Remediation of Cadmium Toxicity on Alfalfa ( Medicago sativa L.) Using Biochar as a Bioadsorbent, Rhizobium meliloti and Arbuscular Mycorrhizal Fungi as Biofertilizers

Abstract

Contamination of agricultural soil is becoming an increasingly serious problem because of long-term exposure to pollutants in irrigation water, sludge, fertilizers, and pesticides. Cadmium (Cd) is one of the most dangerous and potentially toxic metals. Pollution by Cd is especially significant as contaminated soils are used for agriculture; this metal is easily absorbed from soils into crops, inhibiting plant growth and nutrient uptake. So, the present study aimed to elucidate the effect of accumulation Cd over the permissible limits on growth of higher plants, e.g., alfalfa and soil microorganisms, e.g., rhizobium bacteria and arbuscular mycorrhiza fungi. In this study we also attempted to find an optimum solution for the problem of soil pollution with Cd through the application of biochar (BC) as bioadsorbent, rhizobia, (Rh) and arbuscular mycorrhizal fungi (AMF) as biofertilizers. CdCl2 was applied in a pot experiment in presence and absence of BC, AMF and Rh. Cd negatively affected alfalfa growth and yield, content of essential minerals such as N, P, K, Ca and Mg in leaves and roots, activity of nodules nitrogenase and rhizosphere dehydrogenase. AMF colonization % and the total microbial count decreased under Cd stress. Application of BC, AMF and Rh individually or in combination improved alfalfa growth, leaf and root content of essential minerals, fungal population and the microbial count. On the other side, these treatments reduced Cd uptake and translocation from roots to seeds. Solo application of BC contributed in Cd immobilization through the metal adsorption and increasing soil alkalinity. Application of BC together with AMF and Rh significantly promoted alfalfa growth and yield, the leaf and root content of mineral ions, the fungal populations and the microbial count compared to control and Cd stressed plants.