ECOLOGICAL SIGNIFICANCE OF ENDO-/ECTOMYCORRHIZAE IN THE OAK SUB-GENUSERYTHROBALANUS

Abstract

Summary Examination of pin oak (Quercus palustris Muench.) mycorrhizae from a wide range of ecological sites revealed the presence of vesicular-arbuscular (VA) mycorrhizae as well as ectomycorrhizae. Vesicular-arbuscular mycorrhizae have not previously been reported on pin oak, and only rarely reported on other oak species. Soil conditions were considered to be important in the formation of VA mycorrhizae. Greenhouse inoculation tests showed that in addition to pin oak, northern red oak (Quercus rubra L.), also a member of the sub-genus Erythrobalanus, could also form VA mycorrhizae, but white oak (Quercus alba L.) could not. A subsequent study of woodland northern red oak root systems showed that upland trees had significantly more ectomycorrhizae, and lowland trees had significantly more VA mycorrhizae. On both upland and lowland sites, VA mycorrhizae increased when the soils were either very wet or very dry, whereas the more typical ectomycorrhizae were favoured by moderate soil moisture. This flexibility in mycorrhizae formation may explain, in part, the success of pin oak and red oak on diverse sites, such as flood plains, uplands, and urban landscapes.