Leaf natural 15N abundance and total N concentration as potential indicators of plant N nutrition in legumes and pioneer species in a rain forest of French Guiana

The suitability of the natural N-15 abundance and of total N concentration of leaves as indicators of the type of plant N nutrition in a rain forest of French Guiana were tested. Leaf samples from primary legume species, non-legumes (pioneer species) and from the non-N-2-fixing species Dicorynia guianensis were analyzed. Both delta(15)N and total leaf N varied widely (-1 less than or equal to delta(15)N (parts per thousand) less than or equal to 7 and 1 less than or equal to leaf N(%) less than or equal to 3.2) suggesting possible distinctions between diazotrophic and non-fixing plants. The delta(15)N also revealed two statistically distinct groups of non-N-2-fixing species (delta(15)N = 5.14 +/- 0.3 vs delta(15)N = 1.65 +/- 0.17) related to the different ecological behaviors of these species in the successional processes. We conclude that the delta(15)N signature of plant leaves combined with their total N concentration may be relevant indicators for identifying functional groups within the community of non-N-2-fixing species, as well as for detecting diazotrophy. Despite the variability in the delta(15)N Of the non-N-2-fixing species, N-2-fixing groups can still be identified, provided that plants are simultaneously classified taxonomically, by their leaf delta(15)N and total N concentration and by the presence or absence of nodules. The variability in the delta(15)N of the non-fixing species is discussed.