N-fixation rate and leaf N content in two species of Alnus and their relationship to diversity of symbiotic Frankia

This study investigated patterns of nitrogen (N) fixation rates, leaf N content, and geographic diversity in the N-fixing bacterium Frankia occurring in symbiosis with Alnus incana ssp. tenuifolia and A. viridis ssp. fruticosa in early and late successional habitats on the Tanana river floodplain and surrounding uplands in the Bonanza Creek Experimental Forest. Frankia diversity was estimated via polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the nifD-K spacer region, a non-coding region in the nitrogenase-encoding operon. Specific N-fixation rate was measured with a 15N2 uptake assay and leaf N content via mass spectrometry. Additional parameters measured were soil temperature and moisture, leaf del 15N, and specific leaf area.