Factors affecting utilisation of atmospheric CO by soils

Carbon monoxide is an important atmospheric trace gas because it is the main atmospheric sink for the hydroxyl radical. Nevertheless, about a fifth of CO is utilised by soil microorganisms. As the strengths of sources and sinks are currently finely balanced, any change in the strength of the soil sink would lead to changes in the tropospheric CO concentration, which could in turn affect the concentration of radiatively active trace gases such as methane. The factors affecting the rate of CO utilisation by soils have been investigated in laboratory incubations, and in the field using static chambers. Laboratory incubations showed that there was a strong positive correlation between total organic carbon (TOC) content and CO utilisation by soils. The amount of microbial biomass carbon was strongly correlated with TOC content. Rates of CO utilisation by woodland soils were faster than by adjacent arable soils, reflecting the importance of differences in TOC content. Further investigation showed that there was an optimum water content for utilisation for each soil at approximately field capacity. Field measurements showed that temperature was the most important factor affecting CO utilisation rates at any one site. In several cases there was a negative relationship between CO uptake rate and temperature which was attributed to simultaneous CO production from the surface litter layer. In contrast, a fallow arable soil showed an optimum rate at approximately 10°C.