Ericoid Mycorrhizas in Organic Substrates: Distribution of Ericoid Mycorrhizas among Epiphytes in a Costa Rican Cloud Forest and Uptake of Organic Nitrogen by Ericoid, Ecto-, and Arbuscular Mycorrhizal Pygmy Forest Plants

The success of Ericaceae in organic substrates worldwide is frequently attributed to the exceptional ability of ericoid mycorrhizal (ERM) fungi to acquire organic N. However, much of the supporting research has been conducted in axenic laboratory conditions on boreal and arctic species. I investigated the occurrence and morphology of ericoid mycorrhizas in a neotropical forest and assessed the ability of temperate ERM species rooted in soils to acquire intact organic N (glycine-2 ¹³ C, ¹⁵ N) and to acquire N from ¹⁵ N-enriched litter. Co-occurring arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) species were included for comparison.

Terrestrial and epiphytic ericaceous species collected in a neotropical cloud forest (Costa Rica) hosted typical ERM structures, dark septate endophytes (DSE), and, unexpectedly, fungal mantles and pseudo-Hartig nets. This diversity supports the emerging hypothesis that multiple fungal species may occupy ericaceous roots concurrently. Non-ericaceous roots (Araceae, Clusiaceae, Piperaceae) were AM, DSE, or non-mycorrhizal.