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2
Morphophysiological Investigations in
Some Dominant Alien Invasive Weeds
Nivedita Ghayal1 and Kondiram Dhumal2
1Department
of Botany, Abasaheb Garware College, Pune, M.S.
of Botany, University of Pune, Pune, M.S.
India
2Department
1. Introduction
Allelopathy generally refers to any direct or indirect, harmful or beneficial effect of one
plant on other plants, animals including microorganisms, through the production of
chemical compounds that are released into the environment (Rice 1984). These donor plants
affect the germination, growth and development of the recipient plant species (Einhellig
1987). The science of allelopathy has a very crucial role in maintaining the phytodiversity /
biodiversity of a particular region. In fact, the phenomenon of biodiversity is the reflection
of allelopathic interactions in that area. The losses in phytodiversity which are taking place
at an alarming rate throughout the world is mainly ascribed to introduction of invasive /
alien species which substitute the native ones. Invaded plant species and their success as
well as secret have always threatened the world’s biodiversity.
“The invasive plants are also known as alien, exotic or introduced ones, which are new to a
specific area, become dominant, replacing / substituting the native plant species”. These
wide-spreading, non-indigenous species adversely affect the habitats they are invading in.
The most important aspect of the alien plant is their rapid growth, establishment over new
and large areas. Introduced species often find no natural enemies in their new habitat and
therefore spread easily and quickly, especially in open disturbed areas. Invasive plants
reproduce fast, either vegetatively or by seed. Their phenomenal growth allows them to
overwhelm and displace existing vegetation and form dense Monothickets.
1.1 Ecological impacts of invasive plants on the environment
The general ecological impacts of invasive plants on natives and their surrounding
environment are given in nutshell:
Competition with (and/or replacement of) native plants along with rare and
endangered once.
Loss of habitat and food sources of native insects, birds, wildlife and plants including
microorganisms.
Disruption of native plant-animal associations
Elimination of native plant communities
Prevention of establishment of native plants
Acute competition for space, water, sunlight and nutrients due to its reduction
Change of the soil structure and chemistry
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Plants and Environment
Morphophysiological interactions with native flora and fauna through release of
allelochemicals / ecochemicals
1.2 Scope of allelopathy
At present it is well established that allelopathic phenomenon exist in different ecosystems
including forest ecosystem and it can be exploited for increasing the productivity of crops as
well as forest plant species in sustainable manner. According to Reigosa et al. (1999),
allelopathy can affect distribution pattern of plants and biodiversity. They further explained
that in a climax forest, germination and growth of understorey species must cope with
allelochemicals released by the dominant trees. Those trees could release different
chemicals, producing differences in the species composition. Similarly, Carballeira and
Reigosa (1999) also indicated that monocultures (pure stands) allow the accumulation of
particular allelochemicals affecting species composition. The occurrence of some weeds
growing better than others within a monoculture could be a result of accumulation of
allelochemicals. The allelopathic effects can affect small-scale vegetation patterns, by
strengthening the associations between plants or not allowing them to grow in their vicinity.
The research in allelopathy has increased greatly from 1960 onwards (Putnam 1985).
Inderjit et al. (2005a, b) has discussed in detail the challenges, achievements and
opportunities in allelopathy research. They further highlighted that the novel research
findings of allelopathy relevant to enzymes and genes involved in production of putative
allelochemicals, allelochemical persistence in the rhizosphere, the molecular target sites of
allelochemicals in sensitive plant species and the influence of allelochemicals upon other
organisms will lead to enhanced utilization of natural products for pest management or as
pharmaceuticals and nutraceuticals. The research and development in allelopathy is of
extreme urgency for improvement of agriculture, forestry and global environment (Reigosa
and Pedrol, 2002), because it deals majorly with invasive and native plant species.
2. Allelobiogenesis - concept and mechanism
Allelobiogenesis is nothing but the stress created by allelopathic effects of donor plants on
recipient plants. In other words it is biotic stress and at the same time it is abiotic stress also.
Allelobiogenesis is a typical stress combination of biotic and abiotic factors. Plant – plant,
plant – animal and plant – micro-organism interactions can be considered as biotic stress.
The influence / stress of one plant on the other plant is mainly through the phytochemicals
/ ecochemicals / allelochemicals released by these donor plants. Hence the stress is
obviously of abiotic nature. These allelochemicals are mainly secondary metabolites like
alkaloids, glycosides, tannins, flavonoids, phenols etc. and the stress created by such
allelochemicals is abiotic stress. The stress created by such allelopathic interaction or
allelochemicals is allelobiogenesis. A weed exhausting nutrients from the soil voraciously
and producing nutrient stress on associated crop as it shows dominance on associated crop
by its faster growth and encroachment over crop species is biotic allelobiogenesis, e.g.
Parthenium the invasive weed growing in association with Sorghum.
The exotic weed Parthenium is releasing large no. of allelochemicals through root exudation,
leaching and volatilization in the surroundings and these allelochemicals cause very adverse
effects on seed germination and growth and all the metabolic processes such as
photosynthesis, respiration, absorption of water and minerals. This stress can be well
explained as “abiotic allelobiogenesis”.
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
17
Weeds have many ill / negative characters, which cannot be neglected at all. Many of the
weeds cause damages to agroecosystems and also disturb/ reduce natural phytodiversity.
Weeds cause great harm to the crops in various ways as they cause 30 – 40% yield losses,
increase the expenditure of various cultural practices, reduce the efficiency of agricultural
implements. Perennial weeds reduce quality of fertile lands, cause obstacles for water
flowing in canals. Weeds reduce crop yield and its quality as they compete with crops for
resources like soil, water, nutrients and light. Weeds are alternative hosts for many pests
and pathogens. Many weeds like Prosopis, Calotropis etc. reduce the germination capacity of
crops’ seeds due to the phytotoxins/ allelochemicals/ ecochemicals, many a times which are
the secondary metabolites, secreted by them in the soil.
Aquatic weeds like Eichhornia and different types of algae produce toxins, which are
harmful to aquatic flora and fauna. Weeds harbour organisms like mosquitoes, which cause
or transmit diseases. Some weeds are poisonous to humans and produce pollens, which
cause allergies. These studies will be more helpful, if emphasis on interactions among the
plants is highly focused by the researchers. Studies on allelopathic potential and the
biochemical characterization of native and invasive weeds has become the top priority to get
rid of the ill effects of native and invasive weeds.
Diagram 1. Mechanism of action and physiological effects
2.1 Allelopathic interactions between plants
Allelopathic interactions are primarily based on the synthesis and release of secondary
metabolites by higher plants that initiate a wide array of biochemical reactions, which
induce several biological changes, however, many of these are yet to be understood. In
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Plants and Environment
nature, many plant species grow together and interact with each other by inhibiting or
stimulating the growth and development through allelopathic interactions. In any
ecosystem, the dominant plants growing within it are exhibited in the form of pure stands
or monothickets. Such ecosystems always show the zones of inhibition around them (Nilsen
2002, Chase and Leibold 2003). The ecosystems infested by dominant weeds show drastic
alterations in their structure and function.
All the weed species, which are the part of dynamic ecosystems, originate in natural
environment and become hurdle to the crops (Aldrich 1984). These weeds have some
diagnostic features, such as short seed dormancy period, high rate of seed germination,
rapid seedling growth, high reproductive ability, life cycle of a short span, very high
environmental plasticity, self-compatibility, effective and efficient methods of dispersal of
propagules, production of different types of novel ecochemicals or allelochemicals and
tolerance to biotic and abiotic stresses (Baker 1965), which enable them to grow and survive
in varied habitats and inhospitable ecological conditions.
As a result of this these weeds are becoming dominant throughout the world (Colautti and
MacIsaac 2004, Lee and Klasing 2004, Jeschke and Strayer, 2005). As stated by Li et al. (2009),
the invasion of exotic weeds is mainly due to their easier establishment and faster growth
under diverse environmental conditions. Lonsdale (1999) claimed that the propagules’
pressure, adaptive characters and susceptible environment favour the invasibility to which
Carlton (2001) called biological invasion.
2.2 Plant invasions and encroachments
The whole biosphere is facing the problem of invasion of different weed species, hence
studies on plant invasions and allelopathy will help in understanding the mechanism of
invasions, and consequences of them on global biodiversity and ecosystem functioning.
These invasions pose many ecological, economic and social problems. A team approach to
solve these complicated problems is necessary.
According to MacDougall and Turkington (2005), the alien species highly out compete the
native species or escape from adverse environmental conditions and dominate the
community. According to vacant niche hypothesis (Elton 1958) the empty places such as
barren lands, roadsides, open grounds etc. are generally invaded by such weeds. There are
different hypotheses explaining the invasion mechanisms (Inderjit et al. 2005a, b). The
diversity of these weeds is governed by population, ecosystem dynamics, disturbances,
nutrient supply and climatic factors. The biotic restrictions on them, force to skip from their
previous habitat and start surviving in new habitats, helping in the process of invasion. The
enemy release hypothesis advocated by Mack et al. (2000) also supports the above view. If
the invader is resistant enough and tolerant to herbivory, then its competitive ability
increases and it becomes very aggressive due to production of some defensive chemicals
(Carpenter and Cappuccino 2005).
The disturbances by some plant species, grazing pressure, fluctuation in resource
availability (Davis et al. 2000), soil moisture, available light (Meekins and Mc Carthy 2001),
phenotypic plasticity and hybridization (Daehler 2003) results in to successful invasion. The
novel weapon hypothesis (Callaway and Ridenour 2004), biotic resistance hypothesis
(Maron and Vilà 2001), and the genetic shift hypothesis (DeWalt et al. 2004) also explain the
mechanism of invasion. To understand the distribution of invasive weeds and their
associates in a natural community, the eco-distribution mapping is of paramount
importance.
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
19
Biological species invasions alter ecological systems in a multitude of ways. Worldwide an
estimated 80% of endangered species could suffer losses due to competition with or
predation by invasive species.
3. Compilation of updated work
To have the information about the previous work done on allelopathy in general, its role in
different fields of agriculture and botany, different types of interactions such as weed –
weed, weed – crop, the impact of leachates, extracts and residues on recipient plants,
allelochemicals existing in different donor plants, their chemical structures, mode of release
of these ecochemicals in the environment, their accumulation, mechanism of action, their
effect on seed germination, seedling growth, mineral nutrition, microbial activity in the soil
etc. a review of literature is given in nutshell.
Studies on allelopathy were made thousands of years before the term was coined by Molisch
(1937). The term allelopathy is derived from two Latin words Allelon means each other and
pathos means to suffer. He, for the first time studied the effect of numerous plant species and
their plant parts viz.- roots, shoots, leaves, flowers, fruits, leachates, extracts and residues on
seed germination, seedling growth and maturity of crops. Later on many scientists at
different corners of the world, contributed to this field by carrying out the research on
various aspects of allelopathy. At present the research on allelopathy is being carried out in
more than 85 countries. In India, the research in this field took a great speed after 1950.
Vilai-Santisopasri (2003) studied the allelopathic effects of Eupatorium adenophorum Spreng.
on growth of some crops and weeds. Hierro and Callaway (2003) had investigated in detail
the invasion of exotic plants and their role in allelopathy. Many workers like Rice (1979),
Gill and Sandhu (1996), Pawar and Chavan (1999), Chou (1999), Wang et al. (2001), Cheema
et al. (2002) had great contribution in allelopathy through their basic research. Recently,
many researchers like Narwal et al. (2003a, b), Podolska et al. (2003), Navaz et al. (2003),
Batish et al. (2002), Singh and Singh (2003) and Azania et al. (2003) have introduced
multidisciplinary approach in allelopathy.
According to Fujii et al. (2002) allelopathy now refers to any process involving secondary
metabolites produced by plants, microorganisms, viruses and fungi, that influence the
growth and development of agricultural and biological systems. The allelopathy workers
like Bhatt and Chauhan (2000), Singh and NarsingRao (2003) and Leather and Einhellig
(2005) also claimed that secondary metabolites produced by donor plants, when released
into environment, play a key role in ecology and physiology of recipient plants. They
further advocated that the released allelochemicals as well as the phytochemicals present in
the leachates / extracts have stimulatory or inhibitory influence on seed germination,
seedling growth and yield of recipient plants.
The allelopathic impact of invasive weeds on seed germination, seedling growth, growth
parameters like plant height, number of leaves per plant, leaf area, yield contributing
parameters like number of flowers and fruits per plant, weight of fruit and grains etc in
different crops had been studied in detail by Rice (1979), Patil and Hegde (1988), Devi et al.
(1997), Kulvinder et al. (1999), Bhalerao et al. (2000a, b), Wang et al. (2001), Kong and Hu
(2001), Lin et al. (2002), Bhalerao (2003), Jadhav (2006), Hase (2008) and Vaidya (2009).
Presently the allelopathy research work is mainly focused on identification of
allelochemicals, their mode of action and ecological significance.
According to many researchers allelopathy now refers to any process involving secondary
metabolites produced by plants, microorganisms, viruses and fungi that influence the
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Diagram 2. Different pathways of synthesis of allelochemicals
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Plants and Environment
Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
21
growth and development of agricultural and biological systems. The allelopathy workers
also claimed that secondary metabolites produced by donor plants, when released into
environment, play a key role in ecology and physiology of recipient plants. They further
advocated that the released allelochemicals as well as the phytochemicals present in the
leachates / extracts/ residues have stimulatory or inhibitory influence on seed germination,
seedling growth and yield of recipient plants.
Today this subject has come into lime-light because of its multidisciplinary nature, which
covers agriculture, biological sciences, biochemistry, physiology, biotechnology and even
genetic engineering.
3.1 Invasion success of weeds
The light has been thrown on the success of invasive alien weeds outside their native
boundary and probable causes of this. The biological processes and specific characteristics of
invasive weeds are important factors in their introduction, spread, and establishment that
threatens the ecosystems, habitats, or species with economic/ environmental harm.
Therefore the detailed investigations on the ecological, physiological and molecular aspects
of invasive weeds’ allelopathy should be conducted in order to understand community
structure and declining phytodiversity.
3.2 Allelochemicals in invasive and native weed species
Isolation, identification and characterization of allelochemicals present in roots, stems,
leaves, flowers, fruits, seeds, bark, residues, litter, dried leaves (trash) and their leachates,
extracts and residues have a pivotal role in allelopathy research, without which any
predictions, possibilities, hypothesis and explanations are not possible. Asteraceae plants
with their leachates, extracts and residues of different plant parts are well known for their
allelopathic activity because of their allelochemicals like phenolic acids and terpenoids
(Chon et al. 2003).
Many researchers like Ghayal et al. (2007a, b, c) and Li et al. (2009) have given prime
importance for identification of allelochemicals, ecochemicals, novel bioactive compounds
which are the secondary metabolites existing in their leachates, extracts and residues. They
have characterized diverse groups of allelochemicals like terpenoids, flavonoids, phenolic
compounds and essential oils existing in the invasive and native weeds.
4. About the study area
The big campus of University of Pune established in 1949, at Ganeshkhind occupies an area
of 164.8 hectares, which is situated about seven km north-west of Pune city proper and lies
between 18034’ North latitude and 73053’ East longitude at an elevation of about 1880 m. At
present 1/4 th area is occupied by roads, buildings and gardens.
Ganeshkhind stands on pediment surface of amygdaloidal basalt. These rocks are traversed
by many veins and veinlets of silica and chalcedony. The poor soil of study area is reddish
brown on higher grounds and deeper dark brown (black cotton soil) on flat areas. The soils
are alkaline and are of pedocal type (Varadpande 1972). The average rainfall, climate and
other environmental conditions of the campus are more or less similar to that of Pune city.
The railfall is restricted to couple of months in monsoon and the maximum annual rainfall is
31.78cm. The temperature during hot season goes up to 40 – 420C but normally it is cool as
compared to Pune city.
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Plants and Environment
4.1 Weed floristic of study area
The phytosociological studies were conducted at all the four selected sites in Pune
University campus. The different plant species were recorded with respect to their
distribution, frequency, density and abundance. All four study sites (I to IV) showed the
vegetation composition of various types of herbs, shrubs, trees, climbers and twinners.
The results on phytosociological studies at site I reported in Table 1 (a) indicated that this
site was having highest weed diversity. The most abundant weeds at this site with
maximum frequencies were Cassia uniflora (93.33%), Achyranthes (90.00%), Synedrella nodiflora
(90.00%) and Oplismenus (83.33%). These were followed by Acalypha, Bidens, Boerhaavia and
Euphorbia geniculata, all these were at par having frequency (80.00%). Alternanthera tenella
was also showing better population with frequency 76.67%. Remaining native plants like
Cynotis and Calotropis and invasive plants have shown less frequency, density and
abundance.
The results of site II recorded Table 1(b) revealed that at this site, 43 different weed genera
were recorded including about 19 genera of invasive weeds. The most abundant weeds with
maximum frequencies were Synedrella nodiflora (96.67%), Cassia uniflora (93.33%), and Cassia
absus (86.67%). These were succeeded by Acalypha, Bidens and Euphorbia geniculata which
were at par having frequency (83.33%). Remaining plants showed discrete occurrence. At
sites I and II Cassia uniflora was showing very thick population density, as these sites were
exposed to sunlight for longer period.
The results on phytosociological studies of site III reported in Table 1 (c) illustrated that at
this site, only 24 genera were reported including about 12 genera of invasive weeds. The
plants recorded at this site in order of highest frequency were Synedrella nodiflora (93.33%),
Cassia uniflora (80.00%) and Rauwolfia (73.33%). As opposite to sites I and II, at site III, there
was complete dominance of Synedrella nodiflora only, which was virtually forming
monothickets / pure stands. Synedrella nodiflora being shade lover was showing luxuriant
growth and very high dominance at this site. The shady conditions along with high soil
moisture favoured the luxuriant growth of Synedrella nodiflora and Rauwolfia.
The results listed in Table 1 (d) regarding phytosociological studies carried out at site IV
revealed that, there were about 32 genera of weed species including 14 genera of invasive
weeds. The weeds with highest frequency were Cassia uniflora (96.67%), Synedrella nodiflora
(93.33%) and Euphorbia geniculata (76.67%), which were followed by Acalypha, Achyranthes
and Alternanthera. At this site there was highest human interference as compared to the
remaining three sites. The fast growing invasive weed Lantana camara showed successful
invasion only at this site with frequency 63.33%.
No.
1
2
3
4
5
6
7
Dominant
species
Cassia uniflora
Cassia uniflora
Acalypha ciliata
Alternanthera tenella
Synedrella nodiflora
Oplismenus compositus
Euphorbia geniculata
Associated
species
Achyranthes aspera
Blainvillea acmella
Cassia uniflora
Cassia uniflora
Cassia uniflora
--Cassia uniflora
Nature of
association
Very common
Occasional
Rare
Common
Common
Very common
Common
Table 1. (a) Weed-weed interactions at site I in Pune university campus
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
No.
Dominant species
1
2
3
4
5
6
7
Bidens pilosa
Cassia uniflora
Triumfetta rhomboidea
Alternanthera tenella
Cassia absus
Cassia uniflora
Cassia uniflora
Associated
species
Cassia uniflora
Achyranthes aspera
Cassia obtusifolia
Boerhaavia erecta
Achyranthes aspera
Synedrella nodiflora
Parthenium hysterophorus
Nature of
association
Very common
Very common
Common
Common
Common
Occasional
Rare
Table 1. (b) Weed-weed interactions at site II in Pune university campus
No.
Dominant species
1
2
3
4
5
Synedrella nodiflora
Synedrella nodiflora
Cassia uniflora
Cassia uniflora
Rauwolfia tetraphylla
Associated
species
Cassia uniflora
Achyranthes aspera
Tithonia tagetiflora
Achyranthes aspera
Euphorbia geniculata
Nature of
association
Very common
Common
Common
Common
Common
Table 1. (c) Weed-weed interactions at site III in Pune university campus
No.
Dominant species
1
2
3
4
Cassia uniflora
Cassia uniflora
Lantana camara
Acalypha ciliata
Associated
species
Achyranthes aspera
Alternanthera tenella
Cassia uniflora
Cassia uniflora
Nature of
association
Common
Common
Occasional
Common
Table 1. (d) Weed-weed interactions at site IV in Pune university campus
Mishra et al. (1997), Chapin et al. (2000), Kumar et al. (2004), Jadhav (2006), Saswade (2007)
and Thakur and Khare (2009) have also carried out the phytosociological studies on various
invasive and native weeds. The phytosociological studies on Potentilla recta and other
species, the invasive, noxious weed from Eurasia were carried out by Werner and Soule
(1976). Zouhar (2003), Endress and Parks (2004) had also conducted phytosociological
studies on these invasive weeds from U.S. The dominance of Cassia uniflora and Synedrella in
the study area may be attributed to their aggressive nature, allelolpathic potential,
adaptations in morphological and reproductive features along with specific type of
physiological, biochemical and enzymological mechanisms allowing their faster growth and
tolerance to biotic and abiotic stress conditions.
4.2 Invasion components
Along with the two dominant weed species like Cassia uniflora and Synedrella nodiflora at
all the four sites, the major co-occuring species recorded were Acalypha ciliata, Boerhaavia
erecta, Cassia obtusifolia, Lagasca mollis, Peristrophe bicalyculata, Parthenium
hysterophorus and Triumfetta rhomboidea. The fact worth to mention was establishment of
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Plants and Environment
monothickets (Bhakat et al. 2006) of Cassia uniflora at sites I, II and IV and that of Synedrella
at site III.
The results of GPS mapping of weeds in Pune University campus strongly support the
phytosociological observations recorded through quadrat studies. The GPS mapping had
given the exact latitude, longitude and altitude of each plant species. More than 200
waypoints were recorded to confirm the dominance of selected weed species like Cassia
uniflora, Synedrella nodiflora, Alternanthera tenella, Bidens pilosa, Blainvillea acmella, Acalypha
ciliata, Euphorbia geniculata, Triumfetta rhomboidea, Cassia obtusifolia etc. It has also indicated
the dominance of Cassia uniflora and Synedrella nodiflora at all the four selected sites. These
selected weeds were located at 18055’ north latitude and 73082’east longitude and an altitude
of 568.63m and 571.48m respectively.
The Millenium Ecosystem Assessment (2005) have claimed that invasive species are the
most important drivers of ecosystem change, which can very well alter the vegetational set
up of a particular area. Such phytosociological studies on various weeds occurring in crop
ecosystems have been carried out by researchers like Bartariya et al. (2005) and Seal et al.
(2009) have also reported the dominance of invasive weeds in different ecosystems.
4.3 Secrets of invasion / encroachment and aggressiveness
The invasive weeds can exploit many niches left available and keep changing the
phytodiversity of these niches or ecosystems. Unless the phytosociological studies of such
areas are carried out, it is difficult to know the extent of encroachment over natives and
invasion by the invasive plants. Phytosociology will help to understand the growth
characteristics, dominance, distribution and adaptations which enable these plants to
sustain the changes in the environment. These studies help to determine the distribution,
prevalence, competing ability, behaviour and survival of weeds (Rao, 2000). The results
recorded in Tables 1(a, b, c and d) clearly showed the higher dominance of Cassia uniflora
and Synedrella nodiflora, at different sites in the university campus amongst the co-occuring
species. These two invasive weed species have caused the reduction in the native
phytodiversity of Pune University campus. As suggested by Rizvi and Rizvi (1992),
allelopathic interactions of these weeds might be playing a crucial role in existing vegetation
pattern of Pune University campus.
The dominance of Cassia uniflora and Synedrella in the study area may be attributed to their
aggressive nature, allelolpathic potential, adaptations in morphological and reproductive
features along with specific type of physiological, biochemical and enzymological
mechanisms allowing their faster growth and tolerance to biotic and abiotic stress
conditions.
Plants are chemically well defended in their environments, because their exposure to any
stress leads to the qualitative and quantitative changes in the plant biochemicals and
enzymes as a part of defense mechanism. These defensive chemicals are nothing but
allelochemicals only, which act as feeding deterrents or alter the physiology and
development of the attacking organisms (Pathipati UshaRani 2008). Even the different
organic compounds often have role in ecological development which mediates interactions
between the donor plants and the recipient organisms. The defensive allelochemicals and
organic compounds have crucial role in the weed–weed associations formed in the campus
of Pune University. The allelopathic potential of invasive weeds like Cassia and Synedrella
can be ascribed to the above mentioned factors.
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
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Allelochemicals always affect many aspects of plants’ ecology e.g. distribution, growth,
succession, structure of communities, dominance, diversity and productivity (Takeuchi et al.
2001). The population of Cassia uniflora had always shown its shifting nature, i.e. area with
monothickets during first year will show very less population next year on the same spot. It
may be due to the resource exhaust, autotoxicity and heavy accumulation of allelochemicals
making the area inhospitable for its own growth. However, it requires further confirmation
and experimentation in details.
4.4 Morphological specifications of invasive and native weeds
An attempt was made to study the morphological and reproductive features of invasive and
native weeds from Pune university campus (Table 2). The maximum plant height was
recorded for Cassia uniflora, (104.66cm), which was followed by Triumfetta (103.66cm) and
Achyranthes (96.33cm).
The root length indicates easy and proper establishment of the plants. The maximum root
length was recorded for Alternanthera followed by Rauwolfia and Achyranthes.
The highest number of branches per plant was observed in Achyranthes and followed by
Triumfetta, while the weed species like Acalypha and Oplismenus were without any branch.
The number of branches in remaining weeds was next to the above weed species.
Cassia obtusifolia had maximum third leaf area and it was followed by Rauwolfia and
Triumfetta. The third leaf area in remaining weeds was very less as compared to them.
The results on fresh biomass per plant indicated that Cassia obtusifolia was having highest
biomass and Triumfetta was next to it. The weight of fresh biomass in the remaining weeds
was comparatively very less.
The dry biomass per plant showed wide variations ranging from 0.89g to 17.43g. The Cassia
species e.g. C. obtusifolia and C. uniflora were having highest dry biomass 17.43g and 12.4g
per plant respectively.
The highest fresh biomass per m2 area was recorded in Triumfetta, Cassia uniflora and
Blainvillea. The remaining weeds recorded comparatively less biomass per m2 area in the
campus of Pune University.
Many research workers like Sen (1977), Weaver and McWilliams (1980), Wilson (1988) had
given due importance to morphological studies of native and invasive weeds. Ehrenfeld
(2003) proposed that the invasive plants share many physical characteristics and tend to
alter habitats. They have very high productivity and above ground biomass. They grow
earlier in the season and show faster growth rate than native species. All such features
might be applicable to Cassia and Synedrella, because of which they are dominant in the
campus, showing luxuriant growth.
Unless we know the morphological features of weeds, the attempts for their effective
management are difficult. With this view, Sutherland (2004) has described all the
morphological details of different terrestrial and aquatic weeds of India. Similarly Monaco
et al. (2002) had also investigated the various morphological characteristics of different
weeds from USA. The life cycle of a plant can be understood well by its morphological
structures, developmental processes and whole plant activities that occur during each phase
of its life cycle. He further stated that selected phenotypes dominate their neighbours,
because the timing of their life history optimizes their relative fitness and minimizes
mortality. Same explanation may be true for the dominance of different invasive weeds
including Cassia and Synedrella over the natives of Pune University campus.
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Plants and Environment
Root
*Weed Plt. Ht.
length
spp.
cm.
cm.
Cul
Snl
Alt
Eug
Bod
Ach
Bln
Aca
Tum
Cab
Cfl
Bdn
Raw
Opl
p=
104.66
a± 4.18
63.66 e
± 3.18
91 b ±
6.37
73.66 c
± 2.20
46.33 g
± 2.77
96.33 b
± 5.77
66 de ±
2.64
49.66 f
± 3.47
103.66
a± 3.10
52.26
fg± 2.61
71.83
cd±
2.15
55.23 f
± 3.31
63 e ±
4.41
23.12 h
± 0.92
<0.001
17.66 c
± 0.70
17 c ±
0.85
22.66 a
± 1.58
13.3 d ±
0.39
8.16 g ±
0.48
20 b ±
1.2
5.5 h ±
0.22
4.5 hi ±
0.31
9.66 f ±
0.28
11.4 e ±
0.57
13.16 d
± 0.39
7.96 g ±
0.47
20.76 b
± 1.45
3.2.i ±
0.12
<0.001
Fresh
Fresh
Dry
No. of III Leaf
biomass
No. of
leaves / area biomass / biomass
/ m2
Branches/plt.
plt. g
/ plt. g
plt.
cm2
g
7 d ± 0.28
18 e ± 20.41 d 36.3 d ±
12.4±
2316.2 b
0.4
± 0.81
1.45
0.49
± 92.64
14.9 e ± 15.68 g ±
4. 1±
282.42 f
8 c ± 0.4
31a ±1.5
0.74
0.78
0.20
± 14.12
9 b ± 0.63
28 b ± 12.8 ef
21.5 f ±
8.3±
356.84 e
1.96
± 0.89
1.50
0.58
± 24.98
3 h ± 0.09
10 g ± 18.41 d 19.06 f ±
4.6±
114.36 g
0.3
± 0.55
0.57
0.13
± 3.43
4 g ± 0.24
11.8 fg 31.13 e ±
10.7±
108.39 g
15 f ± 0.9
± 0.70
1.86
0.64
± 6.50
11 a ± 0.66
24 d ± 12.2 fg 34.72 d ±
10.2±
347.2 e
1.44
± 0.73
2.08
0.61
± 20.83
6.33 e ± 0.25 7.33 h ± 13 ef ± 12.33 hi ±
1.43±
579.51 c
0.29
0.52
0.49
0.05
± 23.18
0i±0
26 c ± 10.5 g ± 9.33 i ±
1.75±
171.67 g
1.82
0.73
0.65
0.12
± 12.01
11 a ± 0.33
25 cd ± 33.66 c 88.33 b ±
3.1±
2473.24 a
0.75
± 1.00
2.64
0.09
± 74.19
8.33 c ± 0.41 7.33 h ± 18.5 d ± 11.66 hi ±
3.02±
139.92 g
0.36
0.92
0.58
0.15
± 6.99
6.66 de ± 0.19
8.33 c ± 0.49
5.33 f ±0.37
0i±0
<0.001
14.66 f ± 45 a ±
0.43
1.35
9.66 g ±
0.57
20.33 e
±1.42
10 g ±
0.4
<0.001
91.66 a ±
2.74
33.1 c ± 12.9 gh ±
1.98
0.77
42.66 b 56.66 c
± 2.98
±3.96
3.5 h ±
5.35 j ±
0.14
0.21
<0.001
<0.001
17.43±
0.52
366.64 e
± 10.99
2.35±
472.14 d
0.14
± 28.32
9.5±
396.62 e
0.66
±27.76
0.89 ± 112.35 g ±
0.03
4.49
<0.001
<0.001
# Data are the pooled means of three estimates each over two years ±standard deviation. ‘p-value’
denotes the significance of difference between the means by one way ANOVA statistics. a The values
followed by different letters differ significantly by Duncan’s multiple range test at p=0.05.
* Cul: Cassia uniflora Mill.non Spreng ; Snl: Synedrella nodiflora(L) Gaertn; Alt: Alternanthera tenella Colla;
Eug: Euphorbia geniculata Orteg.; Ach: Achyranthes aspera L.; Bod: Boerhaavia erecta L.; Bln: Blainvillea acmella
L.; Aca: Acalypha ciliata Forsk.; Tum: Triumfetta rhomboidea Jacq.; Cab: Cassia absus L.; Cfl: Cassia obtusifolia
L.; Bdn: Bidens biternata Lour.; Raw: Rauwolfia tetraphylla L.; Opl: Oplismenus compositus P.Beauv.
Table 2. Morphological features of invasive and native weeds
4.5 Reproductive capabilities of invasive and native weeds
The invasive and native weeds showed considerable variations in reproductive characters
(Table 3 a). The type of inflorescence in majority of the weeds studied was mostly head,
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27
Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
spike or cyme. Only in Euphorbia, it was cyathium, and in Oplismenus it was panicle. In
almost all the weeds the inflorescence was axillary, but only in Achyranthes and Cassia absus,
it was terminal.
For the number of inflorescences per plant Triumfetta, was at first rank, which was followed
sequentially by Alternanthera, Synedrella and Cassia uniflora. The weed species like Blainvillea,
Acalypha and Achyranthes were at medium position, while the least number was noted in
Oplismenus.
The number of flowers, florets and flowerbuds per inflorescence was also a diagnostic
feature for all the weeds. Acalypha was having highest number of male and female flowers
together, whilst Achyranthes was following it (Table 3a). Oplismenus was in third position
and it was followed by Synedrella. Remaining weeds had very few numbers of flowers/
florets/ flowerbuds and the lowest number of flowers was in Triumfetta.
The number of fruits per inflorescence is very important reproductive character which was
in the order of –
Snl > Ach > Bdn > Alt > Tum > Bln > Aca > Cul > Cfl > Cab > Opl > Eug > Raw (Table 3b).
The number of seeds per plant was not showing the same order as that of number of fruits
(Table 3b). This was due to the number of seeds per fruit, which is again a specific and
variable character for a particular plant. The descending sequence for number of seeds per
plant was:
Cfl > Snl > Ach > Cul > Aca > Bdn > Tum > Cab > Alt > Bod > Bln > Eug > Opl > Raw.
Weed
species
Cul
Snl
Alt
Eug
Bod
Ach
Bln
Aca
Tum
Cab
Cfl
Bdn
Raw
Opl
p=
Type of Inflorescence
Axillary raceme/ subsessile pairs,
Crowded upwards
Axillary heads
Axillary clusters
Cyathium
Umbels in terminal corymbose
panicles
Terminal spikes
Heads in erect terminal cymes
Androgynous spikes
Dense terminal and leaf opposed
cymes
Terminal raceme
Axillary subsessile pairs of flowers
Corymbose panicled heads
Umbelliform cyme
Panicle
38.0 d ± 1.52
No. of flowers, florets
or
floral buds per inflo.
8.0 fgh ± 0.32
60.0 c ± 3.00
75.0 b ± 5.25
9.0 i ± 0.27
21.0 cd ± 1.05
9.0 fgh ± 0.63
8.0 fgh ± 0.24
30.0 e ± 1.8
13.0 efg ± 0.78
21.0 g ± 1.26
25.33 f ± 1.01
23.0 fg ± 1.61
36.0 b ± 2.16
13.0 efg ± 0.52
178.3 a ± 12.48
90.0 a ± 2.7
4.0 h ± 0.12
8.66 i ± 0.43
9.33 i ± 0.27
15.66 h ± 0.93
9.66 i ± 0.67
2.0 j ± 0.08
<0.001
14.0 ef ± 0.7
14.33 ef ± 0.42
16.66 de ± 0.99
7.33 gh ± 0.51
24.0 c ± 0.96
<0.001
No. of Inflo. /
plant
Table 3. (a) Reproductive features of invasive and native weeds
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28
Plants and Environment
The results on reproductive capacity of invasive and native weeds revealed that the highest
reproductive capacity was recorded in Cassia obtusifolia, which was followed by Synedrella.
While Achyranthes and Cassia uniflora were on the third rank. The least reproductive capacity
was reported in Boerhaavia (Table 3b).
No. of No. of fruits / plant No. of
Weed
fruits
seeds / No. of seeds / plant
species
/ inflo.
fruit
Cul
9
2736 f ± 109.44
8
21888 d ± 875.52
Snl
21
26460 a ± 1323
1
26460 b ± 1323
Alt
9
6075 d ± 425.25
1
6075 gh ± 425.25
Eug
8
576 h ± 17.28
3
1728 k ± 51.84
Bod
13
5070 e ± 304.2
1
5070 hi ± 304.2
Ach
32
24192 b ± 1451.52
1
24192 c ± 1451.52
Bln
13
4280.77 e ± 171.23
1
4280.77 ij ± 171.23
Aca
1
4100.9 e ± 287.063
3
12302.7 e ± 861.18
Tum
12
4320 e ± 129.6
2
8640 f ± 259.2
Cab
14
1697.36 g ± 84.86
4
6789.44 g ± 339.472
Cfl
14
1915.91 fg ± 57.47
32
62266.9 a ± 1868.007
Bdn
37
9653.14 c ± 579.18
1
9653.14 f ± 579.18
Raw
7
495.65 h ± 34.6955
2
991.309 k ± 69.39
Opl
24
1152 gh ± 46.08
1
1152 k ± 46.08
p=
<0.001
<0.001
Reproductive
Capacity
18604 c ± 744.16
23814 b ± 1190.7
3037.5 fg ± 212.62
691.2 h ± 20.73
2028 g ± 121.68
19353.6 c ± 1161.21
2996.539 fg ± 119.86
6679.89 e ± 467.59
3247.72 f ± 97.43
3394.72 f ± 169.73
28020.11 a ± 840.60
8205.05 d ± 492.30
7183.4 e ± 502.83
6220.8 e ± 248.83
<0.001
Table 3. (b) Reproductive features of invasive and native weeds
600
a
b
c
Chl-b
ef
TChl
Opl
Raw
Bdn
Cfl
g
ef
cd
h
h
i
egh egh
ef
gh fh
Cab
Alt
0
f
Tum
100
g
g
deg deef eg deg
Aca
bd
Bln
200
f
bc bce
Bod
ab
Chl-a
d
e
Ach
a
a
Snl
300
Cul
mg g-1
400
Eug
500
Weeds
Fig. 1. Photosynthetic pigments in the invasive and native weeds
The role of reproductive capacity of weeds from arid zones was carried out by Sen (1981).
Many researchers like Khanh et al. (2009) had studied the reproductive biology of Russian
thistle, barnyardgrass, Solidago canadensis and Bidens pilosa respectively. Some have
investigated the allelopathic potential of reproductive organs (flowers and fruits) of
Lantana camara and explained their role in successful invasion, encroachment and
dominance of it.
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
29
The role of reproductive capacity of weeds from arid zones was carried out by Sen (1981)
and Kanchan and Jayachandra (1977) for Parthenium hysterophorus. The seed output and
other propagules was studied by Stevens (1957) for different weed species. Many
researchers like Young (1991), Norris (1992), Huang Hua et al. (2007) and Khanh et al. (2009)
had studied the reproductive biology of Russian thistle, barnyardgrass, Solidago canadensis
and Bidens pilosa respectively. Hu and Wang (2001) studied the reproduction of two weedy
vines. Qiaoying Zhang et al. (2009) had investigated the allelopathic potential of
reproductive organs (flowers and fruits) of Lantana camara and explained their role in
successful invasion, encroachment and dominance of it.
The reproductive characters are the probable indicators of plants’ invasiveness and
aggressiveness in the ecosystem. Not only this, but they are also the factors deciding their
density and abundance. Dekker (2005) had also opined similarly indicating the role of
reproductive features in plant invasion. Bhan et al. (1976) also emphasized on the role of
reproductive behavior of Phalaris minor in its dominance and invasion. In the present study
also, the comparison made on the basis of morphological and reproductive characters
between invasive and native weeds revealed that the selected invasive weeds were superior
in all the above-mentioned features, reflecting on their dominance over natives in the
campus of Pune University. Friedman and Waller (1983) also stated that the seeds of plants
act as allelopathic agents, releasing the different types of allelochemicals in their
surrounding environment and which help to establish their dominance.
4.6 Light harvesting components in invasive and native weeds
The results shown in Figure 1 revealed that amongst invasive weeds Cassia uniflora and
Synedrella had higher chlorophyll a, b and total chlorophyll contents, followed by
Alternanthera. Amongst invasive weeds Bidens and Blainvillea are at par for chlorophyll
contents. Amongst the natives Triumfetta was following Achyranthes for photosynthetic
pigments. Remaining invasive and native weeds were at intermediate state for the contents
of photosynthetic pigments. Whilst, Oplismenus and Rauwolfia had shown the lowest
chlorophyll contents. The invasive weeds like Cassia uniflora, Synedrella and Alternanthera
had shown maximum amount of chlorophyll a, chlorophyll b and total chlorophylls.
The results recorded on photosynthetic pigments in different invasive and native weeds
were corroborating with that of photosynthetic rate and other gas exchange parameters
(Table 4 and Figure 1). Ghayal et al. (2009) have quantified the photosynthetic pigments in
different invasive, native, aquatic as well as terrestrial weeds. Pawar (2004), Jadhav (2006),
Castillo et al. (2007), Vaidya (2009) have quantified the photosynthetic pigments in different
invasive, native, aquatic as well as terrestrial weeds. Wang et al. (2004) also recorded
significant contents of chlorophylls and better photosynthetic rate in Eupatorium. Bhalerao
(2003) had made similar observations regarding photosynthetic pigments in fern species like
Tectaria and Pteridium from Mahabaleshwar area.
Photosynthetic pigments are the master molecules in carbon assimilation process, which
govern photosynthetic efficiency. Sampietro et al. (2007) explained that the growth,
development, dominance and allelopathic potential of any plant species mostly depend on
its physiological, biochemical and enzymological characteristics. The growth, development,
dominance and allelopathic potential of any plant species mostly depend on its
physiological, biochemical and enzymological characteristics. The allelochemicals in it are
also important along with above aspects. The amount of photosynthetic pigments usually
correlates with photosynthetic rate, which is directly or indirectly reflected into
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Plants and Environment
accumulation of reserved food materials like starch and dry matter accumulation rate and
dry biomass. Considering this the dominance of Cassia, Synedrella and other native weeds
can be correlated with higher amount of chlorophyll contents, enhanced photosynthetic rate
and increased accumulation of reserved food materials.
4.7 Carbon assimilation rate of invasive and native weeds
The selected invasive weeds like Cassia, Synedrella and Alternanthera had shown the highest
photosynthetic rate, stomatal conductance and transpiration rate as compared to native
weeds such as Achyranthes and Boerhaavia (Table 4). Amongst the natives Achyranthes was
superior in all above mentioned parameters over other weeds like Triumfetta, Boerhaavia,
Cassia absus and Rauwolfia.
The third leaf area was maximum in Cassia obtusifolia, which was followed by Rauwolfia and
Triumfetta. There was no significant difference in water use efficiency (WUE) amongst the
investigated invasive and native weeds. On the basis of dry matter accumulation rate
(DMAR) Cassia uniflora was topmost, which was followed by Synedrella and Alternanthera.
Similarly the results for dry weight per plant (Table 4) indicated highest values for Cassia
obtusifolia followed by Cassia uniflora and Boerhaavia.
According to McDowell (2002) the success of invasion and dominance of invasive weeds in
any ecosystem over co-occurring species can be ascribed to their superiority in physiological
attributes like photosynthetic rate, stomatal conductance, third leaf area and DMAR, but all
such parameters mostly remained unexplained and unexplored. Understanding of such
factors may give valuable insight to resolve the problem of invasion. Photosynthesis is the
key catabolic process in the life cycle of any plant, which synthesizes various types of photoassimilates and reflects into overall productivity and metabolic status of that plant. The
secondary metabolites acting as allelochemicals are mainly derived from carbohydrates
synthesis during photosynthesis.
Research workers like Durand and Goldstein (2001) and Ewe and Sternberg (2003) have also
recorded the significant difference in photosynthetic rate, stomatal conductance,
transpiration rate and total leaf area for the various invasive weeds and claimed that these
weeds were highly dominant over the associated natives because of their superiority in
above parameters.
According to Pattison et al. (1998) successful invasive species should have elite
morphological and physiological traits, which increase their photon capturing ability and
light utilization efficiency. But unfortunately this type of invagination has remained obscure
due to paucity of experimental work, except few reports on light capturing mechanism,
photon-saturated photosynthetic rate, specific leaf area (SLA) investigated in some invasive
weeds by Ewe and Sternberg (2003). According to Durand and Goldstein (2001)
invasiveness of alien species is dependent on photosynthetic efficiency. They further
claimed that invasive species have a higher ability to capture solar radiations at the
minimum cost of energy (ATP), diverting more resources for their growth, development,
reproduction and yield. Coupled with the above distinctive features of photosynthesis, the
invasive weeds have very high abiotic stress tolerance capacity, which enables them to
survive and reproduce successfully, under extremely harsh environmental conditions like
drought.
The water use efficiency (WUE) is always positively co-related with the rate of
photosynthesis, however in present studies it has not shown any significant differences,
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
31
amongst the invasive and native weed species investigated. Funk and Vitousek (2007)
have reported the positive co-relation with leaf traits and WUE in some weeds. Blicker et al.
(2003) had also reported higher water use efficiency in the invasive weed Centaurea maculosa
over three native grasses.
Dry
WUE DMAR
weight
μmolm / m2/
/ plant
day
mol-1
g
20.41 d
1.181 a
25.02 19.16 a ± 12.40 b
Cul
29.55 a ± 4.84 0.353a ± 0.064
± 0.82
± 0.21
± 1.00
0.77
± 0.50
29.122 ab ±
14.90e ±
1.152 ab
25.28
5.90b
4.10g
Snl
0.351ab ± 0.038
6.15
0.75
± 0.242
± 1.26 ± 0.30
± 0.21
12.80ef
1.053 abc
25.93
4.18c
8.30f
Alt
27.3ab ± 0.43
0.34a ± 0.072
± 0.90
± 0.13
± 1.81 ± 0.29
± 0.58
27.137 ab ±
18.41d ±
1.048 bcd
25.89
2.66d
4.60g
Eug
0.318a ± 0.027
3.06
0.55
± 0.033
± 0.78 ± 0.08
± 0.14
1.052 abc
25.88
2.58d 10.20d
27.237 ab ±
12.20fg
Ach
0.324a ± 0.027
± 0.73
± 0.095
± 1.55 ± 0.15
± 0.61
2.01
11.80fg
0.874 cde
25.29
2.62d 10.70cd
Bod 22.1 bc ± 3.79 0.256bc ± 0.041
± 0.71
± 0.16
± 1.52 ± 0.16
± 0.64
23.308 bc ±
13.00ef
0.968 cd
24.08 0.46gh ± 1.43jk ±
Bln
0.272bc ± 0.10
8.59
± 0.52
± 0.28
± 0.96
0.02
0.06
25.84 0.85fg ± 1.75ij
21.833 bc ±
10.50g ±
0.845 cde ± 0.020
Aca
0.253bcd ± 0.006
0.73
0.06
± 0.12
± 1.81
0.45
33.66c ±
0.889 cde
25.29
1.46e 11.35c ±
Tum 22.483bc ± 5.01 0.266bc ± 0.058
1.01
± 0.19
± 0.76 ± 0.04
0.34
18.83d ±
26.68
0.26h
3.02h
Cab
19.5c ± 0.7
0.178de ± 0.014
0.731 def ± 0.038
0.94
± 1.33 ± 0.01
± 0.15
45.00a ±
25.88 0.58gh ± 17.43a ±
Cfl 21.533bc ± 0.51 0.21cde ± 0.018
0.832 cde ± 0.032
1.35
± 0.78
0.02
0.52
33.10c ±
1.016 bcd
26.12 1.09ef ± 2.35hi ±
Bdn 26.542ab ± 3.88 0.309a ± 0.044
1.99
± 0.15
± 1.57
0.07
0.14
25.45
0.32h
9.50e
42.66b ±
0.702 ef
Raw 17.867c ± 1.53 0.143e ± 0.033
± 0.0603
± 1.78 ± 0.02
± 0.66
2.99
3.50h ±
0.592 f
25.82
0.16h
0.98k
Opl 15.283d ± 1.38 0.125e ± 0.015
0.14
± 0.047
± 1.03 ± 0.01
± 0.04
<0.001
<0.001
<0.001
<0.001
0.81
<0.001 <0.001
Weed
Sps.
Photosynthetic
Stomatal
III
rate
conductance leaf area
µmol cm-2 sec-1 mmol cm-2 sec-1 cm2
Transp. rate
mmol
cm-2 sec-1
DMAR – Dry Matter Accumulation Rate
# Data are the pooled means of three estimates each over two years ± standard deviation. ‘p-value’
denotes the significance of difference between the means by one way ANOVA statistics. a The values
followed by different letters differ significantly by Duncan’s multiple range test at p=0.05.
* Cul: Cassia uniflora Mill.non Spreng ; Snl: Synedrella nodiflora(L) Gaertn; Alt: Alternanthera tenella Colla;
Eug: Euphorbia geniculata Orteg.; Ach: Achyranthes aspera L.; Bod: Boerhaavia erecta L.; Bln: Blainvillea acmella
L.; Aca: Acalypha ciliata Forsk.; Tum: Triumfetta rhomboidea Jacq.; Cab: Cassia absus L.; Cfl: Cassia obtusifolia
L.; Bdn: Bidens biternata Lour.; Raw: Rauwolfia tetraphylla L.; Opl: Oplismenus compositus P.Beauv.
Table 4. Photosynthetic parameters of invasive and native weeds
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32
Plants and Environment
Photosynthesis is the unique process that governs the plant productivity and biomass
production. Hence the increased photosynthetic rate in invasive weeds might be able to
increase biomass as the rate of dry matter accumulation rate resulting into higher biomass
production. All these factors might be responsible for the higher dominance of selected
invasive weeds in the study area. The invasive weeds studied in the present investigation
like Cassia uniflora, Synedrella and Alternanthera had shown higher rate of photosynthesis,
stomatal conductance, transpiration and dry matter accumulation rate over other invasive
and native weeds, which might be the basic reason for the success of invasion and
dominance in the campus of University of Pune (M.S.)
4.8 Biochemical nature invasive and native weeds
The results recorded on organic constituents like total sugars and starch indicated that
Cassia uniflora had highest contents, which was followed by Synedrella, Alternanthera and
Bidens. The remaining invasive and native weed species were on par for the contents of total
sugars and starch, while Cassia absus, Rauwolfia and Oplismenus were at par but lower than
the above mentioned weeds for starch and total sugars (Figure 2).
The invasive weeds like Cassia uniflora had shown highest contents of proteins and free
amino acids, which was followed by Synedrella and Alternanthera. While Bidens, Blainvillea
and Euphorbia were at par. The native weed Achyranthes had maximum contents of proteins
and free amino acids, followed by Triumfetta and Boerhaavia. While remaining weed species
had comparatively very less contents of proteins and free amino acids (Figure 3).
The dominant invasive and native weeds were having comparatively higher contents of
reducing and total sugars, starch, proteins etc. They further explained that the superiority in
organic constituents was contributing for the luxuriant growth and allelopathic potential.
The chemicals released from damaged roots, root exudates and leaf leachates such as amino
acids and carbohydrates may not directly act as allelopathic agents, but they can modify the
activities of allelochemicals. The maximum contents of organic constituents like total sugars
and starch have also indicated the better photosynthetic efficiency of these weeds over coexisting ones. The contents of primary metabolites like sugars, carbohydrates, amino acids,
proteins etc. in plants also have allelopathic potential. The higher contents of all above
organic constituents in Cassia and Synedrella might be responsible for their allelopathic
potential.
f
d
g e he
Weeds
Fig. 2. Total sugars and starch contents in the invasive and native weeds
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80
TS
60
Starch
40
20
0
Opl
Bdn
Tum
Aca
Ach
Eug
Alt
Snl
Cul
Bln
ge
50
0
100
bc
Raw
150
100
120
bc
Cfl
250
200
140
a ab ab
a
bc bc
b bc b ef cd
de
bc f
cd
cd cd
Bod
mg g
-1
350
300
a
Cab
400
33
a
b
b
c
FAA
f
Opl
Raw
Cfl
Cab
c ghcd ghcd bc hcd h d
Tum
bcgh
cd
Aca
c
Bln
fg
Bod
b
Ach
Eug
ab ab bc
Alt
a
Protein
de
de
Bdn
d
Snl
90
80
70
60
50
40
30
20
10
0
Cul
mg g
-1
Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
Weeds
#Data columns are the pooled means of three replicates over two years with standard deviation as error
bars. a Different letters at the data points denote significant difference by Duncan’s multiple range test
at p<0.05.
Fig. 3. Protein and free amino acid contentsin the invasive and native weeds
According to Blum (1996, 1997) and Inderjit and Nilsen (2003), allelopathic action can be
explained by investigating the organic compounds in plants, because they may have
additive effect or joint action on various biosynthetic pathways of primary and secondary
metabolites. The contents of various organic constituents existing in plants may indicate
their allelopathic potential, luxuriant growth and aggressive nature. Similar explanations
may be applicable for the luxuriant growth and aggressive nature, faster encroachment and
dominance of Cassia and Synedrella at all the four selected sites in Pune University campus,
as both the weeds were highly superior in photosynthetic pigments, different
photosynthetic parameters and organic constituents like sugar, starch, proteins and free
amino acids.
4.9 ROS scavenging mechanism of invasive and native weeds
As it is well documented that invasive and native weeds have stress tolerant abilities and
sustenance to withstand harsh ecological conditions due to the presence of osmolytes,
antioxidants and ROS scavenging enzymes, an attempt was made for analysis of these
parameters.
The results recorded in Table 5 on various antioxidants/ osmolytes/ compatible solutes like
proline, glycine betaine and phenolics revealed that Cassia uniflora was having highest
contents. It followed by Synedrella and Alternanthera. However the results on glycine betaine
were not significant and for phenolics all the three weed species were at par.
The analysis of MDA content (lipid peroxidation) revealed that Cassia uniflora had lowest
value, which was followed by Synedrella and Alternanthera. While Achyranthes was lowest
amongst the native weeds.
The results on MSI showed that the index was highest in Cassia uniflora which was followed
by Synedrella and Alternanthera.
The results reported in Table 5 on the relative water content of invasive and native weeds
showed that here also Cassia uniflora was topmost, succeeded by Synedrella and
Alternanthera.
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Plants and Environment
Weed
species
Cul
Snl
Alt
Eug
Ach
Bod
Bln
Aca
Tum
Cab
Cfl
Bdn
Raw
Opl
Proline
m moles/g
DW
38.28 a
± 4.68
34.48 b
± 2.63
25.57 c
± 1.02
11.82 de
± 0.35
12.44 d
± 0.74
6.54 gh
± 0.32
9.264ef
± 2.87
6.27 h
± 0.43
8.37 efg
± 0.58
12.41 d
± 0.21
20.84 c
± 0.29
9.486 def
± 0.379
15.24 cd
± 0.31
7.54 fgh
± 0.22
<0.001
Glycine
Betaine
mg/g
0.42 a
± 0.01
0.37 a
± 0.01
0.33 a
± 0.21
0.30 a
± 0.18
0.334 a
± 0.023
0.27 a
± 0.01
0.303 a
± 0.009
0.26 a
± 0.19
0.28 a
± 0.01
0.24 ab
± 0.017
0.26 a
± 0.18
0.305 a
± 0.015
0.059 b
± 0.002
0.054 b
± 0.003
0.024
Phenols
mg/g
8.43 a
± 2.75
8.22 a
± 0.61
8.19 a
± 0.53
6.59 abc
± 1.36
7.36 ab
± 0.47
4.59 bcd
± 1.38
6.17 abc
± 2.85
4.06 d
± 0.38
4.75 cd
± 0.26
5.82 bcd
± 1.75
6.66 abc
± 0.27
6.34 abc
± 2.74
5.69 bcd
± 0.202
4.41 cd
± 0.61
<0.001
Lipid
Peroxidation
T bars
0.03 d
± 1E-04
0.03 cd
± 0.002
0.04 d
± 1E-04
0.04 cd
± 0.061
0.05 bcd
± 0.002
0.05 bcd
± 0.03
0.08 bcd
± 0.08
0.101 bcd
± 0.003
0.1 bcd± 0.005
0.103 bcd
± 0.004
0.13 bc
± 0.008
0.13 bc
± 0.15
0.17 b
± 0.007
0.36 a
± 0.02
<0.001
MSI
RWC
%
75.64 a
± 5.67
70.11ab
± 9.93
65.63 bc
± 2.45
60.76 cd
± 4.55
61.13 cd
± 3.97
48.44 f
± 2.99
57.36 de
± 3.15
47.53 f
± 4.51
50.45 ef
± 3.095
45.53 f
± 1.15
47.38 f
± 3.554
57.94 de
± 4.34
38.66 g
± 2.51
34.57 g
± 2.593
<0.001
64.8 a
± 5.83
49.5 b
± 12.63
41.57 c
± 5.56
27.9 de
± 3.90
36.1 cd
± 5.05
17.6 fg
± 1.40
23.4 efg
± 3.51
15.34 gh
± 2.14
19.65 efg
± 1.37
15.69 gh
± 0.62
18.83 ef
± 2.61
25.9 ef
± 3.88
15.52 gh
± 0.071
12.01 h
± 0.261
<0.001
# Data are the pooled means of three estimates each over two years ±standard deviation. ‘p-value’
denotes the significance of difference between the means by one way ANOVA statistics. a The values
followed by different letters differ significantly by Duncan’s multiple range test at p=0.05.
* Cul: Cassia uniflora Mill.non Spreng ; Snl: Synedrella nodiflora(L) Gaertn; Alt: Alternanthera tenella Colla;
Eug: Euphorbia geniculata Orteg.; Ach: Achyranthes aspera L.; Bod: Boerhaavia erecta L.; Bln: Blainvillea acmella
L.; Aca: Acalypha ciliata Forsk.; Tum: Triumfetta rhomboidea Jacq.; Cab: Cassia absus L.; Cfl: Cassia obtusifolia
L.; Bdn: Bidens biternata Lour.; Raw: Rauwolfia tetraphylla L.; Opl: Oplismenus compositus P.Beauv.
Table 5. Osmolytes and antioxidants in invasive and native weeds
The alien species like Cassia uniflora, Synedrella and Alternanthera have higher contents of
different types of antioxidants as compared to the co- occurring invasive and native weeds
at the selected sites of Pune University campus (Table 5). Along with this lower values of
lipid peroxidation and higher MSI and RWC might be offering them additional mechanisms
for abiotic stress tolerance. As a result of this the selected invasive weeds might have
succeeded to invade and encroach over the native plants of Pune University campus even
during the harsh environmental conditions.
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
35
The enhancement in various antioxidants was reported by many allelopathy workers like
Tambussi et al. (2000), Horling et al. (2003), Guha et al. (2004), Yang and Lu (2005) in
different types of invasive plants growing in terrestrial and boreal forest communities of
North America. The role(s) of different antioxidants and osmolytes existing in the invasive
and native weeds of forest and cropland ecosystems are very much important. They have
explained that the antioxidants were helpful for these weeds to become dominant over cooccuring plant species.
The free radicals are constantly generated under stress conditions which are quenched by
an efficient antioxidant network in the plant body. The complex network of such adaptive
mechanisms at physiological and molecular levels cause changes in the synthesis and
accumulation of various osmolytes, antioxidants and antioxidant enzymes, which provide
stress tolerance to the plants (Bagul et al. 2005, Bhattacharya et al. 2009).
Proline is a major organic osmolyte accumulating in a variety of plant species in response to
biotic and abiotic stresses, though its actual role in plant osmo-tolerance remains
controversial. It is also thought to help in stabilization of sub-cellular structures (e.g.
membranes and proteins), and to scavenge free radicals under stress conditions. Proline is
known to occur widely in higher plants and normally accumulates in large quantities in
response to environmental stresses (Kavi Kishore et al. 2005).
The rapid breakdown of proline upon relief of stress may provide sufficient reducing agents
that support mitochondrial oxidative phosphorylation and generation of ATP for recovery
from stress and repairing of stress induced damages (Zhu 2002). In response to drought or
salinity stress in plants proline also helps for cytoplasmic osmotic adjustment.
Accumulation of proline under stress in many plant species has been correlated with stress
tolerance, and its concentration has been shown to be generally higher in stress - tolerant
than in stress - sensitive plants (Ashraf and Harris 2004, Ashraf and Foolad 2007).
Comparatively higher amount of proline accumulation in Cassia and Synedrella might be
functioning as mentioned above providing stress tolerance to these weeds, as a result of
which both the weeds were able to survive throughout the year and producing large no. of
seeds even under unfavourable stress conditions. These outnumbering seeds of both the
invasive weeds when germinate during favourable season, naturally establish the
monothickets or pure stands which caused substitution of many natives resulting into loss
of phytodiversity of Pune University campus.
Malondialdehyde (MDA) is a product of lipid peroxidation by a thiobarbituric acid reaction.
During drought conditions high activities of antioxidant enzymes are associated with lower
concentration of MDA, being linked to drought tolerance (Gao et al. 2008). Like proline
lowest values of MDA in Cassia and Synedrella can be linked with drought tolerance and
better survival in extremely adverse environmental conditions.
One of the most common responses in plants to abiotic stresses is overproduction of
different types of compatible organic solutes (Serraj and Sinclair 2002), which protect the
plants from stress injuries by cellular osmotic adjustment, detoxification of ROS, protection
of membrane integrity and stabilization of enzymes/ proteins. The antioxidants also protect
cellular components from dehydration injury. These solutes include proline, sucrose,
polyols, trehalose and quaternary ammonium compounds (QACs) such as glycine-betaine,
alanine-betaine, proline-betaine, choline O-sulfate, hydroxyproline-betaine and pipecolatebetaine (Rhodes and Hanson 1993).
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Plants and Environment
Amongst the many quaternary ammonium compounds known in plants, glycine betaine
occurs most abundantly in response to dehydration stress (Venkatesan and Chellappan
1998, Mansour 2000). GB is abundant mainly in chloroplast where it plays a vital role in
adjustment and protection of thylakoid membrane, thereby maintaining photosynthetic
efficiency. The results of present investigation on antioxidants indicated more accumulation
of GB in Cassia and Synedrella as compared to the native weeds at selected sites of Pune
University campus. Along with high proline and low MDA, GB might also be contributing
for stress tolerance and thereby maintaining the photosynthetic efficiency of both the
dominant invasive weeds as suggested by Genard et al. (1991).
RWC has special significance in physiological activities of plants. The results of the present
investigation indicated that Cassia and Synedrella had significantly higher RWC as compared
to other invasive and native weeds. It may be the additional physiological adaptation for
drought tolerance along with above mentioned antioxidants.
Likewise MSI decides the extent of membrane perturbations in structure and dysfunctioning
in the cellular activities during the stress conditions. The membrane stability index (MSI) is
very important parameter that gives idea about the stress tolerance ability of invasive and
native weeds. The MSI of weeds under investigations agree with this. Increase in
allelochemicals in these weeds might also be helping the weeds to get more stress tolerance.
Membranes are barriers isolating aqueous compartments of the cells and the membrane
proteins participate in signal reception and in transport of specific solutes giving them
stability and thereby afford stress tolerance to the plants (Ramadevi et al. 1997). The higher
values of MSI in both the invasive weeds recorded in the present investigation may be
having similar role as mentioned above, because of which these weeds are tolerating
extreme environmental conditions, survive comfortably and invade successfully in the new
habitats. On the contrary the native weeds are not able to tolerate the stress conditions and
hence make the place for highly tolerant invasive weeds. This results in to loss of native
phytodiversity in that particular ecosystem.
4.10 Antioxidant enzymes in invasive and native weeds
The activities of antioxidant enzymes like PPO (Polyphenol oxidase), POX (Peroxidase) and
SOD (Superoxide dismutase) (Figure 4, 5), were stimulated in Cassia uniflora followed by
Synedrella and Alternanthera. The remaining invasive and native weeds followed the above
mentioned weed species. The difference in stimulation of these enzymes might be due to the
difference in stress tolerance ability of these weeds. More accumulation of antioxidants and
stimulated activities of antioxidant enzymes might be becoming helpful for stress tolerance
to these weeds. The results of the present investigations are in agreement with the findings
of Bhalerao (2003), Jadhav (2006), Vaidya (2009) and Ghayal et al. (2009). They have also
reported comparatively higher stimulation of antioxidant enzymes like PPO, POX and SOD
in some invasive as well as native weeds of forest, aquatic and terrestrial ecosystems. They
further concluded that more accumulation of antioxidants and stimulated activities of
antioxidant enzymes were helpful for stress tolerance to these weeds.
Antioxidative enzymes, such as superoxide dismutase (SOD), peroxidases (POD) and
polyphenol oxidase (PPO), are the most important components in the ROS scavenging
system. SOD dismutates O2- to H2O2, POD and PPO subsequently scavenge the H2O2. The
activities of antioxidant enzymes are usually stimulated on exposure to oxidative stress, for
protecting the plants, because these enzymes scavenge the reactive oxygen species (Tanaka
1994). The invasive and native weeds studied in the present investigation had shown very
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37
Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
high stimulation in the activities of above mentioned enzymes in response to stress
conditions, which might be responsible for survival of these weeds in extreme ecological
conditions existing in the campus of Pune University. Ping Lu et al. (2007) supported the
above view.
-1
0.06
a
0.45
a
b
c
bc
a
0.05
0.04
0.4
0.35
b
0.3
d
e
de
e
b
e
e
e
f
0.03
0.25
0.2
PPO
PO X
0.15
0.02
0.01
de d def def
efg
def g
fg def
h
Bdn
Cfl
Cab
Tum
Aca
Bln
Bod
Ach
Eug
Alt
Snl
Cul
0
h
0.1
0.05
0
Opl
c
Raw
Δ OD µg protein min
0.08
0.07
-1
0.09
Weeds
Fig. 4. Activity of polyphenol oxidase and peroxidase in the invasive and native weeds
0.035
a
ab
0.025
-1
units g min
-1
0.03
abc
abc
abc
bcd
0.02
cde
0.015
bcd
cde cde
0.01
de
e
e
e
0.005
Opl
Raw
Bdn
Cfl
Cab
Tum
Aca
Bln
Bod
Ach
Eug
Alt
Snl
Cul
0
Weeds
#Data points are the pooled means of three replicates over two years with standard deviation as error
bars. a Different letters at the data points denote significant difference by Duncan’s multiple range test
at p<0.05.
Fig. 5. Activity of superoxide dismutase in the invasive and native weeds
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Plants and Environment
5. Allelobiogenesis of invasive weeds
To understand the allelopathic nature of any plant, extraction, identification and
characterization of allelochemicals in its roots, stems and leaves has predominant role. In
fact, all the interpretations in allelopathy are mostly based on such investigations. However,
collection, isolation and complete identification, characterization and quantification of
allelochemicals is difficult and a challenge to the allelopathy scientists. The allelochemicals
like terpenes, steroids, flavonoids, alkaloids etc. have major impact on physiology of
recipient plants, right from gene to organism level e.g. the monoterpenes which are the main
constituents of the essential oils from many higher plants, interfere with basic biological
processes like DNA replication, respiration, enzyme activities, seed germination and plant
growth. These monoterpenes have allelopathic action. Triterpenes from many different
weeds like Cassia, Lantana, Mikania are known for their allelopathic responses and great
ecological significance with respect to invasion Ghayal et al. (2007a).
The allelochemicals like terpenoids, steroids, phenols and bitter essential oils present in
roots, stems and leaves of Cassia and Synedrella might be released in to their environment,
through various processes in the form of extracts, leachates, root exudates and even residues
of all above plant parts which in due course of time become allelopathic to associated
invasive and native weeds as a result of which they were suppressed slowly and substituted
by Cassia and Synedrella. This phenomenon was observed at all the four sites of Pune
University campus.
5.1 GC-MS study
The phytosociological dominance of Cassia uniflora and Synedrella nodiflora at the four
selected sites in Pune University campus recorded previously and the inhibitory weed-weed
interaction between these invasive weeds and co-occuring native weeds can be attributed to
the different types of allelochemicals existing in them which are detected with GC-MS. The
allelopathic potential exhibited by both the weeds might be due to different types of
allelochemicals existing in them.
The distribution, quantity and type of allelochemicals depends on various factors such as
age of the plant, growing season, vegetative or reproductive phase, environmental
conditions and habitat. The allelopathic influence of extracts, leachates or residues of such
plants is due to the different types of allelochemicals such as salts, esters, fatty acids,
alkaloids, glycosides, terpenoids, flavonoids and steroids present in them. Their solubility in
different solvents and mechanism of actions of such allelochemicals mostly depend on their
chemical nature. These allelochemicals might be exuded, excreted or released from the
plants. The chemical nature of such allelopathic compounds governs the process of invasion,
dominance, distribution and encroachment over co-occurring species in any ecosystem.
Many researchers have isolated more than ten thousand low molecular weight secondary
metabolites from higher plants and fungi. These compounds or their analogs are new
sources of allelochemicals. Drager (2002), Mashhadi and Rodosevich (2003), Bhalerao
(2003), Haig (2004), Elzaawely et al. (2005), and Alonso-Amelot (2006) had detected different
types of allelochemicals from various weeds and fern species with GC-MS technique and
studied their allelopathic activity. Ru Bai et al. (2009) also reported many allelopathic
compounds by GC-MS in root exudates of Malus prunifolia. Qiaoying Zhang et al. (2009)
detected allelopathic potential of flowers and fruits of Lantana camara which was ascribed to
the allelochemicals by GC-MS. Seal et al. (2009) had also identified different allelochemicals
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Morphophysiological Investigations in Some Dominant Alien Invasive Weeds
39
in weed species like Shepherd’s purse (Capsella bursa-pastoris) by GC-MS and studied its
phytotoxicity.
5.2 IR, NMR, and MASS spectra studies
The dominance, negative weed-weed interaction, encroachment over native weeds as well
as successful invasion of Cassia uniflora and Synedrella recorded at all the four selected sites
in the campus of Pune University can be attributed to the existence of different types of
allelochemicals in the leaves of both the weeds such as 2(4H)- Benzofuranone,5,6,7,7atetrahydro-4,4,7a-trimethyl (Dihydroactinidiolide), 2-pentadecanone, Isobutyl phthalate,
4,4,8-trimethyltricyclo [6.3.1.0(1,5)]dodecane-2,9-diol, Hexadecanoic acid, Phytol, Dioctyl
phthalate, Neophytidiene, Caryophylene oxide and Di-isooctyl phthalate. The presence of
above allelochemicals in both the invasive weeds was well documented by Ghayal et al.
(2007). The presence of allelochemicals such as Dodecane-4- yl butyrate in Cassia leaves and
3-(5-(1-(3-methylpentyloxy) propyl)-tetrahydro-2-oxofuran-3-yl)-dihydrofuran-2(3H)-one in
Synedrella leaves were detected for the first time in the present investigation.
Many allelopathy researchers such as An et al. (2000), Orr et al. (2005) and Santos et al.
(2007) separated, identified and quantified the allelochemicals from different weeds and
tested their phytotoxicity. Yang et al. (2006) also have separated and identified
allelochemicals by NMR in Ageratina adenophora and studied their allelopathic activity on
rice seedlings. Isolation and bioactivity of withaferin A from Withania somnifera roots was
done by Kannan and Kulandaivelu (2007). Leicach et al. (2007, 2009) have used different
methods of chromatography and spectroscopy for alkaloid separation and identification
from different plants and elaborately discussed the importance of extraction, separation and
identification of allelochemicals from different plants having allelopathic activity. Ma et al.
(2009) and Li et al. (2009) have attempted the isolation and identification of allelochemicals
by NMR and Mass in invasive plants Ipomoea cairica and Polygonatum odoratum respectively.
The results of the present investigation are in conformity with the above findings.These
allelochemicals usually had greater adverse impact on the physiological as well as
biochemical processes, enzymological activities, nutrient uptake and assimilation,
reproductive abilities, growth and development of recipient plant species. The changes
induced by allelochemicals at molecular level are also expressed in phenotypes. The
antimicrobial activity in leaf leachates and extracts of Cassia and Synedrella might be due to
the presence of allelochemicals such as terpenoids, steroids, flavonoids, pungent and bitter
essential oils and various types of phenols present in them.
6. Conclusions
The present investigations attempted on phytosociology, physiology, biochemistry and
enzymology of selected weeds, phytochemicals and allelochemicals existing in them, their
allelopathic potential tested through seed germination bioassays, seedling growth and
physiological, biochemical and enzymological changes including treated seedlings of testcrops due to leachates of selected invasive weeds, clearly revealed that the basis for all such
events was allelopathic nature of Cassia and Synedrella.
The weed – crop interactions at molecular, cellular and whole plant level were also
attempted with special emphasis, as these weeds in future are likely to invade
agroecosystems and croplands. At present slowly they are spreading from wastelands to
agricultural lands and competing with the crops of interest and cause significant yield loss.
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40
Plants and Environment
The studies on impact of leachates, extracts and even residues of Cassia and Synedrella
revealed that higher concentrations had severe and very dreadful influence on physiology,
biochemistry and enzymology of test crops and such negative changes were also manifested
on growth and yield attributes of crops interacting with weeds.
These investigations have also thrown a light on successful invasion of both the weeds in the
campus of Pune University, their dominance, aggressiveness and encroachement over
native and even other invasive weeds. The ecological and morphological superiority
enabled them to do so very efficiently and effectively. The exclusive dominant nature of
selected invasive weeds and their allelopathic potential resulted into the loss of native
phytodiversity, which is the major threat of such invasion to any ecosystem. Such
investigations may become the basis for exploring environmental and ecological
degradations in nature.
7. Future research
The need for research and development in allelopathy for the improvement of agriculture,
forestry and different types of ecosystems, community structures and functioning is of
extreme urgency, because the understanding of allelopathy has major role(s) in the
interactions between invasive/ exotic and native weeds, weeds-crops, crops-crops etc. These
studies are of utmost importance in agriculture, forestry and environmental degradation.
Many of these weeds cause damages to agroecosystems and disturb natural phytodiversity.
Their dominance, luxuriant growth, persistence throughout the year, tolerance to biotic and
abiotic stress conditions and allelopathic potential might be the probable factors of
successful invasion in new habitats.
The use of naturally produced huge weed biomass for weedicidal, cytotoxic, larvicidal,
insecticidal and antimicrobial activity is gaining ground in sustainable agriculture. With this
view many research workers have reported the antimicrobial activity in different plant parts
and extracts, leachates or residues of large number of plant species available in plenty.
The richness of bioactive compounds, secondary metabolites and variety of allelochemicals
present in these weeds and other co-dominant weeds can give enticement to screen their
cytotoxic, genotoxic, larvicidal, antimicrobial activities etc. The results of such experiments
could be positive, if the analyses of their bioactive compounds, antioxidants and antioxidant
enzymes is given due importance. The studies on genomics and proteomics of different
weeds, having biotic and abiotic stress tolerance can be exploited with the aid of
biotechnological tools, to have such type of agronomic traits in various crops. Only the
coupling of all the aspects of studies can give an applied touch to the entire field of
allelopathy.
8. References
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Bhalerao, E.B., Laware, S.L., Vaidya, R.R.and Dhumal, K.N. (2000a). Influence of leaf
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Hard cover, 272 pages
Publisher InTech
Published online 17, October, 2011
Published in print edition October, 2011
Changing environmental condition and global population demands understanding the plant responses to
hostile environment. Significant progress has been made over the past few decades through amalgamation of
molecular breeding with non-conventional breeding. Understanding the cellular and molecular mechanisms to
stress tolerance has received considerable scientific scrutiny because of the uniqueness of such processes to
plant biology, and also its importance in the campaign “Freedom From Hungerâ€. The main intention of
this publication is to provide a state-of-the-art and up-to-date knowledge of recent developments in
understanding of plant responses to major abiotic stresses, limitations and the current status of crop
improvement. A better insight will help in taking a multidisciplinary approach to address the issues affecting
plant development and performance under adverse conditions. I trust this book will act as a platform to excel in
the field of stress biology.
How to reference
In order to correctly reference this scholarly work, feel free to copy and paste the following:
Nivedita Ghayal and Kondiram Dhumal (2011). Morphophysiological Investigations in Some Dominant Alien
Invasive Weeds, Plants and Environment, Dr. Hemanth Vasanthaiah (Ed.), ISBN: 978-953-307-779-6, InTech,
Available from: http://www.intechopen.com/books/plants-and-environment/morphophysiological-investigationsin-some-dominant-alien-invasive-weeds
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