Methane oxidation in boreal forest soils: kinetics and sensitivity to pH and ammonium

Abstract

In soil incubation experiments we examined if there are differences in the kinetic parameters of atmospheric methane (CH 4) oxidation in soils of upland forests and forested peatlands. All soils showed net uptake of atmospheric CH 4. One of the upland forests included also managed (clear-cut with or without previous liming or N-fertilization) study plots. The CH 4 oxidation in the forested peat soil had a higher K m (510 μl l −1) and V max (6.2 nmol CH 4 cm −3 h −1) than the upland forest soils ( K m from 5 to 18 μl l −1 and V max from 0.15 to 1.7 nmol CH 4 cm −3 h −1). The forest managements did not affect the K m-values. At atmospheric CH 4 concentration, the upland forest soils had a higher CH 4 oxidation activity than the forested peat soil; at high CH 4 concentrations the reverse was true. Most of the soils oxidised CH 4 in the studied pH range from 3 to 7.5. The pH optimum for CH 4 oxidation varied from 4 to 7.5. Some of the soils had a pH optimum for CH 4 oxidation that was above their natural pH. The CH 4 oxidation in the upland forest soils and in the peat soil did not differ in their sensitivities to (NH 4) 2SO 4 or K 2SO 4 (used as a non-ammonium salt control). Inhibition of CH 4 oxidation by (NH 4) 2SO 4 resulted mainly from a general salt effect (osmotic stress) though NH 4 + did have some additional inhibitory properties. Both salts were better inhibitors of CH 4 oxidation than respiration. The differences in the CH 4 oxidation kinetics in the forested peat soil and in the upland forest soils reveal that there are differences in the physiologies of the CH 4 oxidisers in these soils.