Seed germination, growth and metal uptake of Medicago sativa L. grown in heavy metal contaminated clay loam brown forest soil

The use of plants for heavy metal-polluted soil rehabilitation is an emerging ecologically sound and safe technique. An in vitro laboratory experiment was conducted for 15 days in Petri dishes containing 3 layers of Whatman filter papers wetted by 50 ml of heavy metals Cd, Cu, Ni, Pb and Zn, separately at 0, 10, 20, 40, 80 to 160 µM to determine their impacts on germination rate, root and shoot growth of surface sterilized alfalfa seeds. An in vivo experiment was also conducted in a greenhouse setting, and the alfalfa seeds were grown for 8 weeks in plastic pots containing 2 kg of heavy metal (Cd, Cu, Ni, Pb and Zn) contaminated clay loam brown forest soil at different concentration levels (0, 10, 20, 40, 80 to 160 mg/kg). The results of in vitro demonstrated that the rates of seed germination, root and shoot growth were affected by Cd, Cu, Ni and Pb metals at higher concentrations of 80 and 160 µM. The inhibitory decreasing order of metal toxicity on seed germination was Cd > Cu > Ni > Pb > Zn. However, seed germination increased at all Zn dosages. Meanwhile, the lower concentrations of investigated metals (10 and 20 µM) stimulated the root and shoots length and at 10 and 20 mg/kg concentration levels increase plant biomass. It was found that alfalfa was able to grow efficiently at all Zn concentrations except at 160 mg/kg. The results showed that alfalfa was able to uptake the heavy metals at the applied concentrations ranging from 10 to 160 mg/kg by various degrees. Finally, the alfalfa plants, to some extent, demonstrated their potential in cleaning the soil environment from heavy metals.