This document compares the microbial ecosystem function between the Palmer (PAL) Antarctic marine site and the McMurdo Dry Valley (MCM) polar desert lake sites based on long-term records and recent observations. While the dominant predators are vastly different sizes, basal trophic levels show similarities. Records of bacterial production, primary production, and dissolved organic carbon over time show diverging trends between the sites. Despite distinct microbial community compositions, metabolic inference analysis reveals converging functional potential among dominant taxa at each site, including similar energy acquisition strategies in key oligotrophic specialists. Major climate events in 2001-2002 and 2008-2009 impacted both sites, highlighting responses to common drivers.

1. 1995 2000 2005 2010
0.51.01.52.02.5
Year
BP:PP
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2000 2005 2010
1015202530354045
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DOCgm−2
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2000 2005 2010
1015202530354045
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DOCgm−2
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LakeFryxellWestLobeBonney
2004 2006 2008 2010
0.000.050.100.15
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BP:PP
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1995 2000 2005 2010
0.050.100.150.200.250.30
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BP:PP
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2004 2006 2008 2010
50525456586062
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DOCgm−2
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NorthPalmerRegion
0246
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PPgCm−2
d−1
2004 2006 2008 2010
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0102030405060
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PPmgCm−2
d−1
1995 2000 2005 2010
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05101520253035
Year
PPmgCm−2
d−1
1995 2000 2005 2010
Assessing microbial ecosystem function across two polar extremes:
The Palmer (PAL) and McMurdo Dry Valley (MCM) LTERs
*1
Jeff S. Bowman, 2
Trista J. Vick-Majors, 3
Rachael Morgan-Kiss, 4
Christina Takacs-Vesbach, 1
Hugh W. Ducklow, 2
John C. Priscu
1
Lamont-Doherty Earth Observatory, 2
Montana State University, 3
Miami University, 4
University of New Mexico
*bowmanjs@ldeo.columbia.edu | www.polarmicrobes.org
2015 LTER ASM, Estes Park, CO
Our hypothesis is that polar desert lakes are different
from the coastal Antarctic marine ecosystem. As obvi-
ous as the answer seems - one need only to consider
the size of members of the top trophic levels to appre-
ciate the huge ecological differences between these
environments - making this comparison allows us to
identify both common and unique ecological features
of these sites associated with fundamental processes
that might otherwise be overlooked. The 20+ year
record of key ecosystem parameters at PAL and MCM
provides a further opportunity to explore how these
ecosystems respond to common events, such as the
unusually warm austral summers in 2001-2002 and
2008-2009. To make our comparison we considered:
1. Records of bacterial production (BP), primary pro-
duction (PP), and dissolved organic carbon (DOC).
2. Recent observations of microbial community structure.
3. Metabolic inference-based predictions of microbial metabolic potential.
Function
TrophicLevel
PAL MCM
Pelagibacter Actinobacteria
Whale/seal Rotifer/tardigrade
The difference in the size of top predators at PAL (humpback whale,
left) and MCM (rotifer, right) underscores major differences in ecosys-
tem function. Such obvious differences, however, may mask function-
al similarities that appear as we move toward basal trophic levels
(left). Actinobacteria and Pelagibacter, the dominant bacteria at MCM
and PAL respectively, for example, are both oligotrophic specialists
with large functional overlaps.
1 m
ELB WLB FRX NPAL SPAL
Site/Region
BP:PP
0.0010.010.1110
1 10 100 1000 10000
PP mg C m−2
day−1
BPmgCm−2
day−1
110100
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PP mg C m−3
day−1
0.0010.010.11
0.01 0.1 1 10
BPmgCm−3
day−1
Fryxell
East Lobe Bonney
West Lobe Bonney
North Palmer
South Palmer
1:10
1:5
+
++
+ +
The ratio of BP to PP provides insight into the functioning of the microbial loop. Values in the global pelagic marine
environment tend to center around 1:10 (grey dotted lines). At a ratio of 1:5 (black dotted lines) PP is thought to pro-
vide insufficient C to support both BP and respiration. Autochthonously fixed carbon must be subsidized by a source
outside the photic zone. The three MCM lakes included in this investigation have BP:PP ratios exceeding PAL, despite
their lower DOC concentrations. Lake Fryxell has extreme values of BP:PP suggesting a large subsidy from DOC-rich
water below the photic zone.
The relationship between BP and PP
Temporal trends
The concentration of DOC and rates of BP and PP change with time. Interestingly, while the concentration of DOC
has increased at PAL in recent years, concentrations have decreased since 2000 in the photic zone of Lake Fryxell
and Lake Bonney. Some of the dynamics in BP:PP appear to be driven by extreme events. The summer of
2001-2002 was unusually warm and windy, leading to increased glacial melt and heightened lake levels at MCM.
This influx of lake water may have suppressed PP due to increased turbidity, while stimulating BP with a new
source of labile DOC. Nutrients carried by the meltwater enhanced PP in subsequent years after turbidity re-
turned to normal.
The summer of 2008-2009 was also unusually warm and had a major impact at both PAL and MCM, with BP:PP de-
creasing at both sites as a result of elevated PP. This mutual uncoupling of BP and PP may have been driven by en-
hanced krill grazing at PAL and increased particle export at MCM.
Diverging community structure and converging function
fall_frx_9_b.1
fall_frx_9_b.2
summer_frx_6_b.1
summer_frx_6_b.2
fall_frx_6_b.1
fall_frx_6_b.2
summer_wlb_13_b.2
summer_frx_9_b.2
summer_frx_9_b.1
fall_wlb_13_b.2
summer_wlb_13_b.1
fall_wlb_13_b.1
summer_wlb_18_b.2
summer_wlb_18_b.1
fall_wlb_18_b.2
fall_wlb_18_b.1
summer_nw_shallow_b.2
summer_nw_shallow_b.1
summer_sw_deep_b.1
summer_sw_deep_b.2
winter_ne_shallow_b.2
winter_ne_shallow_b.1
summer_ne_shallow_b.1
summer_ne_shallow_b.2
summer_sw_shallow_b.1
summer_se_shallow_b.1
summer_se_shallow_b.2
summer_sw_shallow_b.2
summer_ne_deep_b.1
summer_se_deep_b.1
summer_se_deep_b.2
summer_nw_deep_b.2
summer_nw_deep_b.1
Candidatus Pelagibacter ubique HTCC1062
Tropheryma whipplei
Acidothermus cellulolyticus 11B
Actinobacteria
Syntrophomonas wolfei Goettingen
Owenweeksia hongkongensis DSM 17368
Polaribacter MED152
Francisella
Alcanivorax
Pelagibacter
Candidatus Amoebophilus asiaticus 5a2
Cytophagia
Acidimicrobidae bacterium YM16 304
Hyphomonas neptunium ATCC 15444
Candidatus Cardinium hertigii
Thermodesulfobium narugense DSM 14796
Caldisericum exile AZM16c01
Parvibaculum lavamentivorans DS 1
Clavibacter michiganensis nebraskensis NCPPB 2581
Polaromonas JS666
Fluviicola taffensis DSM 16823
Clavibacter michiganensis NCPPB 382
Polaromonas naphthalenivorans CJ2
Candidatus Pelagibacter IMCC9063
Octadecabacter
Muricauda ruestringensis DSM 13258
Glaciecola nitratireducens FR1064
Teredinibacter turnerae T7901
Robiginitalea biformata HTCC2501
alpha proteobacterium IMCC1322
665
0
summer_wlb_13_b.2
fall_wlb_18_b.1
fall_wlb_18_b.2
summer_wlb_18_b.2
summer_wlb_18_b.1
fall_wlb_13_b.2
summer_wlb_13_b.1
fall_wlb_13_b.1
fall_frx_9_b.1
fall_frx_6_b.1
fall_frx_6_b.2
summer_frx_9_b.2
summer_frx_9_b.1
fall_frx_9_b.2
summer_frx_6_b.2
summer_frx_6_b.1
summer_nw_shallow_b.2
summer_nw_shallow_b.1
summer_ne_shallow_b.1
summer_ne_shallow_b.2
summer_sw_shallow_b.1
summer_se_shallow_b.2
summer_se_shallow_b.1
winter_ne_shallow_b.1
winter_ne_shallow_b.2
summer_ne_deep_b.1
summer_sw_deep_b.1
summer_sw_deep_b.2
summer_sw_shallow_b.2
summer_se_deep_b.2
summer_se_deep_b.1
summer_nw_deep_b.1
summer_nw_deep_b.2
formate oxidation to CO2
pyruvate fermentation to acetone
pyruvate fermentation to lactate
formaldehyde oxidation I
pyruvate fermentation to ethanol I
pyruvate fermentation to acetate II
methanol oxidation to formaldehyde II
methanol oxidation to formaldehyde I
glycerol degradation III
formate to dimethyl sulfoxide electron transfer
Bifidobacterium shunt
NADH to dimethyl sulfoxide electron transfer
nitrite oxidation
sulfur reduction I
hydrogen production V
mixed acid fermentation
pyruvate fermentation to ethanol II
sulfite oxidation IV
sulfite oxidation III
pyruvate fermentation to ethanol III
hydrogen production II
hydrogen production VI
hydrogen production III
reductive monocarboxylic acid cycle
784
0
long
lat
180
0
90 W 90 E
PAL
MCM
We used PAPRICA to conduct a metabolic inference, matching 16S rRNA gene reads from PAL and MCM with the
closest related completed genomes and associated metabolic pathways. Despite the marine origin of the MCM
Lakes, the composition of the water column microbial community is distinct from the microbial community at
PAL. In particular the oligotrophic specialists best represented by the complete genomes of Tropheryma and Pe-
lagibacter are phylogenetically very distant although they may occupy a similar niche. These clades are non-mo-
tile opportunists, and are likely to posses alternate energy acquisition strategies such as proteorhodopsins. Taxa
that may be associated with particles, such as Polaribacter MED152 and Syntrophomonas Wolfei Goettingen are
shared between these environments, as are their associated metabolisms. This suggests that microniches, such as
regions of low oxygen within particles, may be more important in determining community function than
large-scale environmental factors (such as a terrestrial or marine location).
Community composition as determined by
phylogenetic placement
Key metabolic pathways predicted by metabolic inference
1. While phytoplankton directly provide the carbon for BP at PAL, this is demphasized at MCM.
1a. Phytoplankton derived carbon at MCM is highly subsidized by allochthonous sources.
1b. PP is inherently decoupled from BP at MCM, particularly in Lake Fryxell.
1c. DOC is produced below the chemocline in Lake Fryxell, and diffuses across the chemocline to support BP.
2. Differences in water column structure may drive some of the differences in carbon utilization, with the shallow chemo-
cline limiting particle degradation in the photic zone of MCM lakes.
3. Differences in trophic structure may also account for some differences, with biomass being disproportionately chan-
neled to krill and the higher trophic levels at PAL in some years.
4. As a result of these differences PAL and MCM can have different responses to major perturbations, although sometimes
the response is the same - but for very different reasons!
5. Although the composition of the microbial communities diverge sharply, ecological similarities at the microbial level
allow for strong functional similarities.
Conclusions
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50 µm
Image Wei LiImage JSB