Synergistic effect of mycorrhiza and rock phosphate on phytoremediation potential of solenostemon monostachyus in a heavy metal polluted soil
This study determined the growth of Solenostemon monostachyus under different levels of Pb and Cd contamination in the soil, assessed the uptake of lead and cadmium by Solenostemon monostachyus as well as determined the synergistic effect of mycorrhiza and rock phosphate applications on lead and cadmium accumulation in S. monostachyus. This was with a view to determining the effect of augmentation of mycorrhiza and rock phosphate on the phytoremediation potential of Solenostemon monostachyus in a polluted soil. The experiment was carried out at the screenhouse of the Faculty of Agriculture, Obafemi Awolowo University, Ile-Ife. The experimental design consisted of factorial combination of two heavy metals Pb and Cd in triplicates in a completely randomised design with four treatments (non inoculated, Glomus mosseae, rock phosphate, G. mosseae and rock phosphate (GM+RP)). Metal solutions of Pb and Cd of known concentrations were prepared at the following levels : Pb (0, 25, 50, 75,100) mg/kg-1 and Cd (0, 25, 50, 75,100) mg/kg-1 using PbCl2 and CdCl2 soluble compounds respectively. These concentrations were used to contaminate 3 kg by weight of soil of 120pots. The experiment consisted of 30 pots each of non inoculated, G.mosseae, rock phosphate and GM+RP treatments. Soil inoculum of Glomus mosseae was applied at the rate of 20 g per pot and rock phosphate at the rate of 0.15 g per pot. Five seeds of Solenostemon monostachyus was planted per pot and thinned to two stands per pot at two weeks after planting. The pots were maintained weed free and watered regularly to field moisture capacity. Parameters such as plant height, number of leaves and stem girth were determined fortnightly for a period of twelve weeks. Percentage of root colonization by arbuscular mycorrhizal fungi was determined. Pre - soil and plant test were carried out to determine soil physical and chemical properties using standard methods. At twelve weeks after planting, Solenostemon monostachyus plant was harvested and analysed for lead and cadmium uptake using Atomic Absorption Spectrophotometer (AAS). The data collected were analysed using descriptive and inferential statistics. Comparative assessment of Cd content in soil and plant indicated that Glomus mosseae and rock phosphate treated plants absorbed more Pb and Cd than those with non inoculated, sole treatment with either Glomus mosseae or rock phosphate at all levels of contamination (0-100 mgkg-1). Similarly, the plants treated with Glomus mosseae and rock phosphate also absorbed more lead from the soil than other treatments. The uptake of Pb by Solenostemon monostachyus increased with the increase in the concentration. However, application of Glomus mosseae or rock phosphate alone or in combinations enhanced the Pb uptake. The effect of single application of either Glomus mosseae or rock phosphate on the plant dry weight in a Pb contaminated soil was similar .The concentration of Pb in the soil increased with increase in Pb contamination except at 50-100 mg/kg under dual application of Glomus mosseae and rock phosphate.