Spatial distribution of spore banks of ectomycorrhizal fungus, Rhizopogon togasawarius, at Pseudotsuga japonica forest boundaries

Ectomycorrhizal (EcM) fungal spore banks can facilitate seedling establishment where compatible host tree species are absent. Although Rhizopogon togasawarius spore banks play an important role in the early establishment stage of endangered Japanese Douglas-fir (Pseudotsuga japonica) seedlings, the dispersal ecology of this EcM fungus is poorly understood. The objective of this study was to clarify the spatial distribution and dispersal distance of R. togasawarius spore banks that extend inside and outside extant P. japonica forests. We evaluated R. togasawarius spore banks in five remnant forests and neighboring arbuscular mycorrhizal artificial plantations using Douglas-fir (P. menziesii) seedling bioassays. Forty-five to ninety-five surface soils were collected along lines of increasing distance from P. japonica forests to neighboring plantations. In each forest, 60%-84% of the soils collected inside or within 50 m of forest boundaries of P. japonica forests harbored R. togasawarius spore banks. The occurrence of R. togasawarius decreased significantly with increasing distance from the forest boundaries. Moreover, R. togasawarius was detected in samples several hundred meters away from forest boundaries. These results suggest that R. togasawarius has a dispersal capacity to extend the range of the spore banks outside the forest of host trees.