Abstract
Orchid species are critically dependent on mycorrhizal fungi for completion of their life cycle, particularly during the early stages of their development when nutritional resources are scarce. As such, orchid mycorrhizal fungi play an important role in the population dynamics, abundance, and spatial distribution of orchid species. However, less is known about the ecology and distribution of orchid mycorrhizal fungi. In this study, we used 454 amplicon pyrosequencing to investigate ecological and geographic variation in mycorrhizal associations in fourteen species of the orchid genus Dactylorhiza. More specifically, we tested the hypothesis that variation in orchid mycorrhizal communities resulted primarily from differences in habitat conditions where the species were growing. The results showed that all investigated Dactylorhiza species associated with a large number of fungal OTUs, the majority belonging to the Tulasnellaceae, Ceratobasidiaceae and Sebacinales. Mycorrhizal specificity was low, but significant variation in mycorrhizal community composition was observed between species inhabiting different ecological habitats. Although several fungi had a broad geographic distribution, Species Indicator Analysis revealed some fungi that were characteristic for specific habitats. Overall, these results indicate that orchid mycorrhizal fungi may have a broad geographic distribution, but that their occurrence is bounded by specific habitat conditions.
Highlights
Communities comes from comparisons of mycorrhizal communities across different habitats within a single orchid species
To determine the relative importance of ploidy level and habitat conditions in determining mycorrhizal communities, we sampled fourteen Dactylorhiza species that were characterized by different ploidy levels and occupied distinct habitats, including Mediterranean grasslands and forests (D. sambucina, D. romana, D. insularis and D. markusii), peat bogs (D. sphagnicola, D. maculata), wetlands (D. fuchsii, D. majalis, D. viridis, D. elata), coastal habitats (D. praetermissa, D. incarnata) and alpine-boreal habitats (D. alpestris and D. lapponica)
We asked whether: (1) orchid species from different habitats associated with different mycorrhizal communities; (2) there were specific fungal Operational Taxonomic Units (OTUs) that were significantly associated with a particular habitat type; (3) differences in ploidy level or genome composition had a significant impact on mycorrhizal communities
Summary
Communities comes from comparisons of mycorrhizal communities across different habitats within a single orchid species. Pronounced differences in mycorrhizal communities were reported between dune slack and forest populations of Epipactis species Overall, these results indicate that differences in habitat conditions can affect the occurrence of particular orchid mycorrhizal fungi and impact on plant-fungus interactions in orchids[15]. Compared to other European orchid genera, Dactylorhiza is unusual in that it contains a large number of species with varying ploidy levels, including diploids, triploids, autotetraploids and a vast number of allotetraploid species[18,24,25] The latter comprise groups of species whose origin stemmed from independent hybridization events occurring in various parts of Europe and the Mediterranean Basin. (1) orchid species from different habitats associated with different mycorrhizal communities; (2) there were specific fungal OTUs that were significantly associated with a particular habitat type; (3) differences in ploidy level or genome composition had a significant impact on mycorrhizal communities
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