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Effects of Long-Term CO2 Enrichment on Soil-Atmosphere CH4 Fluxes and the Spatial Micro-Distribution of Methanotrophic Bacteria.

Karbin S, Guillet C, Kammann CI, Niklaus PA - PLoS ONE (2015)

Bottom Line: We did not detect any elevated CO2 effects on CH4 fluxes, but emissions were difficult to quantify due to their discontinuous nature, most likely because of ebullition from the saturated zone.Potential methanotrophic activity, determined by incubation of fresh sieved soil under standardized conditions, also did not reveal any effect of the CO2 treatment.The autoradiographic analyses further indicate that the spatial niche of CH4 oxidation does not shift in response to CO2 enrichment or CH4 concentration, and that the same type of methanotrophs may oxidize CH4 from atmospheric and soil-internal sources.

View Article: PubMed Central - PubMed

Affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland.

ABSTRACT

Background: Effects of elevated atmospheric CO2 concentrations on plant growth and associated C cycling have intensively been studied, but less is known about effects on the fluxes of radiatively active trace gases other than CO2. Net soil-atmosphere CH4 fluxes are determined by the balance of soil microbially-driven methane (CH4) oxidation and methanogenesis, and both might change under elevated CO2.

Methods and results: Here, we studied CH4 dynamics in a permanent grassland exposed to elevated CO2 for 14 years. Soil-atmosphere fluxes of CH4 were measured using large static chambers, over a period of four years. The ecosystem was a net sink for atmospheric CH4 for most of the time except summer to fall when net CH4 emissions occurred. We did not detect any elevated CO2 effects on CH4 fluxes, but emissions were difficult to quantify due to their discontinuous nature, most likely because of ebullition from the saturated zone. Potential methanotrophic activity, determined by incubation of fresh sieved soil under standardized conditions, also did not reveal any effect of the CO2 treatment. Finally, we determined the spatial micro-distribution of methanotrophic activity at less than 5× atmospheric (10 ppm) and elevated (10000 ppm) CH4 concentrations, using a novel auto-radiographic technique. These analyses indicated that domains of net CH4 assimilation were distributed throughout the analyzed top 15 cm of soils, with no dependence on CH4 concentration or CO2 treatment.

Conclusions: Our investigations suggest that elevated CO2 exerts no or only minor effects on CH4 fluxes in the type of ecosystem we studied, at least as long as soil moisture differences are small or absent as was the case here. The autoradiographic analyses further indicate that the spatial niche of CH4 oxidation does not shift in response to CO2 enrichment or CH4 concentration, and that the same type of methanotrophs may oxidize CH4 from atmospheric and soil-internal sources.

No MeSH data available.


Related in: MedlinePlus

CH4 fluxes and related environmental data.(a) CH4 emission rates in ambient (○) and elevated CO2 (●) plots, calculated when concentration changes were linear (mean ± s.e., n≤3 per CO2, depending on the number of plots with emissions following the pattern of Fig 1A). Effects of elevated CO2 were not statistically significant. Periods during which emissions occurred (Fig 1B and 1C) are shaded in gray, indicating that emission rates likely are underestimates. (b) Volumetric soil moisture, averaged across CO2 treatments. (c) Weekly precipitation and water table depth.
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pone.0131665.g002: CH4 fluxes and related environmental data.(a) CH4 emission rates in ambient (○) and elevated CO2 (●) plots, calculated when concentration changes were linear (mean ± s.e., n≤3 per CO2, depending on the number of plots with emissions following the pattern of Fig 1A). Effects of elevated CO2 were not statistically significant. Periods during which emissions occurred (Fig 1B and 1C) are shaded in gray, indicating that emission rates likely are underestimates. (b) Volumetric soil moisture, averaged across CO2 treatments. (c) Weekly precipitation and water table depth.

Mentions: Meaningful emission rates can only be calculated for the linear case (Fig 1A). In the absence of non-linear emissions, soils were net sinks for CH4 (Fig 2A, white background). Soil CH4 uptake during these periods did not differ significantly between CO2 treatments (26.2±4.7 and 28.6±5.2 μmol CH4 m-2 d-1 in ambient and elevated CO2, respectively). During periods in which “bubble emissions” occurred (Fig 2A, grey background), average rates determined from the remaining chambers showing linear emissions were generally positive, i.e. indicated net soil CH4 emissions. These emissions likely are lower bounds of the real fluxes because they do not include the supposedly higher emission rates when “bubbles” are formed.


Effects of Long-Term CO2 Enrichment on Soil-Atmosphere CH4 Fluxes and the Spatial Micro-Distribution of Methanotrophic Bacteria.

Karbin S, Guillet C, Kammann CI, Niklaus PA - PLoS ONE (2015)

CH4 fluxes and related environmental data.(a) CH4 emission rates in ambient (○) and elevated CO2 (●) plots, calculated when concentration changes were linear (mean ± s.e., n≤3 per CO2, depending on the number of plots with emissions following the pattern of Fig 1A). Effects of elevated CO2 were not statistically significant. Periods during which emissions occurred (Fig 1B and 1C) are shaded in gray, indicating that emission rates likely are underestimates. (b) Volumetric soil moisture, averaged across CO2 treatments. (c) Weekly precipitation and water table depth.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492808&req=5

pone.0131665.g002: CH4 fluxes and related environmental data.(a) CH4 emission rates in ambient (○) and elevated CO2 (●) plots, calculated when concentration changes were linear (mean ± s.e., n≤3 per CO2, depending on the number of plots with emissions following the pattern of Fig 1A). Effects of elevated CO2 were not statistically significant. Periods during which emissions occurred (Fig 1B and 1C) are shaded in gray, indicating that emission rates likely are underestimates. (b) Volumetric soil moisture, averaged across CO2 treatments. (c) Weekly precipitation and water table depth.
Mentions: Meaningful emission rates can only be calculated for the linear case (Fig 1A). In the absence of non-linear emissions, soils were net sinks for CH4 (Fig 2A, white background). Soil CH4 uptake during these periods did not differ significantly between CO2 treatments (26.2±4.7 and 28.6±5.2 μmol CH4 m-2 d-1 in ambient and elevated CO2, respectively). During periods in which “bubble emissions” occurred (Fig 2A, grey background), average rates determined from the remaining chambers showing linear emissions were generally positive, i.e. indicated net soil CH4 emissions. These emissions likely are lower bounds of the real fluxes because they do not include the supposedly higher emission rates when “bubbles” are formed.

Bottom Line: We did not detect any elevated CO2 effects on CH4 fluxes, but emissions were difficult to quantify due to their discontinuous nature, most likely because of ebullition from the saturated zone.Potential methanotrophic activity, determined by incubation of fresh sieved soil under standardized conditions, also did not reveal any effect of the CO2 treatment.The autoradiographic analyses further indicate that the spatial niche of CH4 oxidation does not shift in response to CO2 enrichment or CH4 concentration, and that the same type of methanotrophs may oxidize CH4 from atmospheric and soil-internal sources.

View Article: PubMed Central - PubMed

Affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland.

ABSTRACT

Background: Effects of elevated atmospheric CO2 concentrations on plant growth and associated C cycling have intensively been studied, but less is known about effects on the fluxes of radiatively active trace gases other than CO2. Net soil-atmosphere CH4 fluxes are determined by the balance of soil microbially-driven methane (CH4) oxidation and methanogenesis, and both might change under elevated CO2.

Methods and results: Here, we studied CH4 dynamics in a permanent grassland exposed to elevated CO2 for 14 years. Soil-atmosphere fluxes of CH4 were measured using large static chambers, over a period of four years. The ecosystem was a net sink for atmospheric CH4 for most of the time except summer to fall when net CH4 emissions occurred. We did not detect any elevated CO2 effects on CH4 fluxes, but emissions were difficult to quantify due to their discontinuous nature, most likely because of ebullition from the saturated zone. Potential methanotrophic activity, determined by incubation of fresh sieved soil under standardized conditions, also did not reveal any effect of the CO2 treatment. Finally, we determined the spatial micro-distribution of methanotrophic activity at less than 5× atmospheric (10 ppm) and elevated (10000 ppm) CH4 concentrations, using a novel auto-radiographic technique. These analyses indicated that domains of net CH4 assimilation were distributed throughout the analyzed top 15 cm of soils, with no dependence on CH4 concentration or CO2 treatment.

Conclusions: Our investigations suggest that elevated CO2 exerts no or only minor effects on CH4 fluxes in the type of ecosystem we studied, at least as long as soil moisture differences are small or absent as was the case here. The autoradiographic analyses further indicate that the spatial niche of CH4 oxidation does not shift in response to CO2 enrichment or CH4 concentration, and that the same type of methanotrophs may oxidize CH4 from atmospheric and soil-internal sources.

No MeSH data available.


Related in: MedlinePlus