Submitted to: Acta Oecologica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2009
Publication Date: 3/4/2009
Citation: Nippert, J.B., Fay, P.A., Carlisle, J.D., Knapp, A.K., Smith, M.D. 2009. Ecophysiological responses of two dominant grasses to altered temperature and precipitation regimes. Acta Oecologica. 35:400-408. Interpretive Summary: Two predicted manifestations of climate change are continuing increases in surface temperatures and altered precipitation patterns. The responses of dominant plant species in ecosystems play an important role in the resulting changes in net primary productivity, species diversity, and carbon cycling, which in turn determine potential carbon sequestration and carrying capacity for livestock grazing. In order to understand how warming and altered precipitation patterns may affect dominant grass species in a tallgrass prairie ecosystem, leaf level water balance and carbon assimilation were measured in two similar C4 grasses that are abundant and widespread throughout North American tallgrass prairies, Andropogon gerardii, big bluestem, and Sorghastrum nutans, Indiangrass. Individuals of both species were measured in plots that were warmed to 2 – 4 °C above ambient using infrared lamps and watered at longer intervals with larger events than ambient, creating a more extreme precipitation pattern. Both species responded to warming and precipitation treatments, with S. nutans experiencing larger effects in carbon uptake than A. gerardii, suggesting its abundance may change more rapidly under future climate scenarios that include warmer temperatures and more extreme precipitation regimes.
Technical Abstract: Ecosystem responses to climate change will largely be driven by responses of the dominant species. However, if co-dominant species have traits that lead them to differential responses, then predicting how ecosystem structure and function will be altered is more challenging. We assessed differences in response to climate change factors for the two dominant C4 grass species in tallgrass prairie, Andropogon gerardii and Sorghastrum nutans, by measuring changes in a suite of plant ecophysiological traits in response to experimentally elevated air temperatures and increased precipitation variability over two growing seasons. Maximum photosynthetic rates, stomatal conductance, water-use efficiency, chlorophyll fluorescence, and leaf water potential varied with leaf and canopy air temperature as well as with volumetric soil water content (0-15 cm). Both species had similar responses to imposed changes in temperature and water availability, but when differences occurred, responses by A. gerardii were more closely linked with changes in air temperature whereas S. nutans was more sensitive to changes in water availability. Moreover, S. nutans was more responsive overall than A. gerardii to climate alterations. These results indicate both grass species are responsive to forecast changes in temperature and precipitation, but their differential sensitivity to temperature and water availability means that future tallgrass prairie ecosystem structure and function will be determined by their interaction with the type of climate change that occurs.