Assessing microbial metabolic potential
across northern peatlands
Kristine Haynes and Nathan Basiliko
(UTM Geography)
• Peatland ecosystems play important roles in global climate; in part
by acting as sinks for atmospheric carbon dioxide (CO2)
• Carbon (C) is stored in organic soils due to a net imbalance between
plant production and microbial decomposition (build-up of ‘peat’)
• Northern peatlands have stored up to 2/3 of C present in the
atmosphere in the Holocene
• Slow rates of decomposition are primarily due to cold, waterlogged
environments and nutrient poor organic substrate for microbial
decomposers
• Little is known about microbial communities and controls on
activities that decompose peat and produce CO2 which hinders our
ability to predict how these important sites will respond to climate
and other environmental changes
Methods
•
•
Surface peat samples (0-20cm) were collected from a poor, intermediate and rich fen (5
replicates along 40m transect; long term OMNR research sites ) near White River, ON.
Vegetation was collected and dissolved organic matter (DOM) extracts were made by autoclaving
chopped plant parts in distilled water and filtering
•
Synthetic substrates included:
• cellulose (the most abundant plant biomolecule on earth)
• glucose (a potential cellulose derivative)
Plant Extracts
• lignin (another important group of plant structural molecules)
• p-coumaric acid (a lignin derivative from non-woody plant tissues)
• an amino acid mixture (derivatives of proteins)
• Na benzoate (anaerobic phenol derivative; can act as an indirect methanogenic substrate)
•
Substrates (both synthetic and natural) were adjusted to 1mg C/ mL
•
Microbial activity assessed by incubating peat samples covered with 10 mL of each of the 10
organic substrates and a control both aerobically for 24h and anaerobically for 3d
•
Gas samples analyzed for CO2 concentrations using a Qubit
Systems infrared gas analyzer with a N2 carrier
Qubit Systems infrared
gas analyzer
Key Results
1.0
I. Rich Fen
glucose
p-coumaric acid
0
methyl cellulose
4
0.6
Na benzoate
amino acids
0.4
RF sedge
IF sedge
0.2
IF sphagnum
substrate: control ratio
alkali lignin
PF sphagnum
II. Intermediate Fen
2
0
0.0
0
20
40
60
80
Time (hours)
12
III. Poor Fen
Figure 1: CO2 production from rich fen peat with added organic
substrates under anaerobic conditions over 79h period.
Data from intermediate and poor fens exhibit similar trends (not shown).
• The high molecular weight polyphenolic compound lignin induced CO2
production slightly above that of the controls under both aerobic and
anaerobic conditions, while cellulose was not significantly different from
the controls under anaerobic conditions (Figure 1)
• The simple sugar glucose and the mixture of amino acids induced CO2
production significantly above basal respiration, however still less than
with ‘natural’ plant extracts
• Patterns of substrate utilization were generally consistent across the 3
peatland types (e.g. no difference between poor and rich fen)
• In particular preferential mineralization of DOM extracts from plant types
from each peatland was not observed
8
4
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• P-coumaric acid and sodium
benzoate additions suppressed
microbial respiration relative
to controls (Figure 2)
2
control
0.8
mg CO2 / g dry peat
• In both aerobic and anaerobic
incubations, the natural plant
extracts triggered the highest
CO2 production, typically with
extracts from sedges
surpassing CO2 production
resulting from more
chemically complex Sphagnum
mosses (Figures 1, 2)
4
substrate
Figure 2: Ratios of substrate induced respiration to
control (distilled H2O) at the I. rich, II. intermediate, and
III. poor fen under anaerobic conditions (at 48h). The
thin dotted line(s) represent a value of 1.
Discussion and Conclusions
• Addition of both natural and synthetic substrates (low molecular
weight carbohydrates to large, polyphenolic and polymeric compounds)
led to variable responses in microbial respiration over basal
respiration:
This new assay therefore appears to be a valid means of evaluating peat
microbial metabolic potential under aerobic and anaerobic conditions
• Simple aromatic compounds (p-coumaric acid and sodium benzoate)
may not be favourable for microbial utilization; may be inhibitory
Buildup of these metabolites could play a role in slow decomposition
rates in peatlands. (although a natural byproduct of phenolic compound
degradation, the latter has been reported to be anti-microbial and is indeed
often used as a food preservative)
• Slow to no response to additions of high molecular weight polyphenolic
and polymeric compounds (lignin and cellulose) may also explain slow
rates of peat decomposition
Discussion and Conclusions
• Natural substrates were preferentially utilized since either:
– They comprise a mixture of compounds, or
– Microbial communities are better adapted to substrate derived from
wetland plants
• Similar responses to a diverse range of natural and synthetic substrates
across peatland types may indicate that peatland microbial communities
in a particular site type have a large metabolic potential and, given a
particular substrate, can cycle C and nutrients similarly under a diverse
range of hydrologic conditions and plant communities:
Therefore microbial decomposition and C cycling will respond
instantly/rapidly to plant community and/or hydrological changes
predicted under climate and environmental (e.g. high N deposition)
changes
Future potential work: chemical characterization of plant extracts, peat, and microbial diversity
and community structure across the 3 sites