River and lake sediments as sources of infective Frankia (Alnus)

Several Alnus species are commonly found growing along rivers and lakes. Alnus forms root nodules with N-2-fixing Frankia. We used plant bioassays to detect presence of infective Frankia in river and lake sediments from northern Sweden and Alaska. Silty river water and superficial river and lake sediments from all sites contained infective and effective Frankia, but 100-3000 year old lake sediments did not produce nodulated plants. Action by streams, waves and changing water levels transport Frankia in superficial sediments and can provide an inoculum for Alnus roots.