The growth-enhancement of clover by Aspergillus-treated sugar beet waste and Glomus mosseae inoculation in Zn contaminated soil

In a microcosm experiment, using a Zn contaminated soil, we determined the effectiveness on plant growth of treatments such as Aspergillus niger-treated sugar beet waste (SBW, 50 g kg−1 soil), in presence or absence of rock phosphate (RP, 1.5 g kg−1 soil) and arbuscular mycorrhizal (AM) inoculation. An autochthonous, Zn adapted, strain of Glomus mosseae was used and its interaction with amendments was assessed on Trifolium repens growth, nutrition and symbiotic (AM colonization and nodulation) values. Treatments applied resulted alternative strategies for alleviating plant Zn toxicity and for Zn phytoextraction from Zn contaminated soils. A. niger-treated SBW + RP was the most effective amendment in improving plant growth and nutrition. The impact of such treatment on plant N, P and Zn concentration was particularly evident when associated with G. mosseae. Total growth (four harvests) of AM plants growing in SBW + RP-treated soil was about 28 times more than in non-mycorrhizal control plants. The effect of G. mosseae on shoot biomass ranged from 86% (without amendment) to 1192% (with treated SBW + RP). This growth improvement was the consequence of increased N, P and K nutrition and decreased Zn acquisition. Nevertheless, as consequence of an enhanced plant biomass, Zn phytoextraction by these plants increased by 1832% over untreated ones. Treatments applied also improved nodule formation by an inoculated Rhizobium, that were highly depressed in this Zn contaminated soil. Soil enzymatic activities, which are indicative of biological performance in the rhizosphere were also improved by treatments applied. Phosphatase activity was 1257% higher than in control soil by the application of SBW + AM fungus; following a similar trend, dehydrogenase and β-glucosidase activities reached the highest values in SBW + AM treatments. The application of AM fungus and treated SBW + RP amendment for decontaminating a Zn polluted soil can be regarded as a successful biotechnological tool for the recovery of polluted soils and as an important strategy for bioremediation purposes.