ENDOPHYTIC COLONIZATION AND NITROGEN FIXATION BY PAENIBACILLUS POLYMYXA IN ASSOCIATION WITH LODGEPOLE PINE AND WESTERN RED CEDAR

ii In this study I provide evidence of biological nitrogen fixation by endophytic, diazotrophic bacteria as a possible source of nitrogen for lodgepole pine (Pinus contorta var. latifolia (Dougl. Engelm.) and western red cedar (Thuja plicata Donn.); conifers that are known for their ability to grow in the nitrogen-poor forests of western North America. Diazotrophic bacteria were isolated from root, stem and needle tissues of both these tree species, growing on forested sites with contrasting N availability in the interior of British Columbia, Canada. Members of the genera Bacillus and Paenibacillus genera dominated the culturable, endophytic bacterial community in tissues of both tree species. A Paenibacillus polymyxa isolate designated strain P2b-2R from lodgepole pine at the nitrogen deficient site near Williams Lake, BC., demonstrated high (5.1705 μmols C2H4/ml), replicable, nitrogenase activity, under laboratory conditions. P. polymyxa strain P2b-2R inoculated and control lodgepole pine and cedar seedlings were grown in a sand – turface mixture enriched with a 5 atom % excess 15N [Ca(15NO3)2