The influence of the development of temperate fruit tree species on the potential for their uptake of radionuclides

This paper reviews the published literature that describes the phenological development of above and below ground organs of temperate fruit trees (top fruit), particularly with respect to apple (Malus domestica). Critical inf ormation is presented which is considered appropriate in developing an unde rstanding of the potential for top fruit species to take up radionuclide co ntaminants from the atmosphere and the soil. Information is cited on how cl imatic and edaphic factors influence the growth and development of temperat e fruit trees, the phenological production of their leaf area and the devel opment and growth of their fruit and hence the potential for foliar and fru it uptake of radionuclides from the atmosphere. The study also reports on t he importance of the distribution and phenological development of roots in the soil and the potential for their uptake of radionuclides from the soil. The effects of above and below ground management procedures, within temper ate fruit orchards, on potential radionuclide uptake are also considered. I t is concluded that the potential for the uptake of radionuclides by temper ate fruit tree species will depend on a number of phenological and physiolo gical factors. For uptake from the soil these factors include; root distrib ution and density in the soil profile, seasonal changes in the production a nd distribution of roots, and the presence and amount of water in the soil. These factors are themselves influenced by rootstock type and its growth v igour, scion type and its growth vigour, tree age, spacing of trees in the orchard, orchard management practices (presence or absence of weeds or gras s under the trees) and soil type and depth. Direct uptake by the shoot, how ever, will be influenced by the climatic conditions at the time of exposure and the presence of foliage. Deposition and uptake are likely to change wi th leaf area development and the ability of radionuclides to penetrate the cuticle of the leaf changes with seasonal development. Transport of radionu clides to the fruit may also depend on the time of season, as the importanc e of the xylem and phloem transport routes can change with the growth and d evelopment of the fruit. (C) 2000 Elsevier Science Ltd. All rights reserved .