Effect of varying soil water potentials on methanogenesis in aerated marshland soils

Wetlands are characterized by changing water tables, which have an influence on the activity of microorganisms. Particularly, the effect of oxygen on anaerobic methanogenic archaea is of importance for understanding greenhouse gas fluxes in wetlands. In this study the influence of oxygen on CH₄ production in marshland soils was investigated in relation to varying soil water potentials. Water saturated samples as well as samples with drained macropores, and mesopores were used. Under oxic conditions the CH₄ production showed a dependence on the water content. The CH₄ production rates varied between about 213 and 51 nmol g^-1 soil h^-1. In the presence of oxygen a correlation between CH₄ production activity and water potential of the samples could not be demonstrated. Under oxic conditions with defined water potentials the CH₄ production rates varied between about 141 and 58 nmol g^-1 soil h^-1. Cell counts of methanogenic archaea showed similar numbers in oxic and anoxic soil layers, and further illustrated living methanogens in the aerobic horizons of the marshland soil. The presented results are of great importance for modelling of the CH₄ release from wetlands, because up to 25% of the CH₄ is produced in the oxic horizon of the investigated marshland soil.