Nitrogen-fixing Bacillus sp. associated with Douglas-fir tuberculate ectomycorrhizae |
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Authors: | C Y Li H B Massicote L V H Moore |
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Institution: | (1) Forest Service, Pacific Northwest Research Station, US Department of Agriculture, 3200 SW Jefferson Way, 97331 Corvallis, OR, USA;(2) Department of Anaerobic Microbiology, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, 24061 Blacksburg, VA, USA |
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Abstract: | Nitrogenase activities, measured by acetylene reduction, were detected under microaerophilic field conditions in Douglas-fir tuberculate ectomycorrhizae. Tuberculate ectomycorrhizae consist of densely packed clusters of ectomycorrhizal rootlets enclosed in a supplementary fungal peridium-like layer. Nitrogenase activity was primarily in the external layer and was greatly enhanced with added sucrose. The bacterium isolated, a nitrogen-fixing, spore-forming Bacillus sp., is an aerobe but requires anaerobic conditions for nitrogenase activity. Respiration in the tuberculate complex by the fungus, roots, and associated mycorrhizosphere microbes probably contributes to maintaining a microaerophilic niche where nitrogen fixation can take place. Water extracts of peridium or mycorrhizal root tips enhanced nitrogenase activity of this associative Bacillus sp., thereby indicating a close nutritional relationship between this bacterium and the tuberculate mycorrhizae. Thiamine more significantly enhanced bacterial nitrogenase activity than biotin; no activity was detected with p-aminobenzoic acid. Even though the levels ofnitrogenase activities in the tubercles in situ were low, as measured by the present methods, they may indicate a significant contribution to the nitrogen dynamics of these nitrogen-limited Douglas-fir forests over a long-term period. |
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Keywords: | associative diazotrophs Douglas-fir ectomycorrhizae nitrogen fixation tuberculate ectomycorrhizae |
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