Nitrate-reducing capacity of roots and nodules ofAlnus rubra and roots ofPseudotsuga menziesii

Summary Nitrate-reducing capability was demonstrated for root segments of red alder and, at more than twice that rate, for alder nodules. Root segments of Douglas-fir failed to reduce nitrate despite various treatments designed to induce such activity. The reported response of Douglas-fir to nitrate fertilizer may be ascribed either to microbial assimilation of nitrate ions with subsequent liberation of ammonium in the soil or to nitrate assimilation by fungi that form mycorrhizae with Douglas-fir roots.