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Ectomycorrhizal fungi are shared between seedlings and adults in a monodominant Gilbertiodendron dewevrei rain forest in Cameroon

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Ectomycorrhizal networks may facilitate the establishment and survival of seedlings regenerating under the canopies of tropical forests and are often invoked as a potential contributor to monodominance. We identified ectomycorrhizal fungi in a monodominant Gilbertiodendron dewevrei (Fabaceae) rain forest in Cameroon, using sporocarps and ectomycorrhizae of three age categories (seedlings, intermediate trees, and large trees) and tentatively revealed nutrient transfer through ectomycorrhizal networks by measuring spontaneous isotopic (¹³C and ¹⁵N) abundances in seedlings. Sporocarp surveys revealed fewer ectomycorrhizal fungal taxa (59 species from 1030 sporocarps) than molecular barcoding of ectomycorrhizal roots (75 operational taxonomic units from 828 ectomycorrhizae). Our observations suggest that ectomycorrhizal fungal diversity is similar to that in other mixed tropical forests and provide the first report of the Tuber-Helvella lineage in a tropical forest. Despite some differences, all age categories of G. dewevrei had overlapping ectomycorrhizal fungal communities, with families belonging to Thelephoraceae, Russulaceae, Sebacinaceae, Boletaceae, and Clavulinaceae. Of the 49 operational taxonomic units shared by the three age categories (65.3% of the ectomycorrhizal fungal community), 19 were the most abundant on root tips of all categories (38.7% of the shared taxa), supporting the likelihood of ectomycorrhizal networks. However, we obtained no evidence for nutrient transfer from trees to seedlings. We discuss the composition of the ectomycorrhizal fungal community among the G. dewevrei age categories and the possible role of common ectomycorrhizal networks in this rain forest.
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Ectomycorrhizal fungi are shared between seedlings and adults in a monodominant
Gilbertiodendron dewevrei rain forest in Cameroon
Helvyne C. Micha
ella Ebenye
1,2,3,4,5,6,
*, Adrien Taudi
ere
3
, Nogaye Niang
1
, Cheikh Ndiaye
1
, Mathieu Sauve
3
,N
er
ee Onguene Awana
7
,
Mieke Verbeken
8
, Andr
e De Kesel
9
, Seynabou S
ene
1
, Abdala G. Di
edhiou
1
, Violette Sarda
3
, Omar Sadio
10
,Ma
ımouna Cissoko
1
,
Ibrahima Ndoye
1
, Marc-Andr
e Selosse
2,4,
*,and Amadou M. B^
a
5,6,11
*
1
Laboratoire Commun de Microbiologie, IRD/UCAD/ISRA, BP 1386 Dakar, S
en
egal
2
Institut de Syst
ematique,
Evolution, Biodiversit
e (ISYEB UMR 7205 CNRS MNHN, UPMC, EPHE), Mus
eum national d’Histoire naturelle,
Sorbonne Universit
es, 57 rue Cuvier, CP50, 75005 Paris, France
3
UMR 5175, CEFE CNRS Universit
e de Montpellier Universit
e Paul Val
ery Montpellier EPHE, Montpellier, France
4
Department of Plant Taxonomy and Nature Conservation, University of Gdansk, Wita Stwosza 59, 80-308 Gdansk, Poland
5
Laboratoire des Symbioses Tropicales et M
editerran
eennes, UMR113- INRA/AGRO-M/CIRAD/IRD/UM2-TA10/J, Campus International de
Baillarguet, 34398 Montpellier Cedex 5, France
6
Laboratoire de Biologie et Physiologie V
eg
etales, Facult
e des Sciences Exactes et Naturelles, Universit
e des Antilles, BP 592, 97159
Pointe-
a-Pitre, Guadeloupe, France
7
Soil, Water and Atmosphere Department, Institute of Agriculture Research for Development, BP. 2123 Yaound
e, Cameroon
8
Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium
9
Botanic Garden Meise, Nieuwelaan 38, BE-1860 Meise, Belgium
10
IRD, UMR 195 LEMAR (UBO/CNRS/IRD/Ifremer), BP 1386, CP 18524 Dakar, S
en
egal
ABSTRACT
Ectomycorrhizal networks may facilitate the establishment and survival of seedlings regenerating under the canopies of tropical forests
and are often invoked as a potential contributor to monodominance. We identied ectomycorrhizal fungi in a monodominant Gilbertio-
dendron dewevrei (Fabaceae) rain forest in Cameroon, using sporocarps and ectomycorrhizae of three age categories (seedlings, intermedi-
ate trees, and large trees) and tentatively revealed nutrient transfer through ectomycorrhizal networks by measuring spontaneous isotopic
(
13
C and
15
N) abundances in seedlings. Sporocarp surveys revealed fewer ectomycorrhizal fungal taxa (59 species from 1030 sporocarps)
than molecular barcoding of ectomycorrhizal roots (75 operational taxonomic units from 828 ectomycorrhizae). Our observations sug-
gest that ectomycorrhizal fungal diversity is similar to that in other mixed tropical forests and provide the rst report of the Tuber-Hel-
vella lineage in a tropical forest. Despite some differences, all age categories of G. dewevrei had overlapping ectomycorrhizal fungal
communities, with families belonging to Thelephoraceae, Russulaceae, Sebacinaceae, Boletaceae, and Clavulinaceae. Of the 49 operational
taxonomic units shared by the three age categories (65.3% of the ectomycorrhizal fungal community), 19 were the most abundant on
root tips of all categories (38.7% of the shared taxa), supporting the likelihood of ectomycorrhizal networks. However, we obtained no
evidence for nutrient transfer from trees to seedlings. We discuss the composition of the ectomycorrhizal fungal community among the
G. dewevrei age categories and the possible role of common ectomycorrhizal networks in this rain forest.
Abstract in French is available with online material.
Key words:
13
C;
15
N; Caesalpinioideae; common ectomycorrhizal network; ectomycorrhiza; Fabaceae subfamily; internal transcribed spacer; sporocarps.
MANY TREES FORM ECTOMYCORRHIZAL SYMBIOSES WITH DIVERSE
BASIDIOMYCOTA AND ASCOMYCOTA, which play a key role in many
tropical forests (B^aet al. 2012), affecting tree growth and nutrient
absorption as well as protection against pathogens. These associa-
tions also produce sporocarps of ectomycorrhizal (EM) fungi,
many of which are of economic interest (Yun & Hall 2004). Most
known EM tree species are found in temperate and boreal
regions (Smith & Read 2008, Van Der Heijden et al. 2015).
Despite recently increasing interest (B^aet al. 2012), tropical EM
associations are poorly understood, particularly in monodominant
forests.
Monodominant forests are large stands in which a single tree
species comprises more than 60 percent of canopy-level trees
(Torti & Coley 1999, McGuire 2007). Factors that create and
maintain monodominant forests within a matrix of otherwise
high-diversity tropical rain forests remain unexplained (Peh et al.
Received 22 February 2016; revision accepted 25 July 2016.
*These authors equally contributed to this work.
11
Corresponding author; e-mail: amadou.ba@ird.fr
ª2016 The Association for Tropical Biology and Conservation 1
BIOTROPICA 0(0): 1–12 2016 10.1111/btp.12415
2011). The observation that monodominant forests typically con-
tain ectomycorrhizal trees has led to the hypothesis that EM
fungi, supported by adult trees, could facilitate the establishment
of seedlings growing under limited light, thereby competitively
excluding non-EM seedlings (Torti & Coley 1999, McGuire
2007). Enhanced establishment and survival of EM seedlings
near mature EM trees have been reported in monodominant or
mixed stands (Newbery et al. 2000, Onguene & Kuyper 2002,
McGuire 2007). In some cases, seedlings are integrated into an
EM fungal network already supported by mature trees (Selosse
et al. 2006, McGuire 2007, Corrales et al. 2016a). Recently, a
Panamanian monodominant species (Oreomunnea mexicana, Juglan-
daceae) was shown to have potential for such common mycor-
rhizal networks (CMNs) (Corrales et al. 2016a). Although some
aspects remain controversial, CMNs are known to drive nutrient
transfers (including carbon) between plants in some conditions
(Selosse et al. 2006, Teste et al. 2010, Klein et al. 2016). Plants
receiving carbon from CMNs are found in temperate and some
tropical ecosystems, and the compounds received from EM fun-
gal partners usually increase their natural
13
C abundance (Selosse
& Roy 2009). These plants also show high N content and
15
N
abundance, indicating modications of their nitrogen nutrition,
although the mechanism for this remains poorly understood
(Selosse & Roy 2009, Selosse et al. 2016). Candidates for nutrient
transfer can thus be detected by isotopic analyses. However, iso-
topic analyses of seedlings in a mixed Guinean EM forest where
adults and seedlings shared most EM fungi failed to detect
resource transfer to seedlings (Diedhiou et al. 2010). To the best
of our knowledge, resource transfer has not yet been tested in
monodominant tropical rain forests.
The Fabaceae timber tree Gilbertiodendron dewevrei (De Wild.)
J. Leonard of the subfamily Caesalpinioideae (hereafter caesalpin-
ioids) provides a case of almost monospecic forest stands
(>90% of the canopy trees) on >10005000 ha patches in the
Congo basin (Letouzey 1985, Hart 1995, Peh et al. 2011), where
this species dominates in all subcanopy age categories (Hart
1990, 1995). These stands harbor diverse EM sporocarps (e.g.
Buyck 1993, 1994, 1997, Verbeken & Walleyn 2010). Fassi (1960)
described ectomycorrhizae (ECMs) on G. dewevrei, but the distri-
bution of EM fungal communities on roots of the different age
categories of G. dewevrei remains unknown.
Although EM fungi have been identied on G. ogoouense and
Gilbertiodendron sp. roots from mixed Cameroon forests (Tedersoo
et al. 2011), our study is the rst to investigate aboveground and
belowground EM fungal communities of G. dewevrei and their
potential role on seedlings. Gilbertiodendron dewevrei maintains high
densities of seedlings, suggesting that established trees may inocu-
late seedlings, and perhaps even provide carbon resources
through CMNs (Onguene & Kuyper 2002, McGuire 2007). To
identify the potential for CMNs between adult trees and seed-
lings, we determined the EM fungal communities of different age
categories by performing ECM barcoding and sampling sporo-
carps to increase the data set and to obtain specic references
for barcodes. We investigated the following: (1) if trees and seed-
lings share EM fungal taxa; (2) if the composition of the EM
fungal communities varies among different age categories; and (3)
if EM fungi provide carbohydrates and nitrogen to G. dewevrei
seedlings.
METHODS
STUDY AREA.We conducted this project in Southeast Cameroon
during the rainy seasons of 20092012 (Fig. S1). We located our
study area within an 8 ha forest near Nkondon I. Annual rainfall
averaged 1512 mm and fell mainly from August to November
near our study area (Meyibot I: Djuikouo et al. 2010). The area is
densely forested with G. dewevrei, which comprises 81.1 percent
of the basal area and densely regenerates (Djuikouo et al. 2010).
We randomly located three representative sites (0.5-ha per
site) within the 8 ha forest: S1 (2°49002.400N, 13°56054.800E), S2
(2°49030.600N, 13°56040.200 E), and S3 (2°49053.200N, 13°56018.200
E). Sites S1 and S2 were 970 m apart, while sites S2 and S3 were
977 m apart. Soil properties are analyzed in supporting informa-
tion (Table S3). A single individual of EM Uapaca sp. (at S1) and
several individuals of Carapa procera (a non-EM Meliaceae, Bereau
et al. 1997, Wang & Qiu 2006), Irvingia gabonensis (a non-EM
Irvingiaceae, Onguene & Kuyper 2001), and Pentaclethra macro-
phylla (a non-EM Fabaceae, Henkel et al. 2002) co-occurred with
G. dewevrei. We divided each site into ve rectangles of
100 m 910 m in which we identied G. dewevrei individuals
from three main age categories: seedlings, intermediate trees, and
large trees (Table S1).
SAMPLING STRATEGY AND MORPHOTYPING OF ECMS.At each site,
we sampled ECMs from six large trees, six intermediate trees,
and 48 seedlings during the rainy season of 2010. Sampled trees
were at least 8 m apart. For each large or intermediate tree, eight
soil cores were taken at 12 m from the base of the tree trunk
by inserting a 15 cm diameter soil corer to a depth of 30 cm (ap-
proximately 300 g of fresh soil remained attached to the roots) at
sites locally devoid of seedlings. We randomly chose seedlings (6
15 leaves, and height <1 m) and fully harvested them by digging
with a spade (20 cm width and 28 cm depth) to recover approxi-
mately 300 g of fresh soil. All cores were stored in a cooler for
<5 days before being processed. Thus, we evaluated 144 cores
containing the roots of large trees, 144 cores containing these of
intermediate trees, and 144 root systems of seedlings.
We gently washed all root systems over a 250-lm sieve
under running tap water, dispersed them in a dish of water, and
examined them at 109magnication under a dissecting micro-
scope for EM root tips. EM root tips were classied into mor-
photypes according to Thoen and B^a (1989). We counted the
numbers of ECMs and noncolonized root tips to determine the
percentage of EM colonization. In total, we morphotyped 49,888
ECMs.
We maximized the detection of EM fungal diversity at the
barcoding step by choosing representatives of different morpho-
types: we subsampled for molecular analyses 15 EM root tips
from large and intermediate trees and two EM root tips per seed-
ling (i.e., 96 EM root tips per site) by maximizing the number of
2 Micha
ella Ebenye et al.
morphotypes represented. These 828 samples were stored in
CTAB buffer according to Sene et al. (2015).
DNA EXTRACTION AND SEQUENCING.We extracted sporocarp
(Table S2) and ECM DNA using an Extract-N-Amp
TM
Plant
PCR Kit (Sigma-Aldrich, St. Louis, U.S.A.). We performed PCR
amplication and sequencing of the internal transcribed spacers
and 5.8S region (ITS) of the ribosomal DNA with primers ITS1-
F and ITS4, or otherwise ITS1-F and ITS4B as in Sene et al.
(2015). We edited sequences using CodonCode Aligner v.4.1.1
(LI-COR, Inc., MA). We partitioned sequences (accession num-
bers KR819005 to KR819138) into operational taxonomic units
(OTUs) by grouping sequences with more than 97 percent simi-
larity level. In the following section, speciesdescribe fungal taxa
identied from sporocarps, and OTUsdescribe taxa identied
by barcoding. OTUs were identied at the species level when a
sequence presented more than 97 percent full-length similarity to
(i) sequences derived from sporocarps in this study or (ii) well-
identied sequences from the GenBank database using the
BLAST-N algorithm. We identied OTUs at the genus or family
level based on BLAST-N results. Taxa identied from sporocarps
and root tips were assigned to the phylogenetic lineages of EM
fungi dened by Tedersoo et al. (2010a). We considered Helo-
tiales to be EM fungi, although some debate exists in this
respect, and some species may not be EM; Sordariales and Euro-
tiales are likely not EM taxa but were taken into account since
our knowledge of EM taxa remains limited in African tropical
ecosystems.
13
CAND
15
NANALYSES.We investigated the natural
13
C and
15
N abundance in seedlings to assess, by comparison with older
autotrophic plants or EM fungi, whether they showed any iso-
topic enrichment that may reect the gain of compounds from
CMNs. At each site in 2010, we harvested ve leaves from large
trees, intermediate trees, and seedlings of G. dewevrei,aswellas
large trees of Pentaclethra macrophylla, an arbuscular mycorrhizal
(AM) tree, as a control for autotrophic biomass. We also col-
lected G. dewevrei seeds to determine the isotopic abundance of
reserves that contribute to early seedling growth, as well as n=3
replicates taken from the pileus of sporocarps of ve fungal spe-
cies (Clavulina sp.2, Lactiuus longipes,Russula brunneoderma,Russula
sp.1, and Scleroderma sp., Table S4) to estimate the isotopic abun-
dance of the fungal biomass. All leaves were from similar light
conditions and distance to soil and therefore had comparable
photosynthetic conditions and CO
2
sources. Isotopic abundances
were measured as in Tedersoo et al. (2007) and expressed in d
13
C
and d
15
N values in parts per thousand relative to international
standards (respectively, V-PDB and atmospheric N
2
).
STATISTICAL ANALYSES.We performed one-way ANOVA with
XLSTAT2010 software (Addinsoft SARL, Paris) to compare (i)
soil properties at the three sites and (ii) stable isotope abundances
between ectomycorrhizal trees, arbuscular mycorrhizal trees,
seeds, and EM sporocarps. Data were normally distributed. Sig-
nicant differences between pairs were revealed by a Newman-
Keuls test, which is more sensitive to differences than a post-hoc
Tukey test (Abdi & Williams 2010). Species-accumulation curves,
estimates of species richness (rst-order jackknife), and diversity
indices (Fishers alpha, Shannon index) were inferred using Esti-
mateS software version 9.1.0 (Colwell 2013). We assessed the
effects of site, age category, and their interaction on the EM fun-
gal community composition via perMANOVA (permutational
multivariate analysis of variance, Anderson 2001) analysis, using
the function Adonis from the R package Vegan 2.2-1 (Oksanen
et al. 2015). Due to high inter-individual variance, we merged
individual fungal communities by site and age. We, therefore, per-
formed NMDS on the community matrix with OTUs as rows
and nine communities (three sites *three ages). For each signi-
cant factor detected by perMANOVA (site and tree category), we
computed pairwise perMANOVA (Anderson 2001) on balanced
subsamples (e.g., to test for the difference in EM fungal composi-
tion between sites S1 and S2, we sampled the maximum number
of individuals at each site while keeping the number of samples
per site equal). The relative abundance of EM fungal taxa was
calculated as the ratio of the number of ECMs or sporocarps of
a given taxon over the total number of ECMs or sporocarps per
plot and site. Relative frequency of EM fungal lineages was calcu-
lated as the ratio of the number of occurrences of a given lineage
over the total occurrence of lineages per plot and per site. The a
type I error was set at 5 percent.
RESULTS
SPOROCARP IDENTIFICATION.The 1030 sampled sporocarps
(Tables 1 and S2) fell into 11 EM fungal lineages proposed by
Tedersoo et al. (2010a), including 10 from Basidiomycota and 1
from Ascomycota (Fig. 1): /russula-lactarius-lactiuus contributed
the most species (21), followed by /boletus (5), /amanita (5), /
cantharellus (5), /clavulina (4), /ramaria-gautieria (2), /cortinarius
(1), /pisolithus-scleroderma (1), /thelephora-tomentella (1), /tri-
choloma (1), and /tuber-helvella (1). Depending on the site, 59
lineages were fruiting during our surveys. The most fruiting spe-
cies were found in /russula-lactarius-lactiuus, followed by /bole-
tus (Fig. S2). Morphological and molecular identication
(GenBank accessions in Table S4) showed 59 species dominated
by Russula concolora Buyck, R. diffusa Buyck, Russula sp.16, Russula
sp.15, Boletaceae 4, Russula sp.5, Lactiuus sesemotani (Beeli) Buyck,
and Russula sp.2, each contributing more than 3 percent of the
total abundance of sporocarps (Fig. 2). At the species level, the
communities revealed nonuniform composition for the three
sites, with 1434 EM fungal species recorded per site (Fig. 2).
The number of EM fungal species that occurred in two sites ran-
ged from 6 (S1 and S2) to 12 (S1 and S3). The 55 EM fungal
species collected in 2010 (when above- and belowground sam-
pling can be compared) were similar in number to the other sam-
pling years (52, 51, and 50 species in 2009, 2011, and 2012,
respectively; Table S2). Of the 55 species collected in 2010, /rus-
sula-lactarius-lactiuus (25 species) was most prevalent, followed
by /boletus (12), /amanita (4), /cantharellus (4), /clavulina (4), /
ramaria-gautieria (2), /cortinarius (1), /pisolithus-scleroderma (1),
Ectomycorrhizal fungi of G. dewevrei 3
TABLE 1. Number of EM root tips, sporocar ps and OTUs, percentage of mycorrhizal colonization, species richness, and diversity indices from G. dewevrei seedlings (S), intermediate trees (T), and large trees (LT) in a monodominant
forest in Cameroon.
Site 1 Site 2 Site 3 All sites
S T LT S T LT S T LT S T LT
Total No. of
EM root tips
observed
8604 6607 9420 4681 3919 3789 5803 3455 3610 19,088 13,981 16,819
Percentage EM
colonization
a
92.9% a 83.4% b 87.6% c 91.3% a 85.3% b 94.2% ab 94.5% a 88.1% b 85.5% b 92.9% a 85.0% b 88.5% b
No. of EM root
tips extracted
101 93 101 91 92 86 81 98 85 273 283 272
No. of sequences 78 81 72 72 67 61 74 59 65 224 207 198
No.ofOTUs3345 382442 332941 35656863
Rareed number
of OTUs
b
29.2 2.4 38.5 2.6 33.5 4.4 21.7 2.9 38.7 4.2 32.5 2.5 25.5 3.1 41.0 5.0 33.8 1.7 62.0 3.8 67.3 2.5 63.0 2.2
Jackknife1
richness
estimator
43.2 3.2 60.0 3.7 54.8 3.6 32.8 3.0 63.9 3.8 46.7 3.3 40.0 3.3 69.5 3.8 46.9 3.2 85.9 4.6 84.1 4.0 76.9 3.6
Shannons
diversity index
3.1 0.1 3.6 0.0 3.3 0.1 2.6 0.1 3.5 0.0 3.4 0.0 2.9 0.1 3.6 0.0 3.4 0.0 3.7 0.0 4.0 0.0 4.0 0.0
Fishers
alpha per age
23.0 5.1 48.6 12.3 32.7 7.7 12.5 2.6 48.9 12.4 29.7 6.8 17.1 3.7 59.6 15.9 33.2 7.8 31.9 3.6 36.0 4.1 30.9 3.5
Fishers
alpha per site
35.01 5.49 33.45 5.55 31.90 5.35 22.20 3.03
No. of
sporocarps
c
148 74 172 394
No. of
fruiting species
c
29 13 33 55
Common OTUs
d
12.7% 9.2% 19.0% 65.3%
Below-/
aboveground
similarity
e
44.8% 46.2% 33.3% 27.3%
Standard deviations.
a
At each site, percentages followed by different alphabets differ signicantly (P<0.05).
b
Number of OTUs rareed at n=59 sequences for each site and n=198 sequences for all sites, respectively.
c
Collected in 2010 (year where above- and belowground samplings can be compared).
d
Percentage of OTUs occurring on seedlings, intermediate trees, and large trees at each site.
e
Percentage of OTUs found belowground corresponding to species forming sporocarps at each site.
4 Micha
ella Ebenye et al.
/thelephora-tomentella (1), and tricholoma (1), and (Table S2).
Species-accumulation curves reached an asymptote (Figs. S3 and
S4A), indicating that the sporulating EM fungal diversity was well
recovered at all sites.
MOLECULAR IDENTIFICATION OF EM FUNGI ON ROOT TIPS.Over
all sites, 49,888 EM root tips were observed from seedlings,
intermediate trees, and large trees. The percentage of EM roots
ranged from 83.4 to 94 percent, depending on age category
(Table 1). Of the 828 EM root tips subsampled for DNA analy-
sis, 629 (76%) were successfully sequenced and revealed 75 dis-
tinct OTUs (Table 1) from 11 different EM fungal lineages
(Fig. S5). The 75 OTUs included 68 Basidiomycota (90.7% of
the total abundance of OTUs) and 7 Ascomycota (9.3%, Fig. 3).
Among basidiomycetes, /russula-lactarius-lactiuus contributed
the most (40% of all OTUs), followed by /thelephora-tomentella
(23%), /sebacina (12%), /clavulina (8%), /amanita (2.5%), /bole-
tus (2.5%), and /cantharellus (2.5%). Among ascomycetes, the
most highly represented lineages were /marcelleina-peziza gerardii
(4%), /sordariales (2.5%), /elaphomyces (1.5%), and /helotiales
(1.5%). The abundance of OTUs on root tips varied among sites
(Fig. S6): among OTUs representing >5 percent of the total num-
ber of tips, Thelephoraceae 2 dominated S1 (7.3%), Russula sp.5,
Thelephoraceae 1 and Thelephoraceae 2 dominated S2 (10.5%,
10.5%, and 6.5%, respectively), and Russula sp.16, Russulaceae
11, Russula sp.13, and Sebacinaceae 2 dominated S3 (8%, 6.5%,
5%, and 5%, respectively) (Figs. S6 and 3). Overall, 15 OTUs
(20%) matched species found as sporocarps: nine species from
/russula-lactarius-lactiuus, three from /clavulina, one from /
amanita, /boletus, and /thelephora-tomentella. The similarity
between belowground and aboveground EM fungal taxa at each
site ranged from 33.3 to 46.2 percent (Table 1). When consider-
ing OTUs from all sites and all samples, the species-accumulation
curves reached an asymptote, suggesting that the EM fungal
community was exhaustively sampled at this scale (Fig. S4A). We
detected a total of 119 EM fungal taxa from EM root tips and
sporocarps (Table S4).
ECTOMYCORRHIZAL DISTRIBUTION AMONG STUDIED SITES.The
number of OTUs detected on root tips was 71, 65, and 63 at S1,
S2, and S3, respectively (Table 1; Fig. S6). Species-accumulation
curves indicate that the EM fungal community was not exhaus-
tively sampled at each site and that there were no signicant dif-
ferences in the EM fungal species richness among sites
(Fig. S7A). This contrasts with the accumulation curves for
sporocarps, which suggest that although S1 and S3 had similar
diversity, S2 had less than half diversity (Fig. S7B). Although the
three sites shared 69.3 percent (52/75) of OTUs on roots, com-
position differed markedly among sites (df =628, F=2.99,
P=0.001) based on perMANOVA (Table 2). The NMDS
ACBD
HGF
E
I
JK L
PO
N
M
FIGURE 1. Some EM sporocarps harvested under the three age categories of Gilbertiodendron dewevrei: (A) Cantharellus congolensis Beeli, (B) Cantharellus rufopunctatus
var. rufopunctatus (Beeli) Heinem., (C) Clavulina sp.1, (D) Gomphaceae sp.1, (E) Lactiuus pelliculatus (Beeli) Buyck, (F) Lactarius melanogalus Heim., (G) Lactiuus long-
ipes (Verbeken) Verbeken, (H) Lactiuus sesemotani (Beeli) Buyck, (I) Pulveroboletus aberrans Heinem. & Goss.-Font., (J) Russula concolora Buyck, (K) Russula diffusa Buy-
ck, (L) Russula sp.4, (M) Russula substulosa var. apsila Buyck, (N) Thelephoraceae sp., (O) Tylopilus sp.3, (P) Xerocomus virescens.
Ectomycorrhizal fungi of G. dewevrei 5
ordination (stress =0.09) showed an incomplete separation of
communities based on site (Fig. 4B).
ECTOMYCORRHIZAL COMPOSITION BETWEEN LARGE TREES,
INTERMEDIATE TREES,AND SEEDLINGS.The percentage of EM
root tips was signicantly higher for seedlings than for other age
categories at all sites (except for large trees at S2, Table 1).
Ectomycorrhizal fungal species-accumulation curves per age cate-
gory did not reach an asymptote, suggesting that the EM fungal
community was not exhaustively sampled in the three age cate-
gories of trees at each site (Fig. S7A), or even when pooling all
sites (Fig. S4B). In all, we detected 65, 68, and 63 OTUs on
seedlings, intermediate trees, and large trees, respectively
(Table 1). The three age categories shared 49 OTUs, representing
FIGURE 2. Abundance distribution of EM species found among sporocarps collected over 4 years at each site.
FIGURE 3. Abundance distribution of OTUs on EM root tips of G. dewevrei seedlings, intermediate trees, and large trees at all sites.
6 Micha
ella Ebenye et al.
65.3 percent of the diversity found on roots (Table 1; Fig. S8),
and all fungal lineages detected were shared except/helotiales,
which occurred only on seedlings and intermediate trees at all
sites (Fig. S5). S3 had the highest proportion of OTUs shared
between the three tree age categories (19%), followed by S1
(12.7%) and S2 (9.2%, Table 1). The most abundant OTUs,
Thelephoraceae sp.2, Russula sp.5, Russula sp.16, and Russulaceae
sp.11, were associated with the three age categories at all sites
(Fig. 3). Our analyses of diversity (Table 1) revealed homoge-
neous patterns, with no difference among tree categories for
Fishers alpha (ANOVA: df =55, F=0.97, P=0.385; Table 1)
in accordance with the species-accumulation curves (Fig. S4B).
However, there was a signicant difference for Shannon diversity
index (ANOVA: df =55, F=4.002, P=0.024) among tree cat-
egories (intermediate tree: 1.83 0.33; large tree: 1.69 0.38;
seedlings: 1.40 0.67). Using pairwise t-test with P-value adjust-
ment, the only signicant difference in diversity was found for
seedlings against intermediate tree (t-test: t=2.529, P=0.022).
There is a weak but signicant effect of the tree age categories
(perMANOVA: df =628, F=2.16, P<0.001) in the EM fun-
gal community composition (Table 2) reected in NMDS ordina-
tions (Fig. 4A). Pairwise perMANOVA detected signicant
differences between seedlings and large trees (df =407,
F=2.28, P<0.001), as well as between seedlings and interme-
diate trees (df =407, F=2.41, P<0.001), but not between
large trees and intermediate trees (df =407, F=1.40, P=0.06,
Table 2).
13
CAND
15
N Natural Abundances.At all three sites, the foliage
of G. dewevrei and the AM species P. macrophylla was strongly
depleted in
13
C (Figs. 5AC) compared with EM sporocarps: the
foliage and seeds of G. dewevrei were, on average, depleted by 9.3
per mille and 7.9 per mille, respectively, for d
13
C and by 8.5 per
mille and 9.6 per mille, respectively, for d
15
N. The
13
C abundance
increased with age for the G. dewevrei category at two sites (S1
and S2, Figs. 5AC), whereas the
13
C abundance of foliage of
the AM P. macrophylla was not different from that of large G. dew-
evrei trees (Figs. 5AC). Foliage of G. dewevrei did not differ sig-
nicantly as a function of age category in
15
N abundance and C/
N (which did not differ between sites, data not shown)
(Figs. 5DE and S10) but had signicantly higher values than
those of P. macrophylla. Seeds had higher C/N and similar
15
N
abundance compared with foliage for G. dewevrei. EM sporocarps
TABLE 2. Nonparametric perMANOVA on Bray-Curtis distance to test the effects of
site and age category of G. dewevrei on the distribution of OTUs.
SS MS FR
2
P
(A) Effect of site and tree category
Site 2.883 1.44152 2.9904 0.00938 0.001
***
Age category 2.089 1.04468 2.1672 0.00680 0.001
***
Site 9age category 3.968 0.99206 2.0580 0.01291 0.001
***
(B) Pairwise comparison
S1 vs. S2 2.080 1.03988 2.1315 0.00993 0.001
***
S1 vs. S3 1.437 1.43740 2.9514 0.00688 0.001
***
S2 vs. S3 1.022 1.02154 2.0895 0.00488 0.001
***
(C) Pairwise comparison
Seedlings vs. large trees 1.111 1.11090 2.2852 0.0056 0.001
***
Large trees vs.
intermediate trees
0.688 0.68799 1.4008 0.00344 0.063
Seedlings vs.
intermediate trees
1.320 1.32043 2.4109 0.00663 0.001
***
SS, sums of squares; MS, mean squares.
***P˂0.001.
FIGURE 4. Nonmetric multidimensional scaling ordination (NMDS) of EM fungal community (stress =0.09). The two gures represent the effect of age cate-
gory of G. dewevrei (A) and site (B) on EM fungal community composition in seedlings (S), intermediate trees (T), and large trees (LT) at sites 1, 2, and 3. Colored
points represent EM fungal taxa by family. Black squares represent communities.
Ectomycorrhizal fungi of G. dewevrei 7
had higher
15
N abundance and lower C/N than all plants (except
P. macrophylla for C/N, Figs. 5DE and S10).
DISCUSSION
At all three sites of the studied monodominant G. dewevrei forest,
we detected fewer EM fungal taxa from sporocarps (59 species
from 1030 sporocarps) than from EM root tips (75 OTUs from
828 barcoded EM root tips). EM fungal diversity on root tips
differed signicantly depending on tree age category and site.
However, a core community was shared among the three investi-
gated tree age categories (colonizing 65.3% of the barcoded
ECMs) and among the three sites (69.3%). Shared fungi can
form CMNs that link together G. dewevrei plants of different age
categories growing in close vicinity, but we found no evidence
for nutrient transfer from trees to seedlings based on the seed-
lingsnatural isotopic abundances.
LIMITED EM FUNGAL LINEAGE DIVERSITY BUT LARGE SPECIFIC
DIVERSITY.The 119 EM fungal taxa identied here belong to
only 16 EM phylogenetic lineages sensu Tedersoo et al. (2010a).
This high species diversity from a limited number of EM fungal
lineages is consistent with other tropical rain forests, and it com-
plies with the view that tropical forests have a lower diversity of
EM phylogenetic lineages than temperate forests (which usually
display >20 lineages: Tedersoo & Nara 2010). For monodomi-
nant tropical EM forests, Smith et al. (2013) documented 11 EM
fungal lineages in a Guyana forest dominated by the dipterocarp
Pakaraimaea dipterocarpaceae, and Corrales et al. (2016a) found 13
EM lineages on Oreomunnea mexicana in Panama. For mixed tropi-
cal EM forests, Smith et al. (2011) found 17 lineages on three
caesalpinioid species from Guyana; Tedersoo et al. (2011) found
18 lineages on 11 caesalpinioids and one Phyllanthaceae in
Cameroon; Peay et al. (2010) identied 12 EM fungal lineages
under dipterocarps in a Malaysian rain forest; and Diedhiou et al.
(2010) identied seven EM fungal lineages on four caesalpinioids
and one Phyllanthaceae in a Guinean rain forest.
While comparison between studies is difcult because of dif-
ferences in sampling methodologies and failure to saturate spe-
cies-accumulation curves, values of Fishers alpha, a diversity
FIGURE 5. Mean values of d
13
C(&) at site 1 (A), site 2 (B), and site 3 (C), and of d
15
N(D,&) and C/N (E) for the three sites pooled, since they did not dif-
fer signicantly for any age category. Glt, Git, and Gs: G. dewevrei large trees, intermediate trees, and seedlings, respectively; Pm: AM P. macrophylla large trees; S:
EM sporocarps. Se: seeds of G. dewevrei. Signicant differences revealed by Newman-Keuls tests are indicated by different letters (P<0.05).
8 Micha
ella Ebenye et al.
index that corrects for sampling intensity (Table 1), fall in the
range of values reported for tropical forests (Corrales et al.
2016a): based on this index, the diversity is lower than in mon-
odominant Oreomunnea mexicana (Fishers alpha =89.5) but higher
than in Coccoloba uvifera forests (Fishers alpha =3.67 for seedlings
and 3.32 for adult trees; Sene et al. 2015) or under Pakaraimaea
dipterocarpaceae (Fishers alpha =19.8; Smith et al. 2013); yet they
are in the range of mixed EM tropical forests, which is equally
large (Fishers alpha =4183; Corrales et al. 2016a). Thus, the
lower host tree diversity does not necessarily translate into lower
fungal diversity, and ranges of diversity are large in both mixed
and monodominant forests. This nding contrasts with the view
that EM diversity correlates with that of tree species (e.g., Dickie
2007, Ishida et al. 2007, Tedersoo et al. 2008) and suggests that
additional factors drive fungal diversity Richard et al. For exam-
ple, host density (Table S1) inuences EM fungal richness (Teder-
soo et al. 2014), perhaps because a greater availability of roots
provides more resources. Similarly, a recent origin of the EM
symbiosis and/or stress conditions may reduce the fungal diver-
sity (Sene et al. 2015). Finally, the lack of difference in richness of
EM fungal taxa between the mixed and monodominant forests
may, in part, be due to the dominance of generalist EM fungi
(Onguene & Kuyper 2002, Richard et al.Diedhiou et al. 2010,
Henry et al. 2015).
Although our sampling is globally saturated, many OTUs
detected belowground were not found aboveground and vice
versa. Sixty OTUs in all were found on roots only, while 44
(58.9% of sporocarps) were obtained from sporocarps exclusively.
Only 15 OTUs (28.7% of roots tips and 41.1% of sporocarps)
were detected from both approaches. Surveys of sporocarps may
have overlooked inconspicuous sporocarps of the /thelephora-
tomentella and /sebacina lineages (Horton & Bruns 2001), as
well as hypogeous species if any were present. More unexpect-
edly, species well represented by sporocarps, such as those in the
taxa /ramaria-gautieria, /tuber-helvella, /tricholoma, and /piso-
lithus-scleroderma, were not found on root tips, although they
are known to form ECMs (B^aet al. 2012): they may have a lower
investment in EM formation than the other lineages, although we
cannot exclude that their ECMs were deeper than the sampled
soil. Similarly, belowground EM fungal species were sometimes
absent aboveground, e.g. the lineages /sebacina, /marcelleina-
peziza gerardii, /elaphomyces, and /sordariales. Some /russula-
lactarius-lactiuus and /thelephora-tomentella species that were
dominant on root systems were absent from the sporocarp sur-
vey, while the /boletus, /cantharellus, and /clavulina species
dominant on sporocarps were less abundant on root systems.
Similarly, the few species of ascomycetes fungi found from lin-
eages /elaphomyces (1), /sordariales (2), and /helotiales (1) were
present on root only. Interestingly, the lineages /elaphomyces cur-
rently emerge as an African clade requiring further research
(Buyck et al. 2016). These discrepancies further conrm that
although the /russula-lactarius-lactiuus and /thelephora-tomen-
tella lineages clearly dominated this G. dewevrei monodominant
forest, epigeous sporocarps are not perfect indicators of below-
ground richness (see also Gardes & Bruns 1996, Baptista et al.
2015). Moreover, sporocarps revealed >29lower species diversity
in S2 compared with S1 or S3, while OTU diversities on roots
did not differ, the discrepancies have also been reported in other
studies (e.g., Baptista et al. 2015). A better view of the EM fungal
diversity is achieved by combining sporocarp and ECM surveys,
as concluded for other temperate and tropical ecosystems
(Richard et al. 2005, Diedhiou et al. 2010, Sene et al. 2015).
The few species of ascomycetes detected may be due to
their specic ecological requirements more than a methodological
issue (see Tedersoo & Smith 2013). Previous studies in tropical
ecosystems also found low diversity of EM ascomycetes (Peay
et al. 2010, Smith et al. 2011, Tedersoo et al. 2011, Henry et al.
2015, 2016). Among the 16 discovered EM fungal lineages, /tu-
ber-helvella (one OTU, GenBank accession number KR819045)
had not previously been reported from an African tropical forest,
to the best of our knowledge (see Tedersoo et al. 2007, 2010a,
2011, Jairus et al. 2011, B^aet al. 2012). In addition to the Holar-
tic genus Tuber (Bonito et al. 2010), the /tuber-helvella lineage
includes taxa distributed in the austral regions (Tedersoo & Nara
2010). Members of this lineage are probably poorly represented
in the Paleotropic forests. There was also a noticeable absence of
common Holarctic and Austral EM fungal lineages such as /
cenococcum and /laccaria, as well as some panglobal EM fungal
lineages (e.g., /entoloma, /hebeloma-alnicola, and /hysterangium).
SIMILAR STRUCTURE BUT DIFFERENT COMPOSITIONS OF EM FUNGAL
COMMUNITIES AMONG THE AGE CATEGORIES.The composition of
EM fungal communities differed as a function of the G. dewevrei
age category,with communities on seedlings differing from those
on older trees (Table 2). Soil properties were unlikely to drive
between-sites differences (Supporting information, Table S3).
These results partly differ from those obtained by Corrales
et al. (2016a) for Oreomunnea mexicana, the only other example of
monodominant forests investigated for age effect in which the
EM fungal communities of the three age categories did not differ.
Moreover, Corrales et al. (2016b) did not nd evidence for CMN
in O. mexicana based on mesh exclosure experiments and isotopes
analyses. Variation in community composition among sites is con-
sistent with high spatial turnover of tropical EM fungal commu-
nities (even at the kilometer scale: Smith et al. 2011), a patchiness
also known from temperate ecosystems (Richard et al. 2005).
Even so, 19 of the 49 OTUs that occurred in more than
one age category were most abundant on root tips for all three
age categories (38.7% of all sequences). The 30 remaining OTUs
were rare (28.1%). This suggests that the most abundant partners
of nearby conspecic adult trees may be a source of inoculum
for seedlings and potentially for CMN, although physical links are
not directly proven here. Similar observations were made in mul-
ti-aged stands of tropical rain forests. For instance, adults and
seedlings of monodominant Coccoloba uvifera forests share three
EM fungal taxa representing 80 percent of the EM colonization
(Sene et al. 2015). In mixed forests of Madagascar, 88 percent of
ECMs from adults are formed by EM fungal taxa also found on
seedlings, but they encompass less than a half of the taxonomic
diversity (Henry et al. 2015). In a mixed tropical rain forest in
Ectomycorrhizal fungi of G. dewevrei 9
Guinea, EM fungi shared by adults and seedlings represent 79
percent of the EM colonization (Diedhiou et al. 2010). It is dif-
cult to determine whether this simply represents a sampling bias
(with common species more likely to reveal a link to different
age categories) or whether a multi-age strategy is linked to com-
monness in EM fungal species. The EM fungal taxa richness
(based on jackknife 1 and Fishers alpha) was not signicantly dif-
ferent for the three tree categories (Table 1), consistently with
observations on Oreomunnea mexicana (Corrales et al. 2016a).
NOEVIDENCE FOR NUTRIENT TRANSFER FROM TREES TO
SEEDLINGS.Plants from temperate regions that rely on CMNs
are enriched in
13
C,
15
N, and total N (Selosse & Roy 2009,
Selosse et al. 2016), reecting values from the biomass of EM
fungi. The values observed here for EM fungi were concordant
with this pattern, but we detected no
15
N and total N deviation
in understory seedlings versus adult plants (Fig. 5D). For
13
C,
seedlings were even slightly depleted compared with adult plants,
which is the opposite of what could be predicted based on car-
bon transfer. Since the main factors likely to inuence
13
C
abundance were controlled (distance to soil to avoid different
levels of input of CO
2
from soil respiration; light level to avoid
different rates of photosynthesis), this trend was rather unex-
pected. We consider two possible explanations. First, the result
may be affected by carbon from the seed reserves, which are
depleted in
13
C (Cernusak et al. 2009): this carbon source may
have been used to build cell wall polymers earlier in plant devel-
opment. A more sensitive analysis of recently synthesized sol-
uble circulating sugars may reveal some isotopic differences
(Hynson et al. 2012). Second, the carbon issuing from photosyn-
thesis is likely depleted in
13
C for two reasons. Seedlings are
generally more shaded than adult plants, so that systemically cir-
culating carbon may be more
13
C depleted (a lower photosyn-
thetic rate entails a better fractionation against
13
C; Farquhar
et al. 1989). Moreover, smaller trees are closer to the soil and
experience a less elevated
13
CO
2
abundance than higher trees
due to the surrounding soil and plant respiration, combined
with poor ventilation in the understory (Luttge 2008). The same
reasons could apply for the lower
13
C abundance in intermedi-
ate trees compared with large trees, because they also occupy a
lower position in the canopy.
These results and values are consistent with those reported
by Diedhiou et al. (2010), who found no isotopic evidence for
carbon transfer between seedlings and adults of several EM trees
species, including EM caesalpinioid legumes, in mixed rain forest
from a South Guinea forest. We do not fully reject the possibility
of carbon transfer that does not follow the same physiological
pathway as that reported in other CMNs formed by EM fungi,
and thus has different isotopic particularities and fractionations.
Moreover, the tendency of seedlings to have a lower
13
C abun-
dance, as discussed above, may even offset any marginal contri-
bution of fungal C to their biomass. On one hand, we failed to
nd evidence that a nursery effect of CMNs by way of C transfer
could contribute to monodominance; on the other hand, the fact
that seedlings could connect to CMNs that are likely pre-
established at the expense of older trees may be relevant in terms
of carbon budget. This may indeed explain the observed high
EM rate of the seedlings, which is higher than for trees
(Table S1).
Our study highlights the high specic diversity, but poor lin-
eage diversity, of EM fungal communities associated with roots
of G. dewevrei in monodominant stands.Although EM fungal
communities varied between growth stages of G. dewevrei, the
three age categories had partially overlapping EM fungal commu-
nities, and potentially formed CMNs between adults and seed-
lings. Nevertheless, there was no evidence of carbon transfer
from adults to seedlings. CMNs and their impact on the nutri-
tion, growth, and tness of regenerating seedlings should be fur-
ther investigated experimentally in G. dewevrei monodominant
forests.
ACKNOWLEDGMENTS
This research was funded by the Projet Pilote Regional (PPR)
FTH-AC (IRD Cameroon) to A.M. B^a. Michaella Ebenye Hel-
vyne Christelle received a grant from the Institut de Recherche
pour le Developpement (IRD). The molecular analysis was partly
supported by the grant Diversite des champignons mycorhiziens
des plantes(DivMyc) from the network Bibliotheque Du Vivant
(INRA, CNRS & MNHN) to M.-A. Selosse. We warmly
acknowledge David Marsh for English corrections, and the editor
and three anonymous referees for improving previous versions of
this article.
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the
supporting information tab for this article:
TABLE S1. Mean number of stems of G. dewevrei seedlings,
intermediate, and large trees (as dened in main text) in each
site.
TABLE S2. Number of EM fungal species per EM fungal lin-
eage from sporocarps in each year and all sites.
TABLE S3. Soil physical and chemical properties of the three
studied sites (depth 030 cm, n=3, measurement per site).
TABLE S4. Ectomycorrhizal fungal taxa recovered from
sporocarps and root tips of the three age categories of G. dewevrei
in the three sites.
FIGURE S1. Location of studied sites in southeast Cameroon.
FIGURE S2. Distribution of EM fungal lineages from sporo-
carps at each site over 4 years.
FIGURE S3. Species-accumulation curves of sporocarps col-
lected at each year and at all sites.
FIGURE S4. Species-accumulation curves with ECMs and
sporocarp sampling effort at all sites (A), and on EM root tips of
the three age categories of G. dewevrei at all sites (B) in 2010.
FIGURE S5. Distribution of EM fungal lineages on root tips
at each site (A) and on roots tips of seedlings, intermediate trees,
and large trees at all sites (B).
10 Micha
ella Ebenye et al.
FIGURE S6. Distribution of OTUs on EM root tips of seed-
lings, intermediate trees, and large trees of G. dewevrei at site 1
(A), site 2 (B), and site 3 (C).
FIGURE S7. Species-accumulation curves of OTUs on EM
root tips of seedlings, intermediate trees, and large trees (A) and
sporocarps (B) at each site in 2010.
FIGURE S8. Venn diagram showing the number of OTUs
shared by seedlings, intermediate trees, and large trees of G. dew-
evrei.
FIGURE S9. Rarefaction curves of the percentage of OTUs
shared by the three age categories (seedlings, intermediate, and
large trees).
FIGURE S10. Mean values of d
15
N(&) and C/N at site S1
(A, D), S2 (B, E), and S3 (C, F).
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12 Micha
ella Ebenye et al.
... In order to understand the role of PSFs in natural environments, van der Putten et al. (2016) emphasized the need for field study of potential feedback drivers such as ECM fungi. Ectomycorrhizal fungi form diverse communities in tropical forests and different species may vary in functional traits (Ebenye et al., 2017;Henkel et al., 2012;Johnson et al., 1997). Variation in functional traits could in turn influence the strength of PSFs. ...
... This is comparable to the Central African monodominant Gilbertiodendron dewevrei (Fabaceae subfam. Detarioideae) in which 65% of ECM fungal symbionts were shared between sympatric conspecific seedlings and adults (Ebenye et al., 2017). Similar ECM fungal community composition between seedlings and adults might indicate adult-seedling mycorrhizal networking, a form of positive PSF that may contribute to early survival of seedlings (Tedersoo et al., 2020). ...
... Similar ECM fungal community composition between seedlings and adults might indicate adult-seedling mycorrhizal networking, a form of positive PSF that may contribute to early survival of seedlings (Tedersoo et al., 2020). However, Ebenye et al. (2017) utilized carbon and nitrogen isotope data to show that no nutrient transfer occurred between adults and seedlings of G. dewevrei. It remains an open question whether networking is occurring in the Dicymbe system, as circumstantial evidence for it exists but empirical data are lacking (McGuire, 2007). ...
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Ectomycorrhizal tree species may benefit from positive plant-soil feedbacks, where soil environments near adult trees enhance conspecific seedling growth and survival. In tropical monodominant forests, seedling survival is particularly important, as seedling banks help maintain stand-level dominance over generations. Positive plant-soil feedbacks may be mediated by diverse ectomycorrhizal fungal communities, which improve nutrient acquisition of heavily shaded seedlings. Despite the potential importance of these fungi, little is known about ectomycorrhizal fungal community development on seedlings of tropical monodominant trees. In Guyana, we sequentially monitored percent colonization and species composition of ectomycorrhizal fungi on an even-age cohort of seedlings of the tropical monodominant tree Dicymbe cor-ymbosa (Fabaceae subfamily Detarioideae). Ectomycorrhizal fungi found on D. cor-ymbosa seedlings over a 12-month period of early development were compared to those of conspecific adults and four other ectomycorrhizal tree species in the region. Species turnover was high (80%) between 6-and 12-month-old seedlings, though the /russula-lactarius, /clavulina, and /tomentella-thelephora lineages were species-rich on seedlings at all ages. The number of ectomycorrhizal morphotypes per seedling increased with age, but extent of fungal colonization did not. Seedling ectomycorrhizal fungi were shared with sympatric conspecific adults (55%) and, to a lesser extent, regional heterospecific adults (27%), but numerous species were previously unrecorded for Guyana. Over their development D. corymbosa seedlings did not rely strictly on adult trees for their mycobionts but appeared to foster unique assemblages of ecto-mycorrhizal fungi.
... tomycorrhizal associations, on monodominance patterns(Arieira & Cunha, 2006; S. P. Ribeiro & Brown, 2006;Steenbock et al., 2011;Ibanez & Birnbaum, 2014;Kazmierczak et al., 2016;Marimon et al., 2016;Ebenye et al., 2017;Sansevero et al., 2017;Pivello et al., 2018;Steege et al., 2019), our results underscore the importance of taking into account factors that limit species dominance, particularlytemperature, over a broad geographical scale. Recently, Tovar et al. (2019) and Gris et al. (2020) pointed out the importance of precipitation for the maintenance of monodominant forests.Previously,Leathwick and Austin (2001) also demonstrated the influence of mean annual temperature on single-species Nothofagus dominance in New Zealand forests. ...
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Although monodominance has attracted the attention of ecologists for many decades, only a few studies have devoted attention to how abiotic factors could influence the occurrence of monodominant forest patches on the biome scale. Here, we assessed whether the occurrence of monodominant forest patches of Moquiniastrum polymorphum (Less.) G. Sancho (Asteraceae), an early successional tree species with wind‐dispersed seeds, could be predicted by optimum germination temperature and past deforestation. We also verified in what edaphic and climatic conditions the species could reach monodominance; The Atlantic Forest, Brazil We estimated the optimum germination temperature across the species’ geographic range as a function of annual mean temperature based on the results of germination tests available in the literature. Past deforestation (a proxy of suitable habitat for the species’ dispersal and establishment) around monodominant forest patches was estimated by calculating the forest cover in 1985. We also modeled the upper limit of the dominance (relative abundance) as a function of climatic and edaphic variables considered important for the species’ establishment. The results showed that the probability of occurrence of monodominant forest patches is statistically null in places where the germination time can take more than 10 days and the landscape had more than 20% of forest cover. The values of relative density at monodominant condition (> 60%) occurred only in warmer regions with infertile soils and median precipitation conditions (about 1,075 mm to 1,700 mm per year) in the Atlantic Forest. We conclude that only under optimal conditions of germination and dispersal (i.e., regeneration niche) does monodominance occur. This highlights germination traits as an important mechanism for regulating monodominance. In addition, the approach used to predict regions with optimum germination temperature has further implications for understanding species abundance and distribution more generally.
... Trees with large seeds also tend to have shade-tolerant seedlings; seedlings of G. dewevrei are well adapted to the heavily shaded understory, resulting in a competitive advantage over non-shade tolerant pioneer species 11,14 . While not fully considered by Peh, et al. 15 , it is well-established that G. dewevrei adults are heavily EM throughout their trans-Congo range and that seedlings of the species share many EM fungal symbionts with their parents 27 . Gilbertiodendron dewevrei, under a minimal disturbance regime, could attain monodominance, as is described by the mechanisms of Peh, et al. 15 . ...
... Trees with large seeds also tend to have shade-tolerant seedlings; seedlings of G. dewevrei are well adapted to the heavily shaded understory, resulting in a competitive advantage over non-shade tolerant pioneer species 11,14 . While not fully considered by Peh, et al. 15 , it is well-established that G. dewevrei adults are heavily EM throughout their trans-Congo range and that seedlings of the species share many EM fungal symbionts with their parents 27 . Gilbertiodendron dewevrei, under a minimal disturbance regime, could attain monodominance, as is described by the mechanisms of Peh, et al. 15 . ...
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Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees >= 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.
... Trees with large seeds also tend to have shade-tolerant seedlings; seedlings of G. dewevrei are well adapted to the heavily shaded understory, resulting in a competitive advantage over non-shade tolerant pioneer species 11,14 . While not fully considered by Peh, et al. 15 , it is well-established that G. dewevrei adults are heavily EM throughout their trans-Congo range and that seedlings of the species share many EM fungal symbionts with their parents 27 . Gilbertiodendron dewevrei, under a minimal disturbance regime, could attain monodominance, as is described by the mechanisms of Peh, et al. 15 . ...
Article
Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees >= 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.
... Trees with large seeds also tend to have shade-tolerant seedlings; seedlings of G. dewevrei are well adapted to the heavily shaded understory, resulting in a competitive advantage over non-shade tolerant pioneer species 11,14 . While not fully considered by Peh, et al. 15 , it is well-established that G. dewevrei adults are heavily EM throughout their trans-Congo range and that seedlings of the species share many EM fungal symbionts with their parents 27 . Gilbertiodendron dewevrei, under a minimal disturbance regime, could attain monodominance, as is described by the mechanisms of Peh, et al. 15 . ...
Article
Full-text available
Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees≥10cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.
... Trees with large seeds also tend to have shade-tolerant seedlings; seedlings of G. dewevrei are well adapted to the heavily shaded understory, resulting in a competitive advantage over non-shade tolerant pioneer species 11,14 . While not fully considered by Peh, et al. 15 , it is well-established that G. dewevrei adults are heavily EM throughout their trans-Congo range and that seedlings of the species share many EM fungal symbionts with their parents 27 . Gilbertiodendron dewevrei, under a minimal disturbance regime, could attain monodominance, as is described by the mechanisms of Peh, et al. 15 . ...
Article
Full-text available
Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.
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Forest trees compete for light and soil resources, but photoassimilates, once produced in the foliage, are not considered to be exchanged between individuals. Applying stable carbon isotope labeling at the canopy scale, we show that carbon assimilated by 40-meter-tall spruce is traded over to neighboring beech, larch, and pine via overlapping root spheres. Isotope mixing signals indicate that the interspecific, bidirectional transfer, assisted by common ectomycorrhiza networks, accounted for 40% of the fine root carbon (about 280 kilograms per hectare per year tree-to-tree transfer). Although competition for resources is commonly considered as the dominant tree-to-tree interaction in forests, trees may interact in more complex ways, including substantial carbon exchange. © 2016, American Association for the Advancement of Science. All rights reserved.
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Tropical forests are renowned for their high diversity, yet in many sites a single tree species accounts for the majority of the individuals in a stand. An explanation for these monodominant forests remains elusive, but may be linked to mycorrhizal symbioses. We tested three hypotheses by which ectomycorrhizas might facilitate the dominance of the tree, Oreomunnea mexicana, in montane tropical forest in Panama. We tested whether access to ectomycorrhizal networks improved growth and survival of seedlings, evaluated whether ectomycorrhizal fungi promote seedling growth via positive plant–soil feedback, and measured whether Oreomunnea reduced inorganic nitrogen availability. We found no evidence that Oreomunnea benefits from ectomycorrhizal networks or plant–soil feedback. However, we found three-fold higher soil nitrate and ammonium concentrations outside than inside Oreomunnea-dominated forest and a correlation between soil nitrate and Oreomunnea abundance in plots. Ectomycorrhizal effects on nitrogen cycling might therefore provide an explanation for the monodominance of ectomycorrhizal tree species worldwide.
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Ecological restoration in severely disturbed environments can fail because of lack of knowledge of the functioning of the original ecosystem. Nevertheless, facilitating establishment between plant species can help accelerate ecological succession, especially in stressful environments. Mycorrhizal symbiosis plays a key role in plant growth, particularly in harsh environments, and could also play a role in facilitation between plants, as mycorrhizal fungi can form a mycelial network that simultaneously interacts with the root systems of several plant species. In a high-elevation Malagasy tropical rainforest on acidic and iron-rich soil surrounding an active mining site, four genera of ectomycorrhizal plants are locally abundant: Leptolaena, Sarcolaena, Uapaca and Asteropeia. A floristic survey showed that only Asteropeia seedlings can grow on bare soil. Molecular analysis of ectomycorrhizal fungi ITS rDNA enabled us to describe ectomycorrhizal communities and their distribution among these four plant genera. Russulaceae, Boletales, Cortinariaceae and Thelephoraceae are abundant in these forests. There is extensive sharing between ectomycorrhizal communities associated with Asteropeia mcphersonii and other ectomycorrhizal plants. There are also many mycorrhizal fungi species which are common to ectomycorrhizal communities of seedlings and adult trees. This abundance of generalist fungi allows us to envisage the use of A. mcphersonii in the ecological restoration of the mine site. Planting ectomycorrhizal fungi in the bare soil at the beginning of ecological restoration could allow them to grow, thereby establishing a source of inoculum to colonize other ectomycorrhizal plants and consequently facilitate their establishment.
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