Abstract
Upland forest ecosystems are recognized as net sinks for atmospheric methane (CH4), one of the most impactful greenhouse gases. Biological methane uptake in these ecosystems occurs due to the activity of aerobic methanotrophic bacteria. Russia hosts one-fifth of the global forest area, with the most extensive forest landscapes located in West Siberia. Here, we report seasonal CH4 flux measurements conducted in 2018 in three types of stands in West Siberian middle taiga–Siberian pine, Aspen, and mixed forests. High rates of methane uptake of up to −0.184 mg CH4 m−2 h−1 were measured by a static chamber method, with an estimated total growing season consumption of 4.5 ± 0.5 kg CH4 ha−1. Forest type had little to no effect on methane fluxes within each season. Soil methane oxidation rate ranged from 0 to 8.1 ng CH4 gDW−1 h−1 and was negatively related to water-filled pore space. The microbial soil communities were dominated by the Alpha- and Gammaproteobacteria, Acidobacteriota and Actinobacteriota. The major group of 16S rRNA gene reads from methanotrophs belonged to uncultivated Beijerinckiaceae bacteria. Molecular identification of methanotrophs based on retrieval of the pmoA gene confirmed that Upland Soil Cluster Alpha was the major bacterial group responsible for CH4 oxidation.
Highlights
Atmospheric level of methane, the second most important greenhouse gas after CO2, started to rise actively after a period of no growth in 2000–2006 [1,2,3]
Similar values were measured in Russian boreal forests [9,16,17]
We estimated CH4 consumption by studied soils at 4.5 ± 0.5 kg CH4 ha−1 for the whole growing season. It is higher than 86% of estimates for boreal forest soils and 75% of estimates for all forest soils according to the database from [22]
Summary
Atmospheric level of methane, the second most important greenhouse gas after CO2 , started to rise actively after a period of no growth in 2000–2006 [1,2,3] The attribution of this trend to particular sources and sinks is still an unresolved issue for the scientific community. Atmospheric CH4 uptake in forest soils occurs due to the activity of aerobic methanotrophic bacteria, which utilize methane as a source of energy [31,32,33,34]. Besides USCα methanotrophs, upland forest soils may host populations of Methylocystis species and another as-yet-uncultivated clade of methanotrophs, named USCγ group, which is most commonly detected in pH-neutral soils [37,38,40].
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