A New Nitrogen‐fixing Cyanophyte‐hepatic Association: Nostoc and Porella

Porella navicularis , a common leafy liverwort in western North America, was found to possess numerous epiphytic Nostoc colonies. Although the abundance of colonies was variable, the association was found consistently throughout a broad geographic range. Unlike cyanobacteria in other hepatic assocations, the Nostoc occurred as distinct colonies harbored in crevices and curled margins of leaves. Heterocyst frequency was 3–7%. Acetylene reduction activity was present in 85% of samples examined, with an average value of 53.5 nmol C 2 H 4 ∙g dry wt ‐1 ∙hr ‐1 and a maximum of 316 nmol C 2 H 4 ∙g dry wt ‐1 ∙hr ‐1 . This suggests that bryophyte nitrogen‐fixing associations may be more important than previously realized.