Mycorrhizae in Hawaiian Epiphytes!

In surveys in the Hawaiian Islands, mycorrhizae occurred frequently in epiphytic, nonorchidaceous angiosperms and pteridophytes. Both vesicular-arbuscular (VA) and ericoid mycorrhizae were present in epiphytes growing 1-3 m above the forest floor on dead and living tree trunks and on living tree ferns in montane wet forest sites. All eight angiosperm species were mycorrhizal, and 13 of 22 pteridophytes possessed VA mycorrhizae. The high frequency of mycorrhizae in epiphytic species suggests that propagules of mycorrhizal fungi routinely are dispersed to these microsites. Possible means of dispersal are discussed. 1 Manuscript accepted 28 March 1994. 2 Department of Botany, University of Rhode Island, Kingston, Rhode Island 02881. Root samples (10-40 cm long) were collected from plants growing on living and dead trunks of trees (mostly of Metrosideros polymorpha Gaud.) and tree ferns (Cibotium glaucum [J. E. Sm.]" Hook. & Amott) in montane wet forests between July 1987 and IN THE MONTANE WET forests ofthe Hawaiian Islands a dense epiphytic flora of angiosperms and pteridophytes flourishes. Intensive studies of Hawaiian angiosperms and pteridophytes growing in a variety of habitats (Gemma et al. 1992, Koske et al. 1992) revealed that a high percentage of these species form vesicular-arbuscular mycorrhizae (VAM). In those surveys mycorrhizae were found to be common among the epiphytes. Because VA and ericoid mycorrhizae seldom are reported to occur in epiphytic, nonorchidaceous angiosperms and pteridophytes (Boullard 1957, Cooper 1976, Nadkami 1981, Berch and Kendrick 1982, Trappe 1987, Lesica and Antibus 1990, Maffia et al. 1990), we were prompted to sample a greater diversity of species to better assess the prevalence of mycotrophy among Hawaiian epiphytes. MATERIALS AND METHODS June 1990. Roots of the epiphytes typically were growing in thick mats of moss that covered the trunks. Sampled plants were attached to their substrate at elevations of 1-3 m above ground level. Care was taken during collecting to sample individual plants for which roots could be positively identified as belonging to the particular plant. Most collections were made in the Koke'e and Alaka'i Swamp areas (Koke'e State Park) at elevations of ca. 1100 m above sea level on the island of Kaua'i. A few samples were collected from similar sites on the islands of Maui and Moloka'i. Roots were preserved in 50% isopropyl alcohol and later were cleared in hot 2.5% KOH and stained with 0.05% trypan blue in an acidified glycerol solution (Koske and Gemma 1989). Stained roots were mounted on slides in a polyvinyl alcohol-based solution (PVLG) (Koske and Tessier 1983). Entire root systems were examined at 40-60 x with a dissecting microscope, and portions of each root system were examined at 400 x with a compound microscope. The presence of vesicles, arbuscules, hyphal coils, and internal hyphae was noted for each specimen. Only those species in which arbuscules were found were considered to have functional VAM. Extenlqf YAM jI1f~ctj()!1 \V~~ _gl.tantifiedhy asSigning a mycorrhizal index (MI) value of 0-3 to stained root samples, where 0 indicates no VAM infection, 1 = up to 25% of root length infected (i.e., containing any