SOIL under a stand of Alnus rubra Bong. in mixture with conifers was found to contain markedly higher levels of nitrate nitrogen than soil under an adjacent stand of pure conifers1. This phenomenon has substantial implications for the ecology of root pathogens and their antagonists in forest soils. We were particularly interested in Poria weirii Murr., a severely damaging pathogen of conifer roots in western North America, and we have therefore investigated its ability to assimilate nitrate nitrogen.