Soil Carbon Dioxide Distribution and Flux within the Open-top Chamber
Open-top chamber use for exposing plants to various levels of CO2 and pollutant gases is increasing in field studies. In making a C balance of cotton [Gossypium hirsutum (L.) ‘Deltapine-61’] for such a system, soil CO2 fluxes were observed to be significantly greater outside than inside the chamber. To find the cause, CO2 concentration was measured in the soil profile from 5- to 60-cm depths of an Avondale clay loam [fine-loamy, mixed (calcareous), hyperthermic Typic Torrifluvent]. The soil CO2 contents at the various depths sampled outside the chamber were higher than those inside the chamber. The differences in concentration were observable within 2 wk after the blower used to pass ambient of CO2-enriched air through the chamber was turned on. The largest differences were present approximately 16 wk after the system had been in operation. Approximately 30 d was required for the soil CO2 levels inside and outside the chamber to become similar after the blower was turned off. Soil water content was not a factor causing this difference because it was nearly equal at both sites. Pressure differentials inside the growth chamber resulting from the blower operation could lead to a decrease in soil CO2 concentration and fluxes measured using the closed chamber technique.
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