Changes in the diversity of the mycorrhizal fungi of orchids as a function of the water supply of the habitat

Abstract

Studies were made on the symbiotic associations of orchids in four habitats with diverse water regimes in order to determine whether there was any difference in the diversity of the symbiotic fungi of orchids in the various habitats. The habitats were classed along an environmental gradient based on the water supplies as follows: 'floating': an extremely wet floating mat, 'wet': terrestrial fens, 'variable': wet habitats that dry out periodically, and 'dry': drier steppe areas in the vicinity of wet habitats. Nine photosynthesising orchid species were included in the study, some of which were habitat-specific (Liparis loeselii, Hammarbya paludosa), while others had a broader range of habitats and were found on several of the habitats examined (Orchis laxiflora ssp. pallustris, Dactylorhiza incarnata, Epipactis palustris). A total of 94 fungal strains were isolated from the orchid roots and seedlings and were identified using nrITS sequence analysis. Representatives of four widely occurring groups of orchid mycobionts were identified, but they were present in different ratios in each habitat. Opposing habitat preferences were observed for two groups of the anamorphic fungus genus Epulorhiza, which are frequent orchid symbionts. The first group (Epulorhiza 1), which includes the fungal partner of Liparis loeselii, was dominant in the floating habitats, where no members of the Epulorhiza 2 group were found, while the latter were more typical of drier habitats, where they were dominant. The Ceratobasidiaceae fungi, also isolated in considerable numbers, were more dominant in habitats with moderate water supplies, which were also home to representatives of the Sebacinaceae, though these were isolated in smaller numbers. The great variability in the composition of the symbiotic fungi of orchids in the different habitats suggests that efforts to preserve orchids require an accurate knowledge of orchid habitats, including data on potential fungal partners.