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Title: CHAMBER AND MICROMETEOROLOGICAL MEASUREMENTS OF CO2 AND H20 FLUXES FOR THREE C4 GRASSES

Author
item DUGAS, WILLIAM - TAES
item Reicosky, Donald
item Kiniry, James

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/29/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Flux of CO2 and water can be measured with several types of instrumentation. With bermudagrass, a native tallgrass prairie, and sorghum, we measured: 1) evapotranspiration (ET) using a canopy chamber (CC) and Bowen ratio/energy balance (BREB) instrumentation, 2) leaf CO2 uptake using a CC, a leaf chamber (LC), and BREB instrumentation, and 3) soil CO2 fluxes from bare soil measured using a CC and soil chamber (SC). Measurements of ET with the CC were consistently greater than BREB measurements for all grasses. Leaf CO2 uptake measured using the three methods was similar for all grasses. The LC measurements were similar to the measurements, but had much scatter. The CC measurements were consistently smaller than the BREB measurements. CO2 uptake measured by all methods was linearly related to intercepted light for all grasses. Half-hour soil CO2 fluxes from bare soil for both methods showed typical diurnal patterns. Fluxes from the CC were significantly greater for two-thirds of the day on both surfaces. These results show the consistency and accuracy of leaf CO2 uptake and soil CO2 flux measurements with all methods.

Technical Abstract: Measurements of surface fluxes of CO2 and water can be made using several types of instrumentation. We examined the following on bermudagrass, a native tallgrass prairie, and sorghum at the Blackland Research Center, Temple, TX: 1) evapotranspiration (ET) measured using a canopy chamber (CC) and Bowen ratio/energy balance (BREB) instrumentation, 2) leaf CO2 uptake measured using a CC, a leaf chamber (LC), and BREB instrumentation, and 3) soil CO2 fluxes from bare soil measured using a CC and soil chamber (SC). Flux of CO2 into the leaf was considered positive and was expressed per unit ground area. ET measurements with a CC were consistently greater than BREB measurements. Leaf CO2 uptake measured using the three methods was similar. The regression equation for LC measurements as a function of BREB measurements had a slope not statistically different from 1.0, but the scatter was large, likely because of limited leaf area sampled by the LC. For CC measurements, the scatter about the regression line versus BREB measurements was much smaller, but CC measurements were consistently smaller. Half-hour CO2 uptake measured by all methods was linearly related to intercepted photosynthetic photon flux density. Soil CO2 fluxes from bare soil for both methods showed typical diurnal patterns. Fluxes from the CC were significantly greater for two-thirds of the day on both surfaces. Differences of daytime soil CO2 fluxes averaged 0.07 mg m**-2 s**-1. Leaf CO2 uptake and soil CO2 flux measurements with all methods were consistent, repeatable, and accurate.