Complementary N Uptake Strategies between Tree Species in Tropical Rainforest

Area of Science:

• Ecology
• Plant Ecology
• Biogeochemistry

Background:

• Species coexistence in tropical rainforests is often explained by functional complementarity.
• Differential resource use, particularly of soil nitrogen (N) mineral forms (nitrate [NO3-] and ammonium [NH4+]), is a key factor in ecosystem functioning.
• Eperua falcata and Dicorynia guianensis are abundant cooccurring species in French Guiana rainforests, potentially representing distinct N uptake strategies.

Purpose of the Study:

• To investigate if complementary N uptake strategies of Eperua falcata and Dicorynia guianensis are maintained under contrasting soil N resources.
• To assess these strategies across sites with different geological substrates in French Guiana coastal rainforests.
• To determine if leaf nitrogen isotope signatures (δ15N) can indicate the form of inorganic N available in soils.

Main Methods:

• Field study comparing two abundant tree species (Eperua falcata and Dicorynia guianensis) on contrasting geological substrates.
• Analysis of leaf δ15N signatures to infer N uptake strategies.
• Relating leaf δ15N to soil N forms (NO3- and NH4+) to understand N resource partitioning.

Main Results:

• Both species consistently displayed contrasting leaf δ15N signatures across both geological substrates.
• These contrasting signatures confirmed the presence of complementary N uptake strategies for nitrate (NO3-) and ammonium (NH4+).
• Leaf δ15N effectively traced the dominant inorganic N form available in the soils.

Conclusions:

• The complementary N uptake strategies of Eperua falcata and Dicorynia guianensis are robust across different soil N resources and geological substrates.
• Leaf δ15N serves as a reliable indicator of soil inorganic N forms (NO3- and NH4+).
• This finding highlights the role of functional complementarity in maintaining species coexistence and provides a tool for assessing soil N availability in tropical rainforests.