Inhibition of atmospheric methane oxidation by monoterpenes in Norway spruce and European beech soils

Biological oxidation of atmospheric methane (CH 4) in forest soils of the northern hemisphere is an important sink in the global CH 4 cycle. The effect of tree species on atmospheric CH 4 oxidation is not well understood. Previous studies suggest that soils under European beech ( Fagus sylvatica) consume more atmospheric CH 4 than soils under Norway spruce ( Picea abies). A major difference in the chemical constituents of these tree species is the production of monoterpenes. The objectives of the present study were (i) to quantify monoterpenes in leaves, needles, organic horizons (Oi, Oe, Oa), and mineral soil of a Norway spruce site and an adjacent European beech site of a temperate forest (Steigerwald, Germany) and (ii) to evaluate the potential of abundant monoterpenes to inhibit atmospheric CH 4 oxidation. Major compounds were α- and β-pinene, limonene, and camphene. Highest concentrations were measured in Norway spruce samples (up to 63.9 μmol g dw − 1 ). In European beech samples, monoterpene concentrations were close to or below the detection limit (≤0.00015 μmol g dw − 1 ). For limonene, α- and β-pinene, the dose-dependent inhibition on atmospheric CH 4 oxidation was determined. β-Pinene had the highest inhibition efficiency, followed by limonene and α-pinene. Norway spruce roots and mineral soil samples displayed similar monoterpene profiles, suggesting that roots can be considered as a source for inhibitory monoterpenes in Norway spruce soils. Monoterpene addition was always coupled to an increased carbon dioxide production. This indicates that monoterpenes may be microbially mineralized in these soils. In summary, the study revealed that the release of monoterpenes by both roots and litter may be sources in soil and that in situ monoterpene concentrations in spruce soil are high enough to explain reduced atmospheric CH 4 uptake.