The incidence of arbuscular mycorrhiza in two submerged Isoëtes species

We investigated the occurrence of arbuscular mycorrhizal fungi in the roots of Isoëtes lacustris and I. echinospora. These submerged lycopsids are the only macrophyte species inhabiting the bottom of two acidified glacial lakes in the Czech Republic. Arbuscular mycorrhizal (AM) fungi were detected in the roots of both species but the percentage of root colonization was both low and variable. Nevertheless, planting Littorella uniflora in the sediments from Isoëtes rhizosphere revealed high levels of viable AM propagules in both lakes. While AM colonization of Isoëtes roots did not exceed 25%, the average colonization of Littorella roots amounted to more than 80%. Although colonization of quillwort roots by AM fungi is evident, the taxonomic identity and role of these AM fungi in plant growth remain unclear. In addition to AM fungi, root-colonizing dark septate endophytic fungi were observed in both Isoëtes species.

Research highlights
► Arbuscular mycorrhizal (AM) fungi colonized the roots of Isoëtes lacustris and I. echinospora.
► AM colonization rate was low and involved mainly hyphae and vesicles.
► The taxonomic identity and role of AM fungi in Isoëtes growth remain to be elucidated.
► Root colonization by dark septate endophytes was recorded in both Isoëtes species.