|ERNAKOVICH, JESSICA - Commonwealth Scientific And Industrial Research Organisation (CSIRO)|
|LYNCH, LAUREL - Colorado State University|
|BREWER, PAUL - Colorad0 State University|
|WALLENSTEIN, MATTHEW - Colorado State University|
Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2017
Publication Date: 7/7/2017
Publication URL: http://handle.nal.usda.gov/10113/5745881
Citation: Ernakovich, J., Lynch, L., Brewer, P., Calderon, F.J., Wallenstein, M. 2017. The circuitry of ecosystem metabolism: CO2 and CH4 flux from permafrost soils. Soil Biology and Biochemistry. 134:183-200. doi:10.1007/s10533-017-0354-5.
Interpretive Summary: Arctic permafrost soils hold vast amounts of organic matter. Because of this, these soils can become important sources of atmospheric greenhouse gases like methane and carbon dioxide upon thawing. In this study, we thawed permafrost soils and then carried out a detailed set of measurements for a 90 day period. The idea was to quantify the biological and environmental conditions that are responsible for the production of methane and carbon dioxide from the thawed soils. Both carbon dioxide and methane production were mainly determined by different aspects of the soil microbiology and soil organic matter chemistry. We found that methane production follows a more stepwise route, much like a circuit wired in series, where there is a single path of soil organic matter degradation where multiple conditions must be satisfied. In contrast, carbon dioxide production from permafrost is analogous to a circuit wired in parallel, where there are multiple, parallel paths of soil organic matter decomposition leading to carbon dioxide production.
Technical Abstract: Microbial decomposition of thawed permafrost organic matter could release greenhouse gases (GHG) to the atmosphere and accelerate the carbon (C)-climate feedback. Greenhouse gas emissions from thawed permafrost are difficult to predict because they result from complex interactions between abiotic drivers and multiple, often competing, microbial metabolic processes. The objective of this study was to characterize mechanisms controlling methane (CH4) and carbon dioxide (CO2) production from permafrost. We simulated permafrost thaw for the length of one growing season (90 days) under oxic and anoxic conditions at 1 and 15 °C. We measured headspace CH4 and CO2, as well as soil chemical and biological parameters (e.g. dissolved organic carbon (DOC) chemistry, microbial enzyme activity, N2O production, bacterial community structure), and applied an Information Theoretic (IT) approach and the Akaike Information Criterion (AICc) to find the best explanation for mechanisms controlling GHG flux. In addition to temperature and redox status, CH4 production was explained by the relative abundance of methanogens, activity of non-methanogenic anaerobes, and substrate chemistry. Carbon dioxide production was explained by microbial community structure and chemistry of the DOC pool. We suggest that CO2 production from permafrost is analogous to a circuit wired in parallel, where there are multiple, parallel paths of organic matter degradation leading to CO2 production. In contrast, CH4 production is like a circuit wired in series, where there is a single path of organic matter degradation where multiple conditions must be satisfied in order for methanogenesis. The activity of anaerobes higher on the redox ladder inhibits methanogens through competition for energy (i.e. electron donors) and by providing an insufficient supply of substrates necessary for methanogenesis. This concept advances our mechanistic understanding of the processes governing anaerobic GHG flux, which is critical to understanding the impact the release of permafrost C will have on the global C cycle.