Complementary N Uptake Strategies between Tree Species in Tropical Rainforest

Abstract

Within tree communities, the differential use of soil N mineral resources, a key factor in ecosystem functioning, may reflect functional complementarity, a major mechanism that could explain species coexistence in tropical rainforests. Eperua falcata and Dicorynia guianensis , two abundant species cooccurring in rainforests of French Guiana, were chosen as representative of two functional groups with complementary N uptake strategies (contrasting leaf δ 15 N signatures related to the δ 15 N of their soil N source, NO 3 - or NH 4 + ). The objectives were to investigate if these strategies occurred under contrasted soil N resources in sites with distinct geological substrates representative of the coastal rainforests. Results showed that species displayed contrasting leaf δ 15 N signatures on both substrates, confirming their complementary N uptake strategy. Consequently, their leaf 15 N can be used to trace the presence of inorganic N-forms in soils ( NH 4 + and NO 3 - ) and thus to indicate the capacity of soils to provide each of these two N sources to the plant community.