Soil Microbial Activity at High Levels of Carbon Monoxide

Soils are an important sink for atmospheric carbon monoxide (CO) via microbial uptake. In this study, the disappearance of CO during a 24‐h period was used to quantify potential CO uptake rates (V max ) for various soils and treatments. When 2.0 kPa CO was added to the gas phase above forest soil, amounts of this gas declined linearly for 24 h, suggesting a zero‐order or saturated reaction. Amounts of CO remained constant over autoclaved soil. Rates for forest, lawn, and garden soils ranged from 0.56 to 7.41, 0.39 to 0.80, and 0.17 to 0.19 mg CO‐C kg −1 dry soil h −1 , respectively. Ability of roadside soil to consume CO was significantly reduced by a 19‐d incubation at ambient CO levels, but was increased tenfold by repeated exposures to 2 kPa CO. This positive effect of long‐term CO exposure indicated that autotrophic organisms (carboxydobacteria) were active in roadside soil, but did not exclude the presence of heterotrophic organisms, which oxidize CO by cometabolic processes. A strong relationship between CO consumption and soil organic matter content or soil respiration suggested that high potential rates of soil CO consumption in unpolluted environments may reflect microbial exposure to endogenous CO arising from abiotic oxidation of soil C compounds. Forest soils with intact surface organic horizons may be particularly active CO sinks.