VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI, PARTICULARLY GLOMUS-TENUE, INVENEZUELAN BROMELIAD EPIPHYTES

The mycorrhizal status of water-impounding ''tank'' bromeliad epiphyte s from three locales differing in altitude and moisture regime within Venezuelan cloud forest was examined. Species of vesicular-arbuscular mycorrhizal (VAM) fungi found in arboreal soils were compared to VAM f ungi found in terrestrial soils. Sixteen of the 19 epiphytes examined for the presence of VAM fungi had roots with infection stages; 14 of t hese specimens showed growth of the fine endophyte Glomus tenue. Fine endophyte was the only VAM fungus found associated with epiphytes in t he driest locale studied, while coarse VAM fungi (Gigaspora and Scutel lospora spp.) were found at sampling locales receiving more moisture. Root infection was usually composed of intercellular hyphae and peleto ns, few arbuscules were observed. However, abundant extracellular hyph ae were often observed tangled about roots in arboreal soil. It is con cluded that epiphytic bromeliads probably benefit, at least periodical ly, from VAM fungi scavenging for sporadically available nutrients in arboreal soils. Glomus tenue may be particularly important as a coloni zing VAM fungus in drier sites of Venezuelan cloud forest. The species composition of VAM fungi in arboreal soils was different to that of t errestrial soils sampled directly under epiphytic bromeliad perches, s uggesting that VAM fungi species associated with bromeliads are disper sed to their hosts by vagile animal vectors.