Effects of Arbuscular Mycorrhizal Fungi on Growth, Nutrient Status and Biochemical Activities of Triticum aestivum L. and Medicago sativa L. with increasing Zinc and Cadmium Concentrations

Abstract

The effects of mycorrhizal symbiosis on metal accumulation and plants tolerance are not commonly studied in cereal crops or medicinal plants under metal stress. The objective of this study was to assess the impact of mycorrhiza on wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L.) plants with the increase of Zinc (Zn) and cadmium (Cd) toxicity. The experiment was conducted under controlled laboratory conditions in a completely randomized design. Zn and Cd uptake, some biochemical and physiological parameters were studied in eight weeks old wheat and alfalfa plants in response to inoculation or not with arbuscular mycorrhizal fungi (AMF) and with the increase of Zn (0, 100,300, 900 mgkg-I) and Cd concentrations (0, 100, 300, 600 mgkg-I ) in soil. The results showed that mycorrhizal (M) plants generally exhibited tolerance to Zn and Cd up to 300 mg kg_ I in comparison to non-mycorrhizal (NM) plants which exhibited a significant growth reduction at the same soil Zn and Cd level. M inoculation reduced the accumulation of Zn and Cd in shoot parts of plants. Plants showed higher Zn and Cd contents in roots which showed a different Zn and Cd distribution in AMF associated or non associated plants. Mycorrhizal plants increased phosphorus (P) nutrition at all Zn and Cd concentrations except the highest Zn (900 mgkg-I) and Cd (600 mgkg-I ) concentration which cause to decrease the biomass leading to significant alterations in some biochemical contents such as proline, antioxidant enzymes in leaves and also in nutrients (N, P, K, Cu, Ni, Fe, Mn). Zn and Cd toxicity cause to increase the accumulation of pro line in shoots and significant changes in antioxidant enzyme activities were also observed however proline contents were lower in M inoculated plants. Results confirmed that AMF protected wheat and alfalfa plants against Zn and Cd toxicity. This develops a positive association between fungus and plants that cause to improve plants performance. Hence, Glomus species was able to form an efficient symbiosis with wheat and alfalfa plants in moderately contaminated Zn and Cd soils (300 mg.kg-I ) and play an important role in food quality and safety.