Author
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Emmerich, William |
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Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/6/2007 Publication Date: 9/19/2007 Citation: Emmerich, W.E. 2007. Ecosystem water use efficiency in a semiarid shrubland and grassland community. Rangeland Ecology and Management. 60:464-470. Interpretive Summary: Plant uptake of carbon dioxide from the atmosphere to reduce the atmospheric concentration is tied to the ecosystem water use efficiency (EWUE) of different plant communities. EWUE is a measure of the amount of carbon dioxide taken up to the amount of water lost through evapotranspiration (ET). Knowing the EWUE of plant communities is important to the understanding of how they take up carbon and interact. The uptake of carbon dioxide and the loss of water was measured at a shrub and grass site in Arizona. The grass community was 1.4 to 3.6 times more EWUE in taking up carbon dioxide into the plant biomass. Rangeland managers can use this information to help reduce the carbon dioxide concentration in the atmosphere to reduce the tremendous cost to society caused by global warming. Technical Abstract: Ecosystem water use efficiency (EWUE) is defined as the amount of carbon uptake per amount of water lost from the ecosystem and can be a useful measure to determine the differences in functionality of semiarid shrub and grass land communities. It is well known that C4 grass plants themselves have higher water use efficiency (WUE) than C3 shrub plants, though it has been postulated that C4 have lost much of their advantage due to the rising atmospheric CO2 concentrations. The hypothesis for this study was that C4 warm season grass ecosystems have a higher EWUE than C3 shrub ecosystems under the present CO2 concentration and climatic variability. Evapotranspiration (ET) and CO2 flux were measured with Bowen ratio systems at a shrub and grass site for six years in southeastern Arizona. Aboveground biomass was determined in the spring and fall as another measure of carbon uptake during the growing season. Four different methods were used to evaluate growing season EWUE using the ET and CO2 fluxes, and the biomass data. The methods estimated a range of EWUE values for the shrub site of 0.96 to 1.28 g CO2 m-2 mm-1 ET and 1.74 to 3.44 g CO2 m-2 mm-1 ET at the grass site. EWUE was between 1.4 and 3.6 times greater for the grass plant community. Annual precipitation and ET was similar at the two plant communities and with the higher EWUE the grass site was able to take up more carbon. Management could utilize the higher EWUE of the grassland ecosystems for carbon uptake and promote their improvement as a way to alleviate the rising atmospheric CO2 concentration and the related societal costs of global warming. |
