Myco-assisted phytoextraction of heavy metals with vetiver grass: a green technology for cleaning tannery effluent contaminated sites.

Abstract

Metal toxicity affects practically all physiological systems of plants, both directly and indirectly. Amongst various techniques developed to remediate contaminated soils, arbuscular mycorrhizal fungus (AMF)-assisted phytoremediation is an emerging and unexplored eco-sustainable strategy for controlling and managing soil contamination. Hence, this study aims at exploring the myco-assisted phytoremediation of tannery effluent contaminated soil. A pot culture study was carried out using three different strains of AMF and vetiver grass with soil obtained from the tannery effluent contaminated sites of Tamil Nadu, India (Vellore (S1) and Dindigul (S2)) which were rich in chromium (S1-128mgkg-1, S2-112mgkg-1), cadmium (S1-1.17mgkg-1, S2-2mgkg-1), nickel (S1-39mgkg-1, S2-14mgkg-1) and lead (S1-56mgkg-1, S2-30mgkg-1). Results revealed that inoculation of vetiver grass with AMF including R. intraradices (T3), G. mosseae (T2) and mixed (commercial) culture (T4) in the contaminated soil has significantly increased the growth and biomass of the vetiver plants but the level of action varied with the fungus. Amongst several treatments under study, R. intraradices (T3) inoculation in vetiver yielded in shoot biomass (31.76 t ha-1) which was 8%, 18.8%, and 31.2% higher than treatments T2, T4 and T1 respectively, and the root biomass (23.71 t ha-1) was 10.6%, 15.3%, 32% higher than T2, T4 and T1 respectively. Vetiver growing in T3 has higher total C stored in its roots and shoots (24.99%) than in control soil. Furthermore, T3's overall carbon stock is 24.94% larger facilitating carbon sequestration than control's (T1). Furthermore, it was observed that AMF inoculation significantly increased the phytoextraction potential of vetiver and reduced the translocation of metals into the shoots. The treatment T3 (R. intraradices) recorded Cr (19.99mgkg-1), Cd (0.1mgkg-1), Ni (9.43mgkg-1), and Pb (9.35mgkg-1) in the root portion in S1 and was higher to the tune of 89.8%,50%, 88.5%, and 75.9% respectively, compared to the shoot portion. Additionally, the antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were found relatively higher in control where the plant undergone much larger stress than the other treatments. Hence, it can be concluded that AMF could possibly enhance the growth of Vetiver by improving nutrient (nitrogen, phosphorus and potassium) uptake capability while reducing the heavy metal uptake and accumulation in the shoots eventually protecting the plants from stress and metal toxicity.