Role of selected dark septate endophyte species and other hyphomycetes as saprobes on moss gametophytes

Dark septate endophytes (DSEs) live asymptomatically in the roots of vascular plants, are common in arctic and alpine areas, and are thought to play a quasimycorrhizal role. It is not known, however, whether they precede or arrive with their hosts. Previously reported enzymatic abilities of Phialocephala fortinii suggest that DSEs can live on organic debris in the soil, but there is little direct or experimental evidence for this. Phialocephala fortinii, Leptodontidium orchidicola, Cadophora melinii, Cadophora luteo-olivacea, and Lecythophora sp. were inoculated onto autoclaved Hylocomium splendens gametophytes and incubated for 3 months to determine if they degrade this organic material based on observations made using light and scanning electron microscopy. All fungi were able to colonize the bryophyte tissue to some extent. Lecythophora sp. and L. orchidicola penetrated cells by forming bore holes. Cadophora luteo-olivacea and P. fortinii were also observed inside cells, but bore holes through bryophyte cell walls were not observed. Cadophora melinii sporulated and grew abundantly on the surface of gametophytes but did not appear to penetrate cell walls. Phialocephala fortinii and L. orchidicola formed sclerotia in the gametophytes similar to those formed in roots. These results suggest that DSE fungi can persist and produce propagules, i.e., sclerotia and conidia, in the absence of host roots. These observations support the hypothesis that DSE fungi are able to precede their hosts during primary succession events.