Methanotrophs are favored under hypoxia in ammonium-fertilized soils

Methanotrophy of arable soils is affected by N fertilization, but the knowledge about the effect of oxygen level is poorly understood; soil aeration can fluctuate and zones of low oxygen are widespread in soil. We monitored CH 4 oxidation in three mineral soils (Eutric Cambisol, Haplic Podzol, Mollic Gleysol) under laboratory conditions by varying the O 2 level (from 20 to 2% O 2 ), with or without NH 4 + (100 mg N kg −1 ). In controls (without NH 4 + ), CH 4 was oxidized completely in the O 2 range from oxia (20% O 2 ) to high hypoxia (5% O 2 ), while the process was inhibited under microoxia (2% O 2 ). Ammonium application decreased CH 4 consumption in all soils. This negative effect was stronger at 20% and 2% O 2 than under hypoxia. The highest CH 4 oxidation rates and the shortest initial (lag) phases in both control and NH 4 + -amended soils were observed under high (5% O 2 ) and low (10% O 2 ) hypoxia.