USDA - ARS
PHONE: Ft. Collins,CO:
B.S. New Mexico State University 1975 M.S. University of Georgia 1978 Ph.D. University of Georgia 1981
Research interests in photosynthesis, plant/soil water relations, and physiological plant ecology of native grasslands. His major two areas of research are understanding the effects of global climate change on western rangelands, and evaluating the impacts of management practices on the health of rangelands, particularly in regards to C cycling. Increases in atmospheric CO2 concentrations have important implications for rangelands as they are predicted to cause major changes in the global climate, and may already be affecting weather patterns and productivity of western rangelands. Increase in CO2 will also impact rangelands through their direct effects of photosynthesis, growth, water relations, N metabolism and forage quality, and secondarily through effects on soil biology and mineral cycling. Dr. Morgan has been engaged in climate change research for several years with a cadre of scientists from other ARS research units and from Colorado State University, the University of Northern Colorado, and the University of Colorado. The goal of these studies is to better understand how future CO2-enriched atmospheres, warmer temperature and altered precipitation will affect the ecology and sustainability of Great Plains grasslands, and to use that knowledge to develop management practices that will be appropriate for future environments. The C cycling work has been geared to evaluating how different grazing practices affect plant ecology, biodiversity, and ultimately, the C exchange and budget of rangelands. This work has been conducted in shortgrass steppe and northern mixed prairie, but plans are underway to take this work to sagebrush steppe regions in Wyoming.
Dijkstra, F.A., E. Pendall, J.A. Morgan, D.M. Blumenthal, Y. Carillo, D.R. LeCain, R.F. Follett, D.G. Williams. Climate change alters stoichiometry of phosphorus and nitrogen in semiarid grassland. New Phytologist 196:807-815.
Dieleman,W.I.J., S.Vicca , F.A. Dijkstra, F.Hagedorn, M.J. Hovenden, K.S. Larsen, J.A. Morgan, A. Volder, C.S Beier, J. S. Dukes, J. King,S. Leuzinger,S. Linder, Y. Luo, R. Oren, P. DeAngelis, D. Tingey, M. R. Hoosbeek and I.A.Janssens. 2012. Simple additive effects are rare: a quantitative review of plant biomass and soil process responses to combined manipulations of CO2 and temperature. Global Change Biology (2012) 18, 2681-2693.
LeCain, D, R, J. A. Morgan, G. L. Hutchinson, J. D. Reeder and F. A. Dijkstra. 2012. Interactions between elevated atmospheric CO2 and defoliation on North American rangeland plant species at low and high N availability. Grass and Forage Science, 67, 350-360.
Dijkstra, F.A. and J.A. Morgan. 2012. Elevated CO2 and warming effects on soil carbon sequestration and greenhouse gas exchange in agroecosystems: A review. Chapter 27 IN M.A. Liebig, A.J. Franzluebbers, and R.F. Follett (Eds.), Managing Agricultural Greenhouse Gases: Coordinated Agricultural Research through GRACEnet to Address our Changing Climate, 547 pp, Elsevier, London, UK; New York, USA.
Carrillo, Y., F.A. Dijkstra, E. Pendall, J.A. Morgan, and D.M. Blumenthal. 2012. Controls over soil nitrogen pools in a semiarid grassland under elevated CO2 and warming. Ecosystems, 15:761-774.
Parton, W, J. Morgan, D. Smith, S. DelGrosso, L. Prihodko, D. Lecain, R. Kelly and S. Lutz. 2012. Impact of precipitation dynamics on net ecosystem productivity. Global Change Biology,18,915-927
Follett, R.F., S. Mooney, J.A. Morgan, K. Paustian, L.H. Allen, Jr., S. Archibeque, S.J. Del Grosso, J.D. Derner, et al. 2011. Carbon sequestration and greenhouse gas fluxes in agriculture: Challenges and opportunities. Task Force Report No. 142, 106 pp, Council for Agricultural Science and Technology Ames, Iowa, USA.
Izaurralde, R.C., A.M. Thomson, J.A. Morgan, P.A. Fay, H.W. Polley and J.L. Hatfield. 2011. Climate Impacts on Agriculture: Implications for Forage and Rangeland Production. Agronomy Journal, 103:371-381.
Polley, H.W., R.L. Phillips, A.B. Frank, J.A. Bradford, P.L. Sims, J.A. Morgan,and J.R. Kiniry. 2011. Variability in Light-Use Efficiency for Gross Primary Productivity on Great Plains Grasslands. Ecosystems. 14: 15-27.
Jamiyansharav, K., D. Ojima, R.A. Pielke Sr., W. Parton, J. Morgan, A. Beltr?n-Przekurat, D. LeCain, and D. Smith. 2011. Seasonal and interannual variability in surface energy partitioning and vegetation cover with grazing at shortgrass steppe. Journal Arid Environments, 75, 360-370.
Dijkstra, F. A., J. A. Morgan, J. C. von Fischer, and R. F. Follett. 2011. Elevated CO2 and warming effects on CH4 uptake in a semiarid grassland below optimum soil moisture. Journal of Geophysical Research, 116, G01007, doi:10.1029/2010JG001288.
Dijkstra, F.A., G.L. Hutchinson, J.D. Reeder, D.R. LeCain, and J.A. Morgan. 2011. Elevated CO2, but not defoliation, enhances N cycling and increases short-term soil N immobilization regardless of N addition in a semiarid grassland. Soil Biology and Biochemistry 43:2247-2256.
Morgan, J. A., D. R. LeCain, E. Pendall, D. M. Blumenthal, B. A. Kimball, Y. Carrillo, D. G. Williams, J. Heisler-White, F. A. Dijkstra, and M. West. 2011. C4 grasses propser as carbon dioxide eliminates desiccation in warmed semi-arid grassland. Nature 476:202-206.
Carrillo, Y., E. Pendall, F.A. Dijkstra, J.A. Morgan, and J.M. Newcomb. 2011. Response of soil organic matter pools to elevated CO2 and warming in a semi-arid grassland. Plant Soil 347:339-350.
Augustine,D.J., F.A. Dijkstra,E.W. Hamilton III and J.A. Morgan. 2011. Rhizosphere interactions, carbon allocation, and nitrogen acquisition of two perennial North American grasses in response to defoliation and elevated atmospheric CO2. Oecologia 165:755-770.
Chimner, R, J.M. Welker, J.A. Morgan, D.R. LeCain and J. Reeder. 2010. Experimental manipulations of winter snow and summer rain influence ecosystem carbon cycling in a mixed-grass prairie, Wyoming, USA. Ecohydrology 3:284-293
Polley,H.W., J.A. Mogan and P.A. Fay. 2010. Application of a conceptual framework to interpret variability in rangeland responses to atmospheric CO2 enrichment. Journal of Agricultural Science, p 1-14.
Dijkstra, F.A., D. Blumenthal, J.A. Morgan, D.R. LeCain and R.F. Follett. 2010. Elevated CO2 effects on semi-arid grassland plants in relation to water availability and competition. Functional Ecology, 24;1152-1161.
Dijkstra, F.A., J.A. Morgan, D. Blumenthal, R.F. Follett. 2010. Water limitation and plant inter-specific competition reduce rhizosphere-induced C decomposition and plant N uptake. Soil Biology and Biochemistry, 42: 1073-1082.
Dijkstra, F.A., D. Blumenthal, J.A. Morgan, E. Pendall, Y. Carrillo, and R.F. Follett. 2010. Contrasting effects of elevated CO2 and warming on nitrogen cycling in a semiarid grassland. New Phytologist 187: 426-437.
Dijkstra,F.A., J. A. Morgan,.D. R. LeCain,.R.F. Follett. 2010. Microbially mediated CH4 consumption and N2O emission is affected by elevated CO2, soil water content,and composition of semi-arid grassland species.Plant Soil (2010) 329:269-281.
Polley, H.W., W. Emmerich, J.A. Bradford, P.L. Sims, D.A. Johnson, N.Z. Saliendra, T. Svejcar, R.Angell, A.B. Frank, F.L. Phillips, K.A. Snyder, and J.A. Morgan. 2010. Physiological and environmental regulation of interannual variability in CO2 exchange on rangelands in the western United States. Global Change Biology 16:990-1002.
Morgan, J.A., R.F. Follett,.L.H. Allen, Jr., S.D. Grosso, J.D. Derner, F.Dijkstra, A. Franzluebbers, R.Fry, K. Paustian, and M.M.Schoeneberger. 2010. Carbon sequestration in agricultural lands of the United States. Journal of Soil and Water Conservation 65:6A-13A. doi:10.2489/jswc.65.1.6A
Bachman, S., J.L. Heisler-White, E. Pendall, D.G. Williams,
J.A. Morgan,J. Newcomb. 2009. Elevated carbon dioxide alters impacts of precipitation pulses on ecosystem photosynthesis and respiration in a semi-arid
grassland. Oecologia, 162:791-802.
Shim, J.H., E. Pendall, J.A. Morgan, and D.S. Ojima. 2009. Wetting and drying cycles drive variations in the stable carbon isotope ratio of respired carbon dioxide in semi-arid grassland. Oecologia doi 10.1007/s00442-009-1302-4.
Alfieri, J., P. Blanken, J.A. Morgan, and D.P. Smith. 2009. Concerning the measurement and magnitude of heat, water vapor, and carbon dioxide exchange from a semiarid grassland.Journal of Applied Meteorology and Climatology 48(5):982-996.
Schuman, G.E., L.J. Ingram, P.D. Stahl, J.D. Derner, G.F. Vance, and J.A. Morgan. 2009. Influence of management on soil organic carbon dynamics in northern mixed-grass rangeland. In: R. Lal and R.F. Follett (eds.). Soil carbon sequestration and the greenhouse effect. Soil Science Society of America, Special Publication 57, second edition, Madison, WI. pp. 169-180.
Kimball, B.A., M.M. Conley, S. Wang, L. Xingwu, J.A. Morgan and D.P. Smith. 2008. Infra-red heater arrays for warming ecosystem field plots. Global Change Biology 14:309-320
Dijkstra, F.A, E. Pendall, A. Mosier, J. King, D. Milchunas, and J.A. Morgan. 2008. Long-term enhancement of N availability and plant growth under elevated CO2 in a semiarid grassland. Functional Ecology doi:10.1111/j.1365-2435.2008.01398.x.
Svejcar, A.J., R.F. Angell, J. Bradford, W. Dugas, W.E. Emmerich, A.B. Frank, T. Gilmanov, M.R. Haferkamp, D.A. Johnson, H.S. Mayeux Jr, P. Mielnick, J.A. Morgan, N. Saliendra, G.E. Schuman, P.L. Sims, K.A. Snyder. 2008. Carbon fluxes on North American rangelands. Rangeland Ecology and Management. 61:465-474.
Ainsworth, E.A., C. Beier, C., Calfapietra, R. Cuelemans, M. Durand-Tardif, G.D. Farquhar, D.L. Godbold, G.R. Hendrey, T. Hickler, J. Kaduk, D.J. Karnosky, B.A. Kimball, C. Koerner, M. Koornneef, T. Lafarge, A.D.B. Leakey, K.F. Lewin, S.P. Long, R. Manderscheid, D.L. McNeil, T.A. Meis, F. Miglietta, J.A. Morgan, J. Nagy, R.J. Norby, R.M. Norton, K.E. Percy, A. Rogers, J. Soussana, M. Stitt, H. Weigel, and J.W. White. 2008. Next generation of elevated [CO2] experiments with crops: A critical investment for feeding the future world. Plant Cell and Environment. 31:1317-1324.
Burke, I.C., Lauenroth, W.K., Antolin, M.F., Derner, J.D., Milchunas, D.G., Morgan, J.A., Stapp, P. 2008. The future of the shortgrass steppe. In: W.K. Lauenroth and I.C. Burke (eds.). Ecology of the shortgrass steppe: A long?term perspective. Oxford University Press, Oxford, England. pp. 484?510.
Lauenroth, W.K., Burke, I.C., Morgan, J.A. 2008. The shortgrass steppe: The region and research sites. In: W.K. Lauenroth and I.C. Burke (eds.). Ecology of the shortgrass steppe: A long?term perspective. Oxford University Press, Oxford, England. pp. 3?13.
Lauenroth, W.K., Milchunas, D.G., Sala, O.E., Burke, I.C., and Morgan, J.A. 2008. Net primary production in the shortgrass steppe: A long?term perspective. Oxford University Press, Oxford, England. pp. 270?305.
Svejcar, T., R. Angell, J. A. Bradford, W. Dugas, W. Emmerich,A. B. Frank, T. Gilmanov, M. Haferkamp, D. A. Johnson, H. Mayeux, P. Mielnick, J. Morgan, N. Z. Saliendra, G. E. Schuman, P. L. Sims, and K. Snyder. 2008. Carbon Fluxes on North American Rangelands. Rangeland Ecol Manage 61:465-474
Morgan, J.A., J.D. Derner, D.G. Milchunas, and E. Pendall. 2008. Management implications of global change for Great Plains rangelands. Rangelands 30:18-22.
Norton, U., A.R. Mosier, , A.R., J.A. Morgan, J.D. Derner, L.J. Ingram, and P.D. Stahl. Moisture pulses, trace gas emissions and soil C and N in cheatgrass and native grass-dominated sagebrush-steppe in Wyoming, USA. Soil Biology & Biochemistry 40:1421-1431. 2008.
Ayers, E., D.H. Wall, B.L. Simmons, C.B. Field, D. Milchunas, J.A. Morgan and J. Roy. 2008. Belowground grassland herbivores are resistant to elevated atmospheric CO2 concentrations in grassland ecosystems. Soil Biology and Biochemistry 40:978-985.
Kandeler, E., A.R. Mosier, J.A. Morgan, D.G. Milchunas, J.Y. King, S. Rudolph, and D. Tscherko. 2008. Transient elevation of carbon dioxide modifies the microbial community composition in a semi-arid grassland. Soil Biology and Biochemistry 40:162-171.
Parton, W. J., J. A. Morgan, G. Wang and S. Del Grosso. 2007. Projected ecosystem impact of the Prairie Heating and CO2 Enrichment experiment. New Phytologist, 174:823-834.
K?rner, C., J.A. Morgan and R. Norby. 2007. CO2 fertilization: When, where, and how much? In: Canadell JG, Pataki DE, Pitelka LF (eds) Terrestrial Ecosystems in a Changing World. The IGBP Series. pp 9-22. Springer, Berlin.
Wylie, B.K., E.A. Fosnight, T.G. Gilmanov, A.B. Frank, J.A. Morgan, M.R. Haferkamp and T.P. Meyers. 2007. Adaptive Data-Driven Models for Estimating Carbon Fluxes in the Northern Great Plains. Remote Sensing of Environment 106:399-413.
Morgan, J.A.,D.G. Milchunas, D.R. LeCain, M.S. West and A. Mosier. 2007. Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe. Proceedings of the Natl Academy of Sciences, 104(37):14724-14729.
LeCain, D.L., J.A. Morgan, D.G. Milchunas, A.R. Mosier, J.A. Nelson and D.P. Smith. 2006. Root biomass of individual species, and root size characteristics after five years of CO2 enrichment on native shortgrass steppe. Plant and Soil 279:219-228.
Milchunas, D.G., A.R. Mosier, J.A. Morgan, D.R. LeCain, J.Y. King and J.Y. Nelson. 2005. Root production and tissue quality in a shortgrass steppe exposed to elevated CO2: Using a new ingrowth method. Plant and Soil 268:111-122.
Pendall, E., J.Y. King, A.R. Mosier, J. Morgan and D. Milchunas. 2005. Stable isotope constraints on net ecosystem production under elevated CO2. In: L.B. Flanagan, J.R. Ehleringer and D.E. Pataki (eds) Stable Isotopes and Biosphere-Atmospheric Interactions: Processes and Biological Controls. pp 182-198. Elsevier Inc., San Diego, CA.
Milchunas, D.G., A.R. Mosier, J.A. Morgan, D.R. LeCain, J.Y King and J.A. Nelson. 2005. Elevated CO2 and defoliation effects on a shortgrass steppe: forage quality versus quantity for ruminants. Agriculture, Ecosystems and Environment 111:166-184.
Milchunas, D.G., J.A. Morgan, A.R. Mosier and D.R. LeCain. 2005. Root dynamics and demography in shortgrass steppe under elevated CO2, and comments on minirhizotron methodology. Global Change Biology 11:1837-1855.
Gilmanov, T.G., L.L. Tieszen, B.K. Wylie, L.B. Flanagan, A.B. Frank, M.R. Haferkamp, T.P. Meyers and J.A. Morgan. 2005. Integration of CO2 flux and remotely sensed data for primary production and ecosystem respiration analyses in the Northern Great Plains: Potential for quantitative spatial extrapolation. Global Ecology and Biogeography 14:271-292.
Derner, J.D., G.E. Schuman, M. Jawson, S.R. Shafer, J.A. Morgan, H.W. Polley, G.B. Runion, S.A. Prior, H.A. Torbert, H.H. Rogers, J. Bunce, L. Ziska, J.W. White, A.J. Franzluebbers, J.D. Reeder, R. Venterea and L.A. Harper. USDA-ARS Global Change Research on Rangelands and Pasturelands. Rangelands 27:36-42.
Nelson, J.A., J.A. Morgan, D.R. LeCain, A.R. Mosier, D.G. Milchunas, and B.A. Parton. 2004. Elevated CO2 increases soil moisture and enhances plant water relations in a long-term field study in semi-arid shortgrass steppe of Colorado. Plant and Soil 259:169-179.
Morgan, J.A., A.R. Mosier, D.G. Milchunas, D.R. LeCain, J.A. Nelson and W.J. Parton. 2004. CO2 enhances productivity, alters species composition, and reduces forage digestibility of shortgrass steppe vegetation. Ecological Applications 14:208-219.
Reeder, J.D., G.E. Schuman, J.A. Morgan, and D.R. LeCain. 2004. Response of organic and inorganic carbon and nitrogen stocks to long-term grazing of the shortgrass steppe. Environmental Management 10.1007/s00267-003-9106-5.
Pendall, A.R. Mosier, and J.A. Morgan. 2004. Rhizodeposition stimulated by elevated CO2 in a semi?arid grassland. New Phytologist 162:447-458
Reeder, J.D., G.E. Schuman, J.A. Morgan and D.R. LeCain. 2004. Response of organic and inorganic carbon and nitrogen stocks to long-term grazing of the shortgrass steppe. Environmental Management 33:485-495.
King, J.Y., A.R. Mosier, J.A. Morgan, D.R. LeCain, D.G. Milchunas and W.J. Parton. 2004. Plant nitrogen dynamics in shortgrass steppe under elevated atmospheric CO2. Ecosystems 7:147-160.
Milchunas, D.G., J.Y. King, A.R. Mosier, J.C. Moore, J.A. Morgan, M.H. Quirk and J.R. Slusser. 2004. UV radiation effects on plant growth and forage quality in a shortgrass steppe ecosystem. Photochemistry and Photobiology 79:404-410.
Pendall, E., A.R. Mosier and J.A. Morgan. 2004. Rhizodeposition stimulated by elevated CO2 in a semi arid grassland. New Phytologist 162:447-458.
Morgan, J.A., D.E. Pataki, C. Korner, H. Clark, S.J. DelGrosso, J.M. Grunzewig, A.K. Knapp, A.R. Mosier, P.C.D. Newton, P.A. Niklaus, J.B. Nippert, R.S. Nowak, W.J. Parton, H.W. Polley and M.R. Shaw. 2004.Water relations in grassland and desert ecosystems to elevated atmospheric CO2. Oecologia 140:11-25.
Liebig, M.A., J.A. Morgan, J.D. Reeder, B.H. Ellert, H.T. Gollany and G.E. Schuman. 2004. Greenhouse Gas Contributions and Mitigation Potential of Agricultural Practices in Northwestern USA and Western Canada. ASA Meetings (abstract).
Ferretti, D.F., E. Pendall, J.A. Morgan, J.A. Nelson, D.R. LeCain and A.R. Mosier. 2003. Partitioning evapotranspiration fluxes from a Colorado grassland using stabel isotopes: seasonal variations and implication for elevated atmospheric CO 2. Plant and Soil 254:291-303.
Pendall, E., S. Del Grosso, J.Y. King, D.R. LeCain, D.G. Milchunas, J.A. Morgan, A.R. Mosier, D.S. Ojima, W.A. Parton, P.P. Tans, and J.W.C. White. 2003. Elevated atmospheric CO2 effects and soil water feedbacks on soil respiration components in a Colorado grassland. Global Biogeochemical Cycles 17:1-13.
LeCain, D.R., J.A. Morgan, A.R. Mosier and J.A. Nelson. 2003. Soil and plant water relations, not photosynthetic pathway, primarily influence photosynthetic responses in a semi-arid ecosystem under elevated CO2. Annals of Botany 92:41-52.
Mosier, A.R., E. Pendall, and J.A. Morgan. 2003. Effect of water addition and nitrogen fertilization on the fluxes of CH4, CO2, NOx, and N2O following five years of elevated CO2 in the Colorado Shortgrass Steppe. Atmospheric Chemistry and Physics Discussions 3:1-6.
King, J., D. Milchunas, A. Mosier, Moore, J. Morgan, Slusser. 2003. Initial Impacts of Altered UVB Radiation on Plant Growth and Decomposition in Shortgrass Steppe. International Society for Optical Engineering Annual Meeting.
Morgan, J.A. 2002. Looking beneath the Surface. Science 298: 1903-1904.
Lecain, D.R., J.A. Morgan, G.S. Schuman and J.D. Reeder, and R.H. Hart. 2002. Carbon exchange rates and species composition of grazed pastures and exclosures in the shortgrass steppe of Colorado. Agriculture, Ecosystems and Environment 93:421-435.
Gill, R.A., R.H. Kelly, W.J. Parton, K.A. Day, R.B. Jackson, J.A. Morgan, J.M.O. Scurlock, L.L. Tieszen, J. van de Castle, D.S. Ojima, and X.S. Zhang. 2002. Using simple environmental variables to estimate belowground productivity in grasslands. Global Ecology and Biogeography 11(1):79-86.
Mosier, A.R., J.A. Morgan, J.Y. King, D. LeCain and D.G. Milchunas. 2002. Soil-atmosphere exchange of CH4, CO2, NOx, and N2O in the Colorado Shortgrass Steppe under Elevated CO2. Plant and Soil 240:201-211.
Derner, J.D., D.T. Booth, J.A. Morgan, G.E. Schuman and J.D. Reeder. 2002. High Plains Grasslands Research Station - Changing to meet the challenges of a new century. Cow Country 130:4-5
Morgan, J.A., A.R. Mosier, D.R. LeCain, W.J. Parton and D.G. Milchunas. 2001. Elevated CO2 enhances productivity and the C/N ratio of grasses in the Colorado shortgrass steppe. Proceedings of the XIX International Grassland Congress. pp 981-982. Brazilian Society of Animal Husbandry, Sao Pedro, Sao Paulo, Brazil.
Morgan, J.A., P.C.D. Newton, J. N?sberger and C.E. Owensby. 2001. The influence of rising atmospheric CO2 on grassland ecosystems. Proceedings of the XIX International Grassland Congress. pp 973-980. Brazilian Society of Animal Husbandry, Sao Pedro, Sao Paulo, Brazil..
Reeder, J.D., G.E. Schuman, J.A. Morgan, D.R. LeCain and R.H. Hart. 2001. Impact of grazing management strategies on carbon sequestration in a semi-arid rangeland, USA. Proceedings of the XIX International Grassland Congress. pp 211-213. Brazilian Society of Animal Husbandry, Sao Pedro, Sao Paulo, Brazil. XIX International Grassland Congress.
Morgan, J.A., R.H. Skinner, and J.D. Hanson. 2001. Nitrogen and CO2 affect regrowth and biomass partitioning differently in forages of three functional groups. Crop Science 41:78-86.
Morgan, J.A., D.R. LeCain, A.R. Mosier, and D.G. Milchunas. 2001. Elevated CO2 enhances water relations and productivity and affects gas exchange in C3 and C4 grasses of the Colorado Shortgrass Steppe. Global Change Biology 7:451-466.
Schuman, G.E., D.R. LeCain, J.D. Reeder, and J.A. Morgan. 2001. Carbon dynamics and sequestration of a mixed-grass prairie as influenced by grazing. pp. 67-75. In: R. Lal (ed.)Soil Carbon Sequestration and the Greenhouse Effect. Soil Sci. Soc. Am., Special Publ. No. 57. Soil Science Society of America, Madison, WI
LeCain, D.R., J.A. Morgan, G.E. Schuman, J.D. Reeder, and R.H. Hart. 2000. Carbon exchange rates in grazed and ungrazed pastures of Wyoming. J. Range Management. 53: 199-206.
Parton, W.J., J.A. Morgan, R.H. Kelly and D. Ojima. 2000. Modeling soil C responses to environmental change in grassland systems. pp 371-398. In R.F. Follet, J.M. Kimble and R. Lal (eds) The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect, Lewis Publishers, New York.