Tom Horton


Professor, Mycorrhizal Ecology
Recipient of the 2014 William A. Weston Award for Excellence in Teaching - Mycological Society of America

SUNY-College of Environmental Science and Forestry
Department of Environmental and Forest Biology
1 Forestry Drive
Syracuse, NY 13210

Office: 350 Illick Hall
Lab: 425 Illick Hall

Please scroll down for my research interests, a list of folks that work or have worked in my lab present and past, and keep scrolling for a publication list with links to PDFs.



  • EFB 320, General Ecology. 4 credits, Fall
  • EFB 428/628, Mycorrhizal Ecology. 3 credits, Fall even years.
  • EFB 496/796, Advanced Mycology: Basidiomycetes. 2 credits, Fall odd years
  • EFB 797, Graduate seminar courses. 1 credit
    • Mycorrhizal Symbiosis.
    • Plus special topic seminars led by me and/or my graduate students
      • A History of Ecosystem Thought
      • Rhetoric in Science
      • Buller: A Phenomenal Mycologist
      • The Origin of Species


Some useful links dealing with mycorrhizal systems

  • Fungal Environmental Sampling and Informatics Network (FESIN)
  • Use-Friendly Nordic ITS Ectomycorrhiza Database (UNITE)
  • DEEMY: An information system for characterization and DEtermination of EctoMYcorrhizae
  • Photos galore at the Mycorrhizal Image Exchange page (many, but not all, have broken links -- sorry!)

My research interests

All of my research is applicable to various issues in conservation biology of ectomycorrhizal fungi and plants. Mycorrhizal fungi are primarily below ground, cryptic and essentially considered microbial, leading plant and ecosystem ecologists to largely 'black-box' their roles in plant communities and ecosystem dynamics. A second focus of mine is the development and use of PCR-based techniques to identify fungi directly from mycorrhizal root tips and soil hyphae, thus giving us an ability to peek into the black-box (see Horton and Bruns, 2001). It is amazing to me that most textbooks barely mention mycorrhizal symbioses. Indeed, many ecologists still consider mutualisms as special cases (acacia ants, orchid moths). Part of this bias comes from the fact that models of mutualisms predict that they are unstable and therefore should not be common (there are probably some socio-political issues here as well!!). But four examples of very stable mutualisms should put that misunderstanding to rest: chloroplasts in plant cells, mitochondria in eukaryotic cells, N-fixing bacteria in plant roots, and lichens. Further, around 80% of all plants associate with mycorrhizal fungi that are typically mutualistic, so mycorrhizal mutualisms are a fifth case demonstrating the ubiquity of mutualisms in nature. Are mycorrhizal symbioses evolutionarily stable? Mycorrhizal fungi have been associated with plants since they colonized land over 400 million years ago. Oh...and just to check whether you are mycocentric or phytocentric, when you read 'they' in the previous sentence, do you think of fungi or plants?

Current projects: updated May-2012

At the risk of pigeonholing the breadth of their work, my graduate students have investigated or are investigating the role of mycorrhizal fungi in plant community dynamics (Sara Ashkannejhad, Tera Galante, Jeremy Hayward, Mikey O'Brien, Yazmin Rivera), restoration ecology (Kris Dulmer, Chris Hazard, Erin Page, Sam Tourtelott), and ecosystem dynamics (Becka Walling) and development of phylogenetic approaches aimed at elucidating functional roles of EMF (Joe Vineis). See summaries of projects below.

  • Invasion biology
    • Isla Victoria in Argentina had a large number of conifer species introduced about 100 years ago. Today, only a handful have become invasive despite many more having life history traits that would suggest they should be invasive. We recently reported that a lack of mycorrhizal fungi in soils (spore and hyphal inoculum) is inhibiting invasion of conifers at distances away from the plantations. Interestingly, in addition to introduced pines and their fungi, pigs and deer have been introduced as well. This may be leading to a classic case of invasional meltdown given the potentiality that the mammals are now dispersing the ectomycorrhizal spores over long distances in their fecal pellets (see Ashkannejhad and Horton 2003). We are now investigating how mammals, wind, and belowground growth influence fungal spread away from existing plantations, supporting subsequent invasion by the exotic conifers. This project is in collaboration with Dr. Martin Nuñez and Dr. Dan Simberloff at the University of Tennessee. Jeremy Hayward (PhD student)
      • REU Project for summer 2012: Jeremy guided Max Reitmann in an investigation of specificity between native and introduced N-fixing Frankia with native and introduced alder on Isla Victoria, Argentina.
      • Jeremy also investigated the roles of biogeographic and phylogenetic similarity as drivers of ectomycorrhizal compatibility. This may provide some clues why invasions succeed or fail when moving soils between continents. Jeremy finished his Ph.D. -- May 2014 (see Nuñez et al. 2009 Ecology, Nuñez et al. 2013 PLoS One, Hayward et al. 2014 Ecology)
    • Carribean pine was introduced to Puerto Rico and is showing evidence of becoming invasive there. Do mycorrhizal fungi in soils contribute to invasion of conifers at distances away from the plantations? Which species? We also looked at the population genetic structure of one of the EMF introduced with the pines, Pisolithus tinctorius (Rivera et al. 2013). Yazmin Rivera finished her Ph.D. -- May 2012
    • Another study investigates the mycorrhizal associations of Epipactis helleborine, an orchid invading many habitats in North America. This orchid was first recorded in Syracuse in the late 1800s and has since spread across North America. The orchid is associated with ascomycetes, especially truffle species in the genus Tuber. Tuber is a below ground fruiting (hypogeous) fungus best known for the prized edible species in Europe. We have evidence for a number of unidentified Tuber species associated with the orchid in New York, some of which may also have been introduced. Tuber species can be found in a variety of habitats, which may have supported the naturalization and invasion of the orchid across the continent. Dave Muska, Jess Rumburg, Maria Moskalenko (former undergrad students)
    • The role of invasive earthworms on EMF networks and nutrient cycling in hemlock forest soils. Here we start with a basic question of whether EMF show any niche partitioning by soil horizons, linking soil nutirent analyses with each sample. Then, we sample soils at similar depths, but where invasive earthworms are present. The earthworms mix up soil horizons, alter the nutrients, and break up fungal networks. This project is funded by the Mianus River Gorge Preserve and the proposal was written by the grad student on the project, Rebecca Walling (MS).
  • Diversity of macrofungi in tropical and subtropical relict forests in Veracruz, Mexico. Here we are documenting the diversity of macrofungi in these forests with a focus on ectomycorrhizal species in Agaricales, Russulales, and Boletales. This is a collaborative seed project with the following: Victor Bandala (INECOL), Leticia Montoya Bello (INECOL) and Tim Baroni (SUNY-Cortland). We now have our first paper in print from this project on a new species of Laccaria (Montoya et al. 2015)
  • Mycorrhizal status of transgenic American chestnut - Here we ask if transgenic American chestnut lines developed to resist chestnut blight fungus (Cryphonectria parasiticus) will still associate with ectomycorrhizal fungi on the roots. This is a new project and is part of the effort by the American Chestnut Research and Restoration Project in collaboration with Dr. Bill Powell and Dr. Chuck Maynard. Sam Tourtelott (MS student)
  • Population genetics of ectomycorrhizal fungi - We are investigating the population structure of, Suillus spraguei in NY. This is work is in collaboration with Kathleen Pitcher and guided by Dr. Annette Kretzer. Yazmin Rivera PhDone!

Past projects (Gone but not forgotten....send money now!)

  • Fungi Along a Natural Nitrogen Availability Gradient - This is an NSF funded project seeking to add a fungal perspective to the PnET model. Our job on this multi-institution, multi-discipline project is to identify fungi from EM root tips, bulk soils, and in-growth core bags. The first year data from root tips suggests nich partitioning along the nitrogen availability gradient by some EM fungi. We are currently analyzing the second year root tip data, and soil and in-growth core bag data for both years. This project is in collaboration with Erik Hobbie and others (Scott Ollinger, Ruth Varner, Serita Frey) at the University of New Hampshire. Joe Vineis (student) presented his work at the 2009 ESA Annual Meeting in Albuquergue, New Mexico in Organized Oral Session 27, highlighted in a report on the session published in the Bulletin of the Ecological Society of America (Vol. 91, No. 1, pp. 68-79). Joe finished his MS degree December 2011!
  • Oregon Dunes - We have good evidence that suilloid fungi are critical for pines establishing away from mycorrhizal networks under primary succession. We are now looking at why other fungi are less important and how far wind disperses spores. Sara Ashkannejhad (former student; see her New Phytologist pub), Tera Galante (former student; her presentation on spore dispersal by wind at the 2009 MSA/BSA meetings was highlighted in a recent comment in New Phytologist by Peay et al 2010 on page 878.) Tera finished her MS degree December 2009.
  • The myco-heterotrophic plant Pterospora andromedea (pinedrops) is common in the western United States, but rare in the East. An explanation for this regional rarity could be that its specific mycorrhizal symbiont is uncommon in the East. In the western United States several haplotypes of pinedrops exist. These haplotypes are specific to one of two common ectomycorrhizal fungi within the genus Rhizopogon subgenus Amylopogon, both associated with members of Pinaceae. In this study only one eastern pinedrops haplotype/fungal symbiont pair was detected. The plant haplotype was not unique. However, the fungal symbiont is an undescribed species in the subgenus Amylopogon and associates with Pinus strobus. This eastern Rhizopogon species is uncommon in the spore banks of eastern P. strobus forests. The rarity of eastern pinedrops is correlated with the rarity of spores of its fungal symbiont in eastern soils. Chris Hazard (former student)
  • Modeling the Ectomycorrhizal Inoculum Potential in Soils - One can often observe relatively pure stands of eastern hemlock adjacent to relatively pure stands of various maple species. This also marks a shift from EM dominated soils to AM dominated soils. Hemlock (EM) seedlings are less likely to establish in the maple (AM) stands. We have established a field bioassay manipulative experiement across this gradient using hemlock and will use the data model the mycorrhizal potential of these soils. This project was funded by the Mianus River Gorge Preserve supporting Mikey O'Brien who finished his MS degree in May 2009.
  • Biodiversity and biogeography of ectomycorrhizal fungi in Honduran pine stands - We are conducting a survey of ectomycorrhizal fungi found in native pine stands in Honduras. These pine stands are close to the southern limit of the genus and provide a golden opportunity to investigate phylogeographic patterns of ectomycorrhizal fungal species in Central and North America. The project has several facets including monitoring the affects of sustainable forest management on fungal diversity, helping the local people harvest and market choice edible fungi in the Boletus edulis group as a low impact secondary forest product, and teaching molecular techniques to university students in a remote field camp setting. This is a project in collaboration with Operation Wallacea. Sadly...I had to let this project slip away.

Students and Visiting Scholars

Current Grads
Former Grads Former Undergrads Visiting Scholars
Aimee Hudon
Melanie Antonik (MS) Lauren Alteio Tina Bell
Taylor Patterson
Sara Ashkannejhad (MS) Jed Cappellazzi Michael Booth
Claudia Victoroff

Jerome Barner (MS)
Dan Clune Alix Contosta

Kris Dulmer (MS) Anna Conrad (REU) Stephen Leduc

Tera Galante (MS) Ashley Conrad Amy Karpati

Karen Gentile (MPS) Ariel Cowan Maria Moskalenko

Chris Hazard (MS) Erik Facteau Martin Nuñez

Jeremy Hayward (PhD) Dave Gonnella Madeleine Osborn

Elisabeth Holmes (MPS) Kim Hevers Andy Ouimette

Mike Hough (MS)
Kali Lader Dave VanEarden

Samantha Knowlden (MPS) Katie Lawson (REU)

Mikey O'Brien (MS) Gwen Lennox

Marian Orlousky (MPS) Robert Meyer

Erin Page (MS)
Lindsay Miller

Yazmin Rivera (PhD) Dave Muska

Lori Sopchak (MPS) Alex Newman

Marie Terlizzi (MPS) Allison Oakes

Andrew Tomes (MS) Alena Oliver

Sam Tourtellot (MS) Andrea Reinhardt

Joe Vineis (MS) Tanya Rommel

Rebecca Walling (MS) Gabriel Smith

Jesse Spitzer
   Erin Sweeney 

Eva Sztechmiler

Recent book contributions
Horton TR (2017) Spore Dispersal in Ectomycorrhizal Fungi at Fine and Regional Scales. In: Tedersoo L ed. Biogeography of Mycorrhizal Symbiosis: Ecological Studies Vol. 230. Springer. pp. 61-78.

Horton TR (Ed.) (2015) Mycorrhizal Networks: Ecological Studies Vol. 224, Springer. ISBN 978-94-017-7395-9

Peer-reviewed articles

Meyer RT, Weir A, Horton TR (2015) Small-mammal consumption of hypogeous fungi in the central Adirondacks of New York. Northeastern Naturalist 22: 648-651. doi: 10.1656/045.022.0318
Montoya L, Bandala VM, Baroni TJ, Horton TR (2015) A new species of Laccaria in montane cloud forest from eastern Mexico. Mycoscience: 56(6) 597-605 doi:10.1016/j.myc.2015.06.002
Hayward J, Horton TR, Nuñez M (2015) Ectomycorrhizal communities coinvading with Pinaceae species in Argentina: Gringos bajo el bosque. New Phytologist 208: 497-506. doi:10.1111/nph.13453.
Hayward J, Horton TR, Pauchard A, Nuñez MA (2015) A single ectomycorrhizal fungal species can enable a Pinus invasion. Ecology 96: 1438-1444  (See Plate 1 for a great image of a So. American pine invasion!). doi:10.1890/14-1100.1
D’Amico KM, Horton TR, Maynard CA, Stehman SV, Oakes AD, Powell WA (2015) Comparisons of ectomycorrhizal colonization of transgenic American chestnut with that of the wild type, a conventionally bred hybrid, and related fagaceae species. Appl Environ Microbiol 81:100-108. doi:10.1128/AEM.02169-14.
Rivera Y, Kretzer AM, Horton TR (2015) New microsatellite markers for the ectomycorrhizal fungus Pisolithus tinctorius sensu stricto reveal the genetic structure of US and Puerto Rican populations. Fungal Ecology 13:1-9 doi:

Hayward J, Horton TR (2014) Phylogenetic trait conservation in the partner choice of a group of ectomycorrhizal trees. Molecular Ecology 23: 4886-4898.  doi:10.1111/mec12903.

Grubisha LC, Dowie NJ, Miller SL, Hazard C, Trowbridge SM, Horton TR, Klooster MR (2014) Rhizopogon kretzerae sp. nov.: the rare fungal symbiont in the tripartite system with Pterospora andromedea and Pinus strobus. Botany 92:527-534.
Hayward J, Tourtellot SG, Horton TR (2014) A revision of the Alpova diplophloeus complex in North America. Mycologia 106:846-855. doi:10.3852/13-360

Dulmer KM, LeDuc SD, Horton TR (2014) Ectomycorrhizal inoculum potential of northeastern US forest soils for American chestnut restoration: results from field and laboratory bioassays. Mycorrhiza 24 (1), 65-74. doi: 10.1007/s00572-013-0514-y

Nuñez MA,Hayward J, Horton TR, Amico GC, Dimarco RD, Barrios-Garcia MN, Simberloff D (2013) Exotic mammals disperse exotic fungi that promote invasion by exotic trees. PLoS ONE 8(6): e66832.

Horton TR, Swaney DP, Galante TE (2013) Dispersal of ectomycorrhizal basidiospores: the long and short of it. Mycologia 105: 1623-1626.

Horton TR, Hayward J, Tourtellot SG, Taylor DL (2013) Uncommon ectomycorrhizal networks: richness and distribution of Alnus‐associating ectomycorrhizal fungal communities. New Phytologist 198: 978-980

LeDuc SD, Lilleskov EA, Horton TR, Rothstein DE (2013) Ectomycorrhizal fungal succession coincides with shifts in organic nitrogen availability and canopy closure in post-wildfire jack pine forests. Oecologia 172: 257-269.

Kennedy PG, Smith DP, Horton TR, Molina R (2012) Arbutus menziesii (Ericaceae) facilitates regeneration dynamics in mixed evergreen forests by pormoting mycorrhizal fungal diversity and host connectivity. American Journal of Botany 99:1691-1701.

Hayward J, Horton TR (2012) Edaphic factors do not govern the ectomycorrhizal specificity of Pisonia grandis (Nyctaginaceae). Mycorrhiza. 10.1007/s00572-012-0442-2. Mycorrhiza 22:647-652.

Hazard C, Lilleskov EA, Horton TR (2012) Is rarity of pinedrops (Pterospora andromeda) in eastern North America linked to rarity of its unique mycorrhizal host? DOI 10.1007/s00572-011-0414-y. Mycorrhiza 22: 393-402.

Galante TE, Horton TR, Swaney D (2011) 95% of basidiospores fall within one meter of the cap - a field and modeling based study. Mycologia 103:1175-1183.

Karpati AS, Handel SN, Dighton J, Horton TR (2011) Quercus rubra-associated ectomycorrhizal fungal communities of disturbed
urban sites and mature forests. Mycorrhiza 21:537-547.

Molina R, Horton TR, Trappe JM, Marcot BG (2011) Addressing uncertainty: How to conserve and manage rare or little known fungi. Fungal Ecology 4: 134-146.

Lilleskov EA, Hobbie EA, Horton TR (2011) Conservation of ectomycorrhizal fungi: exploring the linkages between functional and taxonomic responses to anthropogenic N deposition. Fungal Ecology 4: 174-183.

O'Brien MJ, Gomola CE, Horton TR (2011) The effect of forest soil and community composition on ectomycorrhizal colonization and seedling growth. Plant Soil 341: 321-331.

van der Heijden MGA, Horton TR (2009) Socialism in soil? The importance of mycorrhizal fungal networks for facilitation in natural ecosystems. Journal of Ecology 97:1139-1150. (Special feature on facilitation in plant communities).

Nuñez MTA, Horton TR, Simberloff D (2009) Lack of belowground mutualisms hinders Pinaceae invasions. Ecology 90:2352-2359.

Horton TR (2006) The number of nuclei in basidiospores of 63 species of ectomycorrhizal Homobasidiomycetes. Mycologia 98: 233-238.

Ashkannejhad S, Horton TR (2006) Ectomycorrhizal ecology under primary succession on coastal sand dunes: interactions involving Pinus contorta, suilloid fungi and deer. New Phytologist 169:345-354.

Becerra A, Zak MR, Horton TR, Micolini J (2005) Ectomycorrhizal and arbuscular mycorrhizal colonization of Alnus acuminata from Calilegua National Park (Argentina). Mycorrhiza 15: 525-531.

Horton TR, Molina R, Hood K (2005) Douglas-fir ectomycorrhizae in 40 and 400 year-old stands: mycobiont availability to late successional western hemlock. Mycorrhiza 15: 393-403.

Fujimura KE, Smith JE, Horton TR, Weber NS, Spatafora JW (2005) Pezizalean mycorrhizas and sporocarps in ponderosa pine (Pinus ponderosa) after prescribed fires in eastern Oregon, USA. Mycorrhiza 15: 79-86.

Nouhra ER, Horton TR, Cazares E, Castellano M (2005) Morphological and molecular characterization of selected Ramaria mycorrhizae. Mycorrhiza 15: 55-59.

Lilleskov EA, Bruns TD, Horton TR, Taylor DL, Grogan P (2004) Detection of forest stand-level spatial structure in ectomycorrhizal fungal communities. FEMS Microbiology Ecology 49: 319-332.

Horton TR (2002) Molecular approaches to ectomycorrhizal diversity studies: variation in ITS at a local scale . Plant and Soil 244: 29-39.

Becerra A, Daniele G, Domínguez L, Nouhra E and Horton T (2002) Ectomycorrhizae between Alnus acuminata H.B.K. and Naucoria escharoides (Fr.:Fr.) Kummer from Argentina. Mycorrhiza: 12:61-66.

Lilleskov EA, Fahey TJ, Horton TR, Lovett GM (2002) Nitrogen deposition and ectomycorrhizal fungal communities: a belowground view from Alaska. Ecology 83: 104 - 115.

Horton, Thomas R. & Bruns, Thomas D (2001)  The molecular revolution in ectomycorrhizal ecology: peeking into the black-box. Molecular Ecology 10 (8): 1855-1871.

Chapela IH, Osher LJ, Horton TR, Henn MR (2001) Ectomycorrhizal fungi introduced with exotic pine plantations induce soil carbon depletion. Soils Biology and Biochemistry 33: 1733-1740.

Baar J, Horton TR, Kretzer A, Bruns TD (1999) Mycorrhizal recolonization of Pinus muricata from resistant propagules after a stand-replacing wildfire . New Phytologist 143: 409-418.

Allen MF, Trappe JM, Horton TR (1999) NATS truffle and truffle-like fungi 8: Rhizopogon mengeisp. nov. (Boletaceae, Basidiomycota). Mycotaxon 70: 149-152.

Stendell ER, Horton TR, Bruns TD (1999) Early effects of prescribed fire on the structure of the ectomycorrhizal fungal community in a Sierra Nevada ponderosa pine forest. Mycological Research 103: 1353-1359.

Horton TR, Bruns TD, and Parker TV (1999) Ectomycorrhizal fungi associated with Arctostaphylos contribute to Pseudotsuga menziesii establishment. Canadian Journal of Botany 77: 93-102.

Horton TR, Bruns TD (1998) Multiple host fungi are the most frequent and abundant ectomycorrhizal types in a mixed stand of Douglas fir (Pseudotsuga menziesii D. Don) and bishop pine (Pinus muricata D. Don). New Phytologist 139(2): 331-339.

Horton TR, Cázares E, Bruns TD (1998) Ectomycorrhizal, vesicular-arbuscular and dark septate fungal colonization of bishop pine (Pinus muricata) seedlings in the first five months of growth after wildfire. Mycorrhiza 8:11-18.

Bruns TD, Szaro TM, Gardes M, Cullings KW, Pan JJ, Taylor DL, Horton TR, Kretzer A, Garbelotto M, Li Y. (1998) A sequence database for the identification of ectomycorrhizal Basidiomycetes by phylogenetic analysis.   Molecular Ecology 7: 257-272.


Book Chapters, Comments and Miscellaneous other articles

Voitk A, Hayward J, Horton T (2011) False truffles of Newfoundland and Labrador. Fungi 45:12-15.

Hayward J, Horton T, Voitk A (2011) Preliminary report from the boletes underground: the false truffles of Newfoundland and Labrador. Omphalina II (8):4-6.

Briggs RD, Horton TR (2011) Out of sight, underground: forest health, edapthic factors, and mycorrhizae. In: Forest Health. Castello J, Teale S. Eds. Cambridge University Press.

Horton TR, Arnold AE, Bruns TD (2008) FESIN workshops at ESA - the mycelial network grows. Mycorrhiza 19:283-28

Horton TR, van der Heijden M (2008) The role of symbioses in seedling establishment and survival. In: Seedling Ecology and Evolution. Leck M, Parker VT, Simpson B, Eds. Cambridge University Press.

Bidartondo et al. (2008) Preserving accuracy in GenBank. Science 319: 1616 (This is signed by many.)

Hobbie EA, Horton TR (2007) Evidence that saprotrophic fungi mobilise carbon and mycorrhizal fungi mobilise nitrogen during litter decomposition. New Phytologist 173: 447–449. This was an invited comment on Lindahl et al. (2007) Spatial separation of litter decomposition and mycorrhizal nitrogen uptake in a boreal forest. New Phytologist 173: 611–620.

Bruns TD, Baar J, Grogan P, Horton TR, Kretzer A, Redecker D, Tan J, Taylor DL (2005) Natural history and community dynamics of ectomycorrhizal fungi following the Mt. Vision fire. pp33-40, In Lessens Learned from the October 1995 Mt. Vision Fire; CD ROM published by Points Reyes National Seashore.

Potente J, Horton T (2004) Tale of a ragged fringe. Long Island Botanical Society Quarterly Newsletter, 13(4): 27-29.

Horton TR (2003) Book review of Mushrooms of Hawai'i: An identification guide, by Hemmes D and Desjardin D. Inoculum 54(2): 18.

Molina R, Caldwell BA, Castellano MA, Horton TR, Smith JE (2002) Mycorrhizae: Ectomycorrhizal fungi. In Encyclopedia of Environmental Microbiology. Ed. Bitton G. pp.2134-2132.

Bruns TD, Kretzer AM, Horton TR, Stendel E"Acey-Ducey", Bidartondo MI, Szaro TM (2002) Current investigations of fungal ectomycorrhizal communities in the Sierra Nevada forest. USDA Forest Service Gen. Tech. Rep. PSW-GTR: pp. 83-89.