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Title: LEAF-TO-AIRCRAFT MEASUREMENTS OF NET CO2 EXCHANGE IN A SAGEBRUSH STEPPE ECOSYSTEM

Author
item SMITH, WILLIAM - WAKE FOREST UNIVERSITY
item KELLY, ROBERT - UNIVERSITY OF WYOMING
item WELKER, JEFFREY - COLORADO STATE UNIVERSITY
item FAHNESTOCK, JACE - COLORADO STATE UNIVERSITY
item REINERS, WILLIAM - UNIVERSITY OF WYOMING
item Hunt Jr, Earle

Submitted to: Journal of Geophysical Research Atmospheres
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2002
Publication Date: 2/12/2003
Citation: Smith, W.K., Kelly, R.D., Welker, J.M., Fahnestock, J.T., Reiners, W.A., Hunt, E.R. 2003. Leaf-to-aircraft Measurements of Net CO2 exchange in a sagebrush steppe ecosystem. Journal of Geophysical Research Atmospheres. 108(D3):15.1-15.9.

Interpretive Summary: Different techniques for measuring carbon dioxide fluxes were made in a high-elevation, sagebrush steppe community in southeastern Wyoming. The first was leaf gas exchange, the second was a community chamber, the third and fourth were eddy-covariance measurements made from a tower and from an aircraft respectively. There was a high degree of homogeneity in plant species composition, density, cover, and the amount of leaf area per unit ground area, as well as little topographic variability, along the flight transect, tower footprint, and intensive study sites. Measurements made on the same day and same time had little variation between the four techniques. With each technique over as little as four days, there was substantial variation with time. Thus for a homogeneous system,frequency of measurements is more important than spatial sampling for fluxes of carbon dioxide.

Technical Abstract: Measurements of net carbon dioxide flux density from a high elevation, sagebrush steppe community in southeastern Wyoming (USA) were compared among four different instrument systems (leaf cuvette and community chamber for gas exchange measurements; tower and aircraft eddy covariance systems). Ground-based flux measurements were recorded at an intensive site located near the midpoint and directly beneath an approximate 20 km flight transect. A high degree of homogeneity in plant species composition, density, cover, and the amount of leaf area per unit ground area, as well as little topographic variability, was measured at the intensive site and along the flight transect. Flux measurements were compared on days with relatively high and low soil moisture availability. Same-day, mean carbon dioxide flux density values between the four measurement systems over identical time intervals (0900 ¿ 1100 hr) varied by a maximum of +/-9% (maximum range 23%). Ground-level measurements taken within plus or minus one day of flight measurements, varied by a minimum of +/-7% (25% maximum range) of aircraft values. Thus, under near ideal conditions of topographic and vegetative homogeneity, temporal heterogeneity in the measurement regime of only a few days resulted in greater disparity in measured carbon dioxide flux density than occurred among the four instrument types.