PARENT SESSION
Oral Session #58: Elevated CO2. Presiding: A. Finzi.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Madison Ballroom C.
The effect of pressure, temperature, and wind on ecosystem gas exchange measurements determined using large open top chambers for exposing plants to elevated atmospheric CO2 in Florida scrub oak.
JOHNSON, DAVID1, HYMUS, GRAHAM1, DORE, SABINA2, HINKLE, C ROSS3, DRAKE, BERT1, 1 2 3
ABSTRACT- Open top chambers (OTC′s) have been used in an ongoing study to determine the effects of elevated atmospheric CO2 on a Florida scrub oak ecosystem. Here, we report results of experiments to determine whether and how much changes in atmospheric pressure, temperature and wind introduce artifacts into measurements of net ecosystem CO2 exchange (NEE) using the chamber as a cuvette. An increase in atmospheric pressure of ca. 5.5 Pa within the chamber, when a top was added to prevent dilution of chamber air with outside air for NEE measurements, was found to suppress soil CO2 efflux by an average amount of 50%. We measured soil respiration using a Li-Cor closed-dynamic soil flux chamber, atmospheric pressure using Omega pressure transducers, and varied the pressure by changing the speed of the blower. The effect of pressure on soil CO2 efflux was dependent on location within the chamber with the greatest effect occurring near the outer wall of the chamber. Partitioning respiration, which was temperature dependent, between above and belowground components accounted for this suppression. Measurements of stem and leaf CO2 efflux indicated no effect of CO2 concentration on dark respiration. Instantaneously changing ambient and elevated CO2 concentrations within the chamber at night did not affect the respiration rates of either. This was taken to be evidence that there were no significant leaks from outside air, consistent with results of N2O dilution tests.
KEY WORDS: elevated CO2 , net ecosystem CO2 exchange, open top chambers, florida scrub oak