Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/29/2011
Publication Date: 6/8/2012
Citation: Liebig, M.A., Dong, X., Mclain, J.E., Dell, C.J. 2012. Greenhouse gas flux from managed grasslands in the U.S. Book Chapter. p. 183-202. IN: Liebig, M.A., A.J. Franzluebbers, and R.F. Follett (Eds.) Managing agricultural greenhouse gases: Coordinated agricultural research through GRACEnet to address our changing climate. Academic Press, San Diego, CA. Interpretive Summary: Grasslands provide a multitude of services with long-term societal benefits. Mitigation of climate change is increasingly looked upon as an important emerging service from grasslands. Assurances of effective greenhouse gas mitigation strategies from grasslands require detailed understanding of carbon dioxide, methane, and nitrous oxide flux. In this report, we sought to summarize grassland management effects on carbon dioxide, methane, and nitrous oxide flux using recently published data from rangelands and pasturelands in the U.S. Most rangeland ecosystems were found, on average, to take up carbon dioxide from the atmosphere. Rangelands in the southwest U.S., however, were found to be sources of carbon dioxide due to a prevalence of high carbonate soils. Pasturelands in the central and eastern U.S. were found to be both net carbon dioxide sinks and sources, limiting generalizations regarding their role to affect carbon dioxide balance of U.S. grasslands. Both rangelands and pasturelands exhibited capacity to serve as minor methane sinks, while wetland landscapes were significant methane sources. Emissions of nitrous oxide from U.S. grasslands were found to be moderate, and increased with woody plant encroachment, invasion of non-native grasses, and N fertilization, but not grazing intensity. While significant progress has been made in recent years, much more work needs to be done to develop robust estimates of greenhouse gas flux across all major grassland categories in the U.S.
Technical Abstract: Managed grasslands are increasingly looked upon to serve as cost-effective sinks for mitigating climate change. Assurances of effective greenhouse gas mitigation strategies require detailed understanding of carbon dioxide, methane, and nitrous oxide flux for rangelands and pasturelands. Summarization of net ecosystem exchange (NEE) findings suggest most rangeland ecosystems in the U.S. are net carbon dioxide sinks, with net assimilation rates ranging from 0.2 to 1.1 Mg C/ha/yr. Rangeland ecosystems in the southwest U.S., however, were found to be net carbon dioxide sources, while pasturelands exhibited both sink and source capacity in a limited number of assessments. Both rangelands and pasturelands exhibit capacity to serve as minor methane sinks (-2.4 to -5.6 g C/ha/d), while wetland landscapes with hydrophytic vegetation are significant methane sources (1.2 kg C/ha/d). Emissions of nitrous oxide from U.S. grasslands are moderate (1.4 to 5.1 g N/ha/d), and increase with woody plant encroachment, invasion of non-native grasses, and N fertilization, but not grazing intensity. While significant progress has been made in recent years, robust estimates of greenhouse gas flux remain elusive due to a lack of measurement across all major grassland categories. [GRACEnet Publication]