HR: 0800h
AN: B11A-0995    [Abstracts]
TI: Separating Autotrophic and Heterotrophic Contributions to Soil Respiration in Maize-Based Agroecosystems Using Stable Carbon Isotope Ratio Mass Spectrometry.
AU: * Amos, B
EM: bamos2@unlnotes.unl.edu
AF: Dept. of Agronomy and Horticulture. University of Nebraska-Lincoln, 279 Plant Sciences Hall, Lincoln, NE 68583-0915 United States
AU: Walters, D T
EM: dwalters1@unl.edu
AF: Dept. of Agronomy and Horticulture. University of Nebraska-Lincoln, 279 Plant Sciences Hall, Lincoln, NE 68583-0915 United States
AU: Madhavan, S
EM: msoundar@unlnotes.unl.edu
AF: Biochemistry Dept. University of Nebraska-Lincoln, N200 George W. Beadle Center for Genetics & Biomaterials Research, Lincoln, NE 68583-0664 United States
AU: Arkebauer, T J
EM: tja@unl.edu
AF: Dept. of Agronomy and Horticulture. University of Nebraska-Lincoln, 279 Plant Sciences Hall, Lincoln, NE 68583-0915 United States
AU: Scoby, D L
EM: dscoby@unlnotes.unl.edu
AF: Dept. of Agronomy and Horticulture. University of Nebraska-Lincoln, 279 Plant Sciences Hall, Lincoln, NE 68583-0915 United States
AB: Any effort to establish a carbon budget for a growing crop by means of a thorough accounting of all C sources and sinks will require the ability to discriminate between autotrophic and heterotrophic contributions to soil surface CO₂ flux. Autotrophic soil respiration (R_a) is defined as combined root respiration and the respiration of soil microorganisms residing in the rhizosphere and using root-derived carbohydrates as an energy source, while heterotrophic respiration (R_h) is defined as the respiration of soil microorganisms and macroorganisms not directly under the influence of the live root system and using SOM as an energy source. We partition soil surface CO₂ flux into its autotrophic and heterotrophic components by combining root exclusion with stable carbon isotope techniques in production scale (~65 ha) maize-based agroecosystems. After flux measurements, small chambers are placed on collars in both root excluded shields and in non-root excluded soil, ambient headspace CO₂ is removed using a soda lime trap, and soil-respired C is allowed to collect in the chambers. Soil respiration samples are then collected in 12mL evacuated exetainers and analyzed for δ¹³C by means of a Finnigan Delta-S isotope ratio mass spectrometer interfaced with a Thermo Finnigan GasBench II and a cryogenic trap to increase CO₂ concentration. These δ¹³C measurements were made throughout the 2005 growing season in maize fields representing three agroecosystems: irrigated continuous maize, irrigated maize-soybean rotation, and rainfed maize soybean rotation. Estimates of autotrophic and heterotrophic soil respiration along with other results of this study will be presented.
DE: 0402 Agricultural systems
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005