FUTURE WORK

1
REFERENCES Bécard, G. and J.A. Fortin. 1988.
Early events of vesicular-arbuscular mycorrhiza
formation on Ri T-DNA transformed roots. New
Phytologist. 108211-218. Blackwell. M. 2000.
Terrestrial Life - Fungal from the Start?
Science. 2891884-1885. Burns, B. 1997.
Vegetation change along a geothermal stress
gradient at the Te Kopia steamfield. Journal of
The Royal Society of New Zealand. 27279-294.
Christiansen, R.L. 1984. Yellowstone magmatic
evolution Its bearing on understanding
large-volume explosive volcanism. Explosive
Volcanism, Its Inception, Evolution and Hazards.
Washington, D.C. National Academy of Sciences.
84-95. Giovannetti, M., C. Sbrana, L. Avio, A.S.
Citernesi, and C. Logi. 1993. Differential
hyphal morphogenesis in arbuscular mycorrhizal
fungi during pre-infection stages. New
Phytologist. 125587-593. Heppell, K.B., D.L.
Shumway, and R.T. Koide. 1998. The effect of
mycorrhizal infection of Abutilon theophrasti on
competitiveness of offspring. Functional
Ecology. 12171-175. Johansen, A., I. Jakobsen,
and E.S. Jensen. 1993. External hyphae of
vesicular-arbuscular mycorrhizal fungi associated
with Triolium subterraneum L. 3. Hyphal transport
of 32P and 15N. New Phytologist. 12461-68.
Johnson, N.C. 1993. Can fertilization of soil
select less mutualistic mycorrhizae? Ecological
Applications. 3749-757. Johnson, N.C., J.H.
Graham, and F.A. Smith. 1997. Functioning of
mycorrhizal associations along the
mutualism-parasitism continuum. New Phytologist.
135575-585. McGonigle, T.P., M.H. Miller, D.G.
Evans, G.L. Fairchild, and J.A. Swan. 1990. A
new method which gives an objective measure of
colonization of roots by vesicular-arbuscular
mycorrhizal fungi. New Phytologist.
115495-501. Newsham, K.K., A.H. Fitter, and
A.R. Watkinson. 1995. Multi-functionality and
biodiversity in arbuscular mycorrhizas. Trends
in Ecology and Evolution. 10407-411. Peng, S.,
D.M. Eissenstat, J.H. Graham, K. Williams, and
N.C. Hodge. 1993. Growth depression in
mycorrhizal citrus at high-phosphorus supply.
Plant Physiology. 1011063-1071. Phillips, J.M.
and D.S. Hayman. 1970. Improved procedures for
clearing roots and staining parasitic and
vesicular-arbuscular mycorrhizal fungi for rapid
assessment of infection. Transactions of the
British Mycological Society. 55158-161. Redecker
, D., J.B. Morton, and T.D. Bruns. 2000.
Molecular phylogeny of the arbuscular mycorrhizal
fungi Glomus sinuosum and Sclerocystis
coremioides. Mycologia. 92282-285. Remy, W.,
T.N. Taylor, H. Hass, and H. Kerp. 1994. Four
hundred-million-year-old vesicular arbuscular
mycorrhizae. Proceedings of the National Academy
of Sciences. 9111841-11843. Smith, S.E. and
D.J. Read. 1997. Mycorrhizal Symbiosis, 2nd
Edition. Academic Press, San Diego. Stahl,
P.D., G.E. Schuman, S.M. Frost, and S.E.
Williams. 1998. Influence of arbuscular
mycorrhiza and plant age on water stress
tolerance of big sagebrush seedlings. Soil
Science Society of America Journal.
621309-13. Stanley, M.R., R.T. Koide, and D.L.
Shumway. 1993. Mycorrhizal symbiosis increases
growth, reproduction and recruitment of Abutilon
theophrasti Medic. in the field. Oecologia. 94
30-35. Stout, R.G., M.L. Summers, T. Kerstetter,
and T.R. McDermott. 1997. Heat- and
acid-tolerance of a grass commonly found in
geothermal areas of Yellowstone National Park.
Plant Science. 1301-9. Subramanian, K.S. and
C. Charest. 1999. Acquisition of N by external
hyphae of an arbuscular mycorrhizal fungus and
its impact on physiological responses in maize
under drought-stressed and well-watered
conditions. Mycorrhiza. 969-75. Zabinski, C.
and R. A. Bunn. In review. Arbuscular
Mycorrhizae in Hydrothermal-Influenced Soils in
Yellowstone National Park. Western North American
Naturalist.

• SUMMARY
• Mycorrhizae resulted in a decreased plant biomass
  at ambient temperatures, under the low nutrient
  conditions.
• In elevated temperatures, D. lanuginosum biomass
  was equal in the mycorrhizal and microbial wash
  plants (ME1).
• With the previous exception, plants receiving a
  microbial wash (without mycorrhizal propagules)
  had the greatest biomass and the mycorrhizal
  plants had the smallest.
• Mycorrhizal plants had significantly lower root
  to total biomass ratios, especially at elevated
  temperatures in contrast, the microbial wash
  treatment did not affect root to total biomass
  mass ratio, which remained consistent across
  sterilized and wash treatments.

• CONCLUSIONS
• The depression in biomass of mycorrhizal
  seedlings (MElt1) is an indication of the cost of
  mycorrhizae (Peng et al. 1993). However, at
  elevated soil temperatures, the mycorrhizal D.
  lanuginosum maintained total biomass (ME1) and
  increased shoot

biomass relative to non-mycorrhizal plants.
Increasing shoot biomass without sacrificing
total biomass might ultimately increase plant
fitness. The mycorrhizal symbiosis appeared
mutualistic for D. lanuginosum growing in
elevated temperatures.

• The mycorrhizae was parasitic for A. scabra under
  both ambient and elevated temperatures. However,
  because the A. scabra seed was from a non-thermal
  area, the data from that species are difficult to
  interpret. The results may be confounded by
  species-specific interactions (thermal fungus and
  non-thermal plant), species' differences (A.
  scabra vs. D. lanuginosum), or ecotypic variation
  (thermal A. scabra vs. non-thermal A. scabra).
• The benefits of the microbial wash may be
  attributed to non-mycorrhizal microorganisms
  (smaller than 8 µm) or hormones present in the
  soil.
• Mycorrhizal plants shifted their carbon
  allocation pattern, forming significantly shorter
  and

and less massive roots. This phenomenon was more
pronounced at elevated temperatures. It is
possible that mycorrhizal associations compensate
for reduced root mass and, as environmental
conditions restrict root growth, (elevated
temperatures) this benefit is more valuable.
Mycorrhizal D. lanuginosum produced greater shoot
biomass in elevated temperatures, which may
ultimately increase plant fitness over a period
longer than this experiment.
Non-mycorrhizal A. scabra
Mycorrhizal A. scabra
Arbuscules in fine root
FUTURE WORK During Summer 2001 we are sampling AM
colonization levels across the season, and
gathering detailed soil chemistry data at eleven
sites in Yellowstones Rabbit Creek Basin. The
soil pH at these sites varies from 3.5 to 9.4
(11 soilwater), and soil temperatures range
from 21 to 64ºC. Subsequent analysis will
provide concentrations of key elements and
nutrients at these sites. The information will
enable us to select field sites for subsequent
experiments, and appropriate locations for soil
and AM fungi collection.
We will continue to explore the ecology of
mycorrhizae in thermal areas by examining each
component of the mycorrhizal symbiosis

• Soil Measure ME across soil temperatures and
  chemistry
• Fungi - Evaluate AM fungal species diversity in
  thermal sites
• Plant and Fungi - Assess species and ecotypic
  differences in mycorrhizal functioning for both
  AM fungi and host plants
• Plant and Fungi - Elucidate AM mechanisms in
  stressful environments

ACKNOWLEDGEMENTS
Figure 3. Scanning electron microscope (SEM)
photograph of a fine root with the tips cortical
tissue stripped away. Fungal hyphae are visible
along the surface of the root. Coupling Energy
Dispersive X-ray Spectrometry (EDX) with SEM
would allow us to investigate mechanisms of plant
tolerance to toxic elements.
Figure 4. ME is dependent on soil parameters and
plant and fungal ecotypes or species.
Thermal Biology Institute Montana Space Grant
Consortium Ann McCauley, Emily Davies, Tamara
Sperber, Abby Ward, and Sara Zimmerley