a level found in most anthropogenic Cd-contaminated soils. Tamarix usneoides should thus be confirmed as a good phytoremediation candidate once its ability to extract, translocate and concentrate Cd has been determined.