Leaf natural N-15 abundance and total N concentration as potential indicators of plant N nutrition in legumes and pioneer species in a rain forest ofFrench 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 o f French Guiana were tested. Leaf samples from primary legume species, non- legumes (pioneer species) and from the non-N-2-fixing species Dicorynia gui anensis were analyzed. Both delta(15)N and total leaf N varied widely (-1 l ess 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) suggesti ng possible distinctions between diazotrophic and non-fixing plants. The de lta(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 t o the different ecological behaviors of these species in the successional p rocesses. We conclude that the delta(15)N signature of plant leaves combine d with their total N concentration may be relevant indicators for identifyi ng functional groups within the community of non-N-2-fixing species, as wel l as for detecting diazotrophy. Despite the variability in the delta(15)N O f the non-N-2-fixing species, N-2-fixing groups can still be identified, pr ovided that plants are simultaneously classified taxonomically, by their le af delta(15)N and total N concentration and by the presence or absence of n odules. The variability in the delta(15)N of the non-fixing species is disc ussed.