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Publications: 

Al-Niemi, T. S. and R. G. Stout (2002) Heat-shock protein expression in a perennial grass commonly associated with active geothermal areas in western North America. J. Thermal Biol. 27:547-553.

Stout, R. G. and T. S. Al-Niemi (2002) Heat-tolerant flowering plants of active geothermal areas in Yellowstone National Park. Ann. Bot. 90:259-267.

Redman, R. S., K. B. Sheehan, R. G. Stout, R. J. Rodriguez, and J. M. Henson (2002) Thermotolerance generated by plant/fungal symbiosis. Science 298:1581.

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 130:1-9.

Introduction: Yellowstone's steaming geysers and turquoise hot springs fascinate millions of visitors every summer, and some of these visitors have recently included scientists attracted to these geothermal features by the thermophilic microorganisms that live in them. But if one looks to the edges of some of these hot springs, or surveys the ground around solfataras or mudpots, one may recognize that the unusually heat-tolerant organisms of Yellowstone are not limited to viruses, bacteria and algae. Indeed, there are some species of mosses and flowering plants that live in steaming soil or adjacent to thermal springs at soil temperatures that would be lethal to most other members of the plant kingdom.

Very little is known about plants adapted to grow and reproduce in geothermally heated environments. Because Yellowstone contains the highest number of surface-geothermal features in the world at a single location, it offers an excellent opportunity to study flowering plants and mosses found in such environments.

Background: Several years ago we began to survey some of the extensive surface geothermal areas within YNP - which is only 90 miles from Bozeman - for the existence of unusually heat adapted plants. Because of the relatively constant geothermal heating compared to diurnal heating by the sun, we suspected that these plants might possess novel cellular mechanisms that allow them to survive extended periods of heat stress.

To date, we have surveyed over fifty surface-geothermal sites (e.g., hot springs outflows or steaming ground) in YNP. The predominant flowering plant at such sites is the perennial grass Dichanthelium lanuginosum (a.k.a., hot springs panic grass). We have found that some individuals of this species can withstand habitual (weeks to months) rhizosphere temperatures at 40^o to 50^o C during the summer, with winter rhizosphere temperatures rarely dropping below 30^o C (86^o F). There are few, if any, reports in the literature of such long-term heat tolerance in land plants.

Plant Growth Studies: We have collected D. lanuginosum seed from many of our study sites and have been successful at germinating and growing the plants in the lab. D. lanuginosum grown in the lab from field-collected seed display significantly higher shoot fresh weight when grown at hot (~ 40^o C) soil temperatures versus controls (~ 25^o C) over the course of several months. Though there is no difference in root fresh weight of plants grown at these two temperature regimes, the roots from the warmer soils are significantly shorter and more highly branched compared to plants grown in the cooler soils (see Stout, R.G. et al. above).

Plant-Microbe Interactions: One of the more frequently asked questions about plants adapted to geothermal environments is the nature of the microbial associations with their roots. Virtually all naturally occurring flowering plants develop such associations. Thus, it's likely that plant-microbe interactions may play significant roles in the adaptation of heat- and acid-tolerant plants to the extreme environments posed by geothermally modified soils.