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 C₂H₄?g dry wt^-1?hr^-1 and a maximum of 316 nmol C₂H₄?g dry wt^-1?hr^-1. This suggests that bryophyte nitrogen-fixing associations may be more important than previously realized.