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Some plants use allelopathy to compete against neighbouring plants, and the ability to induce allelopathic compound production in response to competition is hypothesized to be adaptive, as plants can save costs of metabolite production in the absence of competitors. However, whether plants induce allelopathy has rarely been explored so far. We studied the inducibility of polyacetylenes – putative allelopathic compounds in Solidago altissima – in response to competition. Polyacetylenes were found in natural soil surrounding S. altissima patches within the range of concentration known to inhibit competitor growth. Individual S. altissima plants with higher polyacetylene concentration in roots suppressed the growth of the competitor plants more, suggesting that root polyacetylene levels proximate plants’ allelopathic capacity. Competition induced polyacetylenes in a context‐dependent manner: Whereas introduced Japanese and Australian populations of S. altissima had higher constitutive concentration of polyacetylenes than the native North American populations, inducibility was observed only in Australian plants, where the population is still at an early stage of invasion. Also, induction became more prominent under nutrient depletion, where enhanced allelopathy may be particularly beneficial for suppressing a competitor's exploitative capacity. Finally, we found weak evidence for a tradeoff between constitutive and induced polyacetylenes. The observed patterns suggest that allelopathic plants could respond to competition by inducing allelochemical production, but the benefit of such plasticity may vary across time and space. Shifts in competitor communities in introduced range over time may shape plant's plastic responses to competition, while variation in resource availability may alter competitive environment to influence the degree to which plants induce allelopathy. This article is protected by copyright. All rights reserved.
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© 2019 e Authors. Oikos © 2019 Nordic Society Oikos
Subject Editor: Martijn Bezemer
Editor-in-Chief: Dries Bonte
Accepted 4 June 2019
00: 1–11, 2019
do i: 10.1111/oik. 06389
doi: 10.1111/oik.06389 00 1–11
Some plants use allelopathy to compete against neighbouring plants, and the ability
to induce allelopathic compound production in response to competition is hypoth-
esized to be adaptive, as plants can save costs of metabolite production in the absence
of competitors. However, whether plants induce allelopathy has rarely been explored
so far.
We studied the inducibility of polyacetylenes – putative allelopathic compounds
in Solidago altissima – in response to competition. Polyacetylenes were found in natu-
ral soil surrounding S. altissima patches within the range of concentration known to
inhibit competitor growth. Individual S. altissima plants with higher polyacetylene
concentration in roots suppressed the growth of the competitor plants more, suggest-
ing that root polyacetylene levels proximate plants’ allelopathic capacity. Competition
induced polyacetylenes in a context-dependent manner: Whereas introduced Japanese
and Australian populations of S. altissima had higher constitutive concentration of
polyacetylenes than the native North American populations, inducibility was observed
only in Australian plants, where the population is still at an early stage of invasion.
Also, induction became more prominent under nutrient depletion, where enhanced
allelopathy may be particularly benecial for suppressing a competitor’s exploitative
capacity. Finally, we found weak evidence for a tradeo between constitutive and
induced polyacetylenes.
e observed patterns suggest that allelopathic plants could respond to competition
by inducing allelochemical production, but the benet of such plasticity may vary
across time and space. Shifts in competitor communities in introduced range over
time may shape plant’s plastic responses to competition, while variation in resource
availability may alter competitive environment to inuence the degree to which plants
induce allelopathy.
Keywords: allelochemicals, invasive plants, novel weapons hypothesis, plasticity,
polyacetylenes, Solidago altissima
Context-dependent induction of allelopathy in plants
under competition
AkaneUesugi, RobertJohnson and AndréKessler
A. Uesugi ( (, School of Biological Sciences, Monash Univ., Building 18, Victoria
3800, Australia. – R. Johnson, Dept of Science, Mathematics and Technology, Medaille College, Bualo, NY, USA. – A. Kessler, Dept of Ecology and
Evolutionary Biology, Cornell University, Ithaca, NY, USA.
Plants induce secondary metabolites in response to ever-
changing biotic environments (Karban and Baldwin 1997),
and these plastic responses are often thought to be adaptive
as they can reduce costs of metabolite production in the
absence of stress (Karban and Myers 1989, Agrawalet al.
1999). For instance, plants may increase resistance to her-
bivory by inducing defensive compound production when
damaged, while expressing relatively low levels of constitutive
resistance in the absence of herbivory. While plant-induced
responses to herbivores and pathogens have been extensively
studied (Karban and Baldwin 1997), less is known about
the induction of secondary metabolites in response to other
important biotic interactions, such as competition (Rasher
and Hay 2014).
Besides exploiting limited resources by growing faster
and larger, some plants compete through allelopathy – an
interference of competitor growth through release of chemi-
cal compounds into the environment (Duke 2010). ese
allelopathic compounds that are released as root exudates,
volatile organic compounds, leaf leachate or leaf litter, may
suppress neighbour growth directly, or indirectly by impact-
ing soil microbial mutualists and altering the nutrient
availability (Roberts and Anderson 2001, Inderjitetal. 2011).
Production of allelopathic compounds is likely to be ener-
getically costly (Uesugi and Kessler 2013), and the balance
of benets and costs of allelopathy are likely to vary across
time and space due to variation in competitor communities.
For example, allelopathy may have little impact in disturbed
habitat where plants encounter no or little interspecic com-
petition, but may be benecial in habitats with intense com-
petition. In an introduced range, allelopathic plants may
gain additional advantage during the early phase of invasion,
because their allelochemicals may be highly eective against
naïve recipient communities that did not coevolve with the
novel compounds (the novel weapons hypothesis; Callaway
and Ridenour 2004). e same allelochemicals, however,
may become less eective as the recipient communities evolve
to tolerate the compounds (Callaway and Ridenour 2004,
Lankauetal. 2009). In such heterogeneous competitive envi-
ronments, selection may favour the evolution of induced pro-
duction of allelolopathic compounds, rather than constitutive
(i.e. constant) production of costly allelochemicals at high
levels (Novoplansky 2009, Kegge and Pierik 2010). Despite
its adaptive potential, inducibility of allelopathy in response
to competition remains poorly understood (Songetal. 2008,
Lankau and Kliebenstein 2009, Kato-Noguchi 2011, Rasher
and Hay 2014).
Expression of inducibility may also depend on abi-
otic environmental conditions in which individual plants
compete. For example, the ability to induce production and
release allelochemicals may be particularly benecial under
resource limitation (e.g. low light, nutrient and water), as
suppression of competitor growth via enhanced allelopathy
would limit the exploitative capacity of neighbouring plants
(Songet al. 2008). us, induction may be predicted to be
higher in low-resource environments than in resource-rich
environments. Such context-dependent induction would
require that plants can detect the competitor presence inde-
pendently of resource depletion caused by competition.
Plants may do so by perceiving plant-specic chemical cues
(e.g. volatile infochemicals and root exudates, Pierik et al.
2013) and/or change in light environment due to shading
(i.e. a change in red to far-red ratio of light, Izaguirreetal.
2006). Previous studies in Oryza sativa indicated that nutri-
ent depletion and exposure to competitor’s root exudates can
independently induce allelopathy in a hydroponic system
(Songetal. 2008, Kato-Noguchi 2011). However, whether
plant’s induction behaviour depends on nutrient availability
has not been explored.
If induction of allelochemical production is a cost-saving
mechanism, we expect inducible allelopathy to trade o with
constitutive allelopathy (Korichevaetal. 2004, Morrisetal.
2006). Within a single population, a tradeo should arise if
there is an upper limit to the level of allelopathy – genotypes
that constitutively express high allelopathy may have less room
to induce further, and vice versa (Lankau and Kliebenstein
2009). Consequently, at a geographic scale, plant populations
that colonize heterogeneous competitive landscapes should
be selected for high induced and low constitutive allelopathy,
whereas in populations that consistently face severe compe-
tition, the opposite may be favoured. Alternatively, theories
of adaptive allocation suggest a variety of ways in which
tradeos between energetically costly traits may be masked
by individual-, and population-level variation in allocation
hierarchies (van Noordwijk and de Jong 1986). For instance,
introduced populations that evolved in the absence of her-
bivory may allocate a larger pool of resources into allelopathy
than native populations, given that allelopathy and herbivore
defense trade o (Blossey and Notzold 1995, Uesugiet al.
2017). In this case, introduced populations may exhibit
higher constitutive and induced allelopathy than native pop-
ulations if both forms of allelopathy are favoured in the novel
range (Callaway and Ridenour 2004). While the presence of
tradeos has been explored extensively for plant resistance
against herbivores and pathogens (Koricheva et al. 2004,
Morriset al. 2006, Kempelet al. 2011), no study, thus far,
has explored tradeos for allelopathy.
Despite its adaptive potential, studies examining the
inducibility of allelochemicals are rare, in part due to a di-
culty in providing concrete evidence for the allelopathic func-
tion of compounds in nature (Duke 2010). To demonstrate
allelopathy, one must rst identify the candidate allelochemi-
cals through bioassays, as any crude extract at a high-enough
concentration can show inhibitory eects (Duke 2010).
Second, we must demonstrate that the compounds in
question are present in the soil at the concentration known to
inhibit competitor growth, since many secondary metabolites
can rapidly degrade and/or be adsorbed to soil particles and
become unavailable (Blairetal. 2005, Kauretal. 2009, Duke
2010). ird, bioactivity of the putative allelochemicals in
soil must be demonstrated to show the ecological relevance
of the compounds in competitive interactions. Studies have
applied activated charcoal to neutralize secondary metabolites
in soil in order to tease apart the allelopathic and the direct
exploitative eects of target plants on competitor growth
(Inderjit and Callaway 2003). However, this technique can
produce large experimental artefacts, as charcoal can alter
nutrient availability in the soil that directly inuence plant
growth in some cases (Lau et al. 2008). Alternatively, one
might contrast plant genotypes that vary in allelochemical
production (Belz and Hurle 2005), or transgenic plants that
are silenced for the production of allelochemicals, for their
ability to inhibit neighbour growth in the eld (Baldwin
2003). However, studies using transgenic approaches are rare
so far (but see Inderjitetal. 2009). Due to these methodolog-
ical challenges, ‘good’ examples of allelopathy are currently
limited to a few cases (e.g. juglone in Juglans nigra; Jose and
Gillespie 1998, sorgoleone in Sorghum spp.; Nimbaletal.
1996, and DIBOA/BOA in wheat; Huang et al. 2003,
glucosinolates in Alliaria petiolata; Cantoretal. 2011).
e tall goldenrod, Solidago altissima (Asteraceae),
provides a model system to study induced allelopathy in
response to competition in ecological context. Several lines of
evidence suggest that putative allelopathic compounds (poly-
acetylenes) produced in S. altissima roots have roles in com-
petition under experimental and natural environments. First,
only the fraction of root extracts containing polyacetylenes
inhibited germination and seedling growth of Oryza sativa
(Kobayashi et al. 1980). Four polyacetylene compounds,
including a major compound cis-dehydromatricaria ester
(DME), were subsequently identied, and demonstrated
to have similar inhibitory eects on several other competi-
tor species in petri-dish experiments (Kobayashietal. 1980,
Sawabeetal. 1999, Johnsonetal. 2010, Uesugi and Kessler
2013) and soil experiments (Kobayashietal. 1980). Second,
DME is found in natural soil within a S. altissima patch
(Kobayashietal. 1980), although its spatial variation in soil
concentration is unclear, as the retention of the compound
could heavily depend on the soil type (Kobayashietal. 2004,
Itoet al. 1998). Finally, a long-term removal of herbivory
drove a rapid evolution of increased competitive ability, as
well as increase in root concentration of polyacetylenes in
S. altissima (Uesugi and Kessler 2013). is evolutionary
shift suggests that selection favours increased resource alloca-
tion towards competition via allelopathy in the absence of
herbivory (Uesugietal. 2017).
Using this system, we rst ask if DME is present in nat-
ural S. altissima patches at ecologically relevant concentra-
tions, and how the concentrations vary spatially. Second,
in a pot experiment, we test how the root polyacetylenes
concentration in S. altissima correlates with the growth of a
common grass competitor (Poa pratensis). ird, we test if S.
altissima responds to interspecic competition by inducing
root polyacetylene production. Induction was tested in two
separate common garden experiments that used S. altissima
from a single population in the native North American
range, and from the native and introduced (Japanese and
Australian) populations to sample a wide range of plant
phenotypes. Fourth, we test how nutrient availability inu-
ences the induction behaviour of root polyacetylenes in
response to competition in a factorial experiment. Finally,
we test if constitutive and induced expression of polyacety-
lenes negatively covary, as predicted under a model of strong
tradeos (Korichevaetal. 2004, Morrisetal 2006).
Material and methods
Study system
Solidago altissima is a perennial forb that dominates mid- to
late-successional stages of old elds (Werneret al. 1980).
It is native to eastern North America, but has been intro-
duced globally, including widespread and highly invasive
populations in Japan (Fukuda 1982), and established but
sparse populations in Australia (Atlas of Living Australia).
In its native range, S. altissima commonly competes with an
understory grass, Poa pratensis. Field experiments show that
S. altissima strongly reduces the density of P. pratensis (Carson
and Root 2000), and the laboratory assays demonstrate that
DME extracted from S. altissima inhibits germination and
seedling growth of P. pratensis in agar media (Uesugi and
Kessler 2013). Introduced populations of S. altissima are also
likely to compete with P. pratensis, which is common in Japan
and Australia (Holm et al. 1979). Based on its likelihood
of being a major competitor of S. altissima in both native
and introduced ranges, and its susceptibility to S. altissima
polyacetylenes, we chose P. pratensis as a model interspecic
competitor in the following experiments.
Field soil DME survey
We tested for the spatial variation in soil DME concentra-
tion in ten S. altissima sites, spanning 186 km of its native
range in western and central New York, USA. Soils across this
range are typically silty loams of glacial origin. To examine
microscale variation in DME concentration within each site,
we collected soil samples in September, 2007 at two distances
– 0 and 25 cm away from the margin of S. altissima clones.
Two replicated soil samples were collected from each distance
per site using a hand-held soil corer to a depth of 10 cm. Field
samples were maintained on cold packs and stored at 80°C
in the laboratory. In April 2008, samples were dried at room
temperature overnight in a fume hood to provide a uniform
consistency and limit thermal binding of metabolites to soil
particles. Samples were sifted to remove organic matter; a
2000 mg fraction was taken from each and transferred to a
capped scintillation vial for DME analysis.
Induction experiments
We conducted two experiments to estimate the eect of
competition on polyacetylene concentration in roots using
dierent sets of S. altissima genotypes: one from a single
eld in the native range (hereafter called a ‘single-population
experiment’), and the other from multiple populations across
its native and introduced ranges (‘multi-range experiment’).
e single-population experiment was conducted as a
part of study by Uesugi and Kessler (2013) that showed a
rapid evolution of constitutive polyacetylene production
in response to a long-term removal of herbivory. Here, we
examine if the inducibility of polyacetylenes has evolved in
response to herbivore removal. e eld experiment was
conducted in Whipple Farm, Tompkins Co., Ithaca, NY,
USA, where half of 12 plots (5 × 5 m2 each) were sprayed
with insecticide to remove herbivory for 12 years, while the
other half were exposed to ambient insect herbivory (see
Uesugi and Kessler 2013 for details). Twenty-nine geno-
types originated from insecticide sprayed plots, while 30
genotypes were taken from plots that experienced ambient
herbivory (control plots). In April 2010, we conducted a
common garden experiment on the roof top of Corson Hall,
Cornell University, NY. Four ramets from each genotype
were clonally propagated, and each ramet was grown in a
20-cm pot containing 1:3 ratio of sand and potting soil. e
four clones from each genotype were split into two compe-
tition treatments (no-competition control and inter-specic
competition with P. pratensis). In control, a single S. altissima
plant was placed in the centre of each pot, whereas in com-
petition treatment, a S. altissima plant was surrounded by
P. pratensis plants grown from ca 200 seeds sprinkled evenly
on the soil surface. Poa pratensis plants grew within 10 cm of
the target S. altissima plants in all pots.
Root samples were collected for secondary metabolite
analyses two months after the start of common garden exper-
iments. Approximately 200 mg of root tissue was removed
from living target plants by clipping a few strands of lateral
roots, ash-frozen with liquid nitrogen, and stored at 80°C
for later analyses. At the end of the ve-month growing
season, both S. altissima and the competitor plants were har-
vested, and dried at 45°C for 48 h. Biomass of shoots, ramets,
roots and rhizomes of S. altissima were separately measured.
For P. pratensis, we measured total aboveground biomass of all
individuals growing within each pot. Belowground biomass
of P. pratensis could not be measured accurately, as its ne
roots were easily lost during harvest.
e multi-range experiment was conducted in 2016 to
sample a wider range of plant phenotypes. We used S. altissima
genotypes originating from across the species’ geographic
distribution along the latitudinal gradients of native North
American range and along the introduced ranges of Japan
and Australia (Supplementary material Appendix 1 Table
A1). Eight to nine populations per range, and four genotypes
per population were sampled (total of 105 genotypes), and
each genotype was clonally replicated by four. A common
garden experiment (at ambient temperature of 22–28°C, and
light/dark cycle of L:D = 12:12) started in March 2016 in the
Plant Science Complex greenhouse at Monash University,
VIC, Australia. Each plant grew in a 20-cm pot with 1:3
ratio of sand and potting soil. e competition treatments
mirrored those described above. Two replicates per genotype
grew alone (as no-competition controls), and the other two
grew under competition from P. pratensis. Root samples were
collected and stored for polyacetylene analyses two months
after the start of the common garden experiments.
Nutrient experiment
To determine if soil nutrient depletion induces polyacety-
lenes, and if nutrient availability inuence plastic responses to
competitor presence, we examined S. altissima plant responses
in a 2 × 2 factorial experiment with two nutrient treatments
(high and low), and two competition treatments (with and
without P. pratensis). e experiment was conducted in July
2015, under the same growing conditions as the multi-range
experiment. Eight S. altissima genotypes originating from
New York, USA, were each clonally replicated eight times,
and spread evenly across the factorial treatments. Nutrient
treatments started two weeks after planting, where high- and
low-nutrient-treatment pots received 200 and 10%, respec-
tively, of full-strength Hoagland solution, 100 ml twice a
week until harvest. After two months of growth, root samples
were collected and stored as above.
Secondary metabolite extraction
Soil samples from the Field soil DME survey (2000 mg
sample–1) were each extracted into 3.0 ml dichloromethane
(DCM), with 100 µl of 1.0 mM abietic acid in MeOH as
internal standard. Each sample was sonicated for 6 min and
a 2.0 ml aliquot was ltered through glasswool + NaSO4 to
clarify and dry; the DCM aliquots were then evaporated
under a fume hood and residue resuspended into 0.5 ml
MeOH for HPLC analysis.
Root samples from Induction and Nutrient experiments
(200 mg fresh mass per sample) were extracted in 1.0 ml of
90% methanol using a tissue homogenizer. Samples were
sonicated in extraction buer for 6 min, and left in the dark
at room temperature for 24 h. Samples were centrifuged and
0.5 ml aliquot was ltered with 0.45 µm syringe lter.
HPLC analysis of polyacetylenes
Soil and root samples prepared in 2008 and 2010 were
analysed at Cornell University with HPLC with C18 reverse-
phase column (3 µm, 150 × 4.6 mm). e elution system
consisting of solvents (A) 0.25% H3PO4 in water (pH 2.2)
and (B) acetonitrile was: 0–5 min, 0–20% of B, 5–35 min,
20–95% of B and 35–45 min, 95% of B, with a ow rate
of 0.7 ml min–1 and injection volume of 15 µl (Uesugietal.
2013). Root samples collected in 2015 and 2016 were
analysed at Monash University using Agilent Innity
1260 equipped with C18 reverse-phase column (EC-C18,
2.7 μm, 150 × 3.0 mm). e elution method was modied
from the above, and was: 0–5 min, 0–20% of B; 5–25 min,
20–95% of B and 25–30 min, 95% of B, with a ow rate
of 0.5 ml min–1 and injection volume of 2 µl. We identied
peaks of polyacetylene compounds using UV spectra with
quantication at 254 nm (Sawabe et al. 2000). e abietic
acid internal standard was quantied at 230 nm.
Statistical analysis
All analyses were conducted using RStudio (ver. 1.0.44,
< >), except when stated otherwise.
Does soil DME concentration vary spatially?
DME concentration in soil sample was calculated as peak area
of DME relative to that for abietic acid internal standard,
and expressed as ppm abietic acid equivalent. e value was
square-root transformed to improve normality, and tested
for the site, distance from the S. altissima plants, and their
interaction using ANOVA.
Does polyacetylene concentration correlate with
competitor growth?
Using data from the single-population experiments, we
examined the relationship between root polyacetylene con-
centration and the growth of P. pratensis. Relative concentra-
tion of all polyacetylene compounds in a root sample was
expressed as total polyacetylene peak areas relative to fresh tis-
sue mass. e total biomass of S. altissima plant was included
to control for the eect of biomass on competitive outcome,
as biomass is thought to be a major driver of competition in
many plants (Goldberg and Landa 1991).
In a linear mixed model (lmer function in package lme4;
Bates et al. 2015), total concentrations of polyacetylenes
and S. altissima biomass were modelled as xed eects, and
S. altissima genotype was entered as random eect. Semi-
partial R2 for each xed predictor was determined using
r2beta function in r2glmm package (Jaeger 2017). For visu-
alisation of the results, we extracted the partial eect of each
xed factor on P. pratensis biomass using remef function in
the piecewiseSEM package (Lefcheck 2016).
Does competition induce root polyacetylene production?
To allow comparisons between single-population and
multi-range experiments that used dierent conditions for
HPLC analyses, values of total polyacetylene were scaled
to unit variance (mean = 0, SD = 1). We tested the eect
of competition on root polyacetylene concentration using
a linear mixed model with competition treatment, plant
origin and their interactions as xed eects, and plant
genotype as a random eect. p-values were estimated using
the Anova function in package car (Fox and Weisberg
2011). Post hoc analyses using lsmeans function (package
emmeans, Lenth 2019) were conducted to test induction
within the origin.
Do soil nutrient levels affect plant induced-response to
Eects of nutrient and competition on root secondary
metabolites were examined with a linear mixed model with
both treatments and their interaction as xed eects, and
plant genotype as a random eect. Post hoc analyses using the
lsmeans function were conducted to test induction within
each nutrient treatment.
Do constitutive and induced levels of secondary metabolites
trade off?
Tradeos between constitutive and induced expression of
polyacetylenes were tested using the data from the single-
population and multi-range experiments. In the multi-range
experiment, the analyses were done separately for each range,
as well as across the ranges. For each analysis, we conducted
a regression analysis while controlling for potential spurious
correlations due to measurement error and sampling variation
(outlined and scripted for MATLAB by Morrisetal. 2006).
Data deposition
Data are available from the Dryad Digital Repository: < http:// > (Uesugietal. 2019).
Does soil DME concentration vary spatially?
DME concentration in natural soil varied across sites
(F9,23 = 3.2, p = 0.011), ranging from undetectable level
to 17.3 ppm (Fig. 1). Within a site, the concentra-
tion was greater at the margin of Solidago altissima
clones (mean = 6.3 ± 4.8 ppm, range = 0–17.3 ppm) than
25 cm away from the clone edge (mean = 1.8 ± 2.1 ppm,
range = 0–7.8 ppm, F1,23 = 28.6, p < 0.0001). No interaction
between site and location was observed (F9,23 = 0.9, p = 0.5).
Does root polyacetylene concentration correlate
with competitor growth?
e biomass of Poa pratensis was negatively correlated with
the biomass of the target S. altissima plant (coef = 0.18,
χ2 = 15.4, p < 0.0001, partial R2 = 0.14, Fig. 2b), and the
total polyacetylene concentration (coef = 0.79, χ2 = 6.2,
p = 0.013, partial R2 = 0.08, Fig. 2a). Overall, the target
S. altissima biomass and polyacetylene production explained
21.4% of variance in the competitor biomass.
Does competition induce root polyacetylenes?
Polyacetylene levels were strongly aected by plant origin in
both experiments, with higher overall concentration in the
insecticide-sprayed populations than in the control popula-
tions within the single-population experiment (χ2 = 19.3,
p < 0.0001; results reported in Uesugi and Kessler 2013,
Fig. 3a), and introduced Japanese and Australian popula-
tions than native North American populations in the multi-
range experiment (χ2 = 32.3, p < 0.0001; Fig. 3b). In contrast,
competition treatment had varying eect on polyacetylene
concentration depending on experiments and plant origins.
Overall eect of competition was signicant in the multi-
range experiment (χ2 = 4.6, p = 0.031; Fig. 3b), but not in
single-population experiment (Fig. 3a). Competition treat-
ment and plant origin interacted in the multi-range experi-
ment (χ2 = 9.9, p = 0.007). A post hoc test revealed that
induction was limited to the Australian populations (t = 3.39,
p = 0.01, Fig. 3b).
Do soil nutrient levels affect plant induced-response
to competitors?
Nutrient treatment did not have any eect on polyacetylene
concentration (χ2 = 0.26, p = 0.12), but competition treat-
ment increased the concentration (χ2 = 10.57, p = 0.001,
Fig. 4). Although the interaction between nutrient and com-
petition was not signicant (χ2 = 2.44, p = 0.12), the post
hoc tests revealed that the induced response to competition
was signicant under the low nutrient treatment (t = 3.42,
p = 0.007), but not in the high nutrient treatment (t = 1.16,
p = 0.65).
Do constitutive and induced levels of root
secondary metabolites trade off?
Overall, constitutive and induced levels of polyacetylenes
tended to negatively correlate in both experiments (Fig. 5), but
after controlling for spurious correlation (Morrisetal. 2006),
the negative correlation was marginally signicant in the
single-population experiment (observed correlation = 0.51,
one-sided p = 0.078, Fig. 5a). In the multi-range experi-
ment, Australian populations showed negative correlation
(observed correlation = 0.56, one-sided p = 0.049), but
Soil DME concentration (ppm)
Figure1. DME concentration in soil samples within 11 sites across western and central NY, USA. Light grey boxes indicate DME concen-
tration at the margin of S. altissima clone (0 cm from the plant) and dark grey boxes represent concentration 25 cm away from the clone
margin. Box plots show median, upper and lower quartiles and extremes.
coef = − 0.79
p = 0.013
(a) (b)
−3 −2 −1 012
Polyacetylene [ ]
Partial effects
coef = − 0.18
p < 0.0001
−2 −1 012
Solidago biomass
Figure2. e partial eects of (a) total polyacetylene concentration and (b) Solidago plant biomass on P. pratensis aboveground biomass.
Partial eects were calculated by controlling for other xed eects, and were plotted against standardised values of each xed term for
North American and Japanese populations did not (North
America: observed correlation = 0.50, one-sided p = 0.12,
Japan: observed correlation = 0.05, one-sided p = 0.78),
resulting in non-signicant correlation across the ranges
(observed correlation = 0.19, one-sided p = 0.56, Fig. 5b).
Do root polyacetylenes have allelopathic effect
on P. pratensis?
Polyacetylenes have been previously suggested to have an alle-
lopathic function in Solidago altissima based on their inhibi-
tory eects in petri dish and soil assays (Kobayashietal. 1980,
Johnson et al. 2010, Uesugi and Kessler 2013), and their
evolutionary response to the relaxation of herbivory that pre-
sumably intensied selection for competitive ability (Uesugi
and Kessler 2013). Our study provides additional evidence
for their allelopathic eect in nature, by rst conrming
the presence of a major polyacetylene, DME, in natural soil
surrounding S. altissima plants. On average, soil DME con-
centration at the margin of S. altissima plants was 6.3 ppm,
similar to the level previously reported elsewhere (~6 ppm,
Kobayashietal. 1980). However, the concentration varied
among our study sites, with some samples containing DME
as high as 17.3 ppm. DME concentration rapidly decreased
with distance away from S. altissima plants, but some sites
retained a relatively high concentration (up to 7.8 ppm) at
the distance of 25 cm. ese results indicate that polyacety-
lenes found in the natural soil are associated with S. altissima
plants, and that these compounds are available at the range
of concentrations known to inhibit competitor growth in
laboratory experiments (5–20 ppm: Kobayashi et al. 1980,
Sawabeetal. 1999, Johnsonetal. 2010, Uesugi and Kessler
2013). us, polyacetylenes are likely to have an ecological
function in natural environments, although its availabil-
ity may vary spatially depending on the soil properties and
microbial activities (Itoetal. 1998, Kobayashi et al. 2004,
Kauretal. 2009, Duke 2010).
Experimentally, we further provide evidence for the alle-
lopathic function of polyacetylene compounds: We found a
signicant negative correlation between root polyacetylene
(a) (b)
ctrl spray
Polyacetylene [ ]
bc bc
Figure3. Induction of total polyacetylenes in response to competition from P. pratensis. Boxplots show standardised concentration of poly-
acetylenes in the single-population experiment (a; ‘ctrl’ = populations exposed to ambient herbivory, ‘spray= insecticide-sprayed popula-
tions) and multi-range experiment (b; ‘AMR’ = North American, ‘AUS’ = Australian and ‘JPN’ = Japanese populations). Light grey boxes
represent polyacetylene concentration in no-competition control, and dark grey boxes represent that under competition treatment. Box
plots show median, upper and lower quartiles and extremes. Dots represent outliers. Letters above the box indicate signicance with post
hoc tests.
ab ab
High nutrient Low nutrient
Polyacetylene [ ]
Figure 4. Eects of competition (light grey = control, dark
grey = competition with P. pratensis) and nutrient (high and low)
treatments on root polyacetylene concentration. Box plots show
median, upper and lower quartiles and extremes. Dots represent
outliers. Letters above the box indicate signicance with post
hoc tests.
concentration in S. altissima plants and the biomass of com-
peting Poa pratensis. e result suggests that polyacetylene
production provides a competitive advantage to S. altissima
plants. Biomass of S. altissima plants was also negatively cor-
related with P. pratensis biomass, indicating that exploitative
competition through increased biomass was also an impor-
tant mode of competition in S. altissima (Goldberg and
Landa 1991). However, despite the negative association, S.
altissima biomass and polyacetylene concentration explained
only 14 and 8% of variance in P. pratensis biomass, respec-
tively. Other unmeasured factors are likely to contribute to
the variation: For example, the rate at which polyacetylenes
in roots are released into the environment may vary with S.
altissima genotypes and may inuence how the plants sup-
press their competitors. Examining the relationship between
root concentration and the amount exuded from the roots
across multiple genotypes will test this hypothesis. e inter-
pretation of our results based on trait correlation also requires
caution, as it does not show causal relationship. Nevertheless,
our study provided a rst possible link between polyacety-
lene production in S. altissima roots and the plant’s ability to
suppress neighbouring competitors in soil environment.
Does competition induce root secondary
Because production of polyacetylenes is expected to incur
metabolic costs, we predicted that these compounds could
be induced under competition when allelopathy is benecial
(Novoplansky 2009, Kegge and Pierik 2010). Total poly-
acetylene concentration in roots increased under competi-
tion treatments in two out of three experiments (multi-range
experiment and nutrient experiment, but not in single-popu-
lation experiment), suggesting that plants can actively induce
the production of polyacetylenes in response to competition.
A few studies have explored inducibility of allelopathy
so far. Some demonstrated inducibility of allelochemicals in
response to changes in abiotic conditions, such as light, tem-
perature, and water and nutrient availability (Dayan 2006,
Konget al. 2006, Song et al. 2008, Kato-Noguchi 2011).
Volatile organic compounds from Artemisia tridentata that
inhibit the growth of neighbouring plants were induced by
herbivory, presumably because the same compounds also
deter herbivores (Karban 2007). But studies that tested the
direct eect of competition on allelopathy induction are
limited: Lankau and Kleibenstein (2009) showed in Brassica
nigra that sinigrin, which was found to have both defensive
and allelopathic functions, was induced by a combination of
herbivory and competition, but less so by competition alone.
A rare demonstration of induced allelochemicals in response
to competitor presence was found in Oryza sativa (Kongetal.
2006, Songet al. 2008, Kato-Noguchi 2011), where plants
grown hydroponically with competing plants exuded more
allelochemicals than when grown without competitors
(Kato-Noguchi 2011). Our observation in S. altissima pro-
vides rare evidence that competition can induce allelopathy
in a non-crop plant that is subjected to natural selection.
Nevertheless, the induction of polyacetylenes was incon-
sistent among experiments, which may reect the dierences
in the source of S. altissima genotypes used in the experi-
ments. Under a normal nutrient condition, induction was
not observed in the single-population experiment that
exclusively used genotypes from the native range in North
America, nor was in American populations from the multi-
range experiment. In the latter experiment, both introduced
Japanese and Australian populations had higher constitu-
tive levels of polyacetylenes than the native populations,
corroborating the results by Uesugi and Kessler (2016) that
used fewer populations. However, a signicant induction of
polyacetylenes was observed only in Australian populations.
(a) (b)
−1 012
Constitutive (control)
Induction (competition−control)
−1 012
Constitutive (control)
Figure5. e relationship between constitutive (control) and induced (competition – control) expression of total polyacetylenes in the
single-population experiment (a) and multi-range experiment (b). In the multi-range experiment, the correlation was tested separately for
each population origin (closed circles = North America, open circles = Australia and crosses = Japan). Lines represent linear regressions for
each population.
is geographic variation in constitutive and inducible poly-
acetylenes may suggest rapid evolution of allelopathy in novel
ranges. Allelopathy is expected to be more eective in plant’s
introduced ranges, particularly in its early stage of invasion,
where recipient communities are naïve to novel allelochemi-
cals (Callaway and Ridenour 2004). Colonization of the
novel competitive environments may favour increased abil-
ity to induce secondary metabolites (Zangerl and Rutledge
1996), and may drive a transient evolutionary increase in
plasticity (Lande 2015). is plastic response, however, is
expected to decrease eventually following the genetic assimi-
lation that increases constitutive expression of allelopathy
(Lande 2015). e lack of inducibility in Japanese S. altissima
populations may be explained by the fact that the popula-
tions are rmly established, and are in the later phase of
invasion (Fukuda 1982). Alternatively, founder eects may
explain the dierences observed among introduced ranges,
but the genetic structures of these introduced populations are
currently unknown.
Does soil nutrient level affect plant induced-
response to competitors?
e benet of inhibiting neighbour growth through increased
allelopathy is expected to increase when the competition for
limited resource becomes severe (Songet al. 2008). us,
assuming that induction of allelopathy is adaptive, we pre-
dicted that inducibility of polyacetylenes would be greater in
nutrient depleted environments than in high nutrient envi-
ronments. Consistent with the hypothesis, we found poly-
acetylene induction in response to competition only under
low nutrient treatment. is decoupling of plant response to
competition and nutrient availability suggests that plants are
able to perceive the presence of competitors via plant-specic
chemical (Pierik et al. 2013) or light cues (Izaguirre et al.
2006), rather than indirectly detecting competitors via loss
of nutrients.
e eect of nutrient depletion on allelopathic ability
has been previously studied in rice in articial medium
(Songet al. 2008, Kato-Noguchi 2011). Songet al. (2008)
found that nitrogen limitation caused up-regulation of gene
expression in enzymes associated with allelochemical syn-
thesis, and an increase in allelopathic eects. Kato-Noguchi
(2011) showed that the exposure to root exudates from the
competitor plants also induces rice allelochemical produc-
tion. However, they do not test whether the inducibility
of allelochemicals vary across nutrient environments. Our
results, showing context-dependent induced responses, sug-
gest that S. altissima may be able to respond to competition
adaptively by inducing polyacetylenes more strongly when it
is most needed (i.e. under severe exploitative competition).
Do constitutive and induced levels of polyacetylenes
trade off?
Assuming that allelochemical production is costly, we
expected constitutive and induced allelopathy to trade o.
We found only a weak negative correlation in the single-
population experiment and Australian populations in the
multi-range experiment. Across the ranges, constitutive and
induced polyacetylenes did not correlate. e tradeo may
be masked in the multi-range experiment because of large
population-level variation in resources available for allelopa-
thy (van Noordwijk and de Jong 1986). Exotic populations
that escape herbivory may evolve to allocate a larger pool
of resources to allelopathy than native populations (Blossey
and Notzold 1995, Uesugietal. 2017). us, the relaxation
of herbivory may drive an increased constitutive allelopa-
thy in both exotic popoulations (Uesugi and Kessler 2016).
Further selection for plastic responses may favour coloniza-
tion of heterogeneous competitive environments in early
stages of invasion. Such independent selection for constitu-
tive and induced allelopathy could explain increased levels
of both expression in Australian populations compared to
native North American populations (Fig. 5b). Interestingly,
the negative correlation was most prominent in Australian
populations: these results may indicate that costs of express-
ing allelopathy in the absence of competitors become more
apparent in the novel and heterogeneous environment.
Inducibility of allelochemicals in response to competition was
predicted based on potential metabolic costs of compound
production. We found some evidence that polyacetylenes,
the putative allelopathic compounds in S. altissima, could be
induced in competitive environments. However, inducibility
of polyacetylenes was context-dependent: evolutionary his-
tory of the plant populations, as well as nutrient availability,
seem to inuence the degree to which plants induce poly-
acetylenes. e lack of a strong tradeo between constitu-
tive and induced polyacetylenes may indicate that these two
forms of allelopathy could evolve independently. Further
geographic contrasts of multiple, independently introduced
populations at varying stages of introduction may allow us
to empirically test how the plasticity for allelopathy evolves
in invasive ranges, thereby inuencing invasion dynamics of
the exotic plants.
AcknowledgementsFunding – is research was funded by School
of Biological Sciences at Monash University, Australian Research
Council (DE180101164), National Science Foundation (USA,
NSF-IOS 0950225) and Cornell University.
Author contributions – e rst and second authors led the
designing of experiments, and data collection and analyses. All
authors contributed critically to the drafts and gave nal approval
for publication.
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Supplementary material (available online as Appendix oik-
06389 at < >).
Appendix 1.
... However, the effectiveness of cis-DME on those plant species was not evidently different. Panicum crus-galli 18 [83] The concentration of cis-DME was reported to be of 250-400 ppm in the roots of S. altissima, of 6.3 ppm in the soil under S. altissima [45] and of 0-17.3 ppm in the soil [116]. The concentrations in the soil varied depending on the soil properties and microbial activities [117][118][119]. ...
... cis-DME inhibited the germination and growth of several plant species at the concentration of 1-20 ppm [45,80,82,83,88,113]. Its concentration in the roots of S. altissima and in its rhizosphere soil was of 250-400 ppm and 0-17.3 ppm, respectively [45,116]. These observations suggest that cis-DME may be released into the rhizosphere soil by root exudation, rainfall leachates and/or decomposition processes of plant residues. ...
... trans-DME was also formed by the isomerization of cis-DME in the soil, and its inhibitory activity was the same as cis-DME. Although there has been no information of the concentration of trans-DME in the rhizosphere soil of S. altissima, the concentration of only cis-DME in several soils was over the concentration which was able to cause the growth inhibition [45,116]. In addition, cis-DME possesses nematicidal and insecticidal activities [101,113,121,124] Some flavonoids were also identified in the aerial parts of S. canadensis [78]. ...
Full-text available
Solidago canadensis L. and Solidago altissima L. are native to North America and have naturalized many other continents including Europa and Asia. Their species is an aggressive colonizer and forms thick monospecific stands. The evidence of the allelopathy for S. canadensis and S. altissima has accumulated in the literature since the late 20th century. The root exudates, extracts, essential oil and rhizosphere soil of S. canadensis suppressed the germination, growth and the arbuscular mycorrhizal colonization of several plants, including native plant species. Allelochemicals such as fatty acids, terpenes, flavonoids, polyphenols and their related compounds were identified in the extracts and essential oil of S. canadensis. The concentrations of total phenolics, total flavonoids and total saponins in the rhizosphere soil of S. canadensis obtained from the invasive ranges were greater than those from the native ranges. Allelochemicals such as terpenes, flavonoids, polyacetylene and phenols were also identified in the extracts, essential oil and the rhizosphere soil in S. altissima. Among the identified allelochemicals of S. altissima, the cis-dehydromatricaria ester may be involved in the allelopathy considering its growth inhibitory activity and its concentration in the rhizosphere soil. Therefore, the allelopathy of S. canadensis and S. altissima may support their invasiveness, naturalization and formation of thick monospecific stands. This is the first review article focusing on the allelopathy of both of S. canadensis and S. altissima.
... Solidago altissima (syn. S. canadensis), is a chemically diverse, allelopathic perennial herb that is common in old fields and other open habitats across its native range of Eastern North America (Werner et al. 1980;Meiners et al. 2017;Kalske et al. 2019;Uesugi et al. 2019;Yip et al. 2019). Solidago altissima reproduces clonally through rhizomes and is very diverse in its chemical composition, allowing this species to become a successful invader across Europe, Japan, and Australia (Weber 1998;Uesugi et al. 2019;Yip et al. 2019). ...
... S. canadensis), is a chemically diverse, allelopathic perennial herb that is common in old fields and other open habitats across its native range of Eastern North America (Werner et al. 1980;Meiners et al. 2017;Kalske et al. 2019;Uesugi et al. 2019;Yip et al. 2019). Solidago altissima reproduces clonally through rhizomes and is very diverse in its chemical composition, allowing this species to become a successful invader across Europe, Japan, and Australia (Weber 1998;Uesugi et al. 2019;Yip et al. 2019). Solidago altissima has been used to document ecological impacts of chemical variation (Uesugi and Kessler 2013;Uesugi et al. 2019), impacts on soil microbial communities (Zhang et al. 2009), and variation in plant-microbe interactions (Dong et al. 2015;Howard et al. 2020;Peacher and Meiners 2020), representing a good model system to test for intraspecific variation in plant-soil microbe interactions. ...
... Solidago altissima reproduces clonally through rhizomes and is very diverse in its chemical composition, allowing this species to become a successful invader across Europe, Japan, and Australia (Weber 1998;Uesugi et al. 2019;Yip et al. 2019). Solidago altissima has been used to document ecological impacts of chemical variation (Uesugi and Kessler 2013;Uesugi et al. 2019), impacts on soil microbial communities (Zhang et al. 2009), and variation in plant-microbe interactions (Dong et al. 2015;Howard et al. 2020;Peacher and Meiners 2020), representing a good model system to test for intraspecific variation in plant-soil microbe interactions. ...
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Plant–soil microbe interactions are a key determinant of plant community composition and structure, with each plant species generating a unique soil microbiota. However, the degree of intraspecific variation in plant–soil microbe interactions in controlling plant performance has been much less investigated. We examined the strength of plant–soil microbe interactions across Solidago altissima and Schizachyrium scoparium seedlings grown in soils cultured by 24 genotypes of S. altissima in a greenhouse setting to determine the level of variation within these two target species. We also quantified leaf chemical variation across S. altissima genotypes using HPLC characterization of foliar constituents as a potential driver of below-ground processes. The impacts of soil microbe-mediated effects of genotypes ranged from negative to positive for both target species. Target species responses to the 24 soil microbial communities were positively correlated, although the strength of plant–soil microbe interactions was related to foliar chemistry for S. scoparium, but not for S. altissima. The magnitude of impacts in soils pooled from all 24 S. altissima genotypes was more negative than the average impact of genotypes tested individually, suggesting that this methodology cannot be used to assess ‘average’ effects. Our results strongly argue that intraspecific variation in plant–soil microbe interactions may be a quite large source of variation in systems dominated by clonal plants. Furthermore, simple inocula pooling obscured this variation and resulted in a marked bias toward the more antagonistic components of the soil microbial community.
... Allelochemical biosynthesis may be induced by the presence of competitors, which requires mechanisms of non-self-recognition and is strong evidence for allelopathy as a fitness-enhancing strategy. In Solidago altissima, an invasive plant of North American origin, for example, allelopathic polyacetylenes produced in roots can be induced by competitors in some invasive populations, and induction is more apparent under nutrient-limited conditions (Uesugi et al. 2019). In allelopathic wheat, production of the potent allelochemical 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) is induced in roots by a wide variety of competing plant species (Kong et al. 2018). ...
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Progress in understanding allelopathic interactions among plants has long been hampered by the complexity of the many direct and indirect interactions involved. Plant processes and growth are not only affected by allelochemicals but by resource limitations, pathogens, herbivores, and microbial interactions. Interference mechanisms frequently interact, and the magnitude of effects can depend on the plant’s biotic and abiotic environment. The rhizosphere is chemically complex, with thousands of potentially bioactive allelochemicals produced by plants, microorganisms and soil invertebrates. The rhizosphere is also dynamic, in that concentrations of these metabolites vary as pulses of allelochemicals are released by plant roots and other organisms, as they leach from decaying plant material, as microorganisms degrade and sometimes transform allelochemicals, and as allelochemicals are taken up by plants, bind to soil components, or leach from the root zone. Recent advancements in instrumentation and technologies for the analysis of trace levels of chemical substances in soil, as well as the development of genomics, proteomics, and transcriptomics approaches allow researchers to probe both the biosynthesis of allelochemicals and plant responses to allelochemical exposures. These new technologies will provide much more detailed information on rhizosphere chemistry and about the production and response to metabolites by individual cells. This review describes case studies and current examples that illustrate how these new approaches and tools can enhance our understanding of allelopathic interactions, and argues that to truly advance our understanding of allelopathic interactions, these must be applied in ecologically rigorous and meaningful ways.
... Allelopathic plants reduce interference of allelopathy by regulating related tissue structure, basal metabolism, secondary metabolism, protective enzyme activity and other defensive measures (Sǒln et al., 2022). Especially in plant communities with population competition, plants reduce the adverse effects of allelopathy on competition through defensive responses (Uesugi et al., 2019;Chia and Bittencourt-Oliveira, 2021). Competition between weeds and plants is obviously related to this process. ...
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Scirpus planiculmis, an important weed in rice and cotton fields, stresses crop growth and development, leading to yield loss. However, it is unclear how stressed plants respond to this weed. In this study, we analysed the stress effect of S. planiculmis on cotton under different weed densities, competition periods, and distribution conditions from the perspective of morphogenesis, physiological metabolism and crop yield. The effect of a low dose of herbicide on the relationship between cotton and S. planiculmis was also explored. The results showed that plant height, stem diameter, fresh weight, root length, boll number, single boll weight and yield of cotton all decreased with increasing S. planiculmis density and damage. The spatial distribution of S. planiculmis had no significant effect on plant height, stem diameter, fresh weight or root length of cotton, but crop yield loss decreased with increasing distance. S. planiculmis stress altered cotton chlorophyll, soluble protein and malondialdehyde (MDA) content, and protective enzyme activities. Compared with superoxide dismutase (SOD) and peroxidase (POD) activities, catalase (CAT) activity was increased under different S. planiculmis stress conditions. Therefore, we concluded that CAT plays a key role in protecting enzymes involved in defence responses. Under low-dose herbicide action, the activities of protective enzymes were increased, which helped cotton plants to resist S. planiculmis stress. The results revealed that regulating protective enzyme activities is important in cotton responses to S. planiculmis stress.
... The roots of S. altissima release cis-dehydromatricaria ester (DME), which has allelopathic effects on several plant species (Ito et al. 1998;Kobayashi et al. 1980). Furthermore, S. altissima responds to competition with surrounding plant species, inducing the production of allelopathic chemicals (Uesugi et al. 2019). Therefore, the allelopathic property of S. altissima might contribute to its successful invasion of disturbed habitats and the suppression of native plant species on Jeju Island. ...
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Biological invasions of exotic plant species affect nutrient cycling, soil characteristics, ecosystem stability, and Biodiversity. Therefore, management measures to protect the ecosystem and native species against invasive species are becoming more important. The tall goldenrod, Solidago altissima L., is an invasive alien plant with currently limited distribution on the Jeju island, while successfully invaded areas with similar climates in China and Japan. Therefore, it has a high possibility of invasion and may have an adverse effect on the ecosystem of Jeju Island. The aim of this study was to develop an environmentally friendly management strategy to control S. altissima with understanding of the major factor that makes difference of invasion success between Japan and Jeju island. Plant communities are monitored and allelopathic effects of S. altissima are tested.. Furthermore, the effectiveness of mowing at varying frequencies and timing for the control of S. altissima were applied. S. altissima already dominates several plant communities on Jeju Island, harms the plant community via allelopathy, and reduces biodiversity. However, our study shows that mowing is an effective method to control S. altissima populations. Mowing inhibits early invasion of S. altissima and also reduces dominance and reproductive features of S . altissima where invasion has already processed. Therefore, mowing should be adopted for the management of S. altissima invasion. Mowing is an environmentally friendly management method for the control of S. altissima and could be applied to other invasive species.
... The allelopathic effects that occurred for the parameters of length and weight, indicated that there was a positive influence of the extracts stimulating the development of the seedlings. However, compounds with allelopathic activity that inhibit growth is more commonly reported (Einhellig 1999;Ferreira and Aqüila 2000) acting as an essential factor in interspecific competition (Bieberich et al. 2018;Dhungana et al. 2019;Uesugi et al. 2019). However, there are some studies that report stimuli in seedling growth (Rice 1984;Lin et al. 2004;Sausen et al. 2009). ...
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In Ant-gardens, ants build nests with organic materials and take specific seeds of some species of epiphytes which germinate. In this mutualistic interaction, a variety of other epiphytes could colonize the nests and develop, but it doesn't happen. We assume that there is chemical allelopathy with epiphytes inhibiting the germination and growth of other species of epiphytes, and with ants cutting off non-mutualistic epiphyte species. To investigate this, we performed chemical and prune tests which determine the composition of the epiphyte species of Ant-Gardens of parabiotic ants, Camponotus femoratus (Fabricius, 1804) and Crematogaster levior Longino, 2003. For the chemical allelopathic test, we administered the extract of the stem and leaves of Peperomia macrostachya (Vahl) A. Dietr. and Codonanthe calcarata (Miq.) Hanst. (the most common species in parabiotic AGs) in different concentrations. For the prune test, we used seedlings of the mutualistic plant Peperomia macrostachya and non-mutualistic plant Cucumis sativus as a control, then we inspected the nests to evaluate the ants pruning the seedlings. In the chemical allelopathy tests, the species Codonanthe calcarata decreased the germination speed indexes in relation to the control (distilled water). On the contrary, the length and weight of the seedlings were positively influenced by epiphyte extract. In the prune test, most of the plants pruned were non-mutualistic. The results of the chemical allelopathy and prune experiments showed that both mutualistic epiphytes and ants play a decisive role in the composition of epiphytes in Ant-Gardens.
... Deployment of allelochemicals seems to be tightly connected to neighbour detection, and particularly non-kin neighbours. Active exudation can be triggered by the presence of neighbours, detected through common signals such as (−)-loliolide, jasmonic and salicylic acids Li et al., 2016;Uesugi, Johnson, & Kessler, 2019). Furthermore, allelopathy may only be expressed at certain developmental stages when it is the greatest advantage, particularly during seedling establishment . ...
Plants were traditionally seen as rather passive actors in their environment, interacting with each other only in so far as they competed for the same resources. In the last 30 years, this view has been spectacularly overturned, with a wealth of evidence showing that plants actively detect and respond to their neighbours. Moreover, there is evidence that these responses depend on the identity of the neighbour, and that plants may cooperate with their kin, displaying social behaviour as complex as that observed in animals. These plant–plant interactions play a vital role in shaping natural ecosystems, and are also very important in determining agricultural productivity. However, in terms of mechanistic understanding, we have only just begun to scratch the surface, and many aspects of plant–plant interactions remain poorly understood. In this review, we aim to provide an overview of the field of plant–plant interactions, covering the communal interactions of plants with their neighbours as well as the social behaviour of plants towards their kin, and the consequences of these interactions. We particularly focus on the mechanisms that underpin neighbour detection and response, highlighting both progress and gaps in our understanding of these fascinating but previously overlooked interactions.
Background and aims: Some plant species suppress competitors through release of chemical compounds into the environment. As the production of allelochemicals may be costly, it would be beneficial if the production of these compounds would only be induced when plants experience competition. We tested whether two plant species that frequently co-occur, show evidence for induced allelopathy in response to intra- and interspecific competition. Methods: We used the annual forb Crepidiastrum sonchifolium and the perennial forb Achyranthes bidentata, which are native to China and predominantly occur in ruderal communities, as focal species. We first grew the species without competition, with intraspecific competition and in competition with each other. We chemically analysed aqueous extracts made from these plants to test for evidence that the competition treatments affected the metabolomic profiles of the species. We then tested the effects of the aqueous extracts on seed germination and seedling growth of both plant species. Key results: Metabolomic analysis revealed that competition treatments modified chemical profiles of the two study species. The root lengths of A. bidentata and C. sonchifolium seedlings were reduced by the aqueous plant extracts. For seedling root length of A. bidentata, heterospecific allelopathy was more negative than conspecific allelopathy, but for germination of C. sonchifolium seeds, the reverse was true. Moreover, conspecific allelopathic effects on germination of A. bidentata seeds and on seedling root length of both species were most negative when the aqueous extracts were made from plants that had experienced competition. In the case of seedling root length of A. bidentata, this effect was most negative when the plants had experienced interspecific instead of intraspecific competition. Conclusions: We showed that plants change their metabolomic profiles in response to competition, and that this correlated with allelopathic inhibition of conspecific seed germination and seedling growth. We suggest that autoallelopathy for seed germination could function as a mechanism to avoid strong competition by keeping the seeds in a dormant state.
To survive, all organisms must sense and respond to information from their environment. This is true of many organisms, including plants, which need to do all the things that other organisms do while operating under the limitations of being sessile and lacking a central nervous system. In this article, we explore how information theory can apply to plants and briefly review the types and sources of information and the mechanisms that plants use to perceive and respond to their environment. We identify and describe three primary modes by which a plant receives information: chemical, electromagnetic and mechanical. We describe how plants integrate information to detect the state of their neighbors, capture resources and regulate growth and metabolism. Overall, we find that plants interpret information from their surroundings as an emergent property of distributed information processed by a network of cells. We end with a prospectus of directions for future research including decoding signal from noise, storage of information, additional means of information transmission and two‐way information signaling with biotic partners.
Solidago altissima L. (Asteraceae), a perennial plant native to North America, is considered one of the most invasive weeds in Asia and Europe. The successful invasion of S. altissima is possibly due to its allelopathic effect along with high seed productivity and strong vegetative propagation through rhizomes. Herein, to understand the invasion of S. altissima via the allelopathic effect, we isolated and characterized known and undescribed compounds from the underground parts of S. altissima and evaluated their contribution to the overall allelopathic activity of the plant. NMR spectroscopy and LC-MS analyses clarified the chemical structure of ten specialized metabolites including three undescribed compounds, i.e., (4Z, 8Z)-10-tigloyloxy matricaria lactone, (4Z, 8Z)-10-angeloyloxy matricaria lactone, and (2Z, 8Z)-10-methacryloyloxy matricaria ester. The evaluation of the content and allelopathic ability of each compound showed that cis-dehydromatricaria ester contributes to the allelopathic activities of the S. altissima extract.
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Insect herbivores are important mediators of selection on traits that impact plant defense against herbivory and competitive ability. Although recent experiments demonstrate a central role for herbivory in driving rapid evolution of defense and competition-mediating traits, whether and how herbivory shapes heritable variation in these traits remains poorly understood. Here, we evaluate the structure and evolutionary stability of the G matrix for plant metabolites that are involved in defense and allelopathy in the tall goldenrod, Solidago altissima. We show that G has evolutionarily diverged between experimentally-replicated populations that evolved in the presence versus the absence of ambient herbivory, providing direct evidence for the evolution of G by natural selection. Specifically, evolution in an herbivore-free habitat altered the orientation of G, revealing a negative genetic covariation between defense- and competition-related metabolites that is typically masked in herbivore-exposed populations. Our results may be explained by predictions of classical quantitative genetic theory, as well as the theory of acquisition-allocation trade-offs. The study provides compelling evidence that herbivory drives the evolution of plant genetic architecture. This article is protected by copyright. All rights reserved.
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Herbivory can drive rapid evolution of plant chemical traits mediating defensive and competitive ability. At a geographic scale, plant populations that escape selection from their ancestral herbivores may evolve decreased defense and increased competitiveness. While contrasts between native and invasive populations of plants lend support to this hypothesis, such experiments cannot establish causal links between herbivory and evolved invasive phenotypes. 2.Here, we conducted geographic contrasts, and coupled these with long-term selection experiments that directly test for evolutionary responses to herbivore-exclusion. In common gardens, we contrasted Solidago altissima genotypes that were historically exposed or protected from herbivory across two experimental timescales: 1) a natural experiment where plant populations evolved either with native herbivory (in Minnesota and New York), or evolved relatively free from herbivory for ~100 years in Japan, and 2) a 12-year manipulative experiment where plants were either exposed to ambient herbivory, or treated with insecticide. 3.In both experiments, plant populations responded to herbivore-release by evolving increased production of root allelochemicals and inter-specific competitive ability against Poa pratensis. While plant resistance to a beetle herbivore did not diverge between plant origins, we still observed parallel evolutionary shifts in leaf secondary metabolite and protease inhibitor production, which may confer resistance to diverse herbivore species. 4.Synthesis. Observed evolutionary convergence for multiple plant traits, between the natural and manipulative experiments, emphasises the role of insect herbivores as key drivers of plant adaptation and geographic differentiation. This article is protected by copyright. All rights reserved.
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Maximum likelihood or restricted maximum likelihood (REML) estimates of the parameters in linear mixed-effects models can be determined using the lmer function in the lme4 package for R. As for most model-fitting functions in R, the model is described in an lmer call by a formula, in this case including both fixed- and random-effects terms. The formula and data together determine a numerical representation of the model from which the profiled deviance or the profiled REML criterion can be evaluated as a function of some of the model parameters. The appropriate criterion is optimized, using one of the constrained optimization functions in R, to provide the parameter estimates. We describe the structure of the model, the steps in evaluating the profiled deviance or REML criterion, and the structure of classes or types that represents such a model. Sufficient detail is included to allow specialization of these structures by users who wish to write functions to fit specialized linear mixed models, such as models incorporating pedigrees or smoothing splines, that are not easily expressible in the formula language used by lmer.
The study of allelopathy as a discipline has a long and at times controversial history. Since Hans Molisch coined the term before World War II, allelopathy research has grown from a trickle of papers before 1970 to a burgeoning subdiscipline of chemical ecology represented by hundreds of papers each year. Yet, allelopathy research still suffers from a reputation for papers of poor scientific quality that equate the presence of a phytotoxic phytochemical as proof of an allelochemical function without regard for proving that the compound is bioavailable in soil at sufficient concentrations to affect vegetation either directly or indirectly through effects on soil microbes. Synergism has often been invoked without proof to explain why effects of crude extracts are sometimes greater than even the additive effects of phytotoxins known to be in the extract. Much of this work may be correct, but to be widely accepted more rigorous proof is needed. Much of this literature also makes the assumption that allelochemicals must be highly water soluble, when there are good scientific reasons to hypothesize that the most effective allelochemicals would have very limited water solubility. Very little is known about the mode of action of and mechanisms of resistance to putative allelochemicals. Nevertheless, the quality and quantity of papers on allelopathy has increased steadily over the past several decades and knowledge gaps are being filled at an ever increasing pace. There can be little doubt that allelopathy plays an important role in plant/plant interactions in nature and in agriculture. Translating this growing knowledge to technology to manage weeds in agriculture has been slow. There is only one good case of discovery of an allelochemical (leptospermone) leading to the development of a major class of herbicides (triketones). There are examples of allelopathic cover crops being used for weed management in other crops, as well as other cultural methods to employ allelopathy. However to my knowledge, there are still no cultivars of crops being sold with allelopathic properties as a selling point. Enhancement or impartation of allelopathy in crops through the use of transgenes could eventually be used to produce such a cultivar. Some of the most high profile recent examples of research in our discipline will be discussed. The study of allelopathy appears to have a bright future, especially if we can translate our research into technologies that will reduce our reliance on synthetic herbicides.
Ecologists and evolutionary biologists are relying on an increasingly sophisticated set of statistical tools to describe complex natural systems. One such tool that has gained increasing traction in the life sciences is structural equation modeling (SEM), a variant of path analysis that resolves complex multivariate relationships among a suite of interrelated variables. SEM has historically relied on covariances among variables, rather than the values of the data points themselves. While this approach permits a wide variety of model forms, it limits the incorporation of detailed specifications. Here, I present a fully-documented, open-source R package piecewiseSEM that builds on the base R syntax for all current generalized linear, least-square, and mixed effects models. I also provide two worked examples: one involving a hierarchical dataset with non-normally distributed variables, and a second involving phylogenetically-independent contrasts. My goal is to provide a user-friendly and tractable implementation of SEM that also reflects the ecological and methodological processes generating data.
Most general theories proposed to explain the trophic structure of communities ignore the possibility that insect outbreaks can severely damage vegetation and reduce the abundance of dominant plant species over vast areas. Specialist chrysomelid beetles can irrupt and defoliate goldenrods (Solidago spp.), a group of widespread, long-lived, herbaceous perennials. We examined the long-term effects (10 yr) of suppressing insects, using insecticide in replicated plots on the structure and diversity of an old field dominated by the goldenrod, Solidago altissima. An outbreak of the chrysomelid beetle, Microrhopala vittata, that specializes on S. altissima, occurred during the experiment and persisted several years. Damage caused by this outbreak dramatically reduced the biomass, density, height, survivorship, and reproduction of S. altissima. Herbivore exclusion caused the formation of dense stands of goldenrods with a twofold increase in both standing crop biomass and litter. The understory in these dense stands had significantly lower plant abundance, species richness, flowering shoot production, and light levels; these conditions persisted for years following the outbreak. Thus, M. vittata functioned as a keystone species. Furthermore, insect herbivory indirectly increased the abundance of invading trees, thereby increasing the rate of succession, by speeding the transition of this old field to a tree-dominated stage. We conducted two follow-up experiments to test the hypothesis that insects altered community dynamics by their indirect effect on litter accumulation and light availability in the understory. In the first experiment, we tied back the canopy to increase light into the understory and removed litter in both the insecticide-treated and control plots. We found little effect of removing litter. By contrast, increasing understory light levels significantly increased understory forb abundance and species richness. In the second experiment, we placed rosettes of Hieracium pratense, the dominant understory forb, under nine levels of shade cloth, ranging from 95% shade to full sun. Flowering-shoot production was a linear function of light availability (r2 = 0.92; P < 0.0001). We concluded that insect herbivores indirectly promoted plant species richness and coexistence, primarily by augmenting light availability to suppressed understory species. Insect herbivory may often play a strong role in goldenrod stands, because outbreaks will likely occur at least once, if not more, during the period when goldenrods are dominant. Furthermore, our findings provide compelling evidence for two general mechanisms whereby insect herbivory promotes plant species diversity and coexistence. The first mechanism operates during outbreaks when insects act as keystone species. The second mechanism can operate at less than outbreak levels and occurs whenever insect damage augments light to a sufficient degree to enhance the fecundity of suppressed nonhost species. If this increase in fecundity increases recruitment of subordinate species, then insect herbivory will promote plant species coexistence and diversity. Our data suggest that there is a continuum in the influence of insect herbivory on plant communities from the more subtle, but important, effects of herbivory on the fecundity of nonhost species to the devastating influence of outbreaks. Also, our results demonstrate that long-term experiments are required to elucidate the role of insect herbivores. Finally, we propose that insect outbreaks are common enough in many community types, particularly forests, to warrant explicit consideration in theories of trophic regulation, particularly in terrestrial communities inhabited by long-lived plant species.
Four kinds of acetylenes and three kinds of terpenoids were isolated from Solidago altissima L. and characterized by MS, 1H-NMR and 13C-NMR spectroscopy as methyl (Z) -decaene-4, 6, 8-triynoate (Z-dehydromatricaria esther, 1), methyl 10- [(Z) -2-methyl-2-butenoyloxy] - (2Z, 8Z) -2, 8-decadiene-4, 6-diyoate (2), (4Z) -2, 4-decadiene-6, 8-diyn-4-olide (Z-dehydromatricaria lactone, 3), (4E) -2, 4-decadiene-6, 8-diyn-4-olide (E-dehydromatricaria lactone, 4), 13E, 7α-acetoxyl kolavenic acid (solidagonic acid, 5), kolavenol (6), and D : C-friedours-7-en-3β-ol (ilexol, 7). Bioassay of these compounds on the germination of lettuce seeds showed that compounds 1, 2, 3, 4, and 5 exhibited growth inhibitory activity, whereas compound 7 did not exhibit the activity.
Five weeks after sowing, significant non-linear regressions of target biomass on neighbour density were found for 59% of the 49 species combinations and significant linear regressions on neighbour biomass were found for 51% of the species combinations. The slopes of these regressions represent per-plant and per-gram competition coefficients, respectively. Neighbour species differed strongly in competitive effect per plant. Differences in effect per gram, response per plant, and response per gram were much weaker. Nevertheless, consistent competitive hierarchies were found for both effect and response on both a per-plant and per-gram basis. Neighbour species with larger seed mass and larger maximum potential mass had stronger per-plant competitive effects, whilst neighbour species with higher maximum relative growth rates had stronger per-gram competitive effects. The reverse of this latter pattern was seen for competitive response: target species with lower maximum relative growth rates were better response competitors. -from Authors
I elaborate an hypothesis to explain inconsistent empirical findings comparing phenotypic plasticity in colonizing populations or species with plasticity from their native or ancestral range. Quantitative genetic theory on the evolution of plasticity reveals that colonization of a novel environment can cause a transient increase in plasticity: a rapid initial increase in plasticity accelerates evolution of a new optimal phenotype, followed by slow genetic assimilation of the new phenotype and reduction of plasticity. An association of colonization with increased plasticity depends on the difference in the optimal phenotype between ancestral and colonized environments, the difference in mean, variance and predictability of the environment, the cost of plasticity, and the time elapsed since colonization. The relative importance of these parameters depends on whether a phenotypic character develops by one-shot plasticity to a constant adult phenotype or by labile plasticity involving continuous and reversible development throughout adult life.This article is protected by copyright. All rights reserved.