Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2007
Publication Date: 1/31/2008
Citation: Banowetz, G.M., Azevedo, M.D., Stout, R. 2008. Morphological adaptations of hot springs panic grass (Dichanthelium lanigunosum var sericeum (Schmoll) to thermal stress. Journal of Thermal Biology. V33, P 106-116. Interpretive Summary: Hot springs panic grass (Dichanthelium lanuginosum) has the capacity to survive and thrive in environmental conditions that would be lethal to most other grasses, including major crops like wheat. This grass colonizes thermal areas like those in Yellowstone National Park where soil temperatures can exceed 45 ° C and experience severe drought, high UV irradiation, and cold air temperatures for extended periods of time. The traits that permit this grass to survive where others would perish are poorly understood. An understanding of these traits would be helpful in approaching the genetic improvement of turf and forage grasses as well as the related cereal crops. In this study, we compared leaf surface and ultrastructural characteristics in isolates of this grass from Yellowstone National Park to those isolated from non-thermal environments in western Oregon. Plants isolated from the thermal environments have significantly greater leaf pubescence, hairy structures that provide shading and reduce evaporative water loss from the leaves. The thermal isolates also had increased silicon-containing structures which also serve to prevent surface water loss. The internal structures of leaves from the thermal isolates were more compact, an apparent characteristic to reduce water loss. These traits, which are apparently associated with improved capacity to adapt to stressful environments, are relatively to identify and select for in a conventional plant breeding program.
Technical Abstract: Growth and productivity of most crops is significantly reduced by exposure to temperatures in excess of 35 ° C. Some plants however thrive in geothermally heated soils characterized by chronic temperatures in excess of 40 ° C. The morphological adaptations that enable these plants to colonize thermal environments are poorly understood. We characterized trichome development, silica accumulation, stomatal density, and waxy cuticle development in populations of Dichanthelium lanuginosum var sericeum (Schmoll) with contrasting thermotolerance to identify traits that permit this grass to adapt to chronic exposure to temperatures in excess of 45 ° C. Plants isolated from thermal environments of Yellowstone National Park developed an extensive series of trichomes when exposed to chronic temperatures of 45/35 ° C (day/night). In contrast, isolates from non-thermal environments of western Oregon showed minimal trichome development during exposure to the elevated temperatures. Leaves that developed during exposure to elevated temperatures had reduced thickness, though the reduction was less marked in plants from populations isolated from thermal environments. Plants from populations isolated from thermal environments also had significantly greater numbers of stomata on adaxial leaf surfaces relative to biotypes isolated from nonthermal environments. Epicuticular wax development was greater in plants from thermal environments. D. lanuginosum plants isolated from thermal environments had extensive silica-containing structures, including increased pubescence that appeared to reduce transpiration loss.