Lead (Pb) uptake (mediated by Arbuscular Mycorrhiza) from Soil and Pb Deposit on Cowpea (Vigna unguiculata [L.] Walp) Plant

Abstract

The need to increase cowpea production for the increasing population in cities had led to cultivation of available land in city centres for farming regardless of the level of heavy metal pollution of such land. It has therefore become imperative to assess this practice with the aim of identifying the level of danger inherent in the practice. A glasshouse experiment was conducted to assess the level of tolerance of cowpea (Vigna unguiculata), Ife Brown variety to lead (Pb). The seeds were inoculated with Glomus mosseae (Nicolson & Gerdemann) to enhance nutrient and Pb uptake before planting in
soil enriched with lead (Pb). A field study to determine the response of same crop to Pb fallout from automobiles was also carried out. The field experiment was sited beside a major road leading to a petroleum deport in Ibadan, Nigeria. Vegetative growth of the crop was improved by the microorganism. Though Pb impacted negatively on cowpea growth, only the application of the combination of Pb and G. mosseae led to stunted growth of the crop. In the field, soil Pb decreased as we moved away from the road embankment with soil 15 m away from the road-side containing 17.3 mgkg^-1 while plot closest to the road had 82.3mgkg^-1. Strong correlations existed between soil Pb and root Pb (r=0.918), soil Pb and plant tissue Pb (r=0.973) and between root Pb and plant tissue Pb (r=0.913). The Pb content of root of cowpea at 4, 6, 8,10 and 15 m away from the road-side were lower than the corresponding values in plant tissues indicating that cowpea tissue might have obtained its additional Pb from other sources than from the soil. Cowpea showed some level of tolerance to Pb as only the combination of Pb and G. mosseae led to visible stunting in growth.

Keywords: Cowpea (Vigna unguiculata); Glomus mosseae; rhizobium; lead

J. Trop. Microbiol. Biotechnol. Vol. 3 (2) 2007: pp. 44-50