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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

Typical time-courses of CH4 concentrations during static chamber sampling.(a) Linear concentration changes with time, indicating continuous soil CH4 uptake or release. (b) Step-increase in CH4 concentration, likely caused by emission bursts that could originate from ebullition from the underlying saturated zone. (c) Decrease in CH4 concentrations, starting at substantially above-ambient CH4 concentrations; this pattern is likely caused by a re-distribution of localized CH4 emissions trapped in the static chamber.
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pone.0131665.g001: Typical time-courses of CH4 concentrations during static chamber sampling.(a) Linear concentration changes with time, indicating continuous soil CH4 uptake or release. (b) Step-increase in CH4 concentration, likely caused by emission bursts that could originate from ebullition from the underlying saturated zone. (c) Decrease in CH4 concentrations, starting at substantially above-ambient CH4 concentrations; this pattern is likely caused by a re-distribution of localized CH4 emissions trapped in the static chamber.

Mentions: Our static chamber measurements (S1 Dataset) revealed three characteristic patterns in which CH4 concentrations evolved over the three headspace samplings (Fig 1). During the major part of the measurements, concentrations progressed linearly with time (Fig 1A), either decreasing from ambient to sub-ambient CH4 concentrations (net soil CH4 uptake), or increasing to a few hundred to thousand ppb above ambient concentrations (net soil CH4 emission). However, in other cases, episodic emissions resulted in a sudden increase of concentrations between some of the headspace samplings (Fig 1B, here shown for emission between 1st and 2nd headspace sampling). We refer to these cases as “bubble emission” since they are likely caused by ebullition from deeper soil layers or the water table. Finally, we also observed CH4 concentrations that were markedly above ambient at the first sampling and decreased thereafter (Fig 1C). We termed this pattern “redistribution” since it is likely caused by a localized “bubble emission” prior to the first sampling, followed by redistribution of CH4 in the chamber and soil pore volume. There were also cases suggesting a combination of “bubble emission” and “redistribution”, but these were more difficult to classify.


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)

Typical time-courses of CH4 concentrations during static chamber sampling.(a) Linear concentration changes with time, indicating continuous soil CH4 uptake or release. (b) Step-increase in CH4 concentration, likely caused by emission bursts that could originate from ebullition from the underlying saturated zone. (c) Decrease in CH4 concentrations, starting at substantially above-ambient CH4 concentrations; this pattern is likely caused by a re-distribution of localized CH4 emissions trapped in the static chamber.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0131665.g001: Typical time-courses of CH4 concentrations during static chamber sampling.(a) Linear concentration changes with time, indicating continuous soil CH4 uptake or release. (b) Step-increase in CH4 concentration, likely caused by emission bursts that could originate from ebullition from the underlying saturated zone. (c) Decrease in CH4 concentrations, starting at substantially above-ambient CH4 concentrations; this pattern is likely caused by a re-distribution of localized CH4 emissions trapped in the static chamber.
Mentions: Our static chamber measurements (S1 Dataset) revealed three characteristic patterns in which CH4 concentrations evolved over the three headspace samplings (Fig 1). During the major part of the measurements, concentrations progressed linearly with time (Fig 1A), either decreasing from ambient to sub-ambient CH4 concentrations (net soil CH4 uptake), or increasing to a few hundred to thousand ppb above ambient concentrations (net soil CH4 emission). However, in other cases, episodic emissions resulted in a sudden increase of concentrations between some of the headspace samplings (Fig 1B, here shown for emission between 1st and 2nd headspace sampling). We refer to these cases as “bubble emission” since they are likely caused by ebullition from deeper soil layers or the water table. Finally, we also observed CH4 concentrations that were markedly above ambient at the first sampling and decreased thereafter (Fig 1C). We termed this pattern “redistribution” since it is likely caused by a localized “bubble emission” prior to the first sampling, followed by redistribution of CH4 in the chamber and soil pore volume. There were also cases suggesting a combination of “bubble emission” and “redistribution”, but these were more difficult to classify.

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