Responses of methane effluxes and soil methane concentrations to compaction.

Abstract:

Forest soils host methanotrophic bacterial communities that make them a major methane sink worldwide. Soil compaction resulting from mechanization of forest operations is first affecting soil macroporosity, and thus gas and water transfer within the soil, leading to a reduced oxygenation of the soil. This reduction of soil aeration is expected to reduce the methanotrophic activity leading thus to less CH₄ oxidation and more CH₄ production, affecting the overall soil CH₄budget.

Compaction was applied in 2007 and had created linear ruts. We measured continuously since September 2014, in three different situations (compacted-mound, compacted hollow and control), soil CO₂ and CH₄ effluxes using closed chamber coupled to a cavity ring down spectrometer in an young oak plantation.

Since December 2015, in addition to these measurements, we have implanted hydrophobic tubes to measure vertical soil profiles of CH₄, O₂ and CO₂ concentrations in the 3 situations.

The soil acts as CH₄ sink, with no significant difference in net CH₄uptake between control and both hollow and mound in the compacted treatment.

However, the uptake of CH₄ was significantly lower for the hollows than for the mounds resulting from both a lower diffusion of CH₄ within soil and a higher production of CH4 in deeper layer when the soil is water saturated.