Spatial variation in below‐ground seed germination and divergent mycorrhizal associations correlate with spatial segregation of three co‐occurring orchid species

Abstract

Summary1. Understanding the many factors that affect community composition and coexistence of species in natural environments is one of the central goals in ecology. As germination and establishment of seedlings in orchids are crucially dependent on mycorrhizal availability, the diversity and spatial distribution of orchid mycorrhizal fungi are likely factors that contribute to orchid coexistence.2. In this study, we combined molecular identification techniques with seed germination experiments and spatial point pattern analyses to investigate to what extent differences in mycorrhizal association patterns affected spatial variation in seed germination and the above‐ground distribution of three co‐occurring terrestrial orchid species (Anacamptis morio, Gymnadenia conopsea and Orchis mascula).3. The three species associated with a different set of mycorrhizal fungi, except A. morio and G. conopsea, which shared one fungal associate. The number of fungal lineages detected associating with each species also differed between species, being highest in G. conopsea, which associated with five lineages, and restricted to a single lineage in O. mascula.4. Seed germination experiments showed that below‐ground seed germination was restricted to locations where orchid individuals were most abundant, and quickly declined with increasing distance from the nearest above‐ground congener. Spatial point pattern analyses indicated significant fine‐scale spatial clustering that was highest in O. mascula and lowest in G. conopsea. Moreover, the spatial distributions of the three species were independent from each other, except for A. morio and G. conopsea.5. Synthesis. Our results support previous findings that co‐occurring orchid species tend to use different mycorrhizal partners. Although the possibility that variation in local environmental conditions affected seed germination could not be completely ruled out, our results suggest that the presence of specific mycorrhizal fungi contributed, at least partly, to the spatial distribution and coexistence of the investigated orchid species.