Biogeography of Orchid Mycorrhizas

Abstract

Most orchid mycorrhizal fungi (OMF) are free-living decomposers that do not depend on orchids for establishment or survival. Despite their importance for completion of the orchid life cycle, the geographical distribution of OMF remains poorly understood. Here we review studies that examined the relationship between orchids and their mycorrhizal associates and place them in a biogeographical context. We first describe the diversity of OMF and then examine the patterns of OMF distributions according to geographical locations, biomes, and islands. OMF have been found across all major biogeographic realms and biomes. While the distribution of the major mycorrhizal fungal families that associate with orchids appears to be entirely cosmopolitan, we know little about how the distribution of particular OMF shapes the distribution of the orchids that rely on them. In the face of ongoing rapid anthropogenic influence on the natural environment, more information is needed to show how OMF communities vary across large geographical scales and how this affects the distribution of orchids. In particular, we need to identify the environmental variables (e.g., rainfall, geological substrate) that drive spatial variation in OMF communities. This information will be crucial for setting up future orchid conservation and restoration projects.