Response of the rhizobial-mycorrhizal-lentil symbiosis to arsenic
The thesis focused on the response of the rhizobial-mycorrhizal-lentil symbiosis to arsenic as an environmental contaminant. This was instigated by the concern over the arsenic contaminated irrigation water problem in South East Asia, and in particularly, its impact on Bangladesh agriculture. This led to a holistic approach to the study, by investigating the effect of inoculation with Rhizobium leguminosarum and the AM fungus Glomus mosseae, as well as application of superphosphate and rock phosphate, on lentil growth, nitrogenase activity and nutrient uptake (especially N and P) in the presence of arsenic contaminated irrigation water. Positive effects of mycorrhizal inoculation on lentil (Lens culinaris L.) growth, nitrogen fixation and P nutrition were observed, along with reduced uptake of As in roots, shoots and pods. Decreased plant growth, nitrogen fixation, nutrient uptake, mycorrhizal infection and increased uptake of arsenic in root, shoot and pods were observed due to application of arsenate contaminated irrigation water. The use of a lux based bacterial biosensor test demonstrated that mycorrhizal inoculation reduced arsenic bioavailability in soil and that most of the toxicity was associated with the colloidal and fine particulate soil fraction. When rock phosphate was applied, an increase of P uptake only was observed. In contrast, superphosphate increased both P and As uptake and decreased mycorrhizal infection and activity. In summary, this thesis has shown that mycorrhizal inoculation appears to offer great potential as an effective tool contributing to crop management for technique in minimisation of the total intake of As by human and livestock. The observed decreased in uptake of As into pods of mycorrhizal lentil has particularly important potential implications for human health.