Methane (CH4) flux from soil to the atmosphere is the result of two microbial processes, methanogenesis and CH4 oxidation. Land use may have a profound impact on the relative activities of these groups of organisms. In this study, the CH4 production and consumption potentials of soils from agricultural and nonagricultural ecosystems were assessed in laboratory incubations. Methane production potentials of most soils were low and in the range of 0.02 to 0.35 nmol CH4 g soil-1 h-1; however, soils from two of the agricultural sites that experience periodic water saturation had CH4 production potentials from 100 to 300 nmol CH4 g soil-1 h-1. The high methanogenic potential suggests that CH4 consumers may not be wholly dependent on atmospheric CH4 for their survival and maintenance. The prairie soils exhibited the highest CH4 oxidation under ambient atmospheric CH4 concentrations, and CH4 oxidation activity was markedly enhanced in incubations with an atmosphere enriched in CH4. This stimulated CH4 oxidation activity was generally greater in the agricultural soils as compared with the forest and prairie soils. Methane oxidation appeared to be related to soil nitrogen status. Under ambient atmospheric CH4 concentrations, CH4 oxidation was negatively related to soil mineral N concentration. However, a positive relationship between soil mineral N status and CH4 oxidation activity was observed in incubations with atmospheres enriched in CH4. This pattern suggests that the agricultural lands contain different populations of CH4 oxidizers than the natural systems.
