UPTAKE OF TRITIUM BY PLANTS FROM ATMOSPHERE AND SOIL

Uptake of tritiated water (HTO) by plants was examined under field conditions when tritium was available to leaves from only the atmosphere and when tritium was available from both the soil (root uptake) and the atmosphere. Maple, oak, and elm trees, planted in clean soil, were transported to a tritium-contaminated forest, where the atmospheric tritium concentration was elevated, to examine HTO uptake by tree leaves when the source was only in the atmosphere. The results partially agreed with a diffusion model of tritium uptake by plants. Discrepancies found between predicted and measured leaf HTO/air HTO ratios should be attributed to the existence of some isolated water, which is isolated from the transpiration stream in the leaves, that was not available for rapid turnover. The uptake of tritium by trees, when the source was both in the soil and atmosphere, was also examined using deciduous trees (maple and elm) resident to the tritium-contaminated forest. The results were in agreement with a prediction model.