全 文 ：Received 6 Jun. 2003 Accepted 4 Aug. 2003
Supported by the National Natural Science Foundation of China (30270282) and the Guangdong Provincial Natural Science Foundation, China
(003031).
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Acta Botanica Sinica
植 物 学 报 2004, 46 (7): 757-766
Mechanism and Active Variety of Allelochemicals
PENG Shao-Lin1, 3*, WEN Jun1, GUO Qin-Feng2
(1. South China Institute of Botany, The Chinese Academy of Sciences, Guangzhou 510650, China;
2. U.S.Geological Survey, 8711 37th St.SE, Jamestown, ND 58401, USA;
3. State Key Laboratory for Biocontrol, School of Life Sciences, Zhongshan University, Guangzhou 510275, China)
Abstract: This article summarizes allelochemicals’ active variety, its potential causes and function
mechanisms. Allelochemicals’ activity varies with temperature, photoperiod, water and soils during natural
processes, with its initial concentration, compound structure and mixed degree during functional processes,
with plant accessions, tissues and maturity within-species, and with research techniques and operation
processes. The prospective developmental aspects of allelopathy studies in the future are discussed.
Future research should focus on: (1) to identify and purify allelochemicals more effectively, especially for
agriculture, (2) the functions of allelopathy at the molecular structure level, (3) using allelopathy to explain
plant species interactions, (4) allelopathy as a driving force of succession, and (5) the significance of
allelopathy in the evolutionary processes.
Key words: allelopathy; active variety; functional mechanism
Allelopathy is commonly defined as any direct or indi-
rect effects (stimulation or inhibitory) by one plant, includ-
ing microorganisms, on another through production of
chemical compounds that escape into environment (Rice,
1984). It has long been recognized since Democritus, a Gre-
cian scholar, who realized the chemical interactions between
plants since B.C. 3; in China, such a phenomenon was re-
corded in Qi Min Yao Shu in many agricultural processes.
Since the 1960s, following the rapid advances in chemistry,
plant physiology, biochemistry and ecology, the role of
allelopathy has increasingly become investigated (Anon,
2000; Mallik, 2000). Following the establishments of the
standard phytotoxic bioassay for allelochemicals and the
related nomenclature system, related studies then become
more precise and systemic (Macias et al., 2000a; 2000b).
More recently, growing efforts are being made to examine
the role of allelopathy in controlling the spreads of weeds,
pest insects and diseases.
Allelochemicals are the small molecular weight com-
pounds excreted from plants during the process of second-
ary metabolism (Rice, 1984). These chemicals usually accu-
mulated in plants, soils, and other surrounding organisms.
These compounds also vary in chemical composition, con-
centration and localization in plant tissues and from plant-
to-plant with changes in both biotic and abiotic conditions
(Waller and Einhellig, 1999). As more allelopathic phenom-
ena being discovered and described, studies on the
mechanisms and active variety of allelochemicals have also
dramatically increased. The purposes of this paper are (1)
to review the studies as to how the activity of
allelochemicals, varies with natural process, functional
process, excreting ways and techniques and operational
processes in investigation; (2) to discuss and categorize
the potential causes or mechanisms for these variation;
and (3) to identify future research needs and directions.
1 Variation of the Allelochemicals’ Activities
1.1 Changes in allelochemicals’ activity during natural
processes
Studies on the allelochmicals’ activity need to take many
biotic and abiotic factors into account. Some studies (Xu et
al., 1999; Zhou, 1999; Kong et al., 2002) show that allelopa-
thy is more intensive in the adverse or harsh environment
when water, light or nutrition is limited. Plants often use
allelopathy as a means to increase their competitive ability
and therefore survival rates.
1.1.1 Allelochemiclas’ activity varies with temperature
and photoperiod The intensity of light, photoperiod and
temperature all play important roles in the synthesizing of
allelochemicals. In general, longer photoperiod and higher
temperature favor the allelochmicals’ activity. For example,
Pramanil et al. (2000) found that the autotoxicity of root
exudates from Cucumis sativus changed with temperature
and photoperiod. The rate of root exudation in vegetative
.Review.
Acta Botanica Sinica 植物学报 Vol.46 No.7 2004758
and reproductive stages could be doubled under elevated
temperature and elongated photoperiod. Lobon et al. (2002)
also demonstrated that the allelopathic potential of the exu-
dates of Cistus ladanifer was enhanced by high tempera-
ture and long photoperiod. Chon et al. (2000) found that
prolonging the photoperiod can increase the autotoxicity
of Medicago sativa L.
1.1.2 Allelochemiclas’ activity varies with water Water
is the necessary condition of life and changes in water
conditions pose significant effects on the allelochemicals’
activity. In general, the activity will be enhanced when water
is in shortage. For example, some literature (Li et al., 2001)
reported that the concentration of chlorogenic acid in some
plants may be increased because of the shortage of water.
Some terpenes, such as a-pinene, b-pinene, cineole, cam-
phor and can, increase their volatiles under dry conditions.
Dias and Dias (2000) found that prolonging drought can
increase the allelopathic activity of Datura stramonium.
1.1.3 Effects of soils on allelochemiclas’ activity There
is a massive interface between plant roots and soils, where
material exchanges and reciprocal effects between each
other occur. Therefore, soil is a critical factor that affects
the allelochemicals’ activity. Rojo et al. (2000) found that
phytoplankton structure and dynamics were related to al-
lelopathy in a semiarid wetland following the increase of
eutrophication. The study of Hall et al. (1983) showed that
the input of N, P can reduce the allelopathic inhibitory of
Solidago pacifica Juz, Festuca ovina L. and Helianthus
annuus L. Roth et al. (2000) studied the allelopathy of sor-
ghum on wheat under several tillage systems, and found
that allelopathy might be reduced by prompt tillage and
other practices that promote rapid decomposition of sor-
ghum stover. Kidd and Proctor (2000) examined the growth
response of ecotypes of Holcus lanatus L. in different soil
types in Northwest Europe to phenolic acids, and found
that the allelopathic activity varies with soil pH. Souto et
al. (2000) studied the relationships between phenolics and
soil microorganisms in spruce forests and found that phe-
nolic compounds can stimulate fungi and cellulose
hydrolyzers in the winter, but inhibit cellulose hydrolyzers
in summer. Mattner and Parbery (2001) demonstrated that
rust may enhance the allelopathy of Lolium perenne L.
against Trifolium repens L. Blum et al. (2000) found that
bulk-soil and rhizosphere bacteria can have considerable
influence on the types and concentrations of phytotoxins,
including phenolic acids on the root surface.
1.2 Within-species variations in allelochmicals’ activity
Allelochemicals’ activity is highly species-specific and
changes among tissues and also with maturity of plants of
the same species. Variation in allelochemicals’ activity dur-
ing the excrete process indicates that plant itself is also a
key controlling factor. Some studies (Jensen et al., 2001)
showed that a certain gene controls the output of
allelochemicals and different allelochemicals are controlled
by different genes and in different time. This proves the
feasibility of using genes to study the mechanisms of
allelopathy.
1.2.1 Allelochemicals’ activity varies with plant acces-
sions Different plants, even different accessions of the
same plant, will produce different allelochemicals. Wu et al.
(2000a) analyzed the phenolic acids in root tissues of 58
wheat accessions, and demonstrated that the concentra-
tions of allelochemicals of different accessions were very
different. Wu et al. (2000b) evaluated the allelopathy in the
seedlings of 453 wheat accessions against Lolium rigidum
by using the equal-compartment-agar method (ECMA). He
demonstrated that there was a considerable genetic varia-
tion in allelopathic activity in wheat germplasms. Tang and
Sun (2002) studied allelopathy of 700 rice accessions against
vegetable and their result demonstrated that allelopathic
intensity varied with the accessions and the allelopathy
among local varieties was stronger than that among culti-
vated varieties. Kamara et al. (2000) investigated the ef-
fects extracts from levels and much of 14 trees on maize
germination, growth and yield in the laboratory and field
experiment, and all data showed great variations in
allelochemicals’ activity.
1.2.2 Allelochemicals’ activity varies with plant tissues
Most tissues of plant, such as leaf, flower, fluid, stem, root
and seed, even litter, can release a certain amount of
allelochemicals into the surrounding environments. These
allelochemicals can be very different as different parts or
tissues of plants have different physiological functions.
The extracts from the roots and stems were reported (Mo
and Fan, 2001) that have autotoxicity and inhibit the root-
ing and germination processes of Braguiera gymnorrhiza,
yet other parts of the plants can stimulate its germination.
Wu et al. (2001) examined the changes in allelopathic con-
tent 2,4-dihydroxy-7-methoxy 1,4-benzoxazin 3-one
(DIMBOA) in different parts of wheat, and found that
DIMBOA level in the root tissues is the highest followed
by the stems. Ben-Hammouda et al. (2002) studied barley
autotoxicity from the roots, stems and leaves extraction of
barley, and the result showed that the leaves were the most
important source of allelopathic substances, and the roots
were the last. Ben-Hammouda et al. (2001) also investi-
gated the phytotoxicity of Hordeum vulgare on Triticum
durum and T. aestivum, and showed that the allelopathic
PENG Shao-Lin et al.: Mechanism and Active Variety of Allelochemicals 759
potential increased with physiological maturity, and leaves
and roots were the most phytotoxic plant pats in H. vulgare
plant parts. Huang et al. (2000) studied the changes of total
phenolic content in decomposing Chinese fir, and found
the order of total phenolic content in different parts of
stump-roots was as follows (from the highest to the lowest):
root > stump heartwood > stump-roots.
1.2.3 Allelochemicals’ activity varies with plant maturity
Plant tissues’ maturity also affects the allelochemicals’ con-
tent and intensity. Some studies (Wang et al., 2001; Hu
and Kong, 2002) found that the quantity and content of
allelochemicals in soybean stubs were different in different
decomposing time and growth stages. Sharma et al. (2000)
found that the allelopathic intensity increased by the age
of Populus deltoids. Huang et al. (2000) found the total
phenolic contents in stump-roots of Chinese fir decreased
with increasing age of stump-roots.
1.3 Changes in allelochemicals’ activity during func-
tional processes
Allelochemicals is a kind of small molecular secondary
metabolite. The functional processes in allelopathy are
chemical reactions among plants. The rate and intensity of
chemical reactions are controlled by many factors, among
which the compound structure and initial concentration
are especially important. Therefore, predicting the
allelochemicals’ activity must take compound structure and
detected concentration into account.
1.3.1 Allelochemicals’ activity varies with its initial con-
centration Under certain conditions, the rate of an el-
ementary reaction is positively related to the reactant’s con-
centration with reactive coefficient as product. Wang et al.
(2001) found that malonic acid and 1, 2-benzennedicarboxylic
acid inhibited the day matter accumulation in seeds, plant
height, and germination of soybean, and the allelopathic
intensity increased as concentration increased. Hu and
Kong (2002) found that the allelochemicals, excreted by
root of Arachis hypogaea before four-leaves, stimulated
the seedling growth of rice in low concentration while in-
hibited in high concentration. Sinkkonen (2001) developed
a biological response model for the density-dependent
chemical interference based on the plant responses to many
phytochemicals changes from stimulatory to inhibitory
as the concentration of the phytochemical increases.
Mucciarelli et al. (2000) investigated the effects of 3,
4-dihydroxybenzoic acid on Nicotiana tabacum L.
Their result showed strong inhibitory at the highest con-
centration but stimulation effects at the lowest
concentration.
1.3.2 Effects of compound structure Nilsson et al. (2000)
characterized the different phytotoxic potentials of two
closely related dwarf-shrub species, Empetrum nigrum and
E. hermaphroditum, and found that these negative effects
were related to the different substitution of a bibenzyl in
the two species. Macias et al. (2000c) tested 11 natural and
synthetic podolactones and found that their activities re-
quired specific structure. They then proposed a model for
potential natural herbicide. Goo et al. (2001) extracted the
underground portion of Allium fistulosum and detected
the allelopathic polysaccharide. He showed that sugar
moiety and/or molecular size were important for the
allelochemicals’ activity based on the evidence of their ef-
fects on the growth of rice seedings.
1.3.3 Allelochemicals’ activity varies with mixed degree
Purity and mixture are very different in their chemical and
physical properties. Therefore, allelochemicals’ activity may
vary with the mixed degree. Chaves et al. (2001) detected
11 allelochemicals in the exudates of Cistus ladanifer, and
studied the effect of each of them and their combinations
on germination, cotyledon emergence, root length, and
cotyledon length of Rumex crispus. He discovered that the
later produced a greater negative effect than when acting
alone. Saario et al. (2002) extracted allelochemicals, phe-
nolic acid and benzoic acid from air-dried shoots of
Vaccinium vitisidaea, and found that both pure acids have
strong inhibitory effects on seed germination of Lepidium
sativum while the mixed acid has no allelopathy. Dias and
Moreira (2002) studied the effects of phytotoxic activity of
both single and combined application of water soluble and
volatile compounds of Cistus ladsnifer on the germination
and early root growth of subterranean clover. Antagonism
was found between water solution and volatiles resulting
in a reduction of inhibition or a shift from inhibition to
stimulation, but the early root growth was always inhibited
and only by water solubles. These results showed that the
simultaneous presence of water solubles and volatiles might
lead to changes of the chemical nature of metabolites. Kong
et al. (1998) examined the interactions among allelochemicals
of Ageretum conyzoides and found synergistic actions
among allelochemicals.
1.4 Possible effects of research techniques and opera-
tion processes on allelochemicals’ activity
Many factors can affect the result of extraction and pos-
sible human or operational errors or bias involve extract
selection and extraction conditions during the study. These
factors have not been paid enough attention so far yet
they can make comparison among studies very difficultly.
For this reason, standardization in the extraction and op-
erational processes is thus critically needed.
Acta Botanica Sinica 植物学报 Vol.46 No.7 2004760
1.4.1 Allelochemicals’ activity varies with extraction
The selection of extracts is very important because it di-
rectly affects the feasibility of the operational process and
the quality and quantity of the products, therefore extrac-
tion selection must be taken into account in the study of
allelochemicals’ activity. Yan et al. (2000) studied the soy-
bean soil extracts using water, phosphoric buffer solution-
ether and ethanol on soybean and wheat germination, and
showed the allelopathic potentials were very different when
extracts were used. Kato-Noguchi (2000; 2001) also dis-
covered different allelopathic potentials when n-hexane-
soluble, acetone-soluble and water-soluble were used for
the extracts of Evolvulus alsinoides and Melissa officinalis,
with water extraction having the strongest allelopathic
activity. Burgos and Talbert (2000) studied differential ac-
tivities of 3H-benzoxazolinone (BOA), 2,4-dihydroxy-1,4
(2H) benzoxazine-3-one (DIBOA) and crude water extract
of Secale cereale “Elbon” in culture dish bioassays using
several vegetable and weed species, and showed that
DIBOA extract had the strongest allelopathic intensity.
1.4.2 Allelochemicals’ activity varies with extraction
condition The extraction condition can affect the allelo-
pathic potential as well. For example, temperature affects
the activity and saturation of alleochemicals and time af-
fects the extraction degree of allelochemicals. The compari-
son among allelochemicals obtained from different extract-
ing conditions showed that extracting time and tempera-
ture have important influence on the allelochemicals analy-
sis result (Wang and Zhao, 2001). Prates et al. (2000) evalu-
ated the effect of cold and hot aqueous extracts of Leucaena
leucocephala on germination and growth of Zea mays, and
showed that the extracts obtained using cold water had no
phytotoxic effect on the germination and plant growth while
the extraction using hot water caused reduction in root
length.
1.5 The induced mechanism of the allelochemicals’
variety
There are mainly four parts about the induced mecha-
nism of the allelochemicals’ variety in physiology:
Carbon/Nutrient Balance, CNB hypothesis（Bryant et
al., 1983: Secondary metabolites, such as phenols, terpene
and other compounds whose structure is C, H, O) in plants
associate with C/N; on the contrary, secondary metabolites,
such as alkaloid, are negative correlation with C/N.
Growth/Differentiation Balance, GDB hypothesis
(Wareing and Phillips, 1981): Plants give priority to growth
in plenteous resource while to differentiation in shortage.
Any factors, which affect plant growth more than photo-
synthesis such as undernutrition, low temperature, and high
CO2 concentration, will increase the secondary metabolites.
Optimum Defense, OD hypothesis (Chapin, 1987): Plants
will produce secondary metabolites only when they attain
more defense profits than growth profits.
Resource Availability, RA hypothesis (Coley, 1985):
Resource availability in the environment has been proposed
as the major determinant for both the amount and type of
plant defense. When resources are limited, plants with in-
herently slow growth are favored over those with fast
growth rates; slow growth rates in turn favor more invest-
ments in defenses.
Comparing the four hypotheses above mentioned (Kong
et al., 2000) showed that the most remarkable difference
among them is whether plants produce the secondary me-
tabolites actively or passively. The first two hypotheses
(CNB and GOB) consider the metabolites as passive prod-
ucts due to changes in the surrounding environments that
led to substance accumulation in plants. The last two theo-
ries (OD and RA), however, consider the metabolites as
voluntary products due to changes in the production cost.
Although these four hypotheses cannot explain all the va-
rieties of allelochemicals, they have valuable implications
in practical applications.
2 Mechanisms of Allelochemicals’ Functions
Presently, studies on the allelopathy mechanisms mostly
concentrate on the physiology. Allelochemicals first dam-
age the cytolemma, and then send the stress information
into the cell through the target point on the cytolemma to
affect the adsorption of incretions and ions. The growth of
plant can be either stimulated or inhibited due to cell divi-
sion and photosynthesis caused by the adsorption of
incretions, ions and water.
Studies in physiology can be very insightful for allel-
opathy research. However, most of these studies have fo-
cused on a single plant function and cannot explain the
mechanisms of allelopathy fully. Other mechanism such as
genetics, need to incorporated onto more comprehensive
studies to investigate the similarities and differences in al-
lelopathy therefore to form an integrating allelopathy mecha-
nism theory.
2.1 The effect on cytolemma
Allelochemicals can affect the structure, function and
permeability of cytolemma. For example, Pflumacher (2002)
has shown that algae themselves can produce a
cyanobacterial secondary metabolite, microcystin-LR,
which has a strong allelopathy on aquatic macrophytes
such as Ceratophyllum demersum and Myriophyllum
spicatum by changing the pigment patterns. Galindo et al.
PENG Shao-Lin et al.: Mechanism and Active Variety of Allelochemicals 761
(1999) found a sesquiterpenes, dehydrozaluzanin C, which
can increase the cellar permeability of cucumber cotyledon
and destroy the function of protoplast. Politycka (1999)
used derivatives cinnamic and benzoic acids to treat 7-d
cucumber roots, and found that glucosylated phenolics
and phenol-beta-glucosyltransferase (PGT) can affect the
membrane permeability. Mucciarelli et al. (2000) reported
that 3,4-dihydroxybenzoic acid inhibited Nicotiana tabacum
in the proliferation in leaf explants, callous growth, shoot
regeneration and root growth in micropropagated plants.
2.2 The effect on the adsorption of incretions and ions
The adsorption of incretions and ions can be strongly
affected by allelochemicals. For example, Politycka (1999)
found that phenolic acids can increase the activity of
polyamine oxidase in cucumber seedlings. Baleroni et al.
(2000) found that allelochemicals, ferulic and p-coumaric
acids, affect lipid and fatty acid composition during the
seed germination of Brassica napus. Doan et al. (2000)
studied allelopathic actions of the alkaloid 12-epi-
hapalindole E, isolated from the Cyanobacterium
fischerella, and the indolophenanthridine calothrixin A, from
Calothrix sp. The result showed that both compounds in-
hibited RNA and protein synthesis, but the levels of such
effects strongly depend on the polymerase concentration
and the later also inhibited DNA replication. Muscolo et al.
(2001) studied respiratory enzyme activities and oxidative
pentose phosphate pathway enzymes during the germina-
tion of Pinus laricio seeds treated with phenols extracted
from different forest soils, and found that both enzymes are
inhibited. Some other studies (Li et al., 2001) showed that
excretion of roots and phenolic acids can inhibit the roots
to adsorb ions, and there is a linear relationship between
the inhibition and the contact area between roots and phe-
nolic acids.
2.3 The effect on the growth of plant
Allelochemicals affect the photosynthesis and plant
growth by destroying the chlorophyll. Ervin and Wetzel
(2000) found that aqueous extraction from aboveground
Juncus dffusus tissues retard the Eleocharis obtuso seed-
lings by decreasing the concentration of chlorophyll. Zeng
et al. (2001) studied the allelopathy of Secalonic acid F
(SAF) produced by Aspergillus japonicus. The result
showed that SAF significantly reduced the defensive abili-
ties of plant (i.e. reduced the activibility of superoxide
dismutase and peroxidase, lowered the photosynthetic rate
and the reduction activity of the rot system, damaged the
stratiform structure of the chloroplasts and the membranes
and structure of the nuclei) and then inhibited the plant
growth. Barkosky et al. (2000) studied the effect of caffeic
acid, an allelochemical produced by Antennaria
microphylla, on the respiration, photosynthesis and cal-
lus culture growth of Euphorbia esula, and found that a
disruption of plant water relations is the primary mecha-
nism of plant growth inhibition.
3 Perspectives for Future Research
Almost all types of ecosystems, including ocean (Pawlik,
2000), lake (Schagerl et al., 2002), forest (such as tropic rain
forest (Prugnolle et al., 2001) and boreal forest (Nilsson et
al., 2000), meadow (Bai et al., 2000), wetland (Rojo et al.,
2000) and semi-arid region (Rojo et al., 2000), have
allelopathy. Also, almost all kinds of plants, from algae
(Doan et al., 2000) to macrophytoplankton (Rengefors and
Legrand, 2001), from soybean (Wang et al., 2001) to rice
(Tang and Sun, 2002), from dwarf shrub (Nilsson et al.,
2000) to tall tree (Prugnolle et al., 2001), and from herba-
ceous plant (Kato-Noguchi, 2000) to xylophyte (Sharma
and Samra, 2000) have allelopathy. Although there are dif-
ferences of the explanations (Inderjit and Weiner, 2001;
Federle et al., 2002; Inderjit and Mallik, 2002), allelopathy
has been broadly accepted. As a hotspot in chemical
ecology, allelopahty plays important role in ecosystem
management. Future research should focus on the follow-
ing areas.
3.1 To identify and purify allelochemicals more effectively,
especially for agriculture
Most work (Anon et al., 2000) on the extracting, identi-
fying and purifying allelochemicals has been done since
the 1940s, and hundreds of allelochemicals (Li, 2001) have
also been identified. Rice (1984) has classified these
allelochemicals into 14 categories based on their diversiform
chemical structures. However, how to identify them quickly
and to purify them accurately is still a big challenge.
Therefore, one of major focuses in the future is to renovate
the equipments and improve technologies in a timely
fashion. Increasing studies begin to look for new safer pes-
ticides instead of synthetical pesticides that can cause se-
r i o u s en v i r o n me nt a l an d he a l thy p ro b l ems .
Alleolochemicals, which can inhibit the growth of weeds,
become the most favorable choice for natural pesticides
(Chittapur et al., 2001; Nagabhushana et al., 2001; Reigosa
et al., 2001). There have already been many identified
allelochemicals that can be used to produce natural
weedicides or pesticides (Narwal, 2000; Xuan et al., 2002).
Yet, much remains to be done in order to transform the
laboratory studies into massive commercial products. Some
studies (Nishimura et al., 2000; Olofsdotter et al., 2002)
also show how to use allelochemicals as additives. In short,
Acta Botanica Sinica 植物学报 Vol.46 No.7 2004762
high diversity of allelochemicals means that they can be
used in multiple purposes. Extracting or synthesizing these
compounds has great important ecological significance and
economic potentials. We predict that allelochemicals will
become an important impetus for ecoagricultural
development. On the other hand, studies on allelopathy
can help explain the inhibitory effects or toxicity in the pro-
cesses of rotation, intercrop and mulch and such studies
can also help avoid wasting billions of dollars in worldwide
agricultural practices.
3.2 Functions of allelopathy at the molecular structure level
Presently, studies on the mechanisms of allelopathy
focus on ecophysiology, i.e. how plants affect the growth
of others through allelopathy. However, these studies have
not formed any solid theoretical framework and many re-
lated issues are still debatable. Future studies should pay
more attention to molecular or gene-level phenomena.
Roshchina（2001）has attempted to explain the mecha-
nism of pollen allelopathy at molecular-cellular level in detail.
Yet, even few studies pursue to identify the genes that
produce allelopathy materials. The gene level research will
help explain the mechanisms of allelopathy more completely,
and can help produce allelopathic crops using transgenes
(Weller et al., 2001). This way can avoid using much pesti-
cide thus actualize real green agriculture (Duke et al., 2001).
3.3 Using allelopathy to explain plant species interac-
tions
The relationships among plants can be advantageous,
harmful or neutral (Wang et al., 1995), and most studies on
this have concentrated on the resources of foods and
spaces. Recent studies show that allelopathy is also one of
key factors structuring plant community by controlling
those outputs of species interactions. Regan et al. (2000)
and Ridenour et al. (2001) found that one important factor
causing the success of invasive species is allelopathy.
Mallik (2001) also found that, in some cases, allelopathy
could decrease the species diversity. Foy and Inderjit (2001)
studied the role of allelopathy in altering community struc-
ture and declining plant diversity. There are also many other
related studies (Amzallag and Seligmann, 2000). All those
studies showed that allelopathy can affect the interspecies
relationship but few have investigated the underlying
mechanisms. Therefore, future studies on the species rela-
tionships should not only identify and describe the phe-
nomena but also examine the mechanisms and compare the
similarities and differences in species interactions. When
the general rules in allelopathy have been identified and
the phenomena can be quantitatively studied, correspond-
ing kinetic and theoretical models can be then developed
and evaluated.
3.4 Allelopathy: a driverforce of succession
Succession (Peng, 1996) involves species replacement
process during the community development after
disturbance. Basically almost all the succession theories
suggest that the successional series is caused by plant
development associated with the selection pressure from
the environment. In fact, the driverforces of succession are
multiple. Allelopahty is also a driver force for forest
succession. Booth and Mania (Li et al., 1999) who studied
successions of North American grasslands and Japanese
abandoned field respectively, found that allelopathy was a
major impetus for grassland succession. Rengefors
(Rengefors and Legrand, 2001) found that allelopathy was
an adaptive strategy of winter dinoflagellates that allowed
them to outcompete other phytoplankton species. Tybirk
et al. (2000) found that Empetrum nigrum was a strong
competitor for nutrient due to allelopathy in late succes-
sional stages. Escudero et al. (2000) evaluated the allelo-
pathic potential of Artemisia herba-alba and found that
community spatial pattern in the ectones in the gypsum
environment could be at least partially controlled by
allelopathy. The study of Bai et al.’s (2000) showed that
allelopathy can stimulate the growth of pioneer species in
the grassland. Huang et al. (2002) studied the autotoxicity
of pioneer species on seed germination and seedling growth
and found that allelopathy is an important factor for pio-
neer species replacement. All these studies show that allel-
opathy is an important factor in ecological succession. It
can stimulate or inhibit the successional processes.
However, most studies now mainly concentrate on a cer-
tain successional stage in vegetation, especially grasslands,
future studies should cover all successional stages from
pioneer invasion to climax. The physiological and ecologi-
cal functions can be better understood through studies of
species replacements among dominants across all stages.
3.5 Significance of allelopathy in the evolutionary pro-
cesses
Allelopathy (Peng et al.,1999) is the product of plant
evolution, and meanwhile, it can also pose significant ef-
fects on the plant evolution. Mallik and Pellissier (2000)
studied the effects of Vaccinium myrtillus on regeneration
of Picea mariana, and found that allelopathy was a coevo-
lution result of the long-term plant communities structur-
ing process. Taylor and Irwin (2000) studied altruistic be-
havior in a patch-structured population, and found that
extraction of some allelochemicals favored the survival of
overlapping generations and promoted the productivity.
Nakamaru and Iwasa (2000) found that three strains of the
PENG Shao-Lin et al.: Mechanism and Active Variety of Allelochemicals 763
bacteria Escherichia produced colicin to allot their spatial
patterns in evolutionary processes. Dobson and Bergstrom
(2000) studied the evolution of pollen odors and found that
allelopathy serves multiple functions in both pollination
and defense: by protecting the male gametophyte and in-
creasing its dispersal by animals. These references demon-
strated that allelopathy and evolution exhibit two-way
functions. However, much remains to be done regarding
the production and function of allelopathy during evolu-
tion in the context of many other related factors and how
allelopathy may affect future evolutional processes.
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