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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

Soil micro-autoradiography of typical soil sections collected on October 25, 2011, and incubated under CH4 concentrations around 10000 ppm.Darker pixels indicate higher labelling. Vertical profiles of labelling (right panel), aggregated by 1cm depth intervals (mean ± s.e., n = 3 per CO2 treatment). Elevated CO2 marginally significantly affected the depth distribution of methanotrophic activity (P = 0.06 for depth × CO2).
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pone.0131665.g007: Soil micro-autoradiography of typical soil sections collected on October 25, 2011, and incubated under CH4 concentrations around 10000 ppm.Darker pixels indicate higher labelling. Vertical profiles of labelling (right panel), aggregated by 1cm depth intervals (mean ± s.e., n = 3 per CO2 treatment). Elevated CO2 marginally significantly affected the depth distribution of methanotrophic activity (P = 0.06 for depth × CO2).

Mentions: Visual inspection of autoradiographies revealed heterogeneous label assimilation, with distinct zones of enhanced net CH4 assimilation (Figs 5,6 and 7). These appeared to be along cracks and around aggregate structures (e.g. Fig 6). On both July 6 and October 25, net 14CH4 assimilation was reduced in the top 1–2 centimeters relative to the rest of the soil profile which showed relatively little variation in label intensity with depth.


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)

Soil micro-autoradiography of typical soil sections collected on October 25, 2011, and incubated under CH4 concentrations around 10000 ppm.Darker pixels indicate higher labelling. Vertical profiles of labelling (right panel), aggregated by 1cm depth intervals (mean ± s.e., n = 3 per CO2 treatment). Elevated CO2 marginally significantly affected the depth distribution of methanotrophic activity (P = 0.06 for depth × CO2).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131665.g007: Soil micro-autoradiography of typical soil sections collected on October 25, 2011, and incubated under CH4 concentrations around 10000 ppm.Darker pixels indicate higher labelling. Vertical profiles of labelling (right panel), aggregated by 1cm depth intervals (mean ± s.e., n = 3 per CO2 treatment). Elevated CO2 marginally significantly affected the depth distribution of methanotrophic activity (P = 0.06 for depth × CO2).
Mentions: Visual inspection of autoradiographies revealed heterogeneous label assimilation, with distinct zones of enhanced net CH4 assimilation (Figs 5,6 and 7). These appeared to be along cracks and around aggregate structures (e.g. Fig 6). On both July 6 and October 25, net 14CH4 assimilation was reduced in the top 1–2 centimeters relative to the rest of the soil profile which showed relatively little variation in label intensity with depth.

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