Abstract Detail

Molecular Ecology

Evans, Simone [1], McCormick, Melissa [2], Whigham, Dennis [3].

The web of mycorrhizal fungi: Associations among Galearis spectabilis orchids, Ceratobasidium fungi, and ectomycorrhizal trees.

Interplant nutrient exchange via mycorrhizal fungal networks supports forest ecosystems. Mycorrhizal relationships are particularly important to terrestrial orchids, as they require specific fungal partners to germinate and grow. Orchids represent roughly 10% of flowering plant species, and all are dependent on orchid mycorrhizal fungi (OMF). These relationships favor orchids, so OMF fungi are dependent on external nutrient acquisition from decomposing material (saprotrophic fungi) or mutualistic relations with trees (ectomycorrhizal fungi). Ceratobasidium is one of three main genera known to form mycorrhizal relationships with orchids. Ceratobasidium is typically assumed to be saprotrophic; however, recent research has found taxa that form tripartite relationships with photosynthetic orchids and ectomycorrhizal (ECM) trees. Without identifying the extent of interplant relations or a clear phylogenetic signal for the fungal functional guild, it is difficult to predict ecological roles for plant-fungal associations, something that is necessary for conservation and restoration. We studied Galearis spectabilis, a terrestrial photosynthetic orchid, to determine whether the Ceratobasidium taxa it associates with form mycorrhizal relationships with ECM trees. The study had two main objectives: (1) determine whether Ceratobasidium OMF associated with G. spectabilis also associated with ECM trees and (2) identify a phylogenetic signal within Ceratobasidium that would allow us to predict whether fungi were ectomycorrhizal (ECM) or saprotrophic (SAP). First, we used carbon and nitrogen stable isotopes to determine whether the orchid isotopic composition of G. spectabilis indicated the fungi were ECM or saprotrophic. Second, we used direct PCR to identify fungi on ECM tree roots located immediately adjacent to orchids. We placed our data in the context of previous studies on stable isotopes and public ITS data for the family Ceratobasidiaceae. We found that the isotopic signature of G. spectabilis was significantly enriched in heavy isotopes of C and N, similar to other partially mycoheterotrophic orchids utilizing ECM fungi. We also found fungal sequences obtained from ECM tree roots adjacent to orchids were in the fungi clade specific to G. spectabilis. Phylogenetic analysis indicated that G. spectabilis-associated fungal strains belonged to a clade within Ceratobasidium that was previously identified as ECM, suggesting that the phylogenetic identity of OMF may provide an indication of their ecology beyond associations with orchids. The relationship between G. spectabilis, Ceratobasidium fungi, and ECM trees provides further recognition of   the complexity of mycorrhizal fungi networks and a need to consider all plant-fungal relationships in efforts to conserve native orchids.

1 - 349 S River Clubhouse Rd., Harwood, MD, 20776, United States
2 - Smithsonian Institution, SERC, 647 Contees Wharf Rd, Edgewater, MD, 21037, United States
3 - Smithsonian Environmental Research Center, 647 Contees Wharf Rd, Edgewater, MD, 21037, United States

Keywords:
Ectomycorrhizal fungi
Orchid  
Ceratobasidium
Interplant Relations
stable isotope
ITS
Plant-fungal interaction
Fungal guild.

Presentation Type: Oral Paper
Session: ME1, Molecular Ecology
Location: /
Date: Tuesday, July 20th, 2021
Time: 3:45 PM(EDT)
Number: ME1004
Abstract ID:508
Candidate for Awards:None