Vesicular-Arbuscular Mycorrhizal Associations of Vascular Plants on Heron Island, a Great Barrier Reef Coral Cay

Abstract

Roots of 42 species of angiosperms collected from all vegetation zones on Heron Island were cleared, stained with chlorazol black E and assessed for vesicular-arbuscular mycorrhizae (VAM). Percentage of root length colonized was determined using the gridline intersect method, while stages in internal development of the mycorrhizal association were determined by mounting cleared root pieces on microscope slides and examining them with Nomarski differential interference contrast microscopy. Fifty-seven percent of the species had VAM and of these the percentage of root length colonized varied from 3 to 100%. There were no statistically significant differences among the four vegetation zones of the island in the number of species colonized. About the same proportion of trees and shrubs had VAM as did the herbs. Two species of Brassicaceae, Lepidium virginicum and Sisymbrium orientale, had VAM. All but three species with VAM had both arbuscules and vesicles; arbuscules were not found in Casuarina equisetifolia var. incana, Sisymbrium orientale and Tribulus cistoides.