Title: Pathways of anaerobic organic matter decomposition in tundra soils from Barrow, Alaska
SUPPORTING INFORMATION
Author names and affiliations:
Elizabeth M. Herndona,1*, Benjamin F. Manna, Taniya Roy Chowdhuryb, Ziming Yanga, Stan D.
Wullschlegera, David Grahamb, Liyuan Lianga, Baohua Gua*
a
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
b
Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
1
Present address: Department of Geology, Kent State University, Kent, OH 44242
Corresponding authors:
Elizabeth Herndon, Department of Geology, Kent State University, Kent, OH 44242, USA
(eherndo1@kent.edu)
Baohua Gu, Oak Ridge National Laboratory, P.O. Box 2008, MS-6036, Oak Ridge, TN 37831,
USA (gub1@ornl.gov)
1
Figure S1. Freeze-dried soil (1 g) was spiked with 20 µmol g -1 acetate and then extracted with
20 mL KCl (0.01 M) for 1, 3, or 20 hours to obtain water-soluble carbon. Prior to acetate
addition, the organic soil contained 20 µmol g -1 acetate and 4.0 µmol g -1 formate, and the
mineral soil contained 8 µmol g -1 acetate and 1 µmol g -1 formate. Minor increases in acetate (<
3 µmol g -1) and formate (< 1 µmol g -1 formate) concentrations were observed over the course of
the extraction. pH values were stable within 0.06 units.
2
Figure S2a. FTIR spectra collected on WSC from soils incubated for 0, 30 or 60 d at 2 ° C, 4°C,
or 8°C. Small peaks near 2300 cm-1 result from background CO2 in the atmosphere.
3
Figure S2b. Absolute changes (Δ) in 1400/1640 and 1040/1640 peak ratios for incubated
samples relative to non-incubated samples indicate that all soils exhibited similar increases as
those observed in the trough mineral horizon (Figure 4b).
2.5
Δ Peak Intensity (1400/1640)
30 d
60 d
2.0
1.5
1.0
0.5
0.0
-0.5
-1
0
1
2
3
4
5
Δ Peak Intensity (1040/1640)
4
6
Figure S3. High performance liquid chromatographic analysis of organic compounds in two
WEOC extracts. A reversed-phase multi-step gradient program from 3% acetonitrile in water
with 0.1% formic acid to 95% acetonitrile in water with 0.1% formic acid was employed to
separate compounds along an Agilent Hypersil ODS C18 column protected by a Phenomenex
C18 Guard column. UV absorbance at 260 nm (A260) (measured in mAU and converted to AU)
was normalized to soil mass by dividing by the sample injection volume (0.1 mL), multiplying
by the WEOC extract volume (mL), and normalizing to soil mass (g). Each “difference”
spectrum was calculated by subtracting the t = 0 d sample from the t = 30 or 60 d sample
chromatogram. (a) RO WSC compounds that eluted at 16.4, 33.0, 35.1, and 44.7 min increased
while a compound eluted at 30.4 min decreased. (b) For CM soil incubated at 8°C, organic
compounds eluted at 33.1 and 44.7 min decreased over time. Peaks at 51.5 and 68.8 min were
observed in all samples and in the solvent and are likely derived from residue leached from the
HPLC column.
Retention Time (min)
Retention Time (min)
5
Figure S4. A stacked column plot shows the concentration of acetate (µmol g-SOC-1) that
accumulated as water-extractable organic carbon (black bar) or was consumed in Fe-reduction
reactions (grey bar) or methanogenesis (white bar) in the first 30 days of incubation for each soil
at each temperature. The total height of the bar is equal to acetate production (consumption +
accumulation) during this time. Note that the y-axes differ in magnitude between samples.
6
Table S1. Water-extractable organic carbon (mg g-soil-1) and total soil organic carbon (mg gsoil-1) results obtained for duplicate samples from four soil horizons collected from a highcentered polygon in the Barrow Environmental Observatory. Relative standard deviation (%)
was < 3% for WEOC and < 6% for SOC.
Soil ID
Subsample
NGADG0043-1
NGADG0043-1
NGADG0043-2
NGADG0043-2
NGADG0048-1
NGADG0048-1
NGADG0048-2
NGADG0048-2
1
2
1
2
1
2
1
2
Topographic
Feature
Center
Center
Center
Center
Trough
Trough
Trough
Trough
Soil Horizon
Organic
Organic
Mineral
Mineral
Organic
Organic
Mineral
Mineral
7
WEOC
mg g-soil-1
0.59
0.59
0.84
0.81
2.11
2.04
0.52
0.53
Soil Organic C
mg g-1
92.09
100.54
81.45
87.61
129.57
129.56
73.92
75.77
Table S2. Concentrations of individual organic acids (µmol g-soil-1) in non-incubated soils (0 d) and soils incubated for 30 or 60 days at 2, 4, or 8°C
Sample Temperature
°C
RO
-2
4
8
TO
-2
4
8
CO
-2
4
8
RM
-2
4
8
TM
-2
4
8
CM
-2
4
8
0d
< DL
< DL
18.62
0.26
0.20
0.18
Formate
30 d
0.04
< DL
0.21
0.02
0.73
0.62
2.11
2.72
3.42
0.27
< DL
< DL
0.15
0.56
0.11
0.18
0.19
0.18
60 d
0d
< DL
0.06
0.02
0.02
2.19
< DL
0.27
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
25.29
0.82
0.65
0.80
Acetate
30 d
0.37
0.02
2.38
0.20
5.99
5.99
43.8
58.9
69.3
0.81
0.40
0.20
0.65
0.62
0.72
2.00
1.67
1.57
1
60 d
0d
< DL
0.20
0.09
0.16
38.0
8.45
2.34
< DL
< DL
< DL
< DL
0.01
< DL
0.01
0.03
< DL
0.03
0.29
0.04
0.01
0.02
Propionate
30 d
< DL
< DL
0.75
0.08
1.52
2.77
4.28
6.50
9.23
0.38
0.16
0.31
0.24
0.07
0.34
0.30
0.33
0.20
60 d
0d
< DL
< DL
< DL
< DL
4.48
7.27
6.93
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
Butyrate
30 d
< DL
< DL
< DL
< DL
< DL
< DL
16.7
11.9
10.9
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
DL = 0.06 µmol g-1 soil, estimated from the limit of quantification (LOQ) of the organic acid in the extract solution (LOQ = 1 µM) normalized to soil mass
8
60 d
< DL
< DL
< DL
14.2
7.2
7.7
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL
< DL