Hornwort-cyanobacteria interactions: exploring ontogeny in Nothoceros vincentianus and Dendroceros crispus growing together with Nostoc cyanobacteria.

In hornworts, the infection process by Nostoc begins early in gametophyte development, with multiple cyanobacterial strains often present in the same thallus, suggesting varying levels of specificity in symbiosis. We tested the effect of a Nostoc strain from the rupicolous hornwort Nothoceros vincentianus on spore germination and sporeling development of N. vincentianus and epiphytic Dendroceros crispus. Over 154 days, D. crispus outperformed N. vincentianus, which showed lower survival and growth when associated with Nostoc. These results highlight the complexity of Nostoc-hornwort interactions and suggest Nostoc strains naturally occurring within a species' gametophyte may not perform well in vitro.