Unravelling controls on methane uptake in a temperate forest soil: impacts of ectomycorrhizas

Methane (CH₄) is an important greenhouse gas, globally responsible for 17% of current radiative forcing. Soils can be important net sources or sinks of CH₄ depending on the net balance of two contrasting microbial processes - CH₄ production and CH₄ oxidation. In unsaturated soils, the aerobic methane oxidation process often dominates. These soils form the only global terrestrial CH₄ sink, but estimates are still highly uncertain, both spatially and temporally. Forest soils have shown some of the strongest net CH₄ uptake rates, but this is not consistent across sites and the controls are poorly understood.

In this field study, we focused on the effects of ectomycorrhizas on net CH₄ uptake in an unsaturated, sandy gley podzolic soil of a mature coniferous forest stand dominated by Lodgepole pine (Pinus contorta) in Northern England over three years. Methane fluxes were determined in cores with soil only (roots and ectomycorrhizal mycelium excluded using windows with 1 µm mesh in the cores) and cores with soil and ectomycorrhizal mycelium (only roots excluded with 41 µm mesh). Net CH₄ uptake rates in summer were higher when ectomycorrhizal mycelium was present, whereas the opposite was observed in winter. We will discuss mechanisms that may underpin these ectomycorrhizal impacts on net CH₄ uptake in unsaturated forest soils.