ARS | Publication request: An open system for measuring canopy gas exchange

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 4, 2007
Publication Date: November 8, 2007
Citation: Baker, J.T., Lascano, R., Gitz, D.C., Payton, P.R., Van Pelt, R.S., Garcia, R. 2007. An open system for measuring canopy gas exchange[abstract]. ASA-CSSA-SSSA Joint Annual Meeting. New Orleans, Lousiana. November 4-8, 2007. Abstract No. 239-7.

Technical Abstract: Three portable, CETA (Canopy Evapo-Transpiration and Assimilation) chamber systems were built and evaluated in 2006. This chamber system is an open or flow-through system that, once deployed in the field, can operate unattended for extended periods (e.g. overnight for example). The CETA chamber consists of an aluminum framework, 1 m x 0.75 m in cross-section and 1 m tall covered with transparent film. Differentials between incoming and outgoing atmospheric water vapor and carbon dioxide concentrations are used to calculate evapotranspiration and canopy photosynthesis at 10 s intervals using solenoid valve actuated sample lines connected to an infrared gas analyzer. A programmable data logger controls fan speed and air flow rate in order to control chamber air temperature to within 0.5 ºC of ambient air temperature using a feedback control algorithm. In order to validate the mass balance equations used to calculate canopy evapotranspiration, the CETA chamber was placed over potted plants sitting atop a mini-lysimeter. A wide variety of crop canopies and soil water content were created with greenhouse-grown plants. Preliminary data analysis indicates good agreement between CETA evapotranspiration measurements and the mini-lysimeter over wide ranges of soil moisture contents and canopy leaf area. However, these tests also indicate a physical limitation of the system to resolve very small gas concentration differentials caused by the combination of very low soil moisture content and low canopy leaf area.