1. RESEARCH QUESTIONS
CONCLUSIONS AND FUTUREDIRECTIONS
1. Can methanogens produce CH4 using a non-
traditional, methylotrophic pathway in peatland soils?
2. Can we account for carbon substrates as they are
processed anaerobically in peatland soils?
• The addition of traditional and non-traditional methanogenic
substrates had no significant effect on CH4 or CO2 production in
S1 Bog soil.
• Future 13CH4 and 13CO2 isotopic data from S1 Bog may provide
insight into which methanogenic pathways contribute to CH4/CO2
production.
Anaerobic Decomposition of Carbon in Peatland Soils
Efren Gonzalez1,2
, C.A. Medvedeff1, J.K. Keller1
1Chapman University, Schmid College of Science and Technology
2Citrus College, Glendora, CA
METHYLOTROPHIC PATHWAYINTRODUCTION
• Wetlands, and in particular peatlands, are among the most
important ecosystems in the global carbon cycle. Peatlands
store one-third of the terrestrial soil carbon and are major
contributors of the potent greenhouse gas methane (CH4) to
the atmosphere.
• Ecological theory states that under anaerobic conditions,
decomposition of simple carbon substrates should produce
CO2 and CH4 in a 1:1 ratio (Figure 1).
• However, CO2:CH4 production ratios in many peatland soils
often vastly exceed the predicted 1:1 ratio for reasons which
are not well understood. Possible explanation include non-
traditional pathways of CH4 production and/or inefficient
carbon flow to methanogens.
• A more complete mechanistic understanding of anaerobic
decomposition in peatland soils is crucial for understanding
their role in the global carbon cycle and the global climate.
FATE OF CARBON SUBSTRATES
RESULTS
• Homogenized peat from S1 Bog (0-
25 cm) was placed in serum bottles
and amended with 10 μM of 13C-
labeled traditional or non-
traditional substrates (Figure 2).
• Bottles were flushed with N2 for 15
minutes and incubated in the dark at
180 C.
• CH4 and CO2 production were
analyzed using gas chromatography
on days 1, 3, 7, 10, and 21.
• Homogenized peat from S1 Bog (0-
25 cm) was placed in dialysis tubing
(10,000 Da MWCO). Peat was
amended with equivalent amounts
of glucose, small dextran (15,000
Da) or large dextran (2-4 million Da)
(Figure 3).
• Samples were flooded in Mason
jars, flushed with N2 and incubated
in the dark at 180C.
• CO2 and CH4 (gas chromatography)
and glucose (dinitrosalicylic assay)
were measured on days 1,3, 7, 14,
and 22.
Control
n= 15
4.0g peat
20 ml DDW
Glucose
n= 15
4.0g peat
20 ml DDW
Dextran-S
n= 15
4.0g peat
20 ml DDW
Dextran-L
n= 15
4.0g peat
20 ml DDW
Dextran Small
(10mM)
Dextran Large
(10mM)
Glucose
(10mM)
Peat + DDW
Figure 1. Anaerobic decomposition relies on multiple microbial processes.
Theory predicts that polysaccharides should be broken down into equal
amounts of CH4 and CO2. However, this is rarely the case in peatland soils
for reasons that are not well understood. Non-traditional, methylotrophic
methanogenesis and/or inefficient carbon flow could explain the
discrepancy between theory and ecological reality.
Figure 2. Experimental design of
methylotrophic experiment. DMS =
Dimethylsulfide. MMA = methylamine.
Figure 4. Experimental design
used in carbon substrate
addition experiment.
Figure 3. Cumulative CH4 and CO2 production (mean ±1 SD)
after 21 days of incubation with traditional (blue) or non-
traditional (orange) methanogenic substrates.
CONCLUSIONS AND FUTURE DIRECTIONS
Polysaccharides
Hydrolysis
Fermentation
Acetoclastic
Methanogenesis
Hydrogenotrophic
Methanogenesis Methylotrophic
Methanogenesis
Monomers
Traditional
Substrates
CH4 + CO2
Non-traditional
Substrates
Non-Trad..
Substrate
10 μM
Trad..
Substrate
10 μM
Control
7.0g peat
Peat Only
DMS
MMA
Methanol
Acetate
Bicarbonate + H2
• Added carbon substrates were not recovered as equal
amounts CO2 and CH4 in any treatment. Between 45-
100% of the added substrate could not be explained
by any measured carbon pool.
• Future work to measure other dissolved pools of carbon
may help reveal the fate of this missing carbon.
0
10
20
30
40
50
60
70
80
µmolesCH4/gdw
Day21
0
20
40
60
80
100
120
µmolesCO2/gdw
Day21
• Amendments in S1 bog
soil did not influence CH4
production after 21 days
of anaerobic incubation.
• Amendments in S1 bog
soil did not influence
CO2 production after 21
days of anaerobic
incubation.
Acknowledgements. This research was made possible by the NSF-REU (1359500), Chapman University, and Citrus College. A special thank you to Dr. Jason Keller and Dr. Cassandra Medvedeff for their constant
guidance and expertise throughout the program, Dr. Marianne Smith, Citrus STEM, Dr. Chris Kim, and Dr. Jan Osborn.
• Between 45% and 100% of the added carbon substrates could
not be found in measured carbon pools.
Figure 5. Substrate-derived carbon as CH4, CO2 and glucose in response to
additions of glucose or dextran. Values calculated as treatment – control.
Blue bars represent added carbon not explained by measured pools.
Day 1
Substrate-Derived
Carbon(mol)
0
50
100
150
200
250
300 Day 4
CH4
CO2
Glucose-In
Glucose-Out
Unexplained
Day 8
G
lucoseD
extran-Sm
all
D
extran-Large
Substrate-Derived
Carbon(mol)
0
50
100
150
200
250
300 Day 15
G
lucoseD
extran-Sm
all
D
extran-Large
RESULTS