Plant induced changes in soil properties cannot explain differences in uranium transfer between plants

Transfer of uranium from soil to plant was evaluated for maize, Indian mustard, wheat, pea and ryegrass. An acid and an alkaline soil were spiked with 238U. The aim was to find out to what extent rhizosphere effects may contribute to observed differences between plants in transfer factor. Irrespective of the plant species, highest transfer factors were obtained for plants growing on the alkaline soil, corresponding with higher uranium concentrations in the soil solution and in the exchangeable fraction than in the acid soil. However, there was no relation between plant-species dependent rhizosphere effects and the transfer factors observed within a same soil group. None of the soil parameters analysed nor the organic acid concentrations in the soil solution allowed to explain the variability in observed transfer factors between the five plants. The mechanisms by which plants inhibit or promote root-to-shoot transfer seemed more important than soil characteristics to explain the difference in uranium transfer factors observed.