Mycorhizal symbiosis in trees of the tropical rainforest of French Guiana

Roots of 75 tree species, belonging to 28 families, were sampled on different types of soil in the forest of French Guiana. Both seedlings and mature trees of each species were studied. The roots were first observed for ectomycorrhizas, then thinned and stained to observe and quantify endomycorrhizal associations. Ectomycorrhizas were found only on two genera: Coccoloba (Polygonaceae) and Neea (Nyctaginaceae). All the species studied had zygomycetous endomycorrhizas with hyphal coils and vesicles. It is remarkable that some families (Caesalpiniaceae, Myrtaceae, Tiliaceae, Euphorbiaceae, Lauraceae), considered as frequently ectomycorrhizal in other regions of the world, were not so in our sample. In addition, the results contradict the theory that ectomycorrhizal species are dominant in the poorest soils in tropical rainforests (tropical podzols).