Hogberg P, Nasholm T, Hogbom L, Stahl L
Use of N-15 Labeling and N-15 Natural-Abundance to Quantify the Role of Mycorrhizas in N-Uptake by Plants - Importance of Seed-N and of Changes in the N-15 Labeling of Available-N
New Phytologist: 1994 127:515-519
N-15 labelling and variations in natural N-15 abundance offer possibilities to quantify the importance of mycorrhizas in plant N uptake. When atom % N-15 or N-15 natural abundance of mycorrhizal and non-mycorrhizal plants are compared in experiments, one, however, has to account for dilution effects of seed N and the interaction between changes in labelling of the available pool and N uptake. This has been considered in studies of N-2-fixation by diazotrophs, but has not been explicitly corrected for in studies of N uptake by mycorrhizal plants. An example is given, where ectomycorrhizal plants obtained an atom % N-15 different (P < 0.01) from that of non-mycorrhizal plants, but where this could be ascribed to dilution effects of seed N and differences in N uptake rates interacting with changes in N-15 labelling, rather than to Variations in use of N sources or to isotope fractionation during uptake. Careful N and N-15 budgets based on seed N and sequential harvests, as well as frequent measurements of atom % or abundance of N-15 in available pools of N, are thus necessary in studies of this kind. Regressions of N-15 on total N are a useful alternative to comparisons of means of atom % only.
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