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

Abstract

The suitability of the natural ¹⁵N 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-N₂-fixing species Dicorynia guianensis were analyzed. Both δ¹⁵N and total leaf N varied widely (−1 ?δ¹⁵N (‰) ? 7 and 1 ? leaf N(%) ? 3.2) suggesting possible distinctions between diazotrophic and non-fixing plants. The δ¹⁵N also revealed two statistically distinct groups of non-N₂-fixing species (δ¹⁵N = 5.14 ± 0.3 vs δ¹⁵N = 1.65 ± 0.17) related to the different ecological behaviors of these species in the successional processes. We conclude that the δ¹⁵N signature of plant leaves combined with their total N concentration may be relevant indicators for identifying functional groups within the community of non-N₂-fixing species, as well as for detecting diazotrophy. Despite the variability in the δ¹⁵N of the non-N₂-fixing species, N₂-fixing groups can still be identified, provided that plants are simultaneously classified taxonomically, by their leaf δ¹⁵N and total N concentration and by the presence or absence of nodules. The variability in the δ¹⁵N of the non-fixing species is discussed.