Ecosystem Water Use Efficiency in a Semiarid Shrubland and Grassland Community |
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| Institution: | 1. College of Water Sciences, Beijing Normal University, Beijing 100875, China;2. College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region 010018, China;3. School of Environmental and Life Sciences (Earth Sciences), University of Newcastle, Callaghan, NSW 2308, Australia;1. Synthesis Research Center of Chinese Ecosystem Research Network, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Key Lab of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, China;4. South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China;5. Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;6. Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining 810001, China;1. National Institute for Environmental Studies, Tsukuba, Japan;2. Key Laboratory of Agricultural Water Resources, Hebei Laboratory of Agricultural Water-saving, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China;3. Department of Agroecology–Research Center Foulum, Aarhus University, Tjele, Denmark;4. Sino-Danish Center for Education and Research, Eastern Yanqihu campus, District, Huairou, Beijing, China;5. Institute of Geodesy, University of Stuttgart, Stuttgart, Germany;6. University of Chinese Academy of Sciences, Beijing, China |
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| Abstract: | Ecosystem water use efficiency (EWUE) is defined as the net carbon uptake per amount of water lost from the ecosystem and is a useful measure of the functionality in semiarid shrub and grassland communities. C4 grasses have higher water use efficiency (WUE) than do C3 shrubs, although it has been postulated that C4 plants have lost much of their advantage due to the rising atmospheric CO2 concentrations. The hypothesis was that C4-grass-dominated ecosystems have a higher EWUE than C3-shrub-dominated ecosystems under the present CO2 concentration and climatic variability. Evapotranspiration (ET) and CO2 fluxes were measured with Bowen ratio systems at a shrub and grass site for 6 years in southeastern Arizona. Two different methods were used to evaluate growing season EWUE using the ET and CO2 fluxes. The first method estimated a net daytime growing season EWUE for the grass site at 1.74 g CO2 · mm-1 ET and 1.28 g CO2 · mm-1 ET at the shrub site. The second method estimated maximum EWUE during part of the growing season at 7.35 g CO2 · mm-1 ET for the grass site and 4.68 g CO2 · mm-1 ET for the shrub site, which was considered a significant difference at P = 0.056. Data variability of the first method precluded a statistical difference determination between sites, but the results indicated that the grass-dominated ecosystem was between 1.4 and 1.6 times more water use efficient than the shrub-dominated ecosystem. Mean annual growing season precipitation and ET were similar in the two ecosystems, but the higher EWUE of the grassland system enabled it to take up more carbon during the growing season than the shrub ecosystem. Ecosystem differences in CO2 and H2O flux have important management implications including primary productivity, C sequestration, and rangeland health. |
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