Plateau Marsh Methane Oxidation as affected by Inorganic N

In a series of laboratory incubations using soils of two contrasting sites from a temperate marsh on the QinghaiTibet Plateau,potential methane (CH4) oxidation rates were measured to study the effects of inorganic N inputs on CH4 oxidation. For a drained site,subsurface peat (5-15 cm) at an initial 20 μL CH4 L-1 showed a significantly different (P＜0.05) CH4 oxidation rate compared to other soil depths,with a maximal rate of 20.9 ng CH4 gDW (dry weight)-1h-1; the underlying mineral soil layers (15-30 and 30-50 cm) also had a strong CH4 oxidation capacity at about an initial 2000 μL CH4 L-1. With a waterlogged site,the CH4 oxidation rate in an aerobic incubation was significantly greater (P＜0.05) in the surface soil layer (0-5cm) compared to the 15-30 and 30-50 cm depths. There was generally no or a very weak effect from addition of NO3- on CH4 oxidation. In marked contrast,NH4+ salts,such as (NH4)2SO4,NH4C1 and NH4NO3,exhibited strong inhibitions,which varied as a function of the added salts and the initial CH4 level. Increasing NH4+ usually resulted in greater inhibition and increasing initial CH4 concentrations resulted in less. NH4+ inhibition on CH4 oxidation in natural high-altitude,low-latitude wetlands could be as important as has been reported for agricultural and forest soils. The NH4+ effects on the CH4 oxidation rate need to be further investigated in a wide range of natural wetland soil types.