11:15 〜 11:30
[BCG05-07] Soil methane flux and vertical profile of methane concentration, methanotrophs, and methanogens long a topographical gradient in a cool temperate forest
キーワード：Methane flux, Topography, Methanotrophs, Methanogens
Methane (CH4) is a potent greenhouse gas and the second largest contributor to global warming after carbon dioxide. Globally, upland soils are considered a biological sink of atmospheric CH4, but the sink rate is regulated by soil moisture and nutrient availability. Generally, soil moisture content and nutrients vary across the forested ecosystem, particularly in mountain forests. The objective of this study was to understand the effect of topographic positions on soil CH4 fluxes. We hypothesized that the net CH4 uptake (negative flux) would decrease from slopes to plain areas due to comparatively higher moisture in foot slopes and plain areas than on slopes. We measured soil CH4 fluxes and soil CH4 concentration at different depths of the soil. We also quantified the pmoA and mcrA genes, maker genes for methanogens, and methanotrophs in DNA extracted at different depths.
This study was conducted in a forested upper Yura River watershed around Chojidani (35.34 N; 135.76 E) at the Ashiu Experimental Forest of Kyoto University in northeastern Kyoto Prefecture, Japan. We measured soil CH4 fluxes using closed chambers connected to a cavity-enhanced absorption spectroscopy gas analyzer from the slope (5 points), foot slope (3 points), plain land (5 points), and wetland (1 point). Soil CH4 mole fractions (Δ[CH4]) were measured at three soil depths (10, 20, and 40 cm) close to the soil flux measurement points. A positive gradient (Δ[CH4]) indicates the production exceeds oxidation, while a negative value indicates oxidation dominates over production. In addition, soil samples were collected for DNA extraction to quantify the copies of pmoA and mcrA genes.
Soil CH4 fluxes varied across topographic positions, with the highest uptake on the slopes and the lowest in the foot slopes and plain areas. In contrast, wetland soils emitted CH4 (positive flux). Soil CH4 mole fraction (Δ[CH4]) between 0 and 10 cm decreased below the ambient CH4 concentration at all positions except in the wetland where it increased. Between 10 to 20 cm and 20 to 40 cm, Δ[CH4] was not consistent across the landscape but higher than the Δ[CH4] of the 0-10 cm layer of soil. The ratios of pmoA to mcrA gene copy at depths between 0 and 10 cm were the lowest in the wetland, but surprisingly, it was higher in the plain areas than one slope at depths between 0 and 10 cm in the mineral soil and the top organic layer. Like Δ[CH4], the ratio of pmoA to mcrA did not have consistent spatial patterns deeper in the soil.
The results suggested the critical role of topography and depth-specific microbial communities in regulating soil CH4 fluxes in forested landscapes.
This study was conducted in a forested upper Yura River watershed around Chojidani (35.34 N; 135.76 E) at the Ashiu Experimental Forest of Kyoto University in northeastern Kyoto Prefecture, Japan. We measured soil CH4 fluxes using closed chambers connected to a cavity-enhanced absorption spectroscopy gas analyzer from the slope (5 points), foot slope (3 points), plain land (5 points), and wetland (1 point). Soil CH4 mole fractions (Δ[CH4]) were measured at three soil depths (10, 20, and 40 cm) close to the soil flux measurement points. A positive gradient (Δ[CH4]) indicates the production exceeds oxidation, while a negative value indicates oxidation dominates over production. In addition, soil samples were collected for DNA extraction to quantify the copies of pmoA and mcrA genes.
Soil CH4 fluxes varied across topographic positions, with the highest uptake on the slopes and the lowest in the foot slopes and plain areas. In contrast, wetland soils emitted CH4 (positive flux). Soil CH4 mole fraction (Δ[CH4]) between 0 and 10 cm decreased below the ambient CH4 concentration at all positions except in the wetland where it increased. Between 10 to 20 cm and 20 to 40 cm, Δ[CH4] was not consistent across the landscape but higher than the Δ[CH4] of the 0-10 cm layer of soil. The ratios of pmoA to mcrA gene copy at depths between 0 and 10 cm were the lowest in the wetland, but surprisingly, it was higher in the plain areas than one slope at depths between 0 and 10 cm in the mineral soil and the top organic layer. Like Δ[CH4], the ratio of pmoA to mcrA did not have consistent spatial patterns deeper in the soil.
The results suggested the critical role of topography and depth-specific microbial communities in regulating soil CH4 fluxes in forested landscapes.