Contrasting responses to mycorrhizal inoculation and phosphorus availability in seedlings of two tropical rainforest tree species

This work aimed at understanding the role of mycorrhizal status in phosphorus efficiency of tree seedlings in the tropical rainforest of French Guyana. Mycorrhizal colonization, growth, phosphorus content, net photosynthesis and root respiration were determined on three occasions during a 9-month growth period for seedlings of two co-occurring species (Dicorynia guianensis and Eperua falcata) grown at three soil phosphorus concentrations, with or without inoculation with arbuscular mycorrhizas. Seedlings of both species were unable to absorb phosphorus in the absence of mycorrhizal association. Mycorrhizal seedlings exhibited coils that are specific of Paris-type mycorrhizae. Both species benefited from the mycorrhizal symbiosis in terms of phosphorus acquisition but the growth of E. falcata seedlings was unresponsive to this mycorrhizal improvement of phosphorus status, probably because of the combination of high seed mass and P reserves, with low growth rate. The two species belong to two different functional groups regarding phosphorus acquisition, D. guianensis being an obligate mycotrophic species.