Great Basin Naturalist


To determine the role of the California red-backed vole (Clethrionomys califonicus), the northern flying squirrel (Glaucomys sabrinus), and the deer mouse (Peromyscus maniculatus) in the nitrogen cycle of forest stands in western Oregon, bacterial colonies were isolated and purified from feces, and their nitrogen-fixing ability measured by acetylene-reduction assay. The ability of the bacterial species Azospirillum sp. to withstand freezing was also tested. Fecal extracts were used to test whether fecal pellets can provide the nutrients necessary for growth of the bacteria. All the feces tested contained viable nitrogen-fixing bacteria, and both species can survive drying and one can survive freezing. Azospirillum colonies grew well on liquid medium but required yeast extract for growth and nitrogenase activity. Fecal extracts from flying squirrels and chickarees (Tamiasciurus douglasi) were as effective as the yeast. The results suggest another link in the chain of mutualism that unites small mammals, mycorrhizal fungi, and forest trees.