Ectomycorrhizal associations with Salix humboldtiana in Southern South America: An ancient cross-continental exchange.

MUJIC, ALIJA; NOUHRA E.; KUHAR, FRANCISCO; SMITH M.

Congreso; International mycological congress; 2018

Ectomycorrhizal (ECM) forests in southern South America (SSA) are dominated byNothofagaceae (southern beech) trees. Based upon the fossil record, Nothofagaceae trees and theirECM fungi have been present in SSA for 60 ? 100 million years with little evidence for co-occurring ECMhosts during this time. A second native ECM host tree, Salix humboldtiana (Humboldt?s willow),colonized SSA from the north between 3 ? 15 MYA. This event followed the formation of the Isthmus of Panama during the Great American Biotic Interchange. While Nothofagaceae species and S.humboldtiana overlap in latitudinal range, these trees represent different lineages, occupy differentniches, and seldom inhabit the same forests. Both Salix and Nothofagaceae associate with a diverseassemblage of ECM fungi but the biogeographic origins of these communities is expected to bedifferent (Salix from the Northern Hemisphere and Nothofagaceae from the Southern Hemisphere).However, it is possible the two hosts have exchanged ECM fungi since the colonization of SSA by Salix.In this study we characterize ECM communities associated with S. humboldtiana in Argentina andcompare these communities with Nothofagaceae to investigate the potential for ECM host jumpingbetween these taxa. We sampled rhizosphere soil, ECM root tips, and ECM fungal sporocarps fromstands of S. humboldtiana at 18 sites throughout its range in Argentina from Parque Nacional Calilegua(Northern Argentina) to the Chubut River (Central Patagonia). Since exotic Eurasian Salix spp. werepresent along the same watercourses throughout much of our sampling range, we also sampledrhizosphere soil and ECM root tips from exotic Salix at 5 sites to investigate the potential for shared ECMcommunities between exotic Salix and S. humboldtiana . Fungal communities from soil DNA and ECMroot tips were identified using Illumina Miseq meta-barcoding of the ITS1 region. Operational taxonomicunits (OTUs) were sorted by putative ecological niche (saprobic, pathogenic, mycorrhizal) using acombination of FUNGUILD and Blast searches of NCBI GenBank and our extensive in-house database.Results of our comparative metagenomic analyses indicate that ECM fungal communities of S.humboldtiana are composed of fungi primarily from northern hemisphere ECM lineages and lackrepresentatives from endemic southern hemisphere ECM fungal lineages (eg. Descolea,Phaeohelotium, Austropaxillus). There are several species of exotic ECM Basidiomycota that were likelyintroduced into S. humboldtiana ECM communities from exotic European Salix. Some lineages of ECMhost generalist fungi may also have moved between S. humboldtiana stands and Nothofagaceae forests.Exemplar lineages from our dataset include species of ECM host generalists Hebeloma (Agaricales),which are likely to have moved into Nothofagaceae forests from S. humboldtiana stands or exoticNorthern Hemisphere hosts, and Tomentella (Thelephorales)