ArticlePDF AvailableLiterature Review

Overview of Allelopathic Potential of Lemna minor L. Obtained from a Shallow Eutrophic Lake

Authors:

Abstract

Allelopathy is an interaction that releases allelochemicals (chemicals that act allelopathically) from plants into the environment that can limit or stimulate the development, reproduction, and survival of target organisms and alter the environment. Lemna minor L. contains chemicals that are allelopathic, such as phenolic acids. Chemical compounds contained in L. minor may have a significant impact on the development and the rate of multiplication and lead to stronger competition, which may enhance the allelopathic potential. Allelopathic potential may exist between L. minor and C. glomerata (L) Kütz. because they occupy a similar space in the aquatic ecosystem, have a similar preference for the amount of light, and compete for similar habitat resources. L. minor and C. glomerata can form dense populations on the water surface. Allelopathy can be seen as a wish to dominate one of the plants in the aquatic ecosystem. By creating a place for the development of extensive mats, an interspecific interaction is created and one of the species achieves competitive success. It is most effective as a result of the release of chemicals by macrophytes into the aquatic environment. Therefore, allelopathy plays a significant role in the formation, stabilization, and dynamics of the structure of plant communities.
Citation: Gosty´nska, J.; Pankiewicz,
R.; Romanowska-Duda, Z.; Messyasz,
B. Overview of Allelopathic Potential
of Lemna minor L. Obtained from a
Shallow Eutrophic Lake. Molecules
2022,27, 3428. https://doi.org/
10.3390/molecules27113428
Academic Editor: Piotr
Paweł Wieczorek
Received: 22 April 2022
Accepted: 23 May 2022
Published: 26 May 2022
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4.0/).
molecules
Review
Overview of Allelopathic Potential of Lemna minor L. Obtained
from a Shallow Eutrophic Lake
Julia Gosty ´nska 1, Radosław Pankiewicz 2, Zdzisława Romanowska-Duda 3and Beata Messyasz 1, *
1Department of Hydrobiology, Faculty of Biology, Adam Mickiewicz University in Poznan, Uniwersytetu
Poznanskiego 6, 61-614 Poznan, Poland; julgos@amu.edu.pl
2
Faculty of Chemistry, Adam Mickiewicz University in Poznan, Uniwersytetu Poznanskiego 8, 61-614 Poznan, Poland;
radpan@amu.edu.pl
3Department of Plant Ecophysiology, Faculty of Biology and Environmental Protection, University of Lodz,
Banacha 12/16, 90-237 Lodz, Poland; zdzislawa.romanowska@biol.uni.lodz.pl
*Correspondence: messyasz@amu.edu.pl; Tel.: +48-61-829-5761
Abstract:
Allelopathy is an interaction that releases allelochemicals (chemicals that act allelopathi-
cally) from plants into the environment that can limit or stimulate the development, reproduction,
and survival of target organisms and alter the environment. Lemna minor L. contains chemicals that
are allelopathic, such as phenolic acids. Chemical compounds contained in L. minor may have a
significant impact on the development and the rate of multiplication and lead to stronger competition,
which may enhance the allelopathic potential. Allelopathic potential may exist between L. minor and
C. glomerata (L) Kütz. because they occupy a similar space in the aquatic ecosystem, have a similar
preference for the amount of light, and compete for similar habitat resources. L. minor and C. glomerata
can form dense populations on the water surface. Allelopathy can be seen as a wish to dominate
one of the plants in the aquatic ecosystem. By creating a place for the development of extensive
mats, an interspecific interaction is created and one of the species achieves competitive success. It is
most effective as a result of the release of chemicals by macrophytes into the aquatic environment.
Therefore, allelopathy plays a significant role in the formation, stabilization, and dynamics of the
structure of plant communities.
Keywords:
duckweed; pleustophytes; macroalgae; allelopathy; competition; polyphenols; population
formation; eutrophy
1. Introduction
The plant community is shaped by specific plant species that coexist in a particular
place at a particular time [
1
]. Their presence in a community is determined by many
ecological aspects, including biotic and abiotic factors [
2
]. Interspecies relationships are an
important biotic factor, as a result of which individuals compete with each other. These
interactions take place directly or indirectly in the individual–individual and individual–
environment relationships [
1
]. As a consequence, it is possible to inhibit the development
of one of the co-occurring species, which ensures the competitive success of another
species. One example of such an interaction is allelopathy. Allelopathy is a series of
interactions that occur in the environment between various organisms [
3
]. As a result of this
process, mixtures of allelopathic chemicals are released from plants into the environment [
3
].
Allelochemicals can directly or indirectly limit or stimulate the development, reproduction,
and survival of target organisms, also affecting the environment [4].
1.1. Allelopathic Potential of Lemna minor L.
Allelopathy can have a variety of practical applications in both terrestrial and aquatic
environments. However, it is most commonly used in agriculture, e.g., to remove weeds,
diseases, and microorganisms that are harmful to crops, as well as to improve the condition
Molecules 2022,27, 3428. https://doi.org/10.3390/molecules27113428 https://www.mdpi.com/journal/molecules
Molecules 2022,27, 3428 2 of 17
of crops and to effectively increase their yields [
5
7
]. Allelopathy is probably one of the
most modern and effective methods for agriculture. In turn, allelopathic substances act in a
similar way to herbicides, being an effective tool for controlling weeds in plant crops [
8
].
According to research, Lemna minor L. contains chemicals that are allelopathic [
9
,
10
]. Previous
studies have confirmed that aqueous methanol extracts isolated from L. minor have a
significant effect on monocotyledons (cress, lettuce, and alfalfa) and dicotyledons (rye
grass, timothy, barnyard grass, crab grass, and junglerice) [
5
]. Small amounts of methanol
extract (0.1 g DW eq. extract mL
1
) limit the growth of shoots and roots in cress, lettuce,
and rye grass, as well as timothy and crab grass roots [
5
]. At a higher concentration (1 g
DW eq. extract mL
1
), the development of shoots and roots in barnyard grass, junglerice,
crab grass, and rye grass is inhibited [
5
]. Among the plants studied, methanol extract most
strongly inhibited the development of alfalfa shoots and timothy roots [
5
]. Subsequent
studies have shown that substances present in L. minor, such as flavonoids and fatty
acids, have an inhibitory effect on the growth of walnut biomass [
5
]. As reported in the
literature, plant extracts are also bacteriostatic in nature, which has been demonstrated
in Sphaerotilus natans [
7
]. In L. minor, there are substances with antioxidant and anti-
radical properties and pharmacological properties, such as phytol; campesterol; loliolide;
dihydroactinediol; ascorbic acid; vanillic acid; 2,3-dihydroxybenzoic acid; caffeic acid;
chlorogenic acid; esculetin; esculin; and fraxetin [
10
12
]. A characteristic feature of L. minor
is its simple morphology, rapid biomass growth rate, and high sensitivity to changes in the
ecosystem. As a result, it is often used in toxicological studies of the environment [
8
,
9
,
13
].
Because of its high protein content, Lemna minor is used in agriculture as an effective
biopesticide [
5
,
6
,
13
]. It eliminates phenolic compounds from the aquatic environment,
which arise as a result of industrial development and are toxic to organisms [
13
,
14
]. This
confirms the bioremediation abilities of L. minor [
14
]. Bioremediation consists in improving
the ecological condition of the environment with the use of organisms and their ability to
remove or reduce the concentration of harmful pollutants. Due to the fact that L. minor
is resistant to oxidative stress and the accumulation of reactive oxygen species (ROS),
which are the result of the presence of phenolic compounds in the environment, it may
contribute to the improvement of water quality [
13
,
15
]. The ability to produce biomass
quickly can be used to treat wastewater with a high content of organic compounds or
heavy metals. L. minor has a high tolerance to water contaminated with metals [
16
]. It is a
good hyperaccumulator of lead, nickel, chromium, copper, cadmium, and manganese [
16
].
This plant is also highly effective in removing arsenic, Ni, Zn, Fe, and Cd from aquatic
ecosystems [
16
]. So far, little research has been carried out to confirm the allelopathic
potential of Lemna minor or to explain the mechanism of this phenomenon. Nevertheless,
the use of this plant as a tool for managing the aquatic and terrestrial environment seems
to be an extremely important solution for polluted ecosystems.
1.2. Models of Lemna minor L. and Cladophora glomerata (L.) Kütz Population Formation:
Interactions between Species
Large amounts of nutrients are present in eutrophic water bodies. The consequence of
this is the excessive development of biological life, including the massive appearance of
phytoplankton organisms and other aquatic plants that create blooms on the water surface
and reduce the transparency of the water. An excessive development of green algae, mainly
Cladophora (Chlorophyta) species, is observed in eutrophic water reservoirs. Lemna minor,
belonging to the Lemnaceae family, is also a common aquatic plant.
Lemna minor is a small plant (pleustophyte) with a simple morphological structure.
It consists of a single thallus and has no root [
17
,
18
]. The plant reproduces mainly vege-
tatively [
19
]. In summer, L. minor forms single-species, dense, and compact clusters that
float freely on the water surface [
9
,
20
]. These patches inhibit the development of other
macrophytes, limiting their access to light by up to 99% [
21
]. The increase in plant biomass
over a short time contributes to the eutrophication of the aquatic ecosystem. To survive the
colder months, the pleustophyte forms small turions that are filled with starch and sink
Molecules 2022,27, 3428 3 of 17
to the bottom of the water reservoir [
10
,
22
]. Most often, L. minor occurs in waters with a
temperature of 6 to 33
C. It also has a wide range of pH tolerance, from 5 to 9 [
23
]. L. minor
prefers shallow places with low water turbulence that are rich in electrolytes [
21
,
24
]. The
growth, survival rate, and growth rate are influenced by various ecological factors, e.g.,
pH, water temperature, concentration of nutrients, presence and concentration of toxins
in water, as well as competition with other plants for light and nutrients [
22
]. However,
temperature and light availability are the factors that best stimulate the proper growth and
development of L. minor [
22
]. It has the ability to absorb minerals as well as phosphorus
and potassium that are present in nutrient-rich water [
22
]. A threat to the development of
L. minor is the intense growth of algae, including the green algae of the genus Cladophora,
which limit the plant’s access to light and nutrients [
22
]. As a result, it has limited space
and resources to create dense colonies on the surface of a body of water.
Cladophora glomerata (L) Kütz. is a green alga that dominates in eutrophic waters [
25
,
26
].
Due to the diversified morphology of the plant, the thallus may be long and branched in
flowing waters and short and bushy in stagnant waters [
27
]. The lifting force of water
enables the movement of the thallus, which can change its shape and place of occurrence.
It creates filamentous forms, called grippers, by means of which it attaches to the ground or
floats in the water column [
27
]. C. glomerata forms dense and large populations (“mats”) on
the surface of a water body [
21
,
28
]. Intensive development occurs in spring and autumn, as
a result of which it creates massive blooms [
27
]. The density and size of the biomass often
depend on the growing season and the environmental conditions in which it grows [
29
].
Green alga mats may consist of individuals of one species (Cladophora glomerata) or of
several co-occurring species [
25
]. Although C. glomerata occurs in most types of aquatic
ecosystems (from stagnant waters to flowing waters), it is most numerous in eutrophic
waters with a high concentration of nitrogen and phosphorus [
21
,
25
]. It has preference
for a wide range of temperatures and light conditions; therefore, it easily adapts to the
ecosystem it currently inhabits [
21
,
25
]. Owing to its uncomplicated morphological structure,
rapid multiplication rate, and high ecological tolerance, C. glomerata easily forms large
populations and occupies considerable space [
26
,
29
]. This alga can limit access to light
by up to 70%, create anaerobic conditions, and inhibit the supply of nutrients and thus
inhibit the development of macrophytes [
26
,
29
,
30
]. C. glomerata, similarly to L. minor,
prefers waters with a high content of nutrients as well as nitrogen and phosphorus [
29
]. An
important element for the proper growth of green algae is the optimal chemical composition
of water, in which there is a high concentration of nitrates and orthophosphates [25].
As shown in the above literature data, L. minor and C. glomerata are species with similar
ecological preferences. Both plants occupy a similar space in the aquatic ecosystem, have a
similar preference for the amount of light, and compete for similar habitat resources. Both
L. minor and C. glomerata can form dense populations that float on the water surface. As
a result, they inhibit the growth of other hydro macrophytes as they restrict their access
to light and nutrients. Their chemical composition indicates the presence of substances
with an allelopathic effect. The presence of phenols such as phenyl ester, methoxylphenol,
coumaric acid, and benzoic acid has been found in the thalli of filamentous green algae [
31
].
Unfortunately, there is little research explaining the mechanism of interaction between
these plant species. However, it can be concluded that there is an allelopathy phenomenon
between them, which may be visible when one plant wants to dominate the aquatic
ecosystem. Creating a place for the development of extensive mats allows an interspecific
interaction (allelopathy) to occur, thanks to which one of the species achieves competitive
success. This is an important point that we want to highlight in this article. Therefore, this
paper provides an overview of the allelopathic potential of duckweed and reviews the
studies on models of Lemna minor and Cladophora glomerata population formation with a
focus on their chemical composition. Moreover, with reference to the studies, the aim of
the research presented in the paper is to answer the following questions:
1.
Do Lemna minor and Cladophora glomerata secrete allelopathic substances in coexis-
tence?
Molecules 2022,27, 3428 4 of 17
2. Does the allelopathic potential occur in competing interactions?
2. Chemical Composition of L. minor and C. glomerata
According to the data contained in the literature, the cell wall of Lemna minor consists
of: carbohydrates (51.2%), dry starch (19.9%), cellulose, and pectins (20.3%), along with
galacturonan, xylogalacturonan, rhamnogalacturonan, and hemicellulose (3.5%), with xy-
loglucan and xylan and phenols (0.03%) [
10
]. The chemical composition indicates that in
the dry matter of L. minor, there are: proteins (up to 35%), fibers (up to 17%), fats (up to 5%),
polysaccharides, flavonoids, amino acids, aliphatic compounds, phenolic acids, triterpenes,
micro- and macronutrients, vitamins (A, B, and E), and carotenoids [
10
,
11
,
32
]. Among fatty
acids, the most numerous are polyunsaturated fatty acids (PUFA), which constitute 60-63%
of all fatty acids [
33
]. Among these acids, the highest amounts are found in
α
-linolenic
acid (41–47%) and linoleic acid (17–18%) [
33
];
α
-linolenic acid, linoleic acid, and palmitic
acid also constitute 80% of all fatty acids [10]. In terms of chemical composition, the plant
further includes unsaturated acids (76.7%), mainly oleic and linoleic, and saturated acids
(23.3%), including mainly palmitic and stearic acids [
10
]. L. minor contains essential amino
acids (39.20%), non-essential amino acids (53.64%), and non-proteinogenic amino acids
(7.13%) [
10
]. Their content is presented in Table 1. The following are dominant in essential
amino acids: leucine, isoleucine, and valine (48.67%). In non-essential amino acids, glutamic
acid (25.87%) is dominant [
10
]. The chemical composition also includes citrulline, hydrox-
yproline, taurine, histidine, leucine, lysine, methionine, phenylalanine, threonine, and
tryptophan [
10
], while the lipophilic substances are: hexanal; trans-2-heptenal; caproic acid;
eticaproate; trans-2-octenal; ethylheptanoate; nonanal; 2,6-dimethylcyclohexanol; menthol;
pyrrole-2,5-dione; tetradecane; pentadecane; dihydroactinediol; heptadecane; loliolide;
ethyltetradecanoate; trans-neophytadiene; hexahydrofarnesylactone; cis-neophytadiene;
ethyl pentadecanoate; ethyl palmitate; heneicosan; phytol; tricosan; pentacosan; heptacosan;
spinesterol; stigmasterol; sitosterol; and campesterol [10,11].
Table 1. Amino acid content in L. minor [10].
The Name of the Amino Acid Amino Acid Amount (%)
Glutamic acid 13.53
Leucine 10.27
Aspartic acid 9.89
Alanine 7.88
Valine 7.67
Glycine 7.36
Phenylalanine 6.28
Lysine 6.2
Isoleucine 5.89
Threonine 5.08
Proline 4.88
Arginine 4.67
Serine 4.05
Tyrosine 2.76
Histidine 2.32
Tryptophan 0.85
Methionine 0.39
Cystine Small amounts
In L. minor, there are also substances with antioxidant activity, such as: phytol; campes-
terol; loliolide; dihydroactinediolide; ascorbic acid; vanillic acid; 2,3-dihydroxybenzoic
acid; caffeic acid; chlorogenic acid; esculetin; esculin; and fraxetin [
10
,
11
]. The content of
the chemical elements present in the plant is shown in Table 2[
10
,
11
,
34
]. The literature
emphasizes the importance of the above-mentioned chemical compounds, mainly in the
regulation of plant growth and development. Glutamic acid plays an important role in
Molecules 2022,27, 3428 5 of 17
many physiological processes of plants, responsible for seed germination, stimulation of
plant growth and development, dying, response to environmental stress, and adaptation
to changing ecological conditions [
35
]. It is an amino acid precursor. It plays a significant
role in nitrogen storage and transport, increasing nitrogen absorption in plants, including
L. minor [
36
]. Valine is responsible for the effective functioning of the immune system in
stressful situations for plants. Isoleucine is an essential substrate for protein synthesis, and
leucine is responsible for the synthesis of phytohormones [
33
]. Unsaturated fatty acids
play a major role in the proper functioning of defense systems against stress factors [
37
].
This suggests that the chemical compounds contained in L. minor may have a significant
impact on appropriate development and lead to a faster multiplication rate and stronger
competition, which may strengthen the allelopathic potential.
Table 2. The content of chemical elements in L. minor.
Name Chemical Element The Amount of Chemical
Element (mg/100 g) [10,11]Dry Mass (%) [34]
Calcium 4990 0.18
Potassium 2495 1.53
Silicon 2495 -
Sodium 1870 0.02
Manganese 935 0.03
Iron 934 0.06
Phosphorus 515 0.83
Magnesium 155 1.92
Aluminum 0.93 -
Nickel 0.93 -
Copper 0.78 -
Lead 0.03 -
Molybdenum 0.02 -
Zinc 0.01 0.05
Nitrogen - 8.74
Considering the chemical composition, C. glomerata is composed of carbohydrates,
proteins, lipids, and other chemical compounds (Table 3). The most common minerals in
this species are: potassium, calcium, iron, aluminum, magnesium, sodium, and chrome
(Table 4). Among these elements, the highest dry matter content is that of potassium
(94.1 g
·
kg
1
), followed by those of calcium (56.4 g
·
kg
1
), iron (26.5 g
·
kg
1
), aluminum
(23.1 g
·
kg
1
), magnesium (13.5 g
·
kg
1
), sodium (11.5 g
·
kg
1
), and chrome (0.247 g
·
kg
1
).
Literature data show that in terms of chemical composition, C. glomerata also includes:
n-hexadecanoic acid; mono (2-ethylhexyl) ester; tetradecanoic acid; 2-pentadecanone;
6,10,14-trimethyl; tetradecanoic acid; 12-methyl ester; hexadecanoic acid; ethyl ester; and
9,12 octadecadio-neoyl chloridae (Table 5).
Table 3. Chemical composition of C. glomerata [38].
Chemical Composition Content of Chemical Composition
Carbohydrate 34.7 ±0.4
C (wt.%) 31.33
O (wt.%) 30.67
Protein 26.3 ±0.36
H (wt.%) 4.99
N (wt.%) 4.9
Lipid 2.4 ±0.15
S (wt.%) 1.99
Molecules 2022,27, 3428 6 of 17
Table 4. Mineral metal content in C. glomerata [38].
Mineral Metal Content Dry Mass (g·kg1)
Potassium 94.1
Calcium 56.4
Iron 26.5
Aluminum 23.1
Magnesium 13.5
Sodium 11.5
Chrome 0.247
Table 5. Chemical compounds in C. glomerata [39].
Chemical Compounds Content of Chemical Compounds (%)
n-Hexadecanoic acid (palmitic acid) (C16:0) 45.06
Hexanedioic acid, mono (2-ethylhexyl) ester 19.51
Tetradecanoic acid (myristic acid) (C14:0) 14.55
2–Pentadecanone, 6,10,14-trimethyl (C15:0) 10.53
Tetradecanoic acid, 12-methyl ester 4.48
Hexadecanoic acid, ethyl ester (ethyl palmitate)
2.92
9,12 Octadecadienoyl chloride (linoleoyl
chloride) 2.92
3. Results
3.1. Chemical Composition Analysis of L. minor and C. glomerata
The analysis of the chemical composition of L. minor and C. glomerata showed the
content of chemical elements (Tables 6and 7). In the case of L. minor, the following
elements were identified: potassium, calcium, phosphorus, magnesium, nitrogen, iron,
boron, copper, zinc, and manganese (Table 6). Among all analyzed elements, potassium
(2194 mg
·
kg
1
) and calcium (1,3020 mg
·
kg
1
) were characterized by the highest content in
L. minor compared to other elements. Manganese (68.4 mg
·
kg
1
) had the lowest amount
in L. minor. In the case of C. glomerata, the following elements were identified: calcium,
potassium, magnesium, lead, arsenic, sodium, iron, nickel, manganese, cadmium, copper,
zinc, cobalt, and chrome (Table 7). The highest content was that of calcium (148.2
±
3.1) in
dry mass. Chrome had the lowest content (0.01 ±0.001) in dry mass.
Table 6. Elemental composition observed in the freshwater L. minor filaments.
Element The Element Content (mg·kg1)
Potassium 21,940
Calcium 13,020
Phosphorus 5411
Magnesium 2455
Nitrogen 874
Iron 485
Boron 446
Copper 328
Zinc 94.9
Manganese 68.4
Molecules 2022,27, 3428 7 of 17
Table 7.
Elemental composition observed in the freshwater C. glomerata filaments in the summer of
2021.
Element The Element Content (g·g1of Dry Mass)
Calcium 148.2 ±3.1
Potassium 18.24 ±0.16
Magnesium 3.48 ±0.02
Lead 0.75 ±0.05
Arsenic 0.51 ±0.04
Sodium 0.45 ±0.02
Iron 0.21 ±0.01
Nickel 0.12 ±0.03
Manganese 0.08 ±0.03
Cadmium 0.06 ±0.01
Copper 0.05 ±0.01
Zinc 0.03 ±0.01
Cobalt 0.01 + 0.001
Chrome 0.01 + 0.001
3.2. Analysis of the Morphological Features of Cladophora glomerata and Lemna minor
C. glomerata was analyzed in terms of the mean values of the morphological features,
such as: the length and width of cells at various times (1–30 April 2021; 2–4 June 2021;
3–17 July 2021) (Figures 1and 2). L. minor was analyzed in terms of the mean values of the
morphological features, such as: the diameter and thickness of individuals at various times
(1–30 April 2021; 2–4 June 2021; 3–17 July 2021) (Figures 3and 4). The test sample contained
30 C. glomerata cells and 30 L. minor individuals. Cell length values in C. glomerata were not
statistically significant. The C. glomerata cell width was statistically significant in April (a)
and June (a) in relation to the cell width in July (b). Statistically significant differences were
also observed in the diameters and thicknesses of L. minor cells. The diameters of L. minor
cells showed statistically significant differences among themselves (a, b, c) in April, June,
and July. Cell thicknesses also showed significant differences between themselves (a, b,
c) in April, June, and July. The highest mean cell length (310
µ
m) of C. glomerata was in
July and the lowest in June (276.5
µ
m). The greatest difference was between the average
widths in June (63
µ
m) and July (46.1
µ
m). In the case of L. minor, the highest average
diameter (2048.6
µ
m) and thickness (918
µ
m) of individuals was in July. The smallest
average diameter (1434.6 µm) and thickness (684.5 µm) of individuals was in June.
Molecules2022,27,xFORPEERREVIEW8of17
Figure1.MeanvaluesofC.glomeratafeature(lengthofcells)atdifferenttimes(1–30April2021;2–
4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebarsindicate
meanvalues.Errorbarsrepresentstandarderror.Astatisticallysignificantresultforp≤0.05was
marked.
Figure2.MeanvaluesofC.glomeratafeature(widthofcells)atdifferenttimes(1–30April2021;2–
4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebarsindicate
meanvalues.Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignificancebe
tweentheanalyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
Figure 1.
Mean values of C. glomerata feature (length of cells) at different times (1–30 April 2021;
2–4 June 2021; 3–17 July 2021) presented using the Tukey multiple comparisons test. The bars indicate
mean values. Error bars represent standard error. A statistically significant result for p
0.05 was
marked.
Molecules 2022,27, 3428 8 of 17
Molecules2022,27,xFORPEERREVIEW8of17
Figure1.MeanvaluesofC.glomeratafeature(lengthofcells)atdifferenttimes(1–30April2021;2–
4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebarsindicate
meanvalues.Errorbarsrepresentstandarderror.Astatisticallysignificantresultforp≤0.05was
marked.
Figure2.MeanvaluesofC.glomeratafeature(widthofcells)atdifferenttimes(1–30April2021;2–
4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebarsindicate
meanvalues.Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignificancebe
tweentheanalyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
Figure 2.
Mean values of C. glomerata feature (width of cells) at different times (1–30 April 2021;
2–4 June 2021; 3–17 July 2021) presented using the Tukey multiple comparisons test. The bars indicate
mean values. Error bars represent standard error. A, B, C determines the statistical significance
between the analyzed features. A statistically significant result for p0.05 was marked.
Molecules2022,27,xFORPEERREVIEW9of17
Figure3.MeanvaluesofL.minorfeature(diameterofindividuals)atdifferenttimes(1–30April
2021;2–4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebars
indicatemeanvalues.Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignifi
cancebetweentheanalyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
Figure4.MeanvaluesofL.minorfeature(thicknessofindividuals)atdifferenttimes(1–30April
2021;2–4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebars
indicatemeanvalues.Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignifi
cancebetweentheanalyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
3.3.TheSizeofthePatchesofL.minorandC.glomerataintheLittoralZone
Themeanvalue,theminimumvalue,themaximumvalue,andthestandarddevia
tionwereanalyzedintermsofthesizeofthepatchesofC.glomerataandL.minorinthe
littoralzone(Table8).Thesizeofthepatcheswasanalyzedonthreedifferentdates:30
April2021;4June2021and17July2021.Themeanvalue,theminimumvalue,themaxi
mumvalue,andthestandarddeviationofCladophoraglomeratashowedthatthesmallest
minimum(0.01m
3
)sizeoftheC.glomeratapatchoccurredon30April2021andthelargest
minimal(0.65m
3
)occurredon17July2021.Thesmallestmaximum(0.02m
3
)sizeofa
patchofthisspeciesoccurredon30April2021andthelargestmaximum(0.76m
3
)on17
Figure 3.
Mean values of L. minor feature (diameter of individuals) at different times (1–30 April 2021;
2–4 June 2021; 3–17 July 2021) presented using the Tukey multiple comparisons test. The bars indicate
mean values. Error bars represent standard error. A, B, C determines the statistical significance
between the analyzed features. A statistically significant result for p0.05 was marked.
Molecules 2022,27, 3428 9 of 17
Molecules2022,27,xFORPEERREVIEW9of17
Figure3.MeanvaluesofL.minorfeature(diameterofindividuals)atdifferenttimes(1–30April
2021;2–4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebars
indicatemeanvalues.Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignifi
cancebetweentheanalyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
Figure4.MeanvaluesofL.minorfeature(thicknessofindividuals)atdifferenttimes(1–30April
2021;2–4June2021;3–17July2021)presentedusingtheTukeymultiplecomparisonstest.Thebars
indicatemeanvalues.Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignifi
cancebetweentheanalyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
3.3.TheSizeofthePatchesofL.minorandC.glomerataintheLittoralZone
Themeanvalue,theminimumvalue,themaximumvalue,andthestandarddevia
tionwereanalyzedintermsofthesizeofthepatchesofC.glomerataandL.minorinthe
littoralzone(Table8).Thesizeofthepatcheswasanalyzedonthreedifferentdates:30
April2021;4June2021and17July2021.Themeanvalue,theminimumvalue,themaxi
mumvalue,andthestandarddeviationofCladophoraglomeratashowedthatthesmallest
minimum(0.01m
3
)sizeoftheC.glomeratapatchoccurredon30April2021andthelargest
minimal(0.65m
3
)occurredon17July2021.Thesmallestmaximum(0.02m
3
)sizeofa
patchofthisspeciesoccurredon30April2021andthelargestmaximum(0.76m
3
)on17
Figure 4.
Mean values of L. minor feature (thickness of individuals) at different times (1–30 April 2021;
2–4 June 2021; 3–17 July 2021) presented using the Tukey multiple comparisons test. The bars indicate
mean values. Error bars represent standard error. A, B, C determines the statistical significance
between the analyzed features. A statistically significant result for p0.05 was marked.
3.3. The Size of the Patches of L. minor and C. glomerata in the Littoral Zone
The mean value, the minimum value, the maximum value, and the standard deviation
were analyzed in terms of the size of the patches of C. glomerata and L. minor in the littoral
zone (Table 8). The size of the patches was analyzed on three different dates: 30 April 2021;
4 June 2021 and 17 July 2021. The mean value, the minimum value, the maximum value,
and the standard deviation of Cladophora glomerata showed that the smallest minimum
(0.01 m
3
) size of the C. glomerata patch occurred on 30 April 2021 and the largest minimal
(0.65 m
3
) occurred on 17 July 2021. The smallest maximum (0.02 m
3
) size of a patch of this
species occurred on 30 April 2021 and the largest maximum (0.76 m
3
) on 17 July 2021. The
smallest value of the standard deviation was 0.005 m
3
(30 April 2021). The highest standard
deviation value was 0.055678 m3(17 July 2021). The size of L. minor patches differed from
that of C. glomerata. The smallest minimum size of an L. minor plot was 0.1 m
3
, which
occurred on 30 April 2021 and 4 June 2021. The largest minimum size of a plot of this species
was, however, 0.08 m
3
(17 July 2021). The smallest maximum value of the L. minor plot was
0.1 m
3
(17 July 2021) and the highest 0.19 m
3
(4 June 2021). The smallest average value
of the patch was 0.09 m
3
and occurred on 17 July 2021 and the highest was 0.15 m
3
and
occurred on 30 April 2021 and 4 June 2021. The smallest standard deviation was 0.01 m
3
(17 July 2021) and the largest amounted to 0.05 m3(30 April 2021).
3.4. The Content of Phenolic Acids in L. minor and C. glomerata
Phenolic acids were found in all the tested C. glomerata individuals from Oporzy´nskie
Lake, L. minor individuals from Oporzy´nskie Lake, and L. minor from breeding (Table 9).
The phenol content in C. glomerata was significantly higher than the phenol content in
L. minor. Table 4shows that the lowest minimum concentration of phenols (7.418 mg GAE g
1
)
in C. glomerata occurred on 30 April 2021 and the highest minimum concentration of
phenols (17.934 mg GAE g
1
) was on 4 June 2021. The lowest maximum value of phenol
concentration was 7.601 mg GAE g
1
(30 April 2021), and the highest maximum was
18.459 mg GAE g
1
(4 June 2021). The lowest average concentration of phenols was
7.515 mg GAE g
1
, which occurred on 30 April 2021. The highest average concentration
of phenols was 18.209 mg GAE g
1
, which occurred on 4 June 2021. The concentration
of phenols in L. minor collected from Oporzy´nskie Lake significantly differed from the
concentration of phenols in individuals from the farm and from the concentration of
Molecules 2022,27, 3428 10 of 17
phenols in C. glomerata. The lowest minimum concentration of phenols in the species L. minor
from Oporzy´nskie Lake was 2.111 mg GAE g
1
(30 April 2021), and the highest minimum
concentration of phenols was 9.423 mg GAE g
1
(17 July 2021). The lowest minimum
concentration of phenols was 2.892 mg GAE g1(30 April 2021) and the highest 9.816 mg
GAE g
1
(17 July 2021). The lowest average concentration of phenols was also 2.111 mg
GAE g
1
(30 April 2021), and the highest was 9.582 mg GAE g
1
(17 July 2021). The lowest
minimal (1.794 mg GAE g
1
), the lowest maximum (2.006 mg GAE g
1
), and average
(1.902 mg GAE g
1
) concentrations of phenols in individuals from the cultivation of L. minor
occurred on 30 April 2021. The minimum concentration of phenols (2.029 mg GAE g
1
)
occurred on 17 July 2021 and the highest maximum (2.052 mg GAE g
1
) and the highest
mean were recorded on 4 June 2021.
Table 8.
The mean value, the minimum value, the maximum value, and the standard deviation of the
size of the patches of Cladophora glomerata and Lemna minor (m3).
Date Cladophora glomerata
Mean Minimum Maximum Standard Deviation
30 April 2021 0.015 0.01 0.02 0.005
14 June 2021 0.377 0.32 0.42 0.051
17 July 2021 0.700 0.65 0.76 0.056
Lemna minor
30 April 2021 0.15 0.10 0.20 0.050
14 June 2021 0.15 0.10 0.19 0.046
17 July 2021 0.09 0.08 0.10 0.010
Table 9.
The mean value, the minimum value, the maximum value, and the standard deviation of phenol
concentration of C. glomerata from Oporzy´nskie Lake, L. minor from Oporzy´nskie Lake, and L. minor from
breeding (mg GAE g1).
Date Cladophora glomerata
Mean Minimum Maximum Standard Deviation
30 April 2021 7.515 7.418 7.601 0.092
14 June 2021 18.209 17.934 18.459 0.263
17 July 2021 17.921 17.306 18.269 0.534
Lemna minor (from Oporzy´nskie Lake)
30 April 2021 2.412 2.111 2.892 0.420
14 June 2021 6.480 5.987 6.876 0.452
17 July 2021 9.582 9.423 9.816 0.201
Lemna minor (from breeding)
30 April 2021 1.902 1.794 2.006 0.106
14 June 2021 2.035 2.014 2.052 0.019
17 July 2021 2.034 2.029 2.042 0.007
3.5. Relationships between the Parameters of Dry Mass of L. minor and C. glomerata and the Effect
of Polyphenol Concentration and Time
The results of the dry mass content in C. glomerata (Figure 5) and L. minor (Figure 6)
showed that C. glomerata had a higher dry mass content in June and July than L. minor. In
April, C. glomerata had a slightly lower content of dry mass than L. minor. Considering the
results separately, the dry mass of C. glomerata had the highest mean value in July and the
lowest in April. It was similar for L. minor—the highest average dry mass value was in
July and the lowest in April. Both in C. glomerata and L. minor, the mean value of dry matter
was statistically significant between the tested trials from April, June, and July (a, b, c).
Molecules 2022,27, 3428 11 of 17
Molecules2022,27,xFORPEERREVIEW11of17
Table9.Themeanvalue,theminimumvalue,themaximumvalue,andthestandarddeviation of
phenolconcentrationofC.glomeratafromOporzyńskieLake,L.minorfromOporzyńskie Lake,and
L.minorfrombreeding(mgGAEg
1
).
Date Cladophoraglomerata
MeanMinimumMaximumStandardDeviation
30April20217.515 7.418 7.601 0.092
14June202118.209 17.934 18.459 0.263
17July202117.921 17.306 18.269 0.534
Lemnaminor (fromOporzyńskieLake)
30April20212.412 2.111 2.892 0.420
14June20216.480 5.987 6.876 0.452
17July20219.582 9.423 9.816 0.201
Lemnaminor (frombreeding)
30April20211.902 1.794 2.006 0.106
14June20212.035 2.014 2.052 0.019
17July20212.034 2.029 2.042 0.007
3.5. RelationshipsbetweentheParameters ofDryMass ofL.minorandC.glomerata andthe
EffectofPolyphenolConcentrationandTime
Theresultsofthedry masscontentinC.glomerata (Figure5)andL.minor(Figure 6)
showedthatC.glomeratahadahigherdrymasscontentinJuneandJulythanL.minor.In
April,C.glomerata hadaslightlylowercontentofdrymassthanL.minor.Consideringthe
resultsseparately,thedry massofC.glomeratahadthehighestmeanvalueinJulyandthe
lowestinApril. ItwassimilarforL.minor—thehighestaveragedrymassvaluewasin
July andthelowestinApril. BothinC.glomerata and L.minor,themeanvalueofdry
matterwasstatisticallysignificant betweenthetestedtrialsfromApril,June, and July(a,
b,c).
TheresponseofC.glomerata andL.minortothepolyphenolcontent(Figure 7)and
theeffectoftheobservationtime(Figure 8)wereanalyzed using theGAMmodel. The
first modelshowed thatinbothC.glomerata andL.minor,theconcentration ofpolyphenols
increasedincellsovertime(Figure 7).However,inthecaseofC.glomerata,thebiomass
increasedfaster withincreasingpolyphenolconcentration (Figure7). ThebiomassofL.
minorincreasedsignificantlyslowerwiththeincrease intheconcentrationofpolyphenols
ascomparedtoC.glomerata (Figure7).The secondmodelshowedthatC.glomerataischar
acterized byafasterincrease inbiomassduring theobservation thanL.minor(Figure 8).
Figure5.Mean valueofdrymass(g)ofC.glomerataatdifferenttimes(1–30 April2021; 2–4June
2021;3–17July2021)presentedusingtheTukeymultiple comparisonstest.Thebarsindicatemean
Figure 5.
Mean value of dry mass (g) of C. glomerata at different times (1–30 April 2021; 2–4 June 2021;
3–17 July 2021) presented using the Tukey multiple comparisons test. The bars indicate mean values.
Error bars represent standard error. A, B, C determines the statistical significance between the
analyzed features. A statistically significant result for p0.05 was marked.
Molecules2022,27,xFORPEERREVIEW12of17
values.Errorbarsrepresentstandard error.A,B,Cdeterminesthestatistical significancebetween
theanalyzedfeatures. Astatisticallysignificantresultforp≤0.05wasmarked.
Figure6.Meanvalue ofdrymass(g)ofL.minorindifferent times(1–30April2021;2–4June2021;
3–17July2021)presentedusing theTukeymultiplecomparisons test. Thebars indicate meanvalues.
Errorbarsrepresentstandarderror.A,B,Cdeterminesthestatisticalsignificancebetweentheana
lyzedfeatures.Astatisticallysignificantresultforp≤0.05wasmarked.
Figure7.C.glomerataandL.minorresponsecurves totimeofpolyphenolgradientmodeledbythe
generalizedadditivemodelusingPoissondistributionsmoothtermcomplexityselectedaccording
totheAICcriterion.ThefirstaxisrepresentstheGAE,andthesecond axisrepresentsthedrymass.
Figure 6.
Mean value of dry mass (g) of L. minor in different times (1–30 April 2021; 2–4 June 2021;
3–17 July 2021) presented using the Tukey multiple comparisons test. The bars indicate mean values.
Error bars represent standard error. A, B, C determines the statistical significance between the
analyzed features. A statistically significant result for p0.05 was marked.
The response of C. glomerata and L. minor to the polyphenol content (Figure 7) and the
effect of the observation time (Figure 8) were analyzed using the GAM model. The first
model showed that in both C. glomerata and L. minor, the concentration of polyphenols in-
creased in cells over time (Figure 7). However, in the case of C. glomerata, the biomass increased
faster with increasing polyphenol concentration (Figure 7). The biomass of L. minor increased
significantly slower with the increase in the concentration of polyphenols as compared to
C. glomerata (Figure 7). The second model showed that C. glomerata is characterized by a
faster increase in biomass during the observation than L. minor (Figure 8).
Molecules 2022,27, 3428 12 of 17
Figure 7.
C. glomerata and L. minor response curves to time of polyphenol gradient modeled by the
generalized additive model using Poisson distribution smooth term complexity selected according to
the AIC criterion. The first axis represents the GAE, and the second axis represents the dry mass.
Molecules2022,27,xFORPEERREVIEW13of17
Figure8.C.glomerataandL.minorresponsecurvestotimeofobservation(4month)gradientmod
eledbythegeneralizedadditivemodelusingPoissondistributionsmoothtermcomplexityselected
accordingtotheAICcriterion.Thefirstaxisrepresentsthetimevalues,andthesecondaxisrepre
sentsthedrymass.
4.Discussion
Taxacooccurringinthesameplacemayuseallelopathyasastrategyincompetition
forspace,nutrients,light,andotherecologicalfactors[26,40].Competitioncanresultin
thereplacementorexclusionofaspecies.Itismosteffectiveasaresultofthereleaseof
chemicalsbyhydromacrophytesintotheaquaticenvironment.Therefore,allelopathy
playsasignificantroleintheformation,stabilization,anddynamicsofthestructureof
plantcommunities[6,26,41].BothLemnaminorandCladophoraglomeratainhabitcommon
habitats,showsimilarpreferencesfortheavailabilityoflightandnutrients,andcreate
densematsonthewatersurface.Plantsneedspaceforproperdevelopment,sotheycom
petewitheachotherforthesurfacelayerofwater.
Theconductedanalysesshowedthat:(1)LemnaminorandCladophoraglomeratase
creteallelopathicsubstances,(2)allelochemicalshaveasignificantimpactonthestructure
ofpleustophyteandalgacommunities,and(3)allelopathicpotentialoccursasaresultof
competitionbetweencooccurringspecies.
TheresultsofourresearchshowthattheaveragelengthandwidthofcellsinC.glom
erataaswellasthediameterandthicknessofL.minorindividualsshowedsignificantdif
ferencesintheanalyzedtime(April–June–July).ThehighestmeanlengthofC.glomerata
cellswasinJulyandthelowestinJune.InthecaseofL.minor,thehighestaveragediam
eterandthicknessofindividualswasinJuly(inthefullestofthegrowingseason).The
smallestaveragediameterandthicknessofindividualswasinJune.Consideringthesize
ofthepatchesofC.glomeratainthelittoralzone,thelargestoccurredinJulyandthesmall
estinApril.L.minor,however,hadthelargestpatchesinAprilandthesmallestinJuly.
Additionally,theseresultsshowthatC.glomeratacreatedmoreextensivepatchesonthe
watersurfaceofOporzyńskieLakeascomparedtoL.minor.
ThelengthandwidthofC.glomeratacellsandL.minorindividualsaswellasthesize
oftheirpatches(“mats”)alsoshowedarelationshipwiththetotalphenoliccontentin
thesespecies.ItisworthnotingthatthephenolcontentinC.glomeratawashigherthan
thephenolcontentinL.minor.Thehighestconcentrationofphenolsingreenalgaehad
thehighestandmostsimilarvaluesinJuneandJulyandthelowestinApril.L.minorthat
wascollectedfromOporzyńskieLakehadthehighestconcentrationofphenolsinJuly
andthelowestinApril.L.minorfromthecultivationhadalowercontentofphenols
Figure 8.
C. glomerata and L. minor response curves to time of observation (4 month) gradient
modeled by the generalized additive model using Poisson distribution smooth term complexity
selected according to the AIC criterion. The first axis represents the time values, and the second axis
represents the dry mass.
4. Discussion
Taxa co-occurring in the same place may use allelopathy as a strategy in competition
for space, nutrients, light, and other ecological factors [
26
,
40
]. Competition can result in
the replacement or exclusion of a species. It is most effective as a result of the release of
chemicals by hydro macrophytes into the aquatic environment. Therefore, allelopathy
plays a significant role in the formation, stabilization, and dynamics of the structure of plant
communities [
6
,
26
,
41
]. Both Lemna minor and Cladophora glomerata inhabit common habitats,
show similar preferences for the availability of light and nutrients, and create dense mats
on the water surface. Plants need space for proper development, so they compete with
each other for the surface layer of water.
Molecules 2022,27, 3428 13 of 17
The conducted analyses showed that: (1) Lemna minor and Cladophora glomerata secrete
allelopathic substances, (2) allelochemicals have a significant impact on the structure of
pleustophyte and alga communities, and (3) allelopathic potential occurs as a result of
competition between co-occurring species.
The results of our research show that the average length and width of cells inC. glomerata
as well as the diameter and thickness of L. minor individuals showed significant differences
in the analyzed time (April–June–July). The highest mean length of C. glomerata cells was
in July and the lowest in June. In the case of L. minor, the highest average diameter and
thickness of individuals was in July (in the fullest of the growing season). The smallest
average diameter and thickness of individuals was in June. Considering the size of the
patches of C. glomerata in the littoral zone, the largest occurred in July and the smallest
in April. L. minor, however, had the largest patches in April and the smallest in July.
Additionally, these results show that C. glomerata created more extensive patches on the
water surface of Oporzy´nskie Lake as compared to L. minor.
The length and width of C. glomerata cells and L. minor individuals as well as the size
of their patches (“mats”) also showed a relationship with the total phenolic content in
these species. It is worth noting that the phenol content in C. glomerata was higher than the
phenol content in L. minor. The highest concentration of phenols in green algae had the
highest and most similar values in June and July and the lowest in April. L. minor that was
collected from Oporzy´nskie Lake had the highest concentration of phenols in July and the
lowest in April. L. minor from the cultivation had a lower content of phenols compared
to L. minor and C. glomerata that were collected from the Oporzy´nskie Lake. In this case,
phenols reached their highest values in June and lowest in April.
These results show that both C. glomerata and L. minor have allelopathic potential.
However, C. glomerata shows greater potential and therefore is a stronger taxon in inter-
species competition. C. glomerata has a specific feature. This is the rapid development of
the thallus and dynamic multiplication. At the same time, it produces a large quantity
of phenolic compounds. Our research confirms these features. Both in C. glomerata and
in L.minor, the concentration of polyphenols in the cells increases with time. However, the
biomass of C. glomerata grows much faster compared to that of L. minor. As a result, C. glomerata
can form broad and dense mats on the water surface and successfully compete for space
with duckweed. The macroalga C. glomerata characteristically dominates in eutrophic
waters [
25
] and has a rapid biomass growth over time, and our findings have confirmed
this dependence. As a result, the alga excludes the co-occurring taxon and achieves com-
petitive success over other aquatic plants [
24
,
25
]. This mechanism provides green algae
with a large space for proper development and access to light and nutrients. Phenolic
compounds secreted by C. glomerata may influence the formation of communities of small
pleustophytes, including L. minor.C. glomerata showed a higher total phenolic content than
L. minor. The greater the concentration of green algae in the surface water layers, the more
phenols are released into the environment. This inhibits the development of L. minor and
limits the size of its patches on the water surface. The strategy of freshwater algae in the
process of competition is: intensive development in early spring, taking nutrients from the
water, chemical composition of the thallus (presence of proline in the period of high thallus
density), changes in the morphological structure, secretion of allelopathic substances, and
the formation of spores [26] (from Ozimek 1990).
Lemna minor may also inhibit the development of other hydromacrophytes. This
pleustophyte creates dense mats on the water surface. As a result, it reduces the amount
of light available for the deeper layers of water, which is necessary for other plants to
grow adequately [
20
]. Both the literature data and our results show that this pleustophyte
contains allelopathic chemicals. During coexistence with C. glomerata, a higher content of
phenolic compounds was demonstrated in L. minor individuals than in bred individuals.
This shows that L. minor also has a competitive strategy. Pleustophyte competes with
C. glomerata for space, light, and nutrients, so it uses its allelopathic potential to achieve
competitive success. When bred, L. minor does not have to compete with other plants
Molecules 2022,27, 3428 14 of 17
for space and access to nutrients. Therefore, the total phenolic content is lower as it is
not necessary for survival. It is likely that these allelochemicals may also inhibit the
development of other plants. As a result, L. minor can ensure a competitive advantage in
the aquatic ecosystem [
20
]. However, the mechanism of the allelopathic strategy has not
yet been elucidated.
5. Conclusions
Finally, we would emphasize that our efforts have been directed in two ways: (i) to
review the studies on models of Lemna minor and Cladophora glomerata population formation
with a focus on their chemical composition and (ii) to mark a particular model of seasonal
growth of two species occupying one ecological niche at the same time. In our study, the
concentration of polyphenols in the cells of C. glomerata and in L.minor increases with
time. The role of rapid biomass growth of one of the competing species seems to be crucial.
To assess the effectiveness of Lemna minor allelopathic potential, many factors need to
be determined. The research carried out in this article highlights the poorly understood
relationships between species (duckweed and macroalga) that coexist in the same place at
the same time in the aquatic environment. The mechanisms that would accurately explain
the phenomenon of allelopathy between competing taxa are also unknown. These issues
require further research, which we will certainly undertake in well-defined aquatic systems
during laboratory experiments.
6. Materials and Methods
6.1. Raw Material Collection and Identification
Freshwater Cladophora glomerata thalli and Lemna minor specimens were collected from
the shallow Lake Oporzy´nskie (N 52
55
0
70”, E 17
09
0
60”), situated in the northern part
of the Wielkopolska region (western Poland), in the April–July period of 2021, when the
algal biomass was at its annual minimum and maximum. Characterization of physical and
chemical parameters during the intensive development of C. glomerata in the lake has been
performed earlier [
24
,
25
,
42
]. Morphometric measurements of the length and width of cells
and individuals were taken using a light microscope (LM).
6.2. Element Analysis of Lemna minor and Cladophora glomerata Raw Material
The content of selected elements, such as Ca, Mg, Na, K, Fe, Zn, Cu, As, Cd, Ni, Pb, Cr,
Mn, and Co, was determined in the Lemna and Cladophora biomass. The elemental analysis
was carried out in an inductively coupled plasma–optical emission spectrometer (Varian
ICP-OES VISTA-MPX) by the ICP–OES method. The concentrationof elementswas expressed
as
µ
g
·
g
1
of dry matter or g
·
g
1
of dry matter or mg
·
kg
1
(in the case of Lemna minor). Then
the analysis error was calculated.
6.3. Ultrasound-Assisted Extraction (UAE)
Ultrasound-assisted extracts were made out of raw, powdered material of C. glomerata
and L. minor. In each case, for the preparation of extracts for spectrometric analysis, 10 g of
dry weight of material was extracted in an ultrasonic bath with two portions of methanol as
a solvent (2
×
100 mL), over a total time of 1 h. After 30 min, the first portion of the solvent
was removed and a new portion was added to continue the extraction for another 30 min.
The temperature of the ultrasonic bath did not exceed 35
C. The extracts were filtrated,
and the filtrates were combined. The solvent was removed in the rotary evaporator. To
prepare samples for spectrometric analysis, the methanolic solutions of extracts were made
up to a concentration of 10.00 ±0.06 mg mL1.
6.4. Determination of Total Phenolic Compounds in Extracts
A calibration curve was prepared by dissolving gallic acid in 70% methanol to obtain
a stock solution with a concentration of 1 mg/mL, after which subsequent dilutions were
made in a range of concentrations from 0.1 mg/mL to 1 mg/mL. Then 20
µ
L of gallic
Molecules 2022,27, 3428 15 of 17
acid solution with a particular concentration was added, along with 1.58 mL of distilled
water, 0.1 mL of Folin–Ciocalteu reagent, and 0.3 mL of saturated solution of sodium
bicarbonate (Na2CO3). The final reaction volume was 2 mL, and the final concentration of
gallic acid ranged between 0.001 and 0.01 mg/mL [
43
]. A reaction mixture with real samples
was prepared in the same way as the samples for the calibration curve, and the extract solution
was added instead of gallic acid solution. The result was expressed as gallic acid equivalent (GAE)
using the equation C [mg QE/gextract] = C [mg/mL]
×
(V1 [mL]/V2 [mL])
×
(V3 [mL]/m [g]),
where C (mg/mL) is the concentration from the calibration curve, V1 is the total volume of
the reaction vessel, V2 is the volume of the extract/standard added to the reaction, V3 is
the volume in which the extract was dissolved, and m is the mass of the extract dissolved
in V3 to prepare a real sample of extract. After keeping the reaction vessels in darkness for
2 h, the samples were measured with a UV/VIS spectrometer at 760 nm. Each sample was
prepared and measured in triplicate. Data are the mean ±the SD values.
6.5. Data Analysis
Statistical analyses were performed with STATISTICA software version 12.0. To confirm
the significance of differences between the analyzed Lemna minor and Cladophora glomerata
features in time, a one-way ANOVA followed by Tukey’s RIR post hoc test was used.
Differences were considered to be significant at p< 0.05. These statistical analyses were
performed using the R 3.0.1 statistical package (R Development Core Team 2013, using the
vegan package; [44]).
Changes of Lemna and Cladophora biomass occurrence in response to time were mod-
eled using the GAMs [
45
]. We used Poisson distribution, while smooth term complexity
was selected using the Akaike information criterion [46].
Author Contributions:
Conceptualization, data curation, formal analysis, investigation, method-
ology, writing—original draft preparation, visualization, and writing—review and editing, J.G.;
methodology and funding acquisition, R.P.; writing—review and editing, Z.R.-D.; conceptualization,
formal analysis, methodology, supervision, and writing—review and editing, B.M. All authors have
read and agreed to the published version of the manuscript.
Funding:
This research was funded by the National Science Center, Poland, grant number 2018/31/B/
NZ8/00280.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments:
We wish to thank M. G ˛abka for his helpful advice on design statistical analysis.
Helpful comments of two referees improved an earlier version of the manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability:
Samples of Lemna minor and Cladophora glomerata are available from the authors.
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