Leaf natural N 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 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-fixing species Dicorynia guianensis were analyzed. Both δN and total leaf N varied widely (-1 ?δN (‰) ? 7 and 1 ? leaf N(%) ? 3.2) suggesting possible distinctions between diazotrophic and non-fixing plants. The δN also revealed two statistically distinct groups of non-N-fixing species (δN = 5.14 ± 0.3 vs δN = 1.65 ± 0.17) related to the different ecological behaviors of these species in the successional processes. We conclude that the δN signature of plant leaves combined with their total N concentration may be relevant indicators for identifying functional groups within the community of non-N-fixing species, as well as for detecting diazotrophy. Despite the variability in the δN of the non-N-fixing species, N-fixing groups can still be identified, provided that plants are simultaneously classified taxonomically, by their leaf δN and total N concentration and by the presence or absence of nodules. The variability in the δN of the non-fixing species is discussed.