Efficiency in uptake and use of nitrogen by plants

The 15N isotope method and the non-isotopic difference method for examining nitrogen uptake and the effects of timing, placement and source of fertilizer are compared. The current uses of the isotope method by the direct and indirect approaches are indicated, as are its potential uses for identifying genotypes with high nitrogen use efficiency and for investigating competition in mixed ecosystems and foliar absorption of fertilizer or pollutants. More sophisticated application of fertilizers and especially identification of favourable plant factors for selection in breeding highly efficient genotypes would be facilitated by a better understanding of plant mechanisms in uptake, translocation, storage and retranslocation of N with time. The present and potential uses of 15N methods in examining these factors in uninfected and in mycorrhizal plants are indicated. Existing information is assessed, including present knowledge of some plant 'strategies' in achieving high efficiency in N uptake and use. (author). 54 refs, 1 fig., 1 tab