Bioremediation of soil contaminated by spent diesel oil using Pleurotus pulmonarius Fries (Quelet) and its effects on the growth of Corchorus olitorius (L)

Objectives: To investigate the potential of Pleurotus pulmonarius in the bioremediation of soil contaminated with spent diesel oil at 5, 10 and 15% (v/w) level of contamination over a period of one and two months of incubation.Methodology and results: A pure culture of P. pulmonarius was obtained from the Plant physiology unit of the Department of Botany, University of Ibadan Two sets of control were used. In the first set of control treatments, no contaminant ( spent diesel oil was added to the soils while in the second set, different levels of oil were added to all soils but no inoculation with the fungus). Inoculation was done by adding 10 g of vigorously growing spawn of P. pulmonarius. The soil was contaminated with spent diesel oil to achieve 5 %, 10 % and 15 % (w/v).. The results showed a significant increase (at p3 0.05) in the nutrient contents of the soil samples at all level of contamination compared to the uncontaminated but there was no significant difference in the pH after two months of incubation with P. pulmonarius. The organic carbon increased from 2.176 to 6.960 at 0% and from 7.126 to 8.010 at 15 % level of contaminations. Organic matter increased from 3.765 to 12.03 at 0% level of contamination and from 12.32 to 13.84 at 15%. Phosphorus increased from 15.807 to 18.940 at 0% and 16.017 to 20.627 at 5% level of contaminations while Potassium increased from 0.660 to 0.783 at 0% and 0.540 to 0.837 at 10% level of contamination. The Total Petroleum Hydrocarbon (TPH) degradation (% loss) was 84.41% at 5%, 64.87% at 10% and 44.27% at 15% level of contamination. . A significant (p 30.05) reduction in concentration of the heavy metals Cu and Zn after two month of incubation with P. pulmonarius suggested bioaccumulation. The Copper content reduced from 0.033 to 0.014mg/kg at 0% oil contamination and from 0.027 to 0.021mg/kg at 15% oil contamination while Zinc reduced from 0.076 to 0.059mg/kg at 0% oil, and from 0.057 to 0.056mg/kg at 15% oil contamination. There was an improvement in the growth of Corchorus olitorius in remediated soil at all level of contamination compared to the control. Plant growth in the remediated soil was 11.18 cm high after the sixth week while the control plant was 4.23 cm at 5% level contamination.Conclusion and application: The fungus P.pulmonarius has been found from this study to be a potential white rot fungus that can bioremediate soil contaminated with diesel oil and that the remediated soil was able to support the growth of the test plant at all level of contaminations. The biotechnology is a cost energy input that can also fetch the farmer some income.Key words: Bioremediation, Spent diesel oil, Degradation, P. pulmonarius, Soil nutrient conten

Promiscuous arbuscular mycorrhizal symbiosis of yam (Dioscorea spp.), a key staple crop in West Africa

Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical "tree-aspect" savannas and dry forests that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18-25 vs. 11-16 spp.), but similar for both ecosystems (29-36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70-95 vs. 11-20%). After 8 months of trap culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems prevailing in West Africa