Ecophysiological Adaptations in Alpine Plants

Our current research includes investigations of the upper forest timberline in Wyoming where plants are living at the extreme margins of survival. We are using this ecotone to evaluate potential influences of global climate change on plant community structure across the landscape. Several undergraduate students have been participating in two projects that evaluate the influence of cold temperatures on summer growth. In the alpine, the summer growth period may last less than 90 days and is frequently interrupted by low temperatures that can severely limit photosynthesis, growth, and reproduction. At night, cold clear skies can cool leaf temperatures to below freezing, even though air temperatures may be well above freezing. This condition is commonly referred to as "radiational frost" due to the excessive loss of longwave radiant energy to the cold night sky, the primary cause of leaf temperatures that are below air temperature. Moreover, these are the same wavelenths that are reradiated back to the earth's surface at night, creating the important "greenhouse effect" of the earth's atmosphere. Because these radiational frosts are typically the last frosts to occur in spring and the first to occur in autumn, they may also determine the length of the growth season. Thus, any change in the atmosphere due to an increase in greenhouse gases (e.g., warming) could result in radiative frost patterns and a major impact on the length of the seasonal growth period.

John Zuver has been involved in a project measuring the effective temperature of the night sky using infrared thermometers and evaluating the intensity and frequency of radiational frost, as well as impacts on photosynthesis, growth, and reproduction. Catie Campbell's project focuses specifically on the influence of these radiational frosts on the establishment of seedlings of forest tree species and the stability of the upper treeline.

Mike Bynum is studying a previously unknown phenomenon that appears to be an adaptive response to the frequent rain showers that can occur on even the most clement days of summer in the alpine. In the alpine gentian (Gentiana algida), Mike found that its upright, conical flowers close tightly in response to the cooler air temperatures that precede rainfall by only minutes. By manipulating flowers experimentally so that they remained open during thunderstorms, he also found that pollen is washed from these flowers, resulting in a substantial decline in fertilization success. We are now investigating the ecological impact of this floral response in other species with similar flowers and in habitats with frequent rainfall.

The results of these projects relate directly to the potential impact of global atmospheric warming and changes in cloud cover on species composition and vegetation patterns. Support for undergraduate participation was provided by the National Science Foundation (Research Experiences for Undergraduates Program) and the National Aeronautics and Space Administration (Innovative Grants Program).