Abstract
All strains of Rhizobium isolated from ineffective nodules on white clover (> 50 separate isolations) formed in metal-contaminated soils from a field experiment were demonstrated to be wholly ineffective in nitrogen fixation in plant infection tests on N-free nutrient agar. The plasmid profiles of these isolates were all very similar indicating a lack of genetic diversity in the population surviving in high concentrations of heavy metals. Isolates from comparable field plots of uncontaminated soil had a wide diversity of plasmid profiles. Inoculation of white clover at sowing with a large inoculum of effective Rhizobium leguminosarum bv. trifolii on metal contaminated soil resulted in effective N 2-fixation. However, if the inoculated soils were held for 2 months in a moist condition before sowing with white clover, N 2-fixation was not detected with inoculum doses of 10 7 cells pot −1 or less but was obvious where a very large inoculum of 10 10 cells pot −1 was added. This indicates that white clover rhizobia are unable to survive (or at least unable to remain effective) in the presence of concentrations of heavy metals close to the current Commission of the European Communities guidelines for environmental protection. A rapid method of assessment of the toxic effects of pollutants on populations of Rhizobium spp is described.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call