Induction of enhanced CH4 oxidation in soils:: NH4+ inhibition patterns

The influence of NH4+ on microbial CH4 oxidation is still poorly understood. Therefore, the influence of NH4Cl and (NH4)(2)SO4 on CH4 oxidation was studied in soils at the different stages of the induction of enhanced methanotrophic activity. After a brief peak in the methanotrophic activity, a steady state was observed in which NH4+ inhibited CH4 oxidation at low CH4 concentrations, and stimulated CH4 oxidation at high concentrations. Chloride did not strongly inhibit CH4 oxidation during this phase. During a second phase methanotrophic activity increased again. Ammonium no longer stimulated CH4 oxidation, and Cl- became an important source of uncompetitive inhibition. It was hypothesized that type I methanotrophs dominated during the first, soil-N-dependent phase while N-2-fixing type II methanotrophs dominated the second, soil-N-independent phase. (C) 2003 Elsevier Science Ltd. All rights reserved.