Data from: Mycorrhizal diversity, seed germination and long-term changes in population size across nine populations of the terrestrial orchid Neottia ovata

Orchids rely critically on mycorrhizal fungi for seed germination and seedling establishment, suggesting that the presence of suitable mycorrhizal fungi can exert a major impact on their population dynamics and long-term viability. However, there is little information about the factors determining mycorrhizal availability in natural orchid populations and how it affects orchid population dynamics. In this study, we investigated changes in population size between 2003 and 2013 in 28 populations of the orchid Neottia ovata. In a subset of nine populations, mycorrhizal diversity in both the roots and soil was assessed to test the hypothesis that population size or growth was significantly related to mycorrhizal diversity. Seed germination experiments were performed in situ to test the hypothesis that long-term changes in abundance were related to the ability of seeds to germinate and that seed germination was related to mycorrhizal diversity. Nearly 60% of the studied populations had declined in size (average growth rate across all populations: -0.01). A total of 68 species of putatively mycorrhizal fungi were observed, 21 of which occurred exclusively in roots, 25 that occurred solely in soil and 22 that were observed both in the soil and roots. Seed germination was limited and significantly and positively related to soil moisture content and soil pH, but not to fungal diversity or fungal community composition. Large populations or populations with high population growth rates showed significantly higher germination than small populations or populations declining in size, but no significant relationships were found between population size or growth and mycorrhizal diversity, suggesting that mycorrhizal diversity is not directly limiting the abundance of N. ovata in the study area.