Increasing levels of atmospheric carbon dioxide may reduce the ability of some grassland plant species to survive damage from spring freezes, causing a reduction in the biodiversity of grassland ecosystems. These conclusions are reported in a paper by Daniel Obrist, a graduate research assistant at the Desert Research Institute (DRI) in Reno, Nev., based on data from a six-year study of grassland plants in Switzerland that were exposed to elevated levels of atmospheric CO2.
Obrist said that three species, representing five percent of the vegetation in the study area, experienced a 1.1 C reduction in their freeze resistance.
"This decrease might be meaningless for species with very strong freezing resistance, but it could endanger those that already have low freezing resistance," Obrist said. He identified Cirsium acaule (dwarf thistle), Salvia pratensis (Meadow Cleary-the sunflower family) and Trifolium medium (zigzag clover from the pea family) as the susceptible species in the study.
"This could be an unforseen way in which increased greenhouse gases may result in a reduced biodiversity of a grassland ecosystem," Obrist says. "This type of grassland includes many rare species-including orchids-and make it particularly precious from a conservation standpoint."
Obrist's paper, "In situ effects of elevated atmospheric CO2 on leaf freezing resistance and carbohydrates in a native temperate grassland," has been accepted for publication in the Annals of Botany. Obrist is a Ph.D. candidate in Hydrology at the University of Nevada, Reno, a sister campus to the Desert Research Institute in the University and Community College System of Nevada.
Obrist was actually testing a hypothesis that rising atmospheric CO2 levels would increase the freeze resistance of plants by increasing sugars that have an anti-freeze effect. His paper was first submitted as the winning entry in the Desert Research Institute's 2001 Colin Warden Memorial Paper Competition, a cash prize competition established by a local family to honor a supporter of environmental research.