Direct and indirect effects of warming, elevated CO2 and non-native plant invasion on carbon and water cycling in semiarid grassland

Principle Investigator: David G. Williams, University of Wyoming
Co-Investigators: Elise Pendall, University of Wyoming

Abstract:: Our proposed work builds on the Prairie Heating and CO2 Enrichment (PHACE) experiment underway in semiarid grassland of Wyoming. We will evaluate relative sensitivities of carbon and water cycles to elevated CO2 and temperature, and non-native plant invasion, separately and in combination, and distinguish direct from indirect effects of these factors on ecosystem physiology.

Location: The PHACE experiment is being conducted at the USDA-ARS High Plains Grasslands Research Station, located near Cheyenne, WY. The ecosystem is a northern mixed-grass prairie consisting of C3 and C4 grasses, C3 forbs and C3 sub-shrubs. Laboratory analyses will be conducted at the University of Wyoming in Laramie.

Hypotheses: We will test the following specific hypotheses: 1) Effects of elevated CO2 and warming on water and carbon cycling will be interactive owing to differential indirect effects on soil moisture and labile substrate. 2) Indirect effects of elevated CO2 and warming on ecosystem physiology, through changes in ET and soil moisture, are of greater magnitude than the direct effects of these global change factors; and 3) Invasion of a novel plant functional type will have a greater impact on ecosystem physiology than either climate warming or elevated CO2, and will strongly interact with these global changes to influence ecosystem carbon and water cycles.

Methods: The experiment will include Free-Air CO2 Enrichment, warming with infra-red heaters and experimental establishment of an invasive taprooted forb, in a replicated, multifactor design. Additional irrigation treatments will distinguish direct and indirect effects of global changes on ecosystem physiology. We will measure CO2 and water exchange from leaf and root to plot scale, soil respiration, 13C and 18O of CO2, soil moisture and canopy phenology and architecture to understand underlying processes governing responses of ecosystem CO2 exchange and ET.

Deliverables: We will produce peer-reviewed journal articles and make all the data available in metadata form on the PHACE experiment website. Model simulation results will be available through the project website and model code will be available. Follow-on synthesis activities will involve comparisons with global change experiments conducted in shortgrass and tallgrass prairies. We will train one post-doctoral researcher, one PhD student and several undergraduate students with this project.

last updated: 15 April 2007 PLH