Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/29/2004
Publication Date: 10/31/2004
Citation: Van Pelt, R.S., Baker, J.T. 2004. CETA: A Portable Chamber for Measuring Evapotranspiration and Carbon Assimilation of Whole Field-Grown Plants[abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts.
Interpretive Summary: Atmospheric measurements of whole plant evapotranspiration and carbon assimilation have been limited to artificial environments such as phytotrons and SPAR chambers or to non-aspirated chambers in which the measurements are not steady state or continuous. We have developed and completed the preliminary physical testing on the prototype of a portable, aspirated, and feed-back controlled chamber that will allow continuous measurement of transpiration and carbon assimilation of whole field-grown plants and evaporation and carbon dioxide fluxes from soil surfaces. The chamber is constructed of an aluminum bar stock frame covered with ultraviolet radiation resistant polycarbonate film. Pitot tubes and a pressure transducer measure mass flow rates and the water vapor and carbon dioxide concentrations are measured in the intake and outflow sections with an infrared gas analyzer.
Technical Abstract: Instantaneous measurements of whole-plant evapotranspiration (ET), carbon assimilation (CA), and water use efficiency (WUE) have been limited to soil-plant-atmospheric research (SPAR) chambers or to in-field chamber measurements lasting only a few minutes each. We have designed and built a portable, self aspirated plant growth chamber, the Canopy EvapoTranspiration and Assimilation (CETA), to measure diurnal cycles of water vapor and CO2 flux of cropping systems. This chamber consists of an aluminum frame measuring 1 m high by 0.75 m wide by 1 m long covered by UV resistant polycarbonate film. Water vapor and CO2 fluxes are determined by integrating infra-red gas analyzer (IRGA) measured water vapor and CO2 concentration differences between the intake section and the exhaust section and multiple pitot tube measured air flow rates in the circular exhaust duct. A variable speed fan aspirates the chamber and the flow rate is automatically controlled to maintain a temperature increase of 0.8 - 1.2 deg C between the intake and exhaust sections. Wind speed profiles consistent with the canopy architecture are effected by replaceable polycarbonate baffles between the chamber and the intake and exhaust sections. Additional uses for the CETA are measuring real-time, long-term evaporation and CO2 fluxes from bare ground and, using a gas excluding membrane placed on the soil surface and sealed around the base of the plant, the transpiration component of ET and also plant CA, thus providing real-time measurements of plant WUE.