HR: 0800h
AN: B11A-0991    [Abstracts]
TI: Testing and development of a Tunable Diode Laser for measurements of leaf to ecosystem stable isotope composition of carbon dioxide exchange
AU: * Powers, H
EM: hpowers@lanl.gov
AF: Los Alamos National Laboratory, MS J-495, Los Alamos, NM 87545 United States
AU: Bickford, C
EM: bickford@unm.edu
AF: University of New Mexico, 167 Castetter Hall MSC03 2020 1 University of New Mexico, Albuquerque, NM 87131 United States
AU: Hanson, D
EM: dthanson@unm.edu
AF: University of New Mexico, 167 Castetter Hall MSC03 2020 1 University of New Mexico, Albuquerque, NM 87131 United States
AU: Kern, S
EM: skern@coloradocollege.edu
AF: Los Alamos National Laboratory, MS J-495, Los Alamos, NM 87545 United States
AU: Meyer, C
EM: clifm@lanl.gov
AF: Los Alamos National Laboratory, MS J-495, Los Alamos, NM 87545 United States
AU: McDowell, N
EM: mcdowell@lanl.gov
AF: Los Alamos National Laboratory, MS J-495, Los Alamos, NM 87545 United States
AB: We describe methods for measuring leaf-level carbon isotope discrimination and the isotopic composition of ecosystem respiration using Tunable Diode Laser (TDL) Absorption Spectroscopy. We modified a Campbell Scientific TGA100A for coupling with a Licor Li-6400 photosynthesis system in order to investigate leaf gas exchange continuously with discrimination. Certain applications require particularly low flow rates to generate measurable isotopic patterns, such as measurement of leaf respiration or photosynthetic discrimination of drought stressed Juniper (Juniperus monosperma, e.g. 11 per mil). We discuss the obstacles presented by low sample flow rates (50 mL/min) through the TDL, such as pressure fluctuations and large sample lag times, and the modifications we employed to overcome them. Calibration and measurement precision is assessed for low-flow configurations as well as higher flow (200 mL/min) ecosystem measurements. We attempt to quantify the effects of pressure variations and calibration intervals on the accuracy of measured leaf and ecosystem scale isotopic ratios of oxygen and carbon dioxide. Calibrated measurements were found to typically have prescision of <0.1per mil when measuring carbon isotopes only, and slightly less precise when simultaneously measuring both carbon and oxygen (0.16 and 0.18 per mil, respectively). This level of precision was sufficient to resolve observed carbon isotope ratio differences (reference minus sample) that ranged from 0.5-3 per mil and represented variation in leaf level discrimination of J. monosperma of up to 10 per mil on a single day. Our next goal is to further connect leaf level analysis to atmospheric variation through the addition of branch and soil chambers.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0490 Trace gases
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Biogeosciences [B]
MN: Fall Meeting 2005