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Canopy Gas Exchange Measurements of Cotton in an Open System

^a USDA-ARS, Plant Stress and Water Conservation Laboratory, 302 West I-20, Big Spring, TX, 79720
^b USDA-ARS, Plant Stress and Water Conservation Laboratory, 3810 4th Street, Lubbock, TX 79415

View larger version (74K): [in this window] [in a new window]   Fig. 1. (A) Wilted cotton plants in the canopy evapotranspiration and assimilation (CETA) chamber at the end of a 4-d run used to tune the fan control algorithm on 21 July 2006. Blue arrows indicate the direction of air flow. (B) Potted cotton plants with sealed soil on the weighing scale used to measure transpiration on 29 Aug. 2006. Also shown is the location of the air inlet port to measure entrance mole fractions of H2O (wi) and CO2 (ci) as well as the quantum sensor for measuring internal photosynthetically active radiation (PAR) and the infrared thermometer (IRT) for measuring canopy temperature.

View larger version (13K): [in this window] [in a new window]   Fig. 2. Example of diurnal trends in internal scale measurements used to calculate hourly transpiration rates for 22 to 24 Aug. 2006. The y axis represents the combined mass of the soil media, soil water, pots, and plants

View larger version (24K): [in this window] [in a new window]   Fig. 3. Time-trend in exit air flow rate (uo, filled circles, top panel) and photosynthetically active radiation (PAR, solid line, top panel) on 22 to 24 Aug. 2006. Lower panels: differential between exit (Tout) and entrance (Tin) air temperatures. Desired daytime set-point of 0.5°C is indicated as a horizontal line on the bottom panel.

View larger version (16K): [in this window] [in a new window]   Fig. 4. Response of canopy net assimilation (A) to photosynthetically active radiation (PAR) for 22 to 24 Aug. 2006.

View larger version (13K): [in this window] [in a new window]   Fig. 5. Diurnal canopy transpiration rate (E) from 22 to 24 Aug. 2006 measured using either the (CETA) chamber (open circle) or the internal scale (closed circle).

View larger version (24K): [in this window] [in a new window]   Fig. 6. Transpiration rates (E) measured using the internal scale vs. E measured using the Canopy Evapotranspiration and Assimilation (CETA) chamber and compared to a 1:1 line. Open circles, squares and diamonds are for 24 to 25 July, 22 to 24 Aug. and 29 to 31 Aug. 2006, respectively. Closed circles, squares, and diamonds are for 12 to 14 Sept., 18 to 20 Sept. and 2 to 4 Oct. 2006, respectively.

View larger version (18K): [in this window] [in a new window]   Fig. 7. Transpiration rates (E) measured using the internal vs. external scales to test chamber effects measurement of E and compared with a 1:1 line.