SOME PRINCIPLES BEHIND THE SELECTION OF CROPS TO MINIMIZE RADIONUCLIDE UPTAKE FROM SOIL

Selection of appropriate crops can reduce radionuclide transfer into p lant production. The different physiological mechanisms or morphologic al features causing interspecific variability in radionuclide uptake b y plant roots are discussed. If the diffusive flux of the radionuclide in the soil is lower than the absorption potential of the plant, geno typic differences in radionuclide content result from differences in r oot morphology, rooting depth, root/shoot ratio and relative growth ra te of the plant. Alternatively, if supply meets the interception poten tial of the roots, variability in the plant's radionuclide content dep ends on differences in the relative value of the specific uptake rate to the relative growth rate of the plant. We hypothesize that in this case (1) radionuclide uptake is linked with the uptake of the most clo sest major nutrient and (2) that this relationship is constant for dif ferent species grown in the same conditions. These general principles are used to explain some literature data of interspecific variation in radionuclide uptake. The distribution of radionuclides within plants is considered and some mechanisms explaining the observations are hypo thesized.