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 have worked in my lab present and past, and a publication list with links to PDFs.
- EFB 320, General Ecology.
4 credits, Fall
- EFB 428/628, Mycorrhizal
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
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 will guide a student 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 look at the population genetic structure of one of the EMF introduced with the pines, Pisolithus tinctorius. 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
- 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
Hayward J, Horton TR, Nuñez M (accepted) Ectomycorrhizal communities coinvading with Pinaceae species in Argentina: Gringos bajo el bosque. New Phytologist
Hayward J, Horton TR, Pauchard A , Nuñez MA (accepted) A single ectomycorrhizal fungal species can enable a Pinus invasion. Ecology.
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
Hayward J, Horton TR
(2014) Phylogenetic trait conservation in the partner choice of a group
of ectomycorrhizal trees. Molecular Ecology 23: 4886-4898.
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: 527-534. http://www.nrcresearchpress.com/doi/abs/10.1139/cjb-2013-0309#.U6B5ZLGy73B
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.
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
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:
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
Becerra A, Zak MR, Horton TR, Micolini J (2005) Ectomycorrhizal and arbuscular
mycorrhizal colonization of
Alnus acuminata from Calilegua National Park (Argentina). Mycorrhiza
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
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:
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
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.