Peat loss collocates with a threshold in plant–mycorrhizal associations in drained peatlands encroached by trees

Abstract

Drainage‐induced encroachment by trees may have major effects on the carbon balance of northern peatlands, and responses of microbial communities are likely to play a central mechanistic role.
We profiled the soil fungal community and estimated its genetic potential for the decay of lignin and phenolics (class II peroxidase potential) along peatland drainage gradients stretching from interior locations (undrained, open) to ditched locations (drained, forested).
Mycorrhizal fungi dominated the community across the gradients. When moving towards ditches, the dominant type of mycorrhizal association abruptly shifted from ericoid mycorrhiza to ectomycorrhiza at c. 120 m from the ditches. This distance corresponded with increased peat loss, from which more than half may be attributed to oxidation. The ectomycorrhizal genus Cortinarius dominated at the drained end of the gradients and its relatively higher genetic potential to produce class II peroxidases (together with Mycena) was positively associated with peat humification and negatively with carbon‐to‐nitrogen ratio.
Our study is consistent with a plant–soil feedback mechanism, driven by a shift in the mycorrhizal type of vegetation, that potentially mediates changes in aerobic decomposition during postdrainage succession. Such feedback may have long‐term legacy effects upon postdrainage restoration efforts and implication for tree encroachment onto carbon‐rich soils globally.

Full text

Peat loss collocates with a threshold in plant–mycorrhizal
associations in drained peatlands encroached by trees
Camille E. Defrenne
1
, Jessica A. M. Moore
2
, Colin L. Tucker
3
, Louis J. Lamit
4
, Evan S. Kane
1,3
,
Randall K. Kolka
5
, Rodney A. Chimner
1
, Jason K. Keller
6
and Erik A. Lilleskov
3
1
Michigan Technological University, Houghton, MI 49931, USA;
2
Department of Microbiology, University of Tennessee, Knoxville, TN 37996, USA;
3
USDA Forest Service-Northern
Research Station, Houghton, MI 49931, USA;
4
Department of Biology, Syracuse University, Syracuse, NY 13244, USA;
5
U.S. Forest Service-Northern Research Station, Grand Rapids, MN
55744, USA;
6
Schmid College of Science and Technology, Chapman University, Orange, CA 92866, USA
Author for correspondence:
Camille E. Defrenne
Email: cedefren@mtu.edu
Received: 23 February 2023
Accepted: 14 April 2023
New Phytologist (2023)
doi: 10.1111/nph.18954
Key words: drainage, ectomycorrhizal fungi,
ericoid mycorrhizal fungi, mycorrhizal type,
peatland, plant-mycorrhizal associations,
vegetation gradient.
Summary
Drainage-induced encroachment by trees may have major effects on the carbon balance of
northern peatlands, and responses of microbial communities are likely to play a central
mechanistic role.
We profiled the soil fungal community and estimated its genetic potential for the decay of
lignin and phenolics (class II peroxidase potential) along peatland drainage gradients stretch-
ing from interior locations (undrained, open) to ditched locations (drained, forested).
Mycorrhizal fungi dominated the community across the gradients. When moving towards
ditches, the dominant type of mycorrhizal association abruptly shifted from ericoid mycorrhiza
to ectomycorrhiza at c. 120 m from the ditches. This distance corresponded with increased
peat loss, from which more than half may be attributed to oxidation. The ectomycorrhizal
genus Cortinarius dominated at the drained end of the gradients and its relatively higher
genetic potential to produce class II peroxidases (together with Mycena) was positively asso-
ciated with peat humification and negatively with carbon-to-nitrogen ratio.
Our study is consistent with a plant–soil feedback mechanism, driven by a shift in the
mycorrhizal type of vegetation, that potentially mediates changes in aerobic decomposition
during postdrainage succession. Such feedback may have long-term legacy effects upon
postdrainage restoration efforts and implication for tree encroachment onto carbon-rich soils
globally.
Introduction
Land-use change has profoundly altered northern peatlands, one of
the largest organic carbon pools of the Earth’s terrestrial biosphere.
By the nineteenth century, c.24Mha(c. 5%) of northern peatlands
had been extensively drained for agriculture and forestry practices
(Greifswald Mire Centre, 2019). Historical drainage removed the
anoxic constraint on decomposition, leading to peat carbon loss to
the atmosphere via decomposition and more frequent and extensive
wildfires (Turetsky et al., 2015;Chimneret al., 2017; Harris
et al., 2020; Krause et al., 2021;Maet al., 2022; Fluet-Chouinard
et al., 2023). Yet, this drainage has not affected northern peatlands
uniformly, mostly due to differences in peatland types, climates,
and vegetation changes (Laiho, 2006; Talbot et al., 2010;
Urbanova&Barta, 2016;Krauseet al., 2021; Kokkonen
et al., 2022). Where historical drainage triggered a shift in vegeta-
tion composition, there are potential biological and biogeochemical
feedbacks that lead to uncertainty in decomposition dynamics
(Laiho, 2006;Strakovaet al., 2012).
Acidic peatlands of the northern hemisphere (bogs and poor
fens) are dominated by Sphagnum mosses whose partially decayed
tissues form the bulk of peat-building organic matter (Dorrepaal
et al., 2005). Taking root in the Sphagnum matrix are sedges and
ericaceous shrubs, the latter of which form a mutualistic symbiosis
with ericoid mycorrhizal (ErM) fungi. Growing evidence suggests
that ErM shrubs and fungi promote organic matter accumulation
in Sphagnum peatlands (Wiedermann et al., 2017;Fenner&Free-
man, 2020;H.Wanget al., 2021), alpine tundra (Clemmensen
et al., 2021), and boreal forests (Fanin et al., 2022). In these
carbon-rich soils, both ErM shrubs and fungi produce recalcitrant
tissues; the former produce tissues high in phenolic compounds
(leaves and fine roots), and the latter produce tissue rich in melanin
(mycelium; Joanisse et al., 2009; Adamczyk et al., 2019;Fernandez
et al., 2019;H.Wanget al., 2021). In addition, ErM fungi use a
broad suite of oxidative and hydrolytic enzymes to mobilize nutri-
ents bound in soil organic matter (Martino et al., 2018). Yet, they
lack certain redox enzymes (e.g. ligninolytic class II peroxidases),
which limits their ability to degrade lignin, lignin-like Sphagnum
phenolics, and other complex biopolymers (Bengtsson
et al., 2018). Altogether, the distinct functional traits of ErM plants
and of their fungal symbionts underpin soil organic matter accu-
mulation (reviewed by Ward et al., 2022).
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A shift in peatland ecosystem state from a Sphagnum moss-
dominated to a tree-dominated state can occur as drainage aerates
the upper peat layers, which, overtime, enables persistent conifer-
ous tree encroachment (Ohlson et al., 2001; Pellerin &
Lavoie, 2003; Holmgren et al., 2015;L~ohmus et al., 2015). Cli-
mate, former forest cover and peatland nutrient status all play a
role in the extent and rate of stand development (L~ohmus
et al., 2015). Once established, trees alter peatland decomposi-
tion dynamics through above- (e.g. biomass and litter input) and
belowground processes (e.g. root turnover, rhizodeposition, and
mycorrhizal symbiosis; Klein et al., 2022;Liet al., 2022; Shi
et al., 2022). Across northern peatlands, however, the carbon sink
capacity in response to tree encroachment may either increase
(Minkkinen et al., 2018; Hermans et al., 2022) or decrease
(Simola et al., 2012; Hommeltenberg et al., 2014). A mechanistic
understanding of the effect of drainage-induced tree encroach-
ment on peatland carbon balance remains elusive, in part because
corresponding shifts in the structure and function of soil fungal
communities have seldom been documented (Jaatinen
et al., 2008; Peltoniemi et al., 2012,2021; Andersen et al., 2013;
Kitson & Bell, 2020; Hupperts & Lilleskov, 2022).
The coniferous trees that typically encroach drained, acidic
peatlands associate with ectomycorrhizal (EcM) fungi. Unlike
ErM fungi, some EcM taxa have retained the ability to decay
complex organic compounds using class II peroxidases (B€odeker
et al., 2009; Kohler et al., 2015; Lindahl & Tunlid, 2015; Shah
et al., 2016), presumably to access nitrogen bound in soil organic
matter (N-SOM; Nicolas et al., 2019; Pellitier & Zak, 2021;T.
Wang et al., 2021). These peroxidases have some of the greatest
known capacity to decay soil organic matter (Janusz et al., 2017)
and are necessary to access N-SOM because, in Sphagnum peat-
lands, polypeptides are rapidly complexed into protein-
polyphenol complexes that are largely protected from hydrolytic
enzymes (Bragazza & Freeman, 2007). Hence, following tree
encroachment, a potential increase in organic matter decomposi-
tion could be a function of the EcM fungal community composi-
tion, along with saprotrophs, and fungal guild interactions
(B€odeker et al., 2016; Sterkenburg et al., 2018; Fernandez
et al., 2020; Argiroff et al., 2021).
The community composition of EcM fungi depends on soil
fertility, which typically increases with peatland drainage as a
result of organic matter mineralization (e.g. Hupperts & Lilles-
kov, 2022). Hence, a drainage-induced increase in nitrogen
availability might favor C-strategist Basidiomycota (Competitor)
with enhanced soil organic matter decay potential (mostly EcM
and saprotrophs), whereas acidic soils with low nutrient avail-
ability largely constrain the fungal community to S-strategist
Ascomycota (Stress-tolerator; Sterkenburg et al., 2015). How-
ever, if drainage leads to high net nitrogen mineralization, the
advantage of accessing N-SOM would decline and EcM taxa
with greater abilities to take up inorganic nitrogen would
become dominant (Lilleskov et al., 2019; Argiroff et al., 2021;
Pellitier & Zak, 2021).
Water-table drawdown and subsequent tree encroachment
typically results in intensively humified (less decomposable) peats
due to oxidation and changes in plant litter quantity and quality
(Blodau & Siems, 2012; Urbanova&Barta, 2016; Kane
et al., 2019; Normand et al., 2021;Liet al., 2022; Uhelski
et al., 2022). Consequently, decomposition may become increas-
ingly dependent on oxidative enzymes, as oxidation progresses
during postdrainage succession. In turn, this may favor ligninoly-
tic taxa such as the saprotroph Galerina and the saprotroph/root-
associated Mycena, as well as EcM fungi with a greater genetic
potential to obtain N-SOM (Lindahl & Tunlid, 2015; Argiroff
et al., 2021). Altogether, the functional ability of fungal taxa to
decompose soil organic matter, and, indirectly, their genetic
potential to produce oxidative enzymes is both a response and
effect trait, because it influences the response of fungal taxa to
the degree of peat decomposition, while simultaneously influen-
cing their effect on organic matter decomposition (Koide et al.,
2014).
Temperature increases c.1°C are also expected to induce
encroachment by trees in northern peatlands (Heijmans
et al., 2013), suggesting that long-term drainage and climate
warming have similar effects on vegetation in these ecosystems.
Some studies on climate-induced tree encroachment into carbon-
rich soils have reported a concomitant shift in the fungal commu-
nity composition from root-associated Ascomycota, including
the functional guild ErM fungi and the class Archaeorhizomy-
cetes, to Basidiomycota and Mucoromycota, including
the functional guilds EcM fungi and saprotrophs (Tonjer
et al., 2021; Hewitt et al., 2022). Clemmensen et al.(2021), on
the contrary, showed a change in the assemblage of EcM fungal
functional trait and explained losses of organic matter at the tran-
sition from birch forest to heath tundra by the activity of
rhizomorph-forming EcM genera with class II peroxidases, espe-
cially Cortinarius. Altogether, whether induced by long-term
drainage or climate warming, tree encroachment into carbon-rich
soils might trigger a shift in the dominance of mycorrhizal type
and/or in the taxonomic and functional composition of EcM
communities, with inherently complex effects on decomposition
dynamics (Ritson et al., 2021).
We used drainage gradients in peatlands to investigate the
effect of a century-long drainage on soil fungal communities in
northern Minnesota, the United States. As the peat subsided
along the gradients, the vegetation transitioned from a sedge and
ericaceous shrub dominance (open locations) to tree dominance
(forested locations), with a concomitant decrease in soil carbon-
to-nitrogen ratio (C : N) and an increase in peat humification
(Hupperts & Lilleskov, 2022). We hypothesized that (H1) soil
fungal community structure would shift across the drainage gra-
dients from a higher abundance of root-associated Ascomycota to
a higher abundance of Basidiomycota. We also expected the
dominant type of mycorrhizal association with transition from
ErM in undrained, open locations to EcM in drained, forested
locations. Next, we hypothesized that (H2) as soil C : N decreases
and peat humification increases along the gradients, fungal com-
munities would increasingly be dominated by taxa with enhanced
capacities to decay humified peat, indicated by a high genetic
potential to produce class II peroxidases. However, we expected
these taxa to decline as soil C : N continues to decrease closer to
the ditches.
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Materials and Methods
Drainage gradients
We selected three acidic (pH 3.1–3.7; Hupperts & Lilles-
kov, 2022), nutrient-poor peatlands in north-central Minnesota
adjacent to ditches dug between 1916 and 1918 and separated by
5–15 km (47.083570°N, 92.839133°W; 47.116195°N,
92.796530°W and 47.168103°N, 92.694208°W; Support-
ing Information Fig. S1). The peatlands are within and adjacent
to the Sax-Zim Bog complex, which developed following the last
glacial retreat c. 10 000 yr BP (https://saxzim.org; accessed 08 Jan-
uary 2022). In each peatland, we established a single transect
(c. 215–525 m long) from interior (undrained) to ditch (drained;
for more details, see Hupperts & Lilleskov, 2022). Farther from
the ditches, the ecosystems were dominated by Sphagnum mosses
(S. rubellum Wilson, S. magellanicum Brid., and S. fuscum
(Schimp.) Klinggr), ErM shrubs (Chamaedaphne calyculata L.,
Moench., Kalmia polifolia Wangenh., and Vaccinium oxycoccus
L.), sedges (Carex oligosperma Michx.) and small, widely scattered
black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.),
and tamarack (Larix laricina (Du Roi) K. Koch) trees. Nearest
the ditches, the ecosystems were vegetated by a dense overstory of
EcM trees (predominantly, P. mariana and L. laricina) with an
understory of ErM shrubs (mainly Vaccinium myrtilloides and
Rhododendron groenlandicum) and a moss layer dominated by
Hylocomium splendens.
Peat sampling and environmental variables
In September 2021, we collected 10 peat blocks (20 9
20 940 cm) along each transect at c.20–45-m intervals with
similar microtopography (i.e. lawns) using a serrated knife (steri-
lized with 70% ethanol). Upon collection, cores were cut in half
lengthwise and sectioned into 10-cm-depth increments (0–10,
10–20, 20–30, and 30–40 cm). From each section, a representa-
tive subsample (c. 5 g) was collected by hand using sterile gloves,
wrapped in plastic and foil, stored in liquid nitrogen for 1–3d
and stored at 80°C for c. 1 month until processing. The
remaining peat from each section was analyzed for total carbon
and nitrogen (Costech 4010 Elemental Combustion System,
Costech Analytical Technologies Inc., Valencia, CA, USA), and
for the degree of decomposition using the von Post scale of humi-
fication (von Post, 1924). The von Post scale consists of 10
degrees that correspond to a percentage of decomposition (e.g.
H1 =10%, H5 =50% and H10 =100%). The degrees H1–3
correspond to fibric peat, H4–5 to hemic peat, and H7–10 to
sapric peat. In addition, we surveyed vegetation (shrub ground
cover, % and tree basal area, m
2
ha
1
), measured water table
depth (cm), change in peat height (m) and collected peat samples
for bulk density (g cm
3
), and plant fine-root density (indicator
of belowground resource allocation; g cm
3
) at each sampling
location along the transects (Methods S1; Krause et al., 2021).
For each transect, the distance from ditch represented the average
distance (m) between a given sampling location and the closest
ditch(es). As such, this variable represented a cumulative ditch
effect. For the remaining analyses, we used the variance of the
water table depth (r
2
) calculated for each sampling location at
five time points over 2 yr (Jul, Sep, and Nov 2021; Jun and Aug
2022) because the average water table depth did not change
across the gradients, whereas the variance in water table depth
increased from undrained to drained locations (Fig. S2).
Molecular methods
Peat for the focal dataset presented here was processed from the
10 to 20-cm and 20 to 30-cm-depth increments (60 samples
total: 3 transects 910 sampling locations 92 depth increments).
We avoided the top 10 cm, which was often dominated by green
Sphagnum tissues. Most root biomass was consistently found in
the upper 10–30-cm soil in both intact and degraded locations,
except for two samples collected from the upper 0–10 cm
(Fig. S3). Frozen peat samples were pulverized under liquid
nitrogen using a mortar and pestle, ground to a fine powder using
a sterile coffee grinder and stored at 80°C until DNA extrac-
tion. For each sample, DNA was extracted from 250 mg of frozen
ground peat using the DNeasy PowerSoil Pro Kit (Qiagen)
according to the manufacturer instruction and with the addition
of a heating step (after vortexing the PowerBead Pro tubes, sam-
ples in the buffer CD1 were heated at 65°C for 30 min). Inhibi-
tors of polymerase chain reactions (PCR) were removed using the
DNeasy PowerClean Pro cleanup kit, and DNA was quantified
using a Qubit Fluorometer (Model Q32857; Invitrogen). The
fungal ITS2 gene region was amplified by PCR using the fungal-
specific primers ITS4-Fun (Forward) and 5.8S-Fun (Reverse;
Taylor et al., 2016; Methods S2). Multiplexed libraries were
sequenced on an Illumina MiSeq platform (San Diego, CA,
USA) using 2 9250 bp chemistry (MiSeq Reagent Kit V2, MS-
102-2003), spiked with 20 pM denaturated PhiX.
Bioinformatics
Analyses of amplicon sequences were carried out with forward
reads only because there was insufficient high-quality sequence of
reverse reads. While relevant information is lost when discarding
reverse reads, this approach has been shown to accurately estimate
fungal abundances in complex communities. For example,
Nguyen et al.(2015) found that using single highest quality read
direction (forward reads) provided a more accurate picture of a
mock community of Basidiomycota and Ascomycota species than
applying a paired sequence approach. Taylor et al.(2016) devel-
oped lineage-specific primer (used in the present study) and were
able to accurately estimate fungal abundance in complex mock
communities by carrying out analyses with forward reads only.
Similarly, Pauvert et al.(2019) showed that the use of single for-
ward sequences with DADA2 (Callahan et al., 2016) was a good
option for fungal community characterization.
The forward reads were denoised, dereplicated, trimmed, and
truncated using the DADA2 plugin in QIIME2 on unmerged
paired-end reads (Callahan et al., 2016; Bolyen et al., 2019). In
particular, the large subunit (28S) flank (31 bases) was manually
trimmed from the 50end of the reads, and the 30end of the reads
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was truncated to 200 bases (based on quality scores; note that the
primers were not part of the reads because of the library layout).
We assigned taxonomy to the resulting amplicon sequence var-
iants (ASVs) using a Na€ıve–Bayesian classifier trained with the
UNITE QIIME release for eukaryote database (v.8.3; 97–99%
sequence similarity; Abarenkov et al., 2021).
Fungal guilds and class II peroxidase potential
The primary and secondary lifestyle of each ASV was identified
using the FungalTraits database according to the author’s instruc-
tions (Flores-Moreno et al., 2019;P~olme et al., 2020). We then
used the three variables from the FungalTraits file (Primary_lifet-
syle, Secondary_lifestyle and Comment_on_lifetsyle) in combi-
nation with the Mycocosm database (DOE Joint Genome
Institute, Berkeley, CA, USA; https://mycocosm.jgi.doe.gov;
accessed 12 April 2022) and the literature to classify the ASVs
into seven guilds: EcM; root endophyte; ErM (or putative ErM);
ErM/EcM; saprotroph (litter, wood, soil, or unspecified);
saprotroph/root-associated; and unassigned (ASVs that did not
fit into the above categories). Note that ASVs in the genus Hya-
loscypha that were not identified at the species level were classified
as ‘unassigned’ (Vohnık et al., 2007; Fehrer et al., 2019). The
ASVs assigned to the species Hyaloscypha hepaticicola (deprecated
synonyms: Pezoloma ericae and Rhizoscyphus ericae) were classified
as ErM, and the ASVs assigned to the species Hyaloscypha varia-
bilis (deprecated synonym Meliniomyces variabilis) were classified
as ErM/EcM (Vohnık et al., 2007; Fehrer et al., 2019). The
ASVs assigned to the family Serendipitaceae and to the genera
Oidiodendron and Serendipita were classified as putative ErM
after blasting the representative ITS sequences (blastn against the
UNITE database) to ensure they came from a habitat with ericac-
eous shrubs (Weiß et al., 2016). The ASVs assigned to the species
Clavaria sphagnicola (the only detected species in the genus Cla-
varia) were classified as putative ErM (Straker, 1996; Birkebak
et al., 2013; Olariaga et al., 2015), and those assigned to the
genus Mycena were classified as saprotroph/root-associated
(Thoen et al., 2020; Harder et al., 2021). For the remaining of
the text, we refer to the putative ErM taxa as ‘ErM’ to facilitate
interpretation.
Plant ASVs or those unidentified at the kingdom level were
removed (function subset_taxa, R package phyloseq; McMurdie
& Holmes, 2013; 386 ASVs removed). The count data were then
normalized by scaling with ranked subsampling (Beule & Kar-
lovsky, 2020), aggregated at the genus level (function tax_glom,
phyloseq), and transformed to relative abundance (function
transform_sample_counts, phyloseq). Note that the genus Hya-
loscypha was primarily classified as ErM because the ErM ASVs
had, on average, a higher relative abundance across samples.
Indeed, the genus Hyaloscypha comprised 18 ErM ASVs (relative
abundance of 0.60%, on average), 21 ErM/EcM ASVs (relative
abundance of 0.09%, on average), and 47 unassigned ASVs (rela-
tive abundance of 0.20%, on average).
We assessed the class II peroxidase potential within the
sampled fungal community by calculating the average number of
Auxiliary Activity 2 (AA2) genes for fungal genera in our dataset
using published values from the MycoCosm database and multi-
plying them by the relative abundance of the respective genus in
each sample (Table S1). This approach was used to assess the
potential of individual fungal genera to decay lignin and phenolic
compounds by combining their genetic potential to produce class
II peroxidases with their relative abundance. To obtain the aver-
age AA2 genes for each fungal genus, we had the following cri-
teria: genera without published genomes and/or for which no
guild was assigned were excluded. Although P. sphaerosporum
does not have a published genome, we used its genome as it was
the only species of Piloderma in our dataset (authorization to use
the genome was granted by the principal investigator of the pro-
ject); it is important to point out that the AA2 gene family com-
prises the ligninolytic class II peroxidases (lignin, manganese and
versatile peroxidases) as well as three nonligninolytic peroxidases,
including general, cytochrome-C, and ascorbate peroxidases.
Since ligninolytic class II peroxidases evolved within Agaricomy-
cetes (Nagy et al., 2016; Floudas et al., 2020; Ruiz-Due~nas
et al., 2021), we disregarded AA2 genes in taxa outside this class
(e.g. Cenococcum,Hyaloscypha). In addition, to ensure that we
only targeted class II peroxidases, we manually verified that the
best hit (under protein ID) was indeed a class II peroxidase.
Statistical analyses
Statistical analyses were conducted in R v.4.2.1 (R Core
Team, 2022). We identified multicollinearity between environ-
mental variables measured along the drainage gradients by per-
forming a principal component analysis (PCA). For this analysis,
we used Spearman’s rank correlation coefficients because the rela-
tionships between variables were typically monotonic but not
consistently linear (Fig. S4). The PCA was performed on nine
rank-ordered variables including distance from ditch, water table
depth r
2
, tree basal area, shrub ground cover, peat density, tree
and shrub fine-root density, soil C : N, and peat humification
(function rda, package VEGAN). The first PCA axis (first principal
component) was used as a composite variable in subsequent ana-
lyses because it captured the majority of the environmental
changes across the gradients (shifts in above- and belowground
vegetation structure and peat physicochemical properties;
Fig. 1a).
To test our first hypothesis related to soil fungal community
structure across the drainage gradients, we first calculated the
relative abundance of fungal phyla and guilds at each sampling
location by aggregating data by transect and depth. We then car-
ried out a partial distance-based redundancy analysis (db-RDA)
at the genus level (function capscale, package VEGAN). We used
Bray–Curtis distance measures and the argument Condition to
account for the potential variation associated with differences
among transects. The ordination axes were constrained by the
first PCA axis and tree fine-root density, because the latter was
the only variable strongly correlated with the second PCA axis
(Fig. 1a). The significance of constraints was assessed using a per-
mutation test (function anova.cca, package VEGAN). To accom-
modate the hierarchical structure of our data (depth nested
within sampling location, nested within transect), we restricted
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the permutation design using the argument permutations (with
the function how, package PERMUTE; Simpson, 2022). The sam-
ples were permuted at the level of depth (function within, pack-
age PERMUTE), or at the level of sampling locations (function
Plots, package PERMUTE).
To examine the relationship between mycorrhizal guilds and
environmental changes, we used linear mixed effects models
(function lmer, package LME4). We fitted two separate models,
one for the relative abundance of EcM genera and one for that of
ErM genera. For both models, the first PCA axis and depth were
added as fixed effects and sampling location nested within trans-
ect was added as a random effect. The best fitting models
included the first PCA axis as a first- and second-order term
(quadratic models) based on Akaike information criterion and
marginal R
2
(represents the variance of the fixed effect; function
r2_nakagawa, package performance). For both models, we
visually checked model assumptions (function check_model,
package performance), and assessed the significance of the first
PCA axis and depth with an analysis of variance (function anova,
package STATS).
We explored responses of individual fungal genera using Thresh-
old Indicator Taxa ANalysis (TITAN; package TITAN2; Baker &
King, 2010). This analysis can reveal potential nonlinear transitions
in community data and detect concomitant changes in taxa distri-
butions along a continuous variable (i.e. an environmental gradi-
ent). For every taxon frequency and abundance along a continuous
variable, TITAN identifies the optimum change point (defined by
the sum of z-score maximum) using the indicator species analysis
approach. Data were averaged by depth to account for spatial auto-
correlations, genera that occurred in fewer than three samples were
removed (106 genera removed out of 195 genera total), and dis-
tance from ditch was used to represent the drainage gradients for
ease of interpretation and because it was strongly negatively corre-
lated with the first PCA axis (Fig. 1a).
To test our second hypothesis, related to the relationship
between peat physicochemical properties and fungal functional
composition, we implemented a db-RDA of class II peroxidase
potential within fungal communities. Axes were constrained by
peat humification and tree fine-root density, the argument Condi-
tion was used to account for the potential variation associated
with differences among transects, and we assessed the significance
of constraints using the same methods as above (db-RDA at the
genus level).
Results
Environmental changes across the drainage gradients
Using PCA, we identified two dimensions of variation among
environmental variables, which jointly explained 65% of the
overall variation (Fig. 1a). The first PCA axis accounted for
c. 54% of the total variation and, as expected, represented a gra-
dient from undrained, shrub-dominated locations, with a high
soil C : N, to drained, tree-dominated locations, where the peat
Fig. 1 Interrelated shifts in above- and belowground vegetation structure
and peat physicochemical properties across peatland drainage gradients.
(a) Principal component analysis of environmental variables measured
along transects from undrained, open locations to drained, forested loca-
tions (60 samples total: 3 transects 910 sampling locations 92 depth
increments). Note that this analysis was performed using Spearman’s rank
correlation coefficients. (b) Relationship between the distance from ditch
and selected environmental variables (Supporting Information Fig. S4). S.
ground cover, shrub ground cover (%); Soil C : N, soil carbon-to-nitrogen
ratio; Distance.Ditch, for each transect, the average distance (m) between
a given sampling location and the closest ditch(es); S. root density, shrub
fine-root density (g cm
3
); T. root density, tree fine-root density (g cm
3
);
Water table r
2
, variance of the water table depth (cm); Peat density, peat
bulk density (g cm
3
); T. basal area, tree basal area (m
2
ha
1
); Peat humifi-
cation, degree of peat decomposition (von Post scale).
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was denser, more humified and water table fluctuations were lar-
ger. In particular, the first PCA axis had a strong positive loading
for tree basal area (0.40; Table S2) and a comparably strong nega-
tive loading for shrub fine-root density (0.38; Table S2). The
second PCA axis (c. 11% of total variation) was highly positively
correlated with tree fine-root density (loading of 0.89; Table S2),
and separated samples collected from the upper peat layers (10–
20 cm) from those collected at 20–30 cm depth, where the fine-
root density of trees was generally lower (Fig. S3). Interestingly,
tree fine-root density did not align with the main environmental
gradient because it was unrelated to tree basal area (q=0.38;
Fig. S4).
By contrast with aboveground vegetation structure, below-
ground variables including peat properties, water table variability,
and plant fine-root density did not vary linearly across the gradi-
ents (Figs 1b,S4). Rather, belowground variables exhibited an
abrupt shift between 100 and 150 m from the ditches, which cor-
responded to the onset of peat subsidence (Fig. 1b).
Fungal community structure
Diverse fungal communities were recovered through amplicon
sequencing. We obtained an average of 15 410 (9729) reads
per sample (76 5%), ranging from 2716 to 35 468 reads. The
reads were sorted into 1081 fungal ASVs (136 EcM, 81 ErM,
and 289 saprotrophs and saprotrophs/root associated) and 195
fungal genera, of which 24 were EcM, four ErM, and 88 were
saprotrophs and saprotrophs/root-associated (Table S1). The
EcM and ErM genera predominantly belonged to Agaricales
(Basidiomycota) and Helotiales (Ascomycota) and accounted for
49.3% and 32.4% of the reads, respectively (Table S1).
In support of H1, fungal communities were largely dominated
by Ascomycota in samples collected from undrained locations
(Fig. 2a; locations 1–3), whereas Basidiomycota made up most of
the community in samples collected from increasingly drained
locations (locations 4–10). Fungi in the phyla Mortierellomy-
cota, including Mortierella (saprotroph) and Mucoromycota,
including Umbelopsis (saprotroph) accounted for less than 15%
of the community at each sampling location and their relative
abundance slightly increased from undrained (1–3) to increas-
ingly drained locations (4–10; Figs 2a,S5). The vast majority of
Ascomycota were ErM fungi, whereas most Basidiomycota were
EcM fungi (Fig. 2b). Farther from the ditches, the EcM fungal
community was dominated by Cenococcum (Ascomycota) and
Piloderma (Basidiomycota), while Cortinarius and Amanita made
up most of the community in samples collected from increasingly
drained locations (Fig. 2b).
At the genus level, c. 17% of the variation in fungal taxonomic
composition across samples was captured by the first PCA axis
and tree fine-root density (Fig. 2c; transects contributed an addi-
tional 4%). Most of the variation in fungal community composi-
tion was explained by the environmental changes across the
drainage gradients (PCA axis 1; score =0.98 on CAP1; F=9.60,
P=0.001). On the contrary, tree fine-root density only explained
2% of the total variation (score =0.93 on CAP2) and was not a
robust predictor of fungal taxonomic composition (F=1.57,
P=0.053). Fungal communities in undrained, open locations
(interior) were dominated by ErM genera (ErM and putative
ErM), including Hyaloscypha (Ascomycota), Clavaria (sphagni-
cola; Basidiomycota) and, to a lesser extent, Serendipita (Basidio-
mycota; Fig. 2c), while the EcM community was dominated by
Cenococcum (Ascomycota) and Piloderma (Basidiomycota). At
the tree-dominated end of the drainage gradients (ditch), EcM
genera such as Cortinarius,Lactarius, and Amanita (all Basidio-
mycota) accounted for most of the community. Saprotrophs and
saprotroph/root-associated genera including Mortierella,Umbe-
lopsis, and Mycena tended to be slightly more abundant in
drained, forested locations (Figs 2c,S5).
Consistent with H1, and the aforementioned results, there was
strong evidence that the relative abundance of EcM and ErM
genera was positively and negatively associated with the environ-
mental changes across the drainage gradients (PCA axis 1),
respectively (Fig. 3). For both models, marginal R
2
=0.70,
P<0.001 for PC1, P=0.002 for (PC1)
2
and P=0.879 for
depth. The dominant type of mycorrhizal association shifted
from ErM to EcM at c. 120 m from the ditches (corresponding
to slightly >2 on PCA axis 1; Fig. S6).
Fungal community threshold
The indicator fungal genera had a significant change point at
81 m from the ditches, for the declining genera [fsumz], and
121 m for the increasing genera [fsumz+] (Fig. 4a). Out of the 14
indicator fungal genera, two of the most dominant ErM genera
(ErM and putative ErM), Hyaloscypha and Clavaria (Sphagni-
cola), contributed the most to the threshold for the increasing
genera since their greatest shift in relative abundance occurred at
c. 120 m from the ditches (Fig. 4b). Similarly, the greatest shift
in relative abundance for the EcM genus Cortinarius, and to a les-
ser extent Lactarius, also occurred at or near this distance (small
blue peak on Fig. 4a). Consequently, the threshold in community
structure that occurred at 120 m from the ditches was mostly dri-
ven by mycorrhizal fungi. The free-living saprotrophs Talaro-
myces (Ascomycota), Penicillium (Ascomycota), and the genus
Archaeorhizomyces (Ascomycota) also markedly contributed to
this threshold (Fig. 4b). By contrast, Cenococcum and Piloderma,
two of the dominant EcM genera across the gradients, as well as
the saprotroph/root-associated Mycena, were not identified as
indicator genera.
Fungal functional composition
In support of H2, the degree of peat decomposition (i.e. peat
humification) explained 9% of the variation in class II peroxidase
potential within the sampled fungal community (score =0.87 on
CAP1; F=4.50, P=0.001; Fig. 5a). Fungal communities in
strongly decomposed, sapric peat (with C : N values between 20
and 50) were dominated by Mycena and Cortinarius, which
together represented 16% of the read abundance and had an aver-
age genetic potential of c. 110% (average relative abundance
across samples multiplied by the average number of AA2 genes;
141% for Cortinarius and 78% for Mycena;Fig.5b; Table S1).
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Fig. 2 Fungal community structure across peatland drainage gradients. (a) Relative abundance of fungal phyla and (b) guilds (all and ectomycorrhizal) in
peat samples collected along transects from undrained, open locations to drained, forested locations. Data were aggregated by transects (three transects)
and depths (two depth increments). Only the most abundant ectomycorrhizal genera were included in the inset figure for visualization purposes (11 out of
24 genera for which the sum of the relative abundance values across samples was at least 30%). (c) Plot of fungal genera from a distance-based redun-
dancy analysis of 195 fungal genera in 60 peat samples. Tree root density, tree fine-root density (g cm
3
); PCA axis 1, first axis of the PCA (Fig. 1a). In (b, c),
the ericoid mycorrhizal guild also includes genera classified as putative ericoid mycorrhizal including Oidiodendron,Serendipita, and Clavaria. In (c), the
fungal genera are color-coded by their functional guild and are sized according to their relative abundance averaged across samples.
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The average class II peroxidase potential of fungal communities
in moderately decomposed, hemic peat (with C : N values
between 50 and 80) was eight times lower than that in sapric peat
and was mostly driven by Piloderma (potential of c. 25%), and,
to a lesser extent, Galerina (potential of c. 3%), which jointly
made up c. 12% of the read abundance (Fig. 5b; Table S1). Simi-
lar to findings on taxonomic composition, tree fine-root density
explained only a small portion of the variation in fungal func-
tional composition (2% for class II peroxidase potential;
P=0.011 Fig. 5a).
Discussion
The undrained end of the gradients is dominated by ericoid
mycorrhizal fungi
Farther from the ditches, the above- and belowground domi-
nance of shrubs in the Ericaceae, along with the higher soil C : N,
may largely explain the greater proportion of ErM Ascomycota
relative to Basidiomycota. In particular, the ErM fungal commu-
nity was dominated by the genus Hyaloscypha (Leotiomycetes;
Fig. 2), and mostly by the species H. hepaticicola, which inhabit
the roots of ericaceous shrubs world-wide (Fehrer et al., 2019),
and is common in Sphagnum peatlands (Kennedy et al., 2018;
Lamit et al., 2021). Hyaloscypha species harbor traits related to
Fig. 3 Shift in the dominant type of mycorrhizal association across peatland
drainage gradients. The relative abundance of ectomycorrhizal (green) and
ericoid mycorrhizal (purple) fungal genera in relation to the first axis of the
PCA (PCA axis 1; see Fig. 1a). Note that, for this figure, the relative abundance
was calculated with mycorrhizal genera only, and that the ericoid mycorrhizal
type also includes genera classified as putative ericoid mycorrhizal including
Oidiodendron,Serendipita,andClavaria. For both linear mixed effects models
(quadratic models), marginal R
2
=0.70. Shading associated with the linear
smooths represent 95% confidence intervals. See Supporting Information
Fig. S6 for the relationship between PCA axis 1 and distance from ditch.
Fig. 4 Fungal community threshold detected using genus-level Threshold Indicator Taxa Analysis (TITAN). Only pure (purity ≥0.95) and reliable (reliability
≥0.95) genera were considered (filtered z-scores). Samples were averaged by depth to account for spatial autocorrelations. (a) The upper panel shows the
change points corresponding to increasing [fsumz+, red] and declining genera [fsumz, blue]. Change points are shown as circles with 95th percentile of
their distribution as horizontal lines. The lower panel shows the magnitude of change among increasing and declining genera. Peaks in the values indicate
distances from the ditch(es) at which large amount of change in community composition occur. (b) Change points of indicator fungal genera that contri-
bute to the sum(z) scores (declining genera, top panel, blue curves and increasing genera, bottom panel, red curves). Within each panel, genera change
points are visualized as one or multiple peak(s) representing location(s) of the greatest shift(s) in relative abundance. Ectomycorrhizal and ericoid mycorrhi-
zal genera (including putative ericoid) are shown in green and in purple, respectively.
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stress-tolerance, such as melanized cell walls, slow growth rate,
and long life span, which are commonly associated with harsher
environmental conditions (e.g. nutrient-poor, acidic soils; Teder-
soo et al., 2014; Sterkenburg et al., 2015; Kennedy et al., 2018;
Peltoniemi et al., 2021; Tonjer et al., 2021). Of particular note
are the free-living saprotrophs, which represented only a small
proportion of the broader fungal community in undrained loca-
tions, and were mostly nonligninolytic decomposers such as Mor-
tierella (Mortierellomycota sensu Tedersoo et al., 2018; formerly
Zygomycetes; Figs 2,S5). Several mechanisms may explain their
low abundance in peatlands dominated by Ericaceae. First,
because of their distinct structural and biochemical traits, both
ErM plants and fungi reinforce the nitrogen-limited, acidic envir-
onments created by Sphagnum mosses, under which ErM fungi
are better competitors for soil nutrients than free-living sapro-
trophs (van Breemen, 1995; Bengtsson et al., 2018; Ward
et al., 2022). Second, it was recently proposed that ErM plants
and fungi can form association with Sphagnum mosses, in which
nutrients are internally recycled, which would further impede the
growth of saprotrophs (Shao et al., 2022).
Drainage-induced tree encroachment favors fungal genera
with a greater class II peroxidase potential
Drainage-induced tree encroachment was associated with more
humified peat, where Basidiomycota dominated over ErM Asco-
mycota, and were mainly assigned to genera with a greater class II
peroxidase potential, including Mycena and Cortinarius (Figs 2,
5). The litter basidiomycete Mycena was also recovered from
spruce seedling roots in a previous study across the same
gradients (Hupperts & Lilleskov, 2022). This suggest that
Mycena may exploit different nutritional models in northern
peatlands as previously suggested for arctic and alpine areas
(Thoen et al., 2020; Harder et al., 2021). Although Mycena is
commonly restricted to the uppermost litter layers (Lindahl
et al., 2007; Peltoniemi et al., 2012; Clemmensen et al., 2015), it
appears to extend deeper into the peat in the drained locations
(Fig. S7a), perhaps reflecting a functional shift from litter to
more decayed peat, which may parallel a trophic shift from sapro-
trophy to biotrophy. As such, it may have a strong impact on per-
oxidase activity at greater depth, and on the decomposition of
humified soil organic matter (Kellner et al., 2014;B€odeker
et al., 2016; Kyaschenko et al., 2017a,b).
Interestingly, Cortinarius had a class II peroxidase potential
almost twice as large as that of Mycena (Fig. 5). Since EcM fungi
have access to host-derived photosynthates, they have a competitive
advantage in humified peat because host sugars cover the large
metabolic cost of using oxidative enzymes to mine for organically
bound nutrients, especially nitrogen (Lindahl et al., 2007,2021;
Sterkenburg et al., 2018; Argiroff et al., 2021). By contrast, sapro-
trophs are constrained by both carbon quality and nutrient avail-
ability (Lindahl & Tunlid, 2015). Our findings highlight the key
role that Cortinarius may play in nutrient mobilization from humi-
fied organic matter in drained, forested peatlands, as recently
observed in other ecosystems (Clemmensen et al., 2021; Lindahl
et al., 2021;Pellitier&Zak,2021). However, we acknowledge that
class II peroxidase production is not a general feature of all Corti-
narius species (B€odeker et al., 2014;Lindahlet al., 2021).
Unexpectedly, there was no evidence of a decline in the abun-
dance of Cortinarius with decreasing soil C : N (Figs 2c,5,S7a),
Fig. 5 Distance-based redundancy analysis of class II peroxidase potential within fungal communities in soil samples collected along peatland drainage gra-
dients (based on a sample 9genera matrix of class II peroxidase potential). (a) Plot of samples and (b) plot of genera. Class II peroxidase potential was cal-
culated for 50 out of 195 fungal genera (representing 85% of the read abundance; Supporting Information Table S1). For each genus, the average number
of class II peroxidase genes from publicly available genomes was multiplied by the relative abundance in each sample. Genera with a class II peroxidase
potential equal to zero were included in the analysis. In (a), grey points represent missing soil C : N data and in (b), the fungal genera are color-coded by
their functional guild and are sized according to their class II peroxidase potential averaged across samples. The ericoid mycorrhizal guild also includes gen-
era classified as putative ericoid mycorrhizal including Oidiodendron,Serendipita, and Clavaria. Peat humification was assessed using the von Post scale of
humification; Tree root density, tree fine-root density (g cm
3
). Note the different scales for (a, b).
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unlike in studies over nitrogen deposition gradients (Lilleskov
et al., 2011,2019). In addition, its class II peroxidase potential
tended to increase with soil fertility (Fig. S7b). This suggests that
soil C : N remained high enough (>20) for EcM Basidiomycota
with class II peroxidases and a greater sensitivity to nitrogen
deposition to persist (Sterkenburg et al., 2015; Kyaschenko
et al., 2017b; Argiroff et al., 2021; Pellitier & Zak, 2021).
While assessing the genetic ability of fungal communities to
access specific substrates is critical to understand their contribu-
tion to carbon cycling in peatlands, this approach has limitations.
First, possession of a gene does not necessarily imply that the
gene is expressed or translated, although B€odeker et al.(2014)
revealed a clear link between peroxidase activity and DNA from
Cortinarius species. Second, copy number of a given gene might
not directly predict the magnitude of expression of that gene.
Third, our estimates of class II peroxidase potential are based on
genomes matching only 50 out of the 195 fungal genera in our
study. Although the 50 genera represented 85% of the read abun-
dance, the genetic potential of genera for which no genome was
available might have been underestimated. Nonetheless, our
results provide support for a relationship between peat organic
chemistry and fungal enzyme systems, in which humified peat
with a larger proportion of complex organic compounds
favor oxidative extracellular enzymes (Xu et al., 2021; Xue
et al., 2021).
Existence of a threshold in plant–mycorrhizal associations
The dominant type of mycorrhizal association abruptly shifted
from ErM to EcM at c. 120 m from ditches (Fig. 3). Among the
genera decreasing with distance from ditch, Cortinarius was the
only EcM genus whose shift in relative abundance coincided with
the community threshold, suggesting that Cortinarius was the
most responsive EcM genus to the environmental changes occur-
ring at c. 120 m from the ditches. At this distance, there was no
marked shift in shrub ground cover or tree basal area; rather,
these aboveground variables steadily decreased and increased
across the gradients, respectively (Fig. S4). This suggest that host
plant abundance might not be tightly associated with the sharp
change in the dominant type of mycorrhizal association. By con-
trast, belowground variables, including peat properties, water
table variability, and host plant fine-root density, exhibited a
marked shift at c. 120 m from the ditches (Fig. 1). This distance
corresponded to the onset of peat subsidence and to the ‘ditch
Fig. 6 Conceptual diagram of peatland drainage gradient. The dominant type of mycorrhizal association shifted from ericoid mycorrhiza to ectomycorrhiza
at c. 120 m from the ditches and collocated with the onset of peat subsidence and marked changes in belowground abiotic variables. In the long term, the
decline of slow-growing, melanized ericoid fungi combined with the increase in fungal genera with a relatively higher genetic potential to decay humified
peat may hamper the accumulation of soil organic matter in drained peatlands. Created with BioRender.com.
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effect zone’, where ditches have a detectable effect on peat volume
and carbon loss (Krause et al., 2021). Taken together, our find-
ings suggest that the abrupt shift in plant–mycorrhizal associa-
tions reflected ecological thresholds belowground. However,
experimental manipulations of plant community composition
along with water table variability are necessary to disentangle the
effect of individual variables and directly establish causality.
Nonetheless, postdrainage succession is a slow process and obser-
vations along environmental gradients is required in combination
with manipulative studies to better understand how initial transi-
tional changes affect long-term trajectories of peatland develop-
ment (Laiho, 2006).
The threshold in plant–mycorrhizal associations collocates
with increased peat loss
The dominant type of mycorrhizal association, which shifted
from ErM to EcM at c. 120 m from the ditches, collocated with
the onset of peat subsidence, from which more than half may be
attributed to oxidation (Krause et al., 2021). Indeed, the three
peatlands selected in the present study were included in the study
of Krause et al.(2021), which was aimed to assess the historical
impact of drainage ditches on the peatlands of northern Minne-
sota. Using a model predicting the relative contribution of oxida-
tion to subsidence from years since drainage, Krause et al.(2021)
predicted that approximately half of the peat loss was attributable
to carbon loss via oxidation, while the other half was attributable
to peat compaction.
Although our experimental design does not enable us to
directly assess causality between the fungal community threshold
and peat subsidence, we propose a functional link between the
shift from ErM to EcM dominance and carbon loss via peat oxi-
dation (Fig. 6). In particular, Cortinarius may play a key role
because it was the most abundant EcM genus in drained locations
and the only EcM genus with class II peroxidases whose shift in
relative abundance collocated with the onset of peat subsidence
(Figs 1, 4). Along with a potential role of Cortinarius,Mycena
likely contributed to carbon loss via peat oxidation because it was
the only ligninolytic saprotroph/root-associated genus in increas-
ingly drained areas (Fig. S5), and because saprotrophic Agarico-
mycetes are considered more efficient organic matter decayers
than EcM fungi with peroxidases (Kyaschenko et al., 2017b).
The drained locations in our study are still a net carbon sink
(data not shown); yet, the potential decay of humified peat by
Agaricomycetes Mycena and Cortinarius, and the loss of ErM
plants and fungi may hamper soil organic matter accumulation
in the long term, especially as trees represent a weaker long-term
carbon sink than peat. Furthermore, the by-products of organic
matter decomposition by oxidative enzymes (e.g. quinones
derived from phenol oxidation) serve as important electron
acceptors in anaerobic metabolism (Kellner et al., 2014). In turn,
these compounds may sustain anaerobic respiration and competi-
tively suppress methanogenesis, thereby increasing the release of
CO
2
to the atmosphere while reducing that of CH
4
(Trettin
et al., 2006; Yrjӓlӓet al., 2011; Blodau & Siems, 2012; Kane
et al., 2019).
The drainage gradients stretching from open to forested loca-
tions within acidic peatlands represented a corresponding shift in
belowground fungal communities, from ErM to EcM domi-
nance. Our findings show the interrelated alterations in above-
and belowground vegetation structure, peat properties, and soil
fungal communities that can occur when drainage induces
encroachment by trees in northern peatlands. Although experi-
mental manipulations are needed to assess causality between these
alterations and peat carbon loss, our results suggest a key role of
Mycena and of the ectomycorrhizal genus Cortinarius, as recently
highlighted in other ecosystems. We identified a threshold in
plant–mycorrhizal associations where a shift in peatland ecosys-
tem state occurs, potentially decreasing belowground sink
strength for CO
2
in drained peatlands. Although the relative
importance of increased saprotrophic decomposition vs ectomy-
corrhizal fungal decay under peatland drainage has yet to be
determined, the spatial link between drainage, increased Corti-
narius abundance, and stimulated decomposition is striking, jus-
tifying continued investigation of this novel decay mechanism in
peatland carbon cycling.
Acknowledgements
Funding for this research was provided by NSF DEB Award no.
2031076 to ESK, RKK, RAC and EAL, NSF DEB Award no.
2031085 to JKK and in-kind support from the USDA Forest
Service, Northern Research Station. We thank Stefan Hupperts,
Madeline Peterson, Julia Stuart, and Max Wegner for valuable
laboratory and field support. We also gratefully acknowledge
Francis Martin for valuable insights and authorization to use the
genome of P. sphaerosporum. Thanks to the Journal’s Editor and
reviewers whose comments greatly improved this manuscript.
Competing interests
None declared.
Author contributions
ESK, RKK, RAC, JKK and EAL designed the study. CLT imple-
mented the gradient treatments and environmental sampling.
CED collected, processed, and analyzed fungal community data
and wrote the manuscript with contributions from JAMM, CLT,
LJL and EAL.
ORCID
Rodney A. Chimner https://orcid.org/0000-0001-6515-851X
Camille E. Defrenne https://orcid.org/0000-0003-2767-4892
Evan S. Kane https://orcid.org/0000-0003-1665-0596
Jason K. Keller https://orcid.org/0000-0002-8879-4022
Randall K. Kolka https://orcid.org/0000-0002-6419-8218
Louis J. Lamit https://orcid.org/0000-0002-0385-6010
Erik A. Lilleskov https://orcid.org/0000-0002-9208-1631
Jessica A. M. Moore https://orcid.org/0000-0002-5387-0662
Colin L. Tucker https://orcid.org/0000-0003-2679-5211
Ó2023 The Authors
New Phytologist Ó2023 New Phytologist Foundation
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Data availability
The sequence data have been submitted to the National Center
for Biotechnology Information (NCBI) Sequence Read Archive
under accession no. PRJNA923675 (released on 2023-04-01).
Environmental data are available through Pangea (environmental
variables measured across peatland drainage gradients in Minne-
sota, the United States).
References
Abarenkov K, Zirk A, Piirmann T, P€oh€onen R, Ivanov F, Nilsson H, K~oljalg U.
2021. UNITE QIIME release for eukaryotes. UNITE Community. doi: 10.
15156/BIO/1264819.
Adamczyk B, Sieti€o O, Biasi C, Heinonsalo J. 2019. Interaction between tannins
and fungal necromass stabilizes fungal residues in boreal forest soils. New
Phytologist 223:16–21.
Andersen R, Chapman SJ, Artz RRE. 2013. Microbial communities in natural
and disturbed peatlands: a review. Soil Biology and Biochemistry 57: 979–994.
Argiroff WA, Zak DR, Pellitier PT, Upchurch RA, Belke JP. 2021. Decay by
ectomycorrhizal fungi couples soil organic matter to nitrogen availability.
Ecology Letters 25: 391–404.
Baker ME, King RS. 2010. A new method for detecting and interpreting
biodiversity and ecological community thresholds. Methods in Ecology and
Evolution 1:25–37.
Bengtsson F, Rydin H, Hajek T. 2018. Biochemical determinants of litter
quality in 15 species of Sphagnum. Plant and Soil 425: 161–176.
Beule L, Karlovsky P. 2020. Improved normalization of species count data in
ecology by scaling with ranked subsampling (SRS): application to microbial
communities. PeerJ 8: e9593.
Birkebak JM, Mayor JR, Ryberg KM, Matheny PB. 2013. A systematic,
morphological and ecological overview of the Clavariaceae (Agaricales).
Mycologia 105: 896–911.
Blodau C, Siems M. 2012. Drainage-induced forest growth alters belowground
carbon biogeochemistry in the Mer Bleue bog, Canada. Biogeochemistry 107:
107–123.
B€odeker ITM, Clemmensen KE, de Boer W, Martin F, Olson

A, Lindahl BD.
2014. Ectomycorrhizal Cortinarius species participate in enzymatic oxidation
of humus in northern forest ecosystems. New Phytologist 203: 245–256.
B€odeker ITM, Lindahl BD, Olson

A, Clemmensen KE. 2016. Mycorrhizal and
saprotrophic fungal guilds compete for the same organic substrates but affect
decomposition differently. Functional Ecology 30: 1967–1978.
B€odeker ITM, Nygren CMR, Taylor AFS, Olson

A, Lindahl BD. 2009. ClassII
peroxidase-encoding genes are present in a phylogenetically wide range of
ectomycorrhizal fungi. The ISME Journal 3: 1387–1395.
Bolyen E, Rideout JR, Dillon MR, Bokulich NA, Abnet CC, Al-Ghalith GA,
Alexander H, Alm EJ, Arumugam M, Asnicar F et al. 2019. Reproducible,
interactive, scalable and extensible microbiome data science using QIIME 2.
Nature Biotechnology 37: 852–857.
Bragazza L, Freeman C. 2007. High nitrogen availability reduces polyphenol
content in Sphagnum peat. Science of the Total Environment 377: 439–443.
van Breemen N. 1995. How, Sphagnumbogs down other plants. Trends in
Ecology & Evolution 10: 270–275.
Callahan BJ, McMurdie PJ, Rosen MJ, Han AW, Johnson AJA, Holmes SP.
2016. DADA2: high-resolution sample inference from Illumina amplicon data.
Nature Methods 13: 581–583.
Chimner RA, Pypker TG, Hribljan JA, Moore PA, Waddington JM. 2017.
Multi-decadal changes in water table levels alter peatland carbon cycling.
Ecosystems 20: 1042–1057.
Clemmensen KE, Durling MB, Michelsen A, Hallin S, Finlay RD, Lindahl BD.
2021. A tipping point in carbon storage when forest expands into tundra is
related to mycorrhizal recycling of nitrogen. Ecology Letters 24: 1193–1204.
Clemmensen KE, Finlay RD, Dahlberg A, Stenlid J, Wardle DA, Lindahl BD.
2015. Carbon sequestration is related to mycorrhizal fungal community shifts
during long-term succession in boreal forests. New Phytologist 205: 1525–1536.
Dorrepaal E, Cornelissen JHC, Aerts R, Wallen B, Van Logtestijn RSP. 2005.
Are growth forms consistent predictors of leaf litter quality and
decomposability across peatlands along a latitudinal gradient? Journal of Ecology
93: 817–828.
Fanin N, Clemmensen KE, Lindahl BD, Farrell M, Nilsson M, Gundale MJ,
Kardol P, Wardle DA. 2022. Ericoid shrubs shape fungal communities and
suppress organic matter decomposition in boreal forests. New Phytologist 236:
684–697.
Fehrer J, Reblova M, Bambasova V, Vohnık M. 2019. The root-symbiotic
Rhizoscyphus ericae aggregate and Hyaloscypha (Leotiomycetes) are
congeneric: phylogenetic and experimental evidence. Studies in Mycology
92: 195–225.
Fenner N, Freeman C. 2020. Woody litter protects peat carbon stocks during
drought. Nature Climate Change 10: 363–369.
Fernandez CW, Heckman K, Kolka R, Kennedy PG. 2019. Melanin mitigates
the accelerated decay of mycorrhizal necromass with peatland warming. Ecology
Letters 22: 498–505.
Fernandez CW, See CR, Kennedy PG. 2020. Decelerated carbon cycling by
ectomycorrhizal fungi is controlled by substrate quality and community
composition. New Phytologist 226: 569–582.
Flores-Moreno H, Treseder KK, Cornwell WK, Maynard DS, Milo AM,
Abarenkov K, Afkhami ME, Aguilar-Trigueros CA, Bates S, Bhatnagar JM
et al. 2019. fungaltraits aka funfun: a dynamic functional trait database for the
world’s fungi. Zenodo. doi: 10.5281/zenodo.1216257. [WWW Document]
URL https://github.com/traitecoevo/fungaltraits [accessed 8 December 2022].
Floudas D, Bentzer J, Ahren D, Johansson T, Persson P, Tunlid A. 2020.
Uncovering the hidden diversity of litter-decomposition mechanisms in
mushroom-forming fungi. The ISME Journal 14: 2046–2059.
Fluet-Chouinard E, Stocker BD, Zhang Z, Malhotra A, Melton JR, Poulter B,
Kaplan JO, Goldewijk KK, Siebert S, Minayeva T et al. 2023. Extensive
global wetland loss over the past three centuries. Nature 614: 281–286.
Greifswald Mire Centre. 2019. Global peatland database. [WWW document]
URL https://greifswaldmoor.de/global-peatland-database-en.html [accessed 8
July 2022].
Harder CB, Hesling E, Botnen SS, Dima B, von Bonsdorff-Salminen T,
Niskanen T, Jarvis SG, Lorberau KE, Ouimette A, Hester A et al. 2021.
Mycena species can be opportunist-generalist plant root invaders. BioRxiv. doi:
10.1101/2021.03.23.436563.
Harris LI, Roulet NT, Moore TR. 2020. Drainage reduces the resilience of a
boreal peatland. Environmental Research Communications 2: 065001.
Heijmans MMPD, van der Knaap YAM, Holmgren M, Limpens J. 2013.
Persistent versus transient tree encroachment of temperate peat bogs: effects of
climate warming and drought events. Global Change Biology 19: 2240–2250.
Hermans R, McKenzie R, Andersen R, Teh YA, Cowie N, Subke J-A. 2022. Net
soil carbon balance in afforested peatlands and separating autotrophic and
heterotrophic soil CO
2
effluxes. Biogeosciences 19: 313–327.
Hewitt RE, Alexander HD, Miller SN, Mack MC. 2022. Root-associated fungi
not tree density influences stand nitrogen dynamics at the larch forest–tundra
ecotone. Journal of Ecology 110: 1419–1431.
Holmgren M, Lin C-Y, Murillo JE, Nieuwenhuis A, Penninkhof J, Sanders N,
van Bart T, van Veen H, Vasander H, Vollebregt ME et al. 2015. Positive
shrub-tree interactions facilitate woody encroachment in boreal peatlands.
Journal of Ecology 103:58–66.
Hommeltenberg J, Schmid HP, Dr€osler M, Werle P. 2014. Can a bog drained
for forestry be a stronger carbon sink than a natural bog forest? Biogeosciences
11: 3477–3493.
Hupperts SF, Lilleskov EA. 2022. Predictors of taxonomic and functional
composition of black spruce seedling ectomycorrhizal fungal communities
along peatland drainage gradients. Mycorrhiza 32:67–81.
Jaatinen K, Laiho R, Vuorenmaa A, del Castillo U, Minkkinen K, Pennanen T,
Penttil€a T, Fritze H. 2008. Responses of aerobic microbial communities and
soil respiration to water-level drawdown in a northern boreal fen.
Environmental Microbiology 10: 339–353.
Janusz G, Pawlik A, Sulej J,

Swiderska-Burek U, Jarosz-Wilkołazka A,
Paszczynski A. 2017. Lignin degradation: microorganisms, enzymes
involved, genomes analysis and evolution. FEMS Microbiology Reviews 41:
941–962.
New Phytologist (2023)
www.newphytologist.com
Ó2023 The Authors
New Phytologist Ó2023 New Phytologist Foundation
Research
New
Phytologist
12
14698137, 0, Downloaded from https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.18954 by Michigan Tech University, Wiley Online Library on [07/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

Joanisse GD, Bradley RL, Preston CM, Bending GD. 2009. Sequestration of
soil nitrogen as tannin–protein complexes may improve the competitive ability
of sheep laurel (Kalmia angustifolia) relative to black spruce (Picea mariana).
New Phytologist 181: 187–198.
Kane ES, Veverica TJ, Tfaily MM, Lilleskov EA, Meingast KM, Kolka RK,
Daniels AL, Chimner RA. 2019. Reduction-oxidation potential and dissolved
organic matter composition in northern peat soil: interactive controls of water
table position and plant functional groups. Journal of Geophysical Research:
Biogeosciences 124: 3600–3617.
Kellner H, Luis P, Pecyna MJ, Barbi F, Kapturska D, Kr€uger D, Zak DR,
Marmeisse R, Vandenbol M, Hofrichter M. 2014. Widespread occurrence of
expressed fungal secretory peroxidases in forest soils. PLoS ONE 9: e95557.
Kennedy PG, Mielke LA, Nguyen NH. 2018. Ecological responses to forest age,
habitat, and host vary by mycorrhizal type in boreal peatlands. Mycorrhiza 28:
315–328.
Kitson E, Bell NGA. 2020. The response of microbial communities to peatland
drainage and rewetting: a review. Frontiers in Microbiology 11: 582812.
Klein K, Schellekens J, Grob-Schm€olders M, von Sengbusch P, Alewell C,
Leifeld J. 2022. Characterizing ecosystem-driven chemical composition
differences in natural and drained Finnish bogs using pyrolysis-GC/MS.
Organic Geochemistry 165: 104351.
Kohler A, Kuo A, Nagy LG, Morin E, Barry KW, Buscot F, Canb€ack B, Choi
C, Cichocki N, Clum A et al. 2015. Convergent losses of decay mechanisms
and rapid turnover of symbiosis genes in mycorrhizal mutualists. Nature
Genetics 47: 404–415.
Koide RT, Fernandez C, Malcolm G. 2014. Determining place and process:
functional traits of ectomycorrhizal fungi that affect both community structure
and ecosystem function. New Phytologist 201: 433–439.
Kokkonen N, Laine AM, M€annist€o E, Meht€atalo L, Korrensalo A, Tuittila E-S.
2022. Two mechanisms drive changes in boreal peatland photosynthesis
following long-term water level drawdown: species turnover and altered
photosynthetic capacity. Ecosystems 25: 1601–1618.
Krause L, McCulloughKJ, Kane ES, Kolka RK, Chimner RA, Lilleskov EA. 2021.
Impacts of historical ditching on peat volume and carbon in northern Minnesota
USA peatlands. Journal of Environmental Management 296:113090.
Kyaschenko J, Clemmensen KE, Hagenbo A, Karltun E, Lindahl BD. 2017a.
Shift in fungal communities and associated enzyme activities along an age
gradient of managed Pinus sylvestris stands. The ISME Journal 11: 863–874.
Kyaschenko J, Clemmensen KE, Karltun E, Lindahl BD. 2017b. Below-ground
organic matter accumulation along a boreal forest fertility gradient relates to
guild interaction within fungal communities. Ecology Letters 20: 1546–1555.
Laiho R. 2006. Decomposition in peatlands: reconciling seemingly contrasting
results on the impacts of lowered water levels. Soil Biology and Biochemistry 38:
2011–2024.
Lamit LJ, Romanowicz KJ, Potvin LR, Lennon JT, Tringe SG, Chimner RA,
Kolka RK, Kane ES, Lilleskov EA. 2021. Peatland microbial community
responses to plant functional group and drought are depth-dependent.
Molecular Ecology 30: 5119–5136.
Li J, Zhao L, Li M, Min Y, Zhan F, Wang Y, Sheng L, Bian H. 2022. Changes
in soil dissolved organic matter optical properties during peatland succession.
Ecological Indicators 143: 109386.
Lilleskov EA, Hobbie EA, Horton TR. 2011. Conservation of ectomycorrhizal
fungi: exploring the linkages between functional and taxonomic responses to
anthropogenic N deposition. Fungal Ecology 4: 174–183.
Lilleskov EA, Kuyper TW, Bidartondo MI, Hobbie EA. 2019. Atmospheric
nitrogen deposition impacts on the structure and function of forest mycorrhizal
communities: a review. Environmental Pollution 246: 148–162.
Lindahl BD, Ihrmark K, Boberg J, Trumbore SE, H€ogberg P, Stenlid J, Finlay
RD. 2007. Spatial separation of litter decomposition and mycorrhizal nitrogen
uptake in a boreal forest. New Phytologist 173: 611–620.
Lindahl BD, Kyaschenko J, Varenius K, Clemmensen KE, Dahlberg A, Karltun
E, Stendahl J. 2021. A group of ectomycorrhizal fungi restricts organic matter
accumulation in boreal forest. Ecology Letters 24: 1341–1351.
Lindahl BD, Tunlid A. 2015. Ectomycorrhizal fungi–Potential organic matter
decomposers, yet not saprotrophs. New Phytologist 205: 1443–1447.
L~ohmus A, Remm L, Rannap R. 2015. Just a ditch in forest? Reconsidering draining
in the context of sustainable forest management. Bioscience 65: 1066–1076.
Ma L, Zhu G, Chen B, Zhang K, Niu S, Wang J, Ciais P, Zuo H. 2022. A
globally robust relationship between water table decline, subsidence rate, and
carbon release from peatlands. Communications Earth & Environment 3: 254.
Martino E, Morin E, Grelet G-A, Kuo A, Kohler A, Daghino S, Barry KW,
Cichocki N, Clum A, Dockter RB et al. 2018. Comparative genomics and
transcriptomics depict ericoid mycorrhizal fungi as versatile saprotrophs and
plant mutualists. New Phytologist 217: 1213–1229.
McMurdie PJ, Holmes S. 2013. PHYLOSEQ: an R package for reproducible
interactive analysis and graphics of microbiome census data. PLoS ONE 8:
e61217.
Minkkinen K, Ojanen P, Penttil€a T, Aurela M, Laurila T, Tuovinen J-P, Lohila
A. 2018. Persistent carbon sink at a boreal drained bog forest. Biogeosciences 15:
3603–3624.
Nagy LG, Riley R, Tritt A, Adam C, Daum C, Floudas D, Sun H, Yadav JS,
Pangilinan J, Larsson K-H et al. 2016. Comparative genomics of early-
diverging mushroom-forming fungi provides insights into the origins of
lignocellulose decay capabilities. Molecular Biology and Evolution 33: 959–970.
Nguyen NH, Smith D, Peay K, Kennedy P. 2015. Parsing ecological signal from
noise in next generation amplicon sequencing. New Phytologist 205: 1389–1393.
Nicolas C, Martin-Bertelsen T, Floudas D, Bentzer J, Smits M, Johansson T,
Troein C, Persson P, Tunlid A. 2019. The soil organic matter decomposition
mechanisms in ectomycorrhizal fungi are tuned for liberating soil organic
nitrogen. The ISME Journal 13: 977–988.
Normand AE, Turner BL, Lamit LJ, Smith AN, Baiser B, Clark MW, Hazlett
C, Kane ES, Lilleskov E, Long JR et al. 2021. Organic matter chemistry drives
carbon dioxide production of peatlands. Geophysical Research Letters 48:
e2021GL093392.
Ohlson M, Økland RH, Nordbakken J-F, Dahlberg B. 2001. Fatal interactions
between Scots pine and Sphagnum mosses in bog ecosystems. Oikos 94: 425–432.
Olariaga I, Salcedo I, Dani€els PP, Spooner B, Kautmanova I. 2015. Taxonomy
and phylogeny of yellow Clavaria species with clamped basidia–Clavaria
flavostellifera sp. Nov. and the typification of C. Argillacea,C. Flavipes and C.
Sphagnicola.Mycologia 107: 104–122.
Pauvert C, Buee M, Laval V, Edel-Hermann V, Fauchery L, Gautier A, Lesur I,
Vallance J, Vacher C. 2019. Bioinformatics matters: the accuracy of plant and
soil fungal community data is highly dependent on the metabarcoding pipeline.
Fungal Ecology 41:23–33.
Pellerin S, Lavoie C. 2003. Reconstructing the recent dynamics of mires using a
multitechnique approach. Journal of Ecology 91: 1008–1021.
Pellitier PT, Zak DR. 2021. Ectomycorrhizal fungal decay traits along a soil
nitrogen gradient. New Phytologist 232: 2152–2164.
Peltoniemi K, Adamczyk S, Fritze H, Minkkinen K, Pennanen T, Penttil€aT,
Sarjala T, Laiho R. 2021. Site fertility and soil water-table level affect fungal
biomass production and community composition in boreal peatland forests.
Environmental Microbiology 23: 5733–5749.
Peltoniemi K, StrakovaP,FritzeH,Ira izoz PA, Pennanen T, Laiho R. 2012. How
water-level drawdown modifies litter-decomposing fungal and actinobacterial
communities in boreal peatlands. Soil Biology and Biochemistry 51:20–34.
P~olme S, Abarenkov K, Henrik Nilsson R, Lindahl BD, Clemmensen KE,
Kauserud H, Nguyen N, Kjøller R, Bates ST, Baldrian P et al. 2020.
FungalTraits: a user-friendly traits database of fungi and fungus-like
stramenopiles. Fungal Diversity 105:1–16.
von Post L. 1924. Das genetische System der organogenen Bildungen Schwedens.
International Committee of Soil Science: 287–304.
R Core Team. 2022. R: a language and environment for statistical computing.
Vienna, Austria: R Foundation for Statistical Computing. [WWW document]
URL https://www.R-project.org/
Ritson JP, Alderson DM, Robinson CH, Burkitt AE, Heinemeyer A, Stimson AG,
Gallego-Sala A, Harris A, Quillet A, Malik AA et al.2021.Towards a microbial
process-based understanding of the resilience of peatland ecosystem service
provisioning –aresearchagenda.Science of the Total Environment 759: 143467.
Ruiz-Due~nas FJ, Barrasa JM, Sanchez-Garcıa M, Camarero S, Miyauchi S,
Serrano A, Linde D, Babiker R, Drula E, Ayuso-Fernandez I et al. 2021.
Genomic analysis enlightens agaricales lifestyle evolution and increasing
peroxidase diversity. Molecular Biology and Evolution 38: 1428–1446.
Shah F, Nicolas C, Bentzer J, Ellstr€
om M, Smits M, Rineau F, Canb€ack B,
Floudas D, Carleer R, Lackner G et al. 2016. Ectomycorrhizal fungi
Ó2023 The Authors
New Phytologist Ó2023 New Phytologist Foundation
New Phytologist (2023)
www.newphytologist.com
New
Phytologist Research 13
14698137, 0, Downloaded from https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.18954 by Michigan Tech University, Wiley Online Library on [07/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

decompose soil organic matter using oxidative mechanisms adapted from
saprotrophic ancestors. New Phytologist 209: 1705–1719.
Shao S, Wu J, He H, Moore TR, Bubier J, Larmola T, Juutinen S, Roulet NT.
2022. Ericoid mycorrhizal fungi mediate the response of ombrotrophic
peatlands to fertilization: a modeling study. New Phytologist 238:80–95.
Shi F-X, Chen H-M, Wang X-W, Mao R. 2022. Alder encroachment alters
subsoil organic carbon pool and chemical structure in a boreal peatland of
Northeast China. Science of the Total Environment 850: 157849.
Simola H, Pitk€anen A, Turunen J. 2012. Carbon loss in drained forestry
peatlands in Finland, estimated by re-sampling peatlands surveyed in the
1980s. European Journal of Soil Science 63: 798–807.
Simpson GL. 2022. PERMUTE: functions for generating restricted permutations of
data. R package v.0.9-7. [WWW document] URL https://CRAN.R-project.
org/package=permute [accessed 8 June 2022].
Sterkenburg E, Bahr A, Brandstr€om Durling M, Clemmensen KE, Lindahl BD.
2015. Changes in fungal communities along a boreal forest soil fertility
gradient. New Phytologist 207: 1145–1158.
Sterkenburg E, Clemmensen KE, Ekblad A, Finlay RD, Lindahl BD. 2018.
Contrasting effects of ectomycorrhizal fungi on early and late stage
decomposition in a boreal forest. The ISME Journal 12: 2187–2197.
Straker CJ. 1996. Ericoid mycorrhiza: ecological and host specificity. Mycorrhiza
6: 215–225.
Strakova P, Penttil€a T, Laine J, Laiho R. 2012. Disentangling direct and indirect
effects of water table drawdown on above- and belowground plant litter
decomposition: consequences for accumulation of organic matter in boreal
peatlands. Global Change Biology 18: 322–335.
Talbot J, Richard PJH, Roulet NT, Booth RK. 2010. Assessing long-term
hydrological and ecological responses to drainage in a raised bog using
paleoecology and a hydrosequence. Journal of Vegetation Science 21: 143–156.
Taylor DL, Walters WA, Lennon NJ, Bochicchio J, Krohn A, Caporaso JG,
Pennanen T. 2016. Accurate estimation of fungal diversity and abundance
through improved lineage-specific primers optimized for illumina amplicon
sequencing. Applied and Environmental Microbiology 82: 7217–7226.
Tedersoo L, Bahram M, P~olme S, K~oljalg U, Yorou NS, Wijesundera R, Ruiz
LV, Vasco-Palacios AM, Thu PQ, Suija A et al. 2014. Global diversity and
geography of soil fungi. Science 346: 1256688.
Tedersoo L, Sanchez-Ramırez S, K~oljalg U, Bahram M, D€oring M, Schigel D,
May T, Ryberg M, Abarenkov K. 2018. High-level classification of the fungi
and a tool for evolutionary ecological analyses. Fungal Diversity 90: 135–159.
Thoen E, Harder CB, Kauserud H, Botnen SS, Vik U, Taylor AFS, Menkis A,
Skrede I. 2020. In vitro evidence of root colonization suggests ecological
versatility in the genus Mycena.New Phytologist 227: 601–612.
Tonjer L, Thoen E, Morgado L, Botnen S, Mundra S, Nybakken L, Bryn A,
Kauserud H. 2021. Fungal community dynamics across a forest–alpine
ecotone. Molecular Ecology 30: 4926–4938.
Trettin CC, Laiho R, Minkkinen K, Laine J. 2006. Influence of climate change
factors on carbon dynamics in northern forested peatlands. Canadian Journal of
Soil Science 86: 269–280.
Turetsky MR, Benscoter B, Page S, Rein G, van der Werf GR, Watts A. 2015.
Global vulnerability of peatlands to fire and carbon loss. Nature Geoscience 8:
11–14.
Uhelski DM, Kane ES, Chimner RA. 2022. Plant functional types drive Peat
Quality differences. Wetlands 42: 51.
UrbanovaZ,Barta J. 2016. Effects of long-term drainage on microbial
community composition vary between peatland types. Soil Biology and
Biochemistry 92:16–26.
Vohnık M, Fendrych M, Kolarık M, Gryndler M, Hrselova H, AlbrechtovaJ,
Vosatka M. 2007. The ascomycete Meliniomyces variabilis isolated from a
sporocarp of Hydnotrya tulasnei (Pezizales) intracellularly colonises roots of
ecto- and ericoid mycorrhizal host plants. Czech Mycology 59: 215–226.
Wang H, Tian J, Chen H, Ho M, Vilgalys R, Bu Z-J, Liu X, Richardson CJ.
2021. Vegetation and microbes interact to preserve carbon in many wooded
peatlands. Communications Earth & Environment 2: 67.
Wang T, Persson P, Tunlid A. 2021. A widespread mechanism in
ectomycorrhizal fungi to access nitrogen from mineral-associated proteins.
Environmental Microbiology 23: 5837–5849.
Ward EB, Duguid MC, Kuebbing SE, Lendemer JC, Bradford MA. 2022. The
functional role of ericoid mycorrhizal plants and fungi on carbon and nitrogen
dynamics in forests. New Phytologist 235: 1701–1718.
Weiß M, Waller F, Zuccaro A, Selosse M. 2016. Sebacinales –one thousand and
one interactions with land plants. New Phytologist 211:20–40.
Wiedermann MM, Kane ES, Potvin LR, Lilleskov EA. 2017. Interactive plant
functional group and water table effects on decomposition and extracellular
enzyme activity in Sphagnum peatlands. Soil Biology and Biochemistry 108:1–8.
Xu Z, Wang S, Wang Z, Dong Y, Zhang Y, Liu S, Li J. 2021. Effect of drainage
on microbial enzyme activities and communities dependent on depth in
peatland soil. Biogeochemistry 155: 323–341.
Xue D, Liu T, Chen H, Liu J, Hu J, Liu L. 2021. Fungi are more sensitive than
bacteria to drainage in the peatlands of the Zoige Plateau. Ecological Indicators
124: 107367.
Yrj€
al€
aK, Tuomivirta T, Juottonen H, Putkinen A, Lappi K, Tuittila E-S,
Penttil€
aT, Minkkinen K, Laine J, Peltoniemi K et al. 2011. CH
4
production
and oxidation processes in a boreal fen ecosystem after long-term water table
drawdown. Global Change Biology 17: 1311–1320.
Supporting Information
Additional Supporting Information may be found online in the
Supporting Information section at the end of the article.
Fig. S1 Transect locations in three peatlands in Minnesota, the
United States.
Fig. S2 Variance and average of the water table depth in relation
to distance from ditch.
Fig. S3 Relationship between distance from ditch and vascular
plant fine-root density.
Fig. S4 Relationships between environmental variables.
Fig. S5 Relative abundance of saprotroph and saprotroph/root-
associated genera.
Fig. S6 Relationship between distance from ditch and PCA axis 1.
Fig. S7 Linkages between ectomycorrhizal fungi and soil C : N.
Methods S1 Environmental data collection.
Methods S2 Detailed PCR protocol.
Table S1 Fungal genera in peat samples collected along peatland
drainage gradients.
Table S2 Principal component analysis of environmental
variables.
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