FACE Experiments at Maricopa, Arizona


Steven W. Leavitt and PIs/Collaborators over the years (Hyrum Johnson, Paul Pinter, Eldor Paul, Gary Wall, Elise Pendall, Talbot Brooks, Li Cheng, George Hendry, Bruce Kimball, Hyrum Johnson, Hugo Rodgers, Dave Williams, and many, many others)


Free-Air CO2 Enrichment (FACE) experiments are now being conducted around the world. These experiments are conducted outdoors without the confining elements of indoor growth chamber and outdoor chamber experiments, thereby adding greater realism to experimental conditions. Generally there are ambient control plots with CO2 concentrations of the current atmosphere, and enriched treatments with CO2 concentrations elevated by at least 200 ppmV relative to the control. A distribution of pipes with holes facing inward to the plot is used to add CO2 with valves controlling distribution depending on wind direction.



At Maricopa, Arizona, FACE experiments have taken place since 1989 with enriched CO2 plots at ambient+200ppmV:


1989, 1990, 1991 Cotton (CO2 x H2O)

1992-93, 1993-94 Wheat (CO2 x H2O)

1995-96, 1996-97 Wheat (CO2 x N)

1998, 1999 Sorghum (CO2 x H2O)


Since 1991, we have been using isotopes in the experiment in a wide range of activities such as:


Isotopic consistency of source of tank CO2

Independent verification of intended CO2 concentration in enriched treatments

Assessing variability of spatial isotopic homogeneity in enriched treatments



Water-Use Efficiency estimation

Homogeneity of soil organic carbon (SOC) isotopic composition

C inputs to SOC pools

C losses from SOC pools

SOC isotopic signal through time

soil respiration evidence

Specific plant compounds




In tracing carbon into soils, the isotopic composition of the tank CO2 and the plants provides a tracer to follow carbon into the soil organic carbon (SOC) pools and out via soil respiration. In the 1999 FACE sorghum experiment, the isotopic compositon of the plants was very 13C-enriched relative to the SOC (d13C = -23.5):

The shift in carbon isotopic composition of the SOC before and after the experiment can be used to estimate the carbon inputs:



Maricopa Isotope Publications/Presentations:


Cheng, L., Leavitt, S.W., Brooks, T. J., Matthias, A.D., Williams, D.G., Thompson, T.L., Kimball, B.A., Wall, G.W., Pinter Jr., P.J., 2002. Seasonal soil respiration and soil CO2 under elevated CO2 in a C4-sorghum agroecosystem. Ecological Society of America Annual Meeting, 4-9 August, Tucson.

Cheng, L., Leavitt, S.W., Kimball, B.A., Pinter, P.J. Jr., Ottman, M.J., Matthias, A., Wall, G.W., Brooks, T., Williams, D.G., and Thompson, T.L., 2007. Dynamics of labile and recalcitrant soil carbon pools in a sorghum free-air CO2 enrichment (FACE) agroecosystem. Soil Biology and Biogeochemistry in press.

Cheng, L., Martens, D., Leavitt, S.W., Kimball, B.A., Matthias, A.D., Ottman, M.J., Williams, D.G., Wall, G.W. and Pinter, P.J., Jr., 2003. Free Air-CO2 Enrichment (FACE) of C4-Sorghum: Biochemical Composition and Decomposition of Sorghum Tissues Grown Under Elevated CO2. ASA-CSSA-SSSA Annual Meeting, Denver, Colorado, 2-6 November.

Derner, J.D., Johnson, H.B., Kimball, B.A., Pinter, P.J. Jr., Polley, H.W., Tischler, C.R., Boutton, T.W., LaMorte, R.L., Wall, G.W., Adam, N.R., Leavitt, S.W., Ottman, M.J., Matthias, A.D. and Brooks, T.J., 2003. Above- and belowground responses of C3-C4 species mixtures to elevated CO2 and soil water availability. Global Change Biology. 9: 452-460

Johnson, H.B., Kimball, B., and Leavitt, S., 1994. Carbon isotope assessment of intrinsic water use efficiency of C3 plants in two FACE experiments. Ecological Society of America Annual Meeting, Knoxville, Tennessee, August 7-11. Bull. Ecol. Soc. Am. 75: 122-123 (supplement part 2).

Leavitt, S.W., Paul, E.A., Kimball, B.A., Hendrey, G.R., Mauney, J.R., Rauschkolb, R., Rogers, Jr., H., Lewin, K.F., Nagy, J., Pinter, Jr., P.J. and Johnson, H.B., 1994. Carbon isotope dynamics of CO2-enriched FACE cotton and soils. Agricultural and Forest Meteorolology 70: 87-101.

Leavitt, S.W., Follett, R.F. and Paul, E.A., 1996. Estimation of slow and fast-cycling organic carbon pools from 6N HCl hydrolysis. Radiocarbon 38: 231-239.

Leavitt, S.W., Paul, E.A., Pendall, E., Pinter, P.J. and Kimball, B.A., 1996. Field variability of carbon isotopes in soil organic carbon. Nuclear Instruments and Methods in Physics Research B 123: 451-454.

Leavitt, S.W., Paul, E.A., Galadima, A., Nakayama, F.S., Danzer, S.R., Johnson, H. and Kimball, B.A., 1997. Carbon isotopes and carbon turnover in cotton and wheat FACE experiments. Plant and Soil 187: 147-155.

Leavitt, S.W., Pendall, E., Paul, E.A., Brooks, T., Kimball, B.A., Pinter, P.J. Jr., Johnson, H.B., Matthias, A., Wall, G.W., and LaMorte, R.L., 2001. Stable-carbon isotopes and soil organic carbon in wheat under CO2 enrichment. New Phytologist 150: 305-314.

Matthias, A.D., Leavitt, S.W., Thompson, T.L., Kimball, B.A., Pinter Jr., P.J., Wall, G.W., Rauschkolb, R.S., Ottman, R.L., Roth, R.L., Brooks, T.J., Adam, N.R., LaMorte, R.L., Wechsung, G., Wechsung, F., Adamsen, F.J., Williams, D.G., Nakayama, F.S., Hunsaker, D.J., Watson, J., White, S.A., and Welzmiller, J., 2001. Free-air CO2 enrichment effects on wheat and sorghum at Maricopa, Arizona, USA. In Carbon Dioxide and Vegetation: Advanced International Approaches for Absorption of CO2 and Responses to CO2. National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan. March 18, 1999, pp. 87-96.

Pendall, E., Leavitt, S.W., Brooks, T. and Kimball, B., 1997. Enhanced soil respiration and decomposition under elevated carbon dioxide. 7th Annual V.M. Goldschmidt Conference, 2-6 June, Tucson. LPI Contribution No. 921, Lunar and Planetary Institute, Houston, p. 162.

Pendall, E., Leavitt, S.W., Brooks, T., Kimball, B.A., Pinter, P.J. Jr., Wall, G.W., LaMorte, R.L., Wechsung, G., Wechsung, F., Adamsen, F., Matthias, A.D., Thompson, T.L., 2001. Elevated CO2 stimulates soil respiration in a FACE wheat field. Basic and Applied Ecology 2: 193-201.

Thompson, T.L., White, S.A., Leavitt, S.W., Pendall, E., and Matthias, A.D., 1998. Nitrogen and carbon dynamics in a wheat agroecosystem under elevated atmospheric CO2. In Proc. of the Dahlia Greidinger International Symposium on Fertilization and the Environment, Mordvelt, J.J, ed., pp. 182-192.

Williams, D.G., Gempko, V., Fravolini, A., Leavitt, S.W., Wall, G.W., Kimball, B.A., Pinter, P.J. Jr., LaMorte, R.L., and Ottman, M., 2001. Carbon isotope discrimination by Sorghum bicolor under CO2 enrichment and drought. New Phytologist 150: 285-293.


List of All FACE Publications