Vesicular-Arbuscular Mycorrhizae of Some Hawaiian Dune Plants!

The mycorrhizal status of dune plants from the island of Hawaii was investigated. All plants, including Batis maritima, Cocos nucifer, Ipomoea brasiliensis, Pennisetum setaceum , Prosopis pallida, Scaevola taccada, and Sporobolus sp., had vesicular urbuscular mycorrhizae (VAM) . Levels of colonization by VAM fungi ranged from less than 10% to 100% of the root length and were highest in Ipomoea , Pennisetum, and Sporobolus. Twelve species ofVAM fungi were recovered, half of which are undescribed. The most frequently recovered species were Sclerocystis sinuosa, Glomus microaggregatum, an undescribed Glomus sp., and an undescribed Scutellospora (Gigaspora) sp. The composition of the VAM funga l communities of the black sand dunes differed from those of the quartz and carbonate dunes. The community of Hawaiian dune mycorrhizal fungi was very distinct from dune communities of Australia, San Miguel Island (California), the Atlantic Coast of the United States, Scotland, and Italy. The presence or absence ofVAM fungi in dunes may have been ofcritical importance to the successful colonization of the Hawaiian Islands by some vascular plants, and these fungi may thus have influenced the subsequent development of the native flora . THE IMPORTANCE OF vesicular-arbuscular mycorrhizae (VAM) in the establishment and growth of sand dune-colonizing plants was first suggested by Nicolson in 1959. Since that time, the role of VAM fungi in alleviating the effects of low soil phosphate and water stress on plants in a variety of habitats has been well documented (e.g., Harley and Smith 1983). Sand dune soils appear to be especially favor able to development of VAM because of their low phosphorus content (Koske and Halvorson 1981, Ranwell 1972), and VAM appear to be required for significant sand dune stabilization to occur (Koske and Polson 1984). VAM have now been identified from maritime and lacustrine dunes in numerous temperate locations, including the continental United States (Bergen and Koske 1984, Friese 1984, Koske 1987, Koske and Halvorson 1981, Koske and Tews 1987, Sylvia 1986, Tews and Koske 1986), Canada (Koske et al. 1975), Scotland 1 Manu script accepted 23 July 1987. 2 University of Rhode Island , Department of Botany, Kingston , Rhode Island 02881. (Nicolson 1959, 1960, Nicolson and Johnston 1979), and Italy (Giovannetti 1985, Giovannetti and Nicolson 1983). VAM also have been reported from maritime dunes of subtropical Australia (Jehne and Thompson 1981, Koske 1975). In addition to benefitting the host plant directly through improved phosphate nutrition and indirectly by reducing water stress (e.g., Huang et al. 1985), VAM fungi contribute to stabilization of sand dunes by binding sand grains into larger aggregates and improving soil structure (Clough and Sutton 1978, Forster and Nicolson 1981, Koske et al. 1975, Sutton and Sheppard 1976). Such improved soil structure is significant in influencing plant succession on the dunes, which occurs as they age (Nicolson 1960, Olson 1958, Ranwell 1972). Previous studies of VAM in sand dunes have concerned those associated with continents . The unusually large size of VAM fungal spores (up to 1 mm diameter) restricts their dispersal by wind in comparison to other fungi, and these one-celled propagules may not survive as long in the upper atmosphere