The Occurrence of Mycorrhizae in Vascular Epiphytes of Two Costa Rican Rain Forests

Epiphytic vascular plant and soil samples were collected from recently fallen trees at two rain forest sites in Costa Rica: tropical wet forest at La Selva and lower montane rain forest at Monteverde. Plant samples were examined for mycorrhizal colonization. Soils were analyzed for a number of chemical properties and bioassayed for vesiculararbuscular mycorrhizal inoculum. Six of 14 orchid species examined supported typical orchid mycorrhizae, and all four ericaceous species examined supported ericoid mycorrhizae. Of the remaining 50 species examined, representing 14 families, 9 species in 6 families showed low levels of vesicular-arbuscular colonization. Most of the species lacking vesicular-arbuscular mycorrhizae came from families generally considered to be mycorrhizal. Canopy derived soils were highly organic, acidic, and high in extractable phosphorus. Bioassays using onion failed to produce vesiculararbuscular mycorrhizae. We suggest that a number of ecological factors act to limit occurrence of vesicular-arbuscular mycorrhizae in the epiphyte assemblages examined.