Nitrogen Fixation in the Canopy of Temperate Forest Trees: A Re-examination

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Abstract
15N2 studies and acetylene reduction assays of leaves and shoots of Douglas fir and other forest trees do not confirm previous reports that extensive nitrogen fixation occurs on leaf surfaces and it is concluded that the importance of nitrogen fixation in the canopy of forest trees has been exaggerated. The presence of nitrogen-fixing bacteria on the leaves of trees is confirmed, however, and they have been identified as Enterobacter agglomerans, Clostridium butyricum and Bacillus sp. Their distribution on leaves is fortuitous since dead oak leaves and artificial leaves become colonized to the same extent as living oak leaves.