Title: Field Evaluation of Open System Chambers for Measuring Whole Canopy Gas Exchanges Authors
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2013
Publication Date: January 31, 2014
Citation: Baker, J.T., Gitz, D.C., Lascano, R.J. 2014. Field Evaluation of Open System Chambers for Measuring Whole Canopy Gas Exchanges. Agronomy Journal. 106(2):537-544. Interpretive Summary: Plants grow by using sunlight to capture carbon dioxide out of the air and fixing this into simple sugars in a process called photosynthesis. At the same time, plants loose water to the atmosphere in a process called transpiration. Both of these processes are good indicators of how various environmental factors, such as drought, influence plant growth and crop yield. We developed and tested four portable transparent chambers that can be placed over plants in the field and used to measure the rates of both photosynthesis and transpiration. We found good agreement among these chambers in measurement of photosynthesis, transpiration and the ratio of these two measurements called water use efficiency. This approach will provide a valuable tool for future research on crop water use and water use efficiency.
Technical Abstract: The ability to monitor whole canopy CO2 and H2O fluxes of crop plants in the field is needed for many research efforts ranging from plant breeding to the study of Climate Change effects on crops. Four portable, transparent, open system chambers for measuring canopy gas exchanges were field tested on well watered and fertilized cotton (Gossypium hirsutum, L.) over six days at Lubbock, TX, USA in 2010. Our goal was to examine “chamber effects” on chamber environmental variables as well as characterizing chamber-to-chamber variability in measured gas exchange parameters expressed both on a per unit ground area basis and a leaf area basis. Chamber wall materials reduced photosynthetically active radiation (PAR) by about 13%. Programmable data loggers controlled variable speed fans and, with one minor exception, limited heat buildup in the chambers to a maximum of less than 1.0° C above ambient air temperature. Differentials between incoming and outgoing atmospheric CO2 and H2O concentrations were used to calculate canopy net assimilation (A) and transpiration (E) at 10 s intervals using solenoid valve actuated sample lines connected to an infrared gas analyzer. Water use efficiency (WUE=A/E) was then calculated and these data were averaged over both five minute and hourly intervals. Coefficient of variation (CV) for midday A, E and WUE averaged 12.3, 9.7, and 5.8 %, respectively. Expressing these parameters on a canopy leaf area basis produced similar CV results. These results will help guide experimental design for future research using these or similar chambers.