Document: MEL-3-35-10

Specialization and species distribution in orchid-fungal symbioses.

MCCORMICK, M.K.*, K.L.O'MALLEY, D.F.WHIGHAM and J.P.O'NEILL

Smithsonian Environmental Research Center, Edgewater, MD 21037 USA ¹

Abstract:
The distribution of orchids may depend on the distribution and diversity of appropriate symbionts. Orchids depend on mycorrhizal fungi early in life and continue these fungal associations as adults. We examined symbiotic associations between fungi and four orchid species with distributions ranging from widespread to narrow. We hypothesized that narrowly distributed orchids (Corallorhiza odontorhiza and Liparis lilifolia) would associate with fewer fungi than widespread species (Goodyera pubescens and Tipularia discolor). Fungi isolated from adult plants and protocorms of each species were used in lab experiments with seedlings of L. lilifolia and G. pubescens to determine whether fungi affected orchid growth differently as a function of growth medium, and hence might affect distributions. We also examined whether multiple fungi were beneficial to seedling growth. We found that C. odontorhiza and L. lilifolia each associated with one fungal type, while G. pubescens and T. discolor associated with multiple fungi. In the lab, only seedlings of G. pubescens obtained differential benefits from fungi as a function of growth medium. Its seedlings also grew as well with two fungi as with one. Seedlings of L. lilifolia showed no differential effect of medium on fungal benefit and grew less well with two fungi than with one fungus. These preliminary results suggest that the ecological distribution of these four orchids may be a function of the diversity of mycorrhizal fungi they are able to utilize.

Keywords: orchid, mycorrhizae

This abstract is being presented at: 9:45 AM in session:
Oral Session #5: Mutualisms.