Seed germination and seedling growth response of Leymus chinensis to the allelopathic influence of grassland plants.

Allelopathy has a profound impact on the germination and growth of plants, influencing the establishment of plant populations and shaping community ecological patterns. However, the allelopathic potential of many grassland species remains poorly understood. In this study, we prepared aqueous extracts from 17 herbaceous plants to investigate their allelopathic effects on the seed germination and seedling growth of Leymus chinensis, a dominant grassland species. Our results revealed that the response of L. chinensis to allelopathic compounds was dependent on the specific plant species, extract concentration, and target plant organ. Notably, Fabaceae plants exhibited a stronger allelopathic potential than Poaceae, Asteraceae, and other plant families. Moreover, we observed that root growth of L. chinensis was more sensitive to allelopathy than shoot growth, and seed germination was more affected than seedling growth. Generally, the germination of L. chinensis was strongly inhibited as the donor plant extract concentration increased. The leachate of Fabaceae plants inhibited the seedling growth of L. chinensis at concentrations ranging from 0.025 to 0.1 g mL-1. On the other hand, the leachate from other families' plants exhibited either inhibitory or hormetic effects on the early growth of L. chinensis, promoting growth at 0.025 g mL-1 and hindering it at concentrations between 0.05 and 0.1 g mL-1. These findings highlight the significant allelopathic potential of grassland plants, which plays a critical role in establishing plant populations and associated ecological processes. In addition, they shed light on the coexistence of other plants with dominant plants in the community.

Allelochemicals of Alexandrium tamarense and its algicidal mechanism for Prorocentrum donghaiense and Heterosigma akashiwo.

The effects of culture filtrate of Alexandrium tamarense on Prorocentrum donghaiense and Heterosigma akashiwo were investigated, including determination of algal density, photosynthesis, intracellular enzyme content and activity. The filtrate of A. tamarense had a stronger inhibitory effect on P. donghaiense than H. akashiwo, and the inhibitory effect decreased with higher temperature treatment of the filtrate. Instantaneous fluorescence (Ft) and maximum quantum yield of photosystem II (Fv/Fm) values of both kinds of target algae were reduced as exposed to the filtrate of A. tamarense, which proved that allelopathy could inhibit the normal operation of photosynthetic system. The increase of Malondialdehyde (MDA) content of the two kinds of target algae indicated that the cell membrane was seriously damaged by allelochemicals released by A. tamarense. The different responses of Superoxide Dismutase (SOD) and Catalase (CAT) activity in two kinds of target algae demonstrated the complexity and diversity of allelopathic mechanism. The filtrate of A. tamarense also influenced the metabolic function (ATPases) of P. donghaiense and H. akashiwo, and the influence on P. donghaiense was greater. Liquid-liquid extraction was used to extract and isolate allelochemicals from the filtrate of A. tamarense. It was found that only component I with molecular weight of 424.2573 and 434.2857 could inhibit the growth of P. donghaiense by HPLC-MS.

Benzoxazinoids secreted by wheat root weaken the pathogenicity of Fusarium oxysporum f. sp. fabae by inhibiting linoleic acid and nucleotide metabolisms.

KEY MESSAGE: The regulatory action of BXs secreted by wheat on the pathogenicity of FOF causing Fusarium wilt in faba bean were analyzed. DIMBOA and MBOA weakened the pathogenicity of FOF. A large number of pathogenic bacteria in continuous cropping soil infect faba bean plants, leading to the occurrence of wilt disease, which restricts their production. Faba bean-wheat intercropping is often used to alleviate this disease. This study investigates the effect of benzoxazinoids (BXs) secreted by wheat root on the pathogenicity of Fusarium oxysporum f. sp. Fabae (FOF) and underlying molecular mechanisms. The effects of DIMBOA(2,4-dihydroxy-7-methoxy-1,4-benzoxazine-4-one) and MBOA(6-methoxybenzoxazolin-2-one) on the activity of cell-wall-degrading enzymes in FOF(cellulase, pectinase, amylase, and protease), FOF Toxin (fusaric acid, FA) content were investigated through indoor culture experiments. The effect of BXs on the metabolic level of FOF was analyzed by metabonomics to explore the ecological function of benzoxazines intercropping control of Fusarium wilt in faba bean. The results show that the Exogenous addition of DIMBOA and MBOA decreased the activity of plant-cell-wall-degrading enzymes and fusaric acid content and significantly weakened the pathogenicity of FOF. DIMBOA and MBOA significantly inhibited the pathogenicity of FOF, and metabolome analysis showed that DIMBOA and MBOA reduced the pathogenicity of FOF by down-regulating related pathways such as nucleotide metabolism and linoleic acid metabolism, thus effectively controlling the occurrence of Fusarium wilt in faba bean.

Physiological and molecular insights into the allelopathic effects on agroecosystems under changing environmental conditions.

Allelopathy is a natural phenomenon of competing and interfering with other plants or microbial growth by synthesizing and releasing the bioactive compounds of plant or microbial origin known as allelochemicals. This is a sub-discipline of chemical ecology concerned with the effects of bioactive compounds produced by plants or microorganisms on the growth, development and distribution of other plants and microorganisms in natural communities or agricultural systems. Allelochemicals have a direct or indirect harmful effect on one plant by others, especially on the development, survivability, growth, and reproduction of species through the production of chemical inhibitors released into the environment. Cultivation systems that take advantage of allelopathic plants' stimulatory/inhibitory effects on plant growth and development while avoiding allelopathic autotoxicity is critical for long-term agricultural development. Allelopathy is one element that defines plant relationships and is involved in weed management, crop protection, and microbial contact. Besides, the allelopathic phenomenon has also been reported in the forest ecosystem; however, its presence depends on the forest type and the surrounding environment. In the present article, major aspects addressed are (1) literature review on the impacts of allelopathy in agroecosystems and underpinning the research gaps, (2) chemical, physiological, and ecological mechanisms of allelopathy, (3) genetic manipulations, plant defense, economic benefits, fate, prospects and challenges of allelopathy. The literature search and consolidation efforts in this article shall pave the way for future research on the potential application of allelopathic interactions across various ecosystems.

Potential molecular mechanism of photosynthesis regulation by PeMPK7 in poplar under para-hydroxybenzoic acid stress.

Due to continuous plantation of poplar, its growth and biomass accumulation may be negatively affected by the accumulation of allelochemicals such as para-hydroxybenzoic acid (pHBA) in soil. As photosynthesis is the most fundamental process in plants, it can be negatively impacted by pHBA stress. Therefore, it is crucial to improve photosynthetic capacity under pHBA stress to facilitate poplar plant growth. The mitogen-activated protein kinase (MAPK) cascade pathway is widely involved in environmental stress responses in plants. However, the regulation mechanisms of photosynthesis-related pathways by MAPK pathway genes under pHBA stress are still unclear. In this study, through transcriptome analysis and weighted gene co-expression network analysis, we observed that PeMPK7 overexpression in poplar can regulate the expression of photosynthesis-related genes and transcription factor genes, namely, WRKY1, WRKY33, and ERF3, during the early stage of pHBA stress. In addition, PeMPK7 can improve photosynthesis in poplar under long-term pHBA stress. Moreover, yeast two-hybrid and pull-down assays confirmed the interaction between PeMPK7 and PeMKK7/10. Based on these results, a schematic diagram of the pathways involved in the regulation of photosynthesis by PeMPK7 was constructed. This study provided novel insights into the molecular mechanisms of regulation of pHBA stress via MAPK cascade pathway.

Microenvironment created by Plantago lagopus L. may affect cover and diversity of coexisting species in urban vegetation.

Some plant species may exhibit new microenvironments which lead to significant changes in the cover and diversity of the coexisting species. In this investigation, we evaluated the effects of Plantago lagopus L. on the cover and diversity of the associated plant species in the urban vegetation. A total of 70 plots were conducted in sites with- and without this species in urban gardens. Cover of the associated species and different diversity indices including species richness, Shannon-Wiener, evenness, and Simpson indices were measured. The allelopathic potential of P. lagopus was verified using its rhizosphere and non-rhizosphere soils on two target species existing within the same environment. Some soil criteria and seed sizes of the associated species were also determined. Most of the coexisting weeds were reduced in terms of their cover in plots with Plantago. The reduction of plant diversity depended on its cover. Besides, the aboveground biomass was reduced in sites comprising Plantago. The degree of inhibition was not related to the seed size of the species found. This species reduced the incident solar radiation and the local temperature over the soil surface. The locations exhibiting such species contained lower contents of available potassium and zinc. Rhizosphere soil of P. lagopus substantially inhibited germination and growth of Amaranthus viridis, but it didn't do so for Medicago lupulina. Reduction in cover, diversity, and biomass of the urban weeds associated with P. lagopus may be related to the reduction of received solar radiation, soil temperature, and nutrient availability. The allelopathic potential of P. lagopus may have a partial role in this reduction. These results suggest that P. lagopus may create a microenvironment of new conditions not favorable for most of the coexisting species.

Deciphering the Genetic Basis of Allelopathy in japonica Rice Cultivated in Temperate Regions Using a Genome-Wide Association Study.

Allelopathy has been considered as a natural method of weed control. Despite the nature of allelochemical compounds has been studied, little is known about the genetic basis underlying allelopathy. However, it is known that rice exhibits diverse allelopathic potentials across varieties, and breeding for rice plants exhibiting allelopathic potential conferring an advantage against weeds in paddy fields would be highly desirable. Knowledge of the gene factors and the identification of the genomic regions responsible for allelopathy would facilitate breeding programs. Taking advantage of the existing genetic diversity in rice, particularly in temperate japonica rice, we conducted a comprehensive investigation into the genetic determinants that contribute to rice allelopathy. Employing Genome-Wide Association Study, we identified four Quantitative Trait Loci, with the most promising loci situated on chromosome 2 and 5. Subsequent inspection of the genes located within these QTLs revealed genes associated with the biosynthesis of secondary metabolites such as Phenylalanine Ammonia Lyase (PAL), a key enzyme in the synthesis of phenolic compounds, and two genes coding for R2R3-type MYB transcription factors. The identification of these two QTLs associated to allelopathy in rice provides a useful tool for further exploration and targeted breeding strategies.

Effect of phenolics on soil microbe distribution, plant growth, and gall formation.

Phenolic compounds, abundant secondary metabolites in plants, profoundly influence soil ecosystems, plant growth, and interactions with herbivores. In this study, we explore the intricate relationships between phenolics, soil microbes, and gall formation in Ageratina adenophora (A. adenophora), an invasive plant species in China known for its allelopathic traits. Using metabolomic and microbial profiling, significant differences in soil microbial composition and metabolite profiles were observed between bulk and rhizosphere soil samples. Phenolics influenced bacterial communities, with distinct microbial populations enriched in each soil type. Additionally, phenolics impacted soil metabolic processes, with variations observed in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis between different soil treatments. Analysis of phenolic content in plant and soil samples revealed considerable variations, with higher concentrations observed in certain plant tissues and soil types. Bioactive phenols extracted from plant and soil samples were identified using gas chromatography/mass spectrometry (GC-MS), providing insights into the diverse chemical composition of these compounds. Furthermore, the effects of phenolics on plant growth and gall formation were investigated. Phenols exhibited both stimulatory and inhibitory effects on plant growth, with optimal concentrations promoting emergence but higher concentrations hindering growth. Gall formation was influenced by phenolic concentrations, leading to structural alterations in stem tissue and gall morphology. Histochemical analysis revealed starch and lipid accumulation in gall tissues, indicating metabolic changes induced by phenolics. The presence of phenolics disrupted tissue structures and influenced vascular bundle orientation in gall tissues. Overall, our study highlights the multifaceted roles of phenolic compounds in soil ecosystems, plant development, and gall formation, facilitating the utilization of secondary metabolites in agriculture.

Response of the toxic dinoflagellate Alexandrium minutum to exudates of the eelgrass Zostera marina.

Biotic interactions are a key factor in the development of harmful algal blooms. Recently, a lower abundance of planktonic dinoflagellates has been reported in areas dominated by seagrass beds, suggesting a negative interaction between both groups of organisms. The interaction between planktonic dinoflagellates and marine phanerogams, as well as the way in which bacteria can affect this interaction, was studied in two experiments using a non-axenic culture of the toxic dinoflagellate Alexandrium minutum exposed to increasing additions of eelgrass (Zostera marina) exudates from old and young leaves and to the presence or absence of antibiotics. In these experiments, A. minutum abundance, growth rate and photosynthetic efficiency (Fv/Fm), as well as bacterial abundance, were measured every 48 h. Toxin concentration per cell was determined at the end of both experiments. Our results demonstrated that Z. marina exudates reduced A. minutum growth rate and, in one of the experiments, also the photosynthetic efficiency. These results are not an indirect effect mediated by the bacteria in the culture, although their growth modify the magnitude of the negative impact on the dinoflagellate growth rate. No clear pattern was observed in the variation of toxin production with the treatments.

Meta-analysis to identify inhibition mechanisms for the effects of submerged plants on algae.

Submerged plants inhibit algae through shading effects, nutrient competition, allelopathy, and combinations of these mechanisms. However, it is unclear which mechanism is dominant, and how the inhibition intensity results from the traits of the plant and algae. In this study, we performed meta-analysis to quantitatively identify the dominant mechanisms, evaluate the relationship between inhibition intensity and the species and functional traits of the submerged plants or algae, and reveal the influences of external environmental factors. We found that allelopathy caused stronger inhibition than the shading effect and nutrient competition and dominated the combined mechanisms. Although the leaf shapes of the submerged plants influenced light availability, this did not change the degree of algae suppression. Algal species, properties (toxic or nontoxic) and external environmental factors (e.g., lab/mesocosm experiments, co-/filtrate/extract culture, presence or absence of interspecific competition) potentially influenced inhibition strength. Cyanobacteria and Bacillariophyta were more strongly inhibited than Chlorophyta, and toxic Cyanobacteria more than non-toxic Cyanobacteria. Algae inhibition by submerged plants was species-dependent. Ceratophyllum, Vallisneria, and Potamogeton strongly inhibited Microcystis, and can potentially prevent or mitigate harmful algal blooms of this species. However, the most common submerged plant species inhibited mixed algae communities to some extent. The results from lab experiments and mesocosm experiments both confirmed the inhibition of algae by submerged plants, but more evidence from mesocosm experiments is needed to elucidate the inhibition mechanism in complex ecosystems. Submerged plants in co-cultures inhibited algae more strongly than in extract and filtrate cultures. Complex interspecific competition may strengthen or weaken algae inhibition, but the response of this inhibition to complex biological mechanisms needs to be further explored. Our meta-analysis provides insights into which mechanisms contributed most to the inhibition effect and a scientific basis for selecting suitable submerged plant species and controlling external conditions to prevent algal blooms in future ecological restoration of lakes.

Mass spectrometry-based metabolomics for the elucidation of alkaloid biosynthesis and function in invasive Vincetoxicum rossicum populations.

The genus Vincetoxicum includes a couple of highly invasive vines in North America that threaten biodiversity and challenge land management strategies. Vincetoxicum species are known to produce bioactive phenanthroindolizidine alkaloids that might play a role in the invasiveness of these plants via chemical interactions with other organisms. Untargeted, high-resolution mass spectrometry-based metabolomics approaches were used to explore specialized metabolism in Vincetoxicum plants collected from invaded sites in Ontario, Canada. All metabolites corresponding to alkaloids in lab and field samples of V. rossicum and V. nigrum were identified, which collectively contained 25 different alkaloidal features. The biosynthesis of these alkaloids was investigated by the incorporation of the stable isotope-labelled phenylalanine precursor providing a basis for an updated biosynthetic pathway accounting for the rapid generation of chemical diversity in invasive Vincetoxicum. Aqueous extracts of aerial Vincetoxicum rossicum foliage had phytotoxic activity against seedlings of several species, resulting in identification of tylophorine as a phytotoxin; tylophorine and 14 other alkaloids from Vincetoxicum accumulated in soils associated with full-sun and a high-density of V. rossicum. Using desorption-electrospray ionization mass spectrometry, 15 alkaloids were found to accumulate at wounded sites of V. rossicum leaves, a chemical cocktail that would be encountered by feeding herbivores. Understanding the specialized metabolism of V. rossicum provides insight into the roles and influences of phenanthroindolizidine alkaloids in ecological systems and enables potential, natural product-based approaches for the control of invasive Vincetoxicum and other weedy species.

A laboratory study of the increasing competitiveness of Karenia mikimotoi under rising CO2 scenario.

Ocean acidification (OA) driven by elevated carbon dioxide (CO2) levels is expected to disturb marine ecological processes, including the formation and control of harmful algal blooms (HABs). In this study, the effects of rising CO2 on the allelopathic effects of macroalgae Ulva pertusa to a toxic dinoflagellate Karenia mikimotoi were investigated. It was found that high level of CO2 (1000 ppmv) promoted the competitive growth of K. mikimotoi compared to the group of present ambient CO2 level (420ppmv), with the number of algal cell increased from 32.2 × 104 cells/mL to 36.75 × 104 cells/mL after 96 h mono-culture. Additionally, rising CO2 level weakened allelopathic effects of U. pertusa on K. mikimotoi, as demonstrated by the decreased inhibition rate (50.6 % under the original condition VS 34.3 % under the acidified condition after 96 h co-culture) and the decreased reactive oxygen species (ROS) level, malondialdehyde (MDA) content, antioxidant enzymes activity (superoxide dismutase (SOD), peroxidase (POD), glutathione peroxidase (GPX), glutathione reductase (GR) and catalase (CAT) and non-enzymatic antioxidants (glutathione (GSH) and ascorbic acid (ascorbate, vitamin C). Indicators for cell apoptosis of K. mikimotoi including decreased caspase-3 and -9 protease activity were observed when the co-cultured systems were under rising CO2 exposure. Furthermore, high CO2 level disturbed fatty acid synthesis in U. pertusa and significantly decreased the contents of fatty acids with allelopathy, resulting in the allelopathy weakening of U. pertusa. Collectively, rising CO2 level promoted the growth of K. mikimotoi and weakened allelopathic effects of U. pertusa on K. mikimotoi, indicating the increased difficulties in controlling K. mikimotoi using macroalgae in the future.

Isolation and identification of allelochemicals and their activities and functions.

Allelopathy is the interaction between donor plants and receiver plants through allelochemicals. According to a great number of publications, allelopathy may be involved in several ecological aspects such as the formation of monospecific stands and sparse understory vegetation for certain plant species. Allelopathy also contributes to the naturalization of invasive plant species in introduced ranges. Autotoxicity is a particular type of allelopathy involving certain compounds. Many medicinal plants have been reported to show relatively high allelopathic activity. We selected plant species that show high allelopathic activity and isolated allelochemicals through the bioassay-guided purification process. More than 100 allelochemicals, including novel compounds have been identified in some medicinal and invasive plants, plants forming monospecific stands, plants with sparse understory vegetation, and plants showing autotoxicity. The allelopathic activity of benzoxazinones and related compounds was also determined.

Management of Rumex dentatus L. in Vicia faba L. cultivations via Ononis vaginalis Vahl. As a potential bioherbicide.

Biological control of undesirable weeds associated with crop cultivation is a sustainable approach that can reduce chemical herbicide dependence. The current study aimed to assess the bio-herbicidal potential of the donor species Ononis vaginalis Vahl. on germination efficiency as well as various growth and physiological parameters of the recipient species Rumex dentatus L., a major broad bean pest (Vicia faba L.). To assess the greatest inhibitory allelopathic effect on the recipient species in mixed (Rumex dentatus L. and Vicia faba L.) and pure cultures (each one separately), two experiments were conducted under laboratory conditions. A Petri dish experiment using O. vaginalis shoot aqueous extract (5%, 10%, 20%, and 40%) and a pot experiment using O. vaginalis shoot crude powder (1%, 2%, 5%, and 10%) were conducted to investigate its biological activity on some growth and physiological parameters of both crop and weed species. O. vaginalis underwent a general phytochemical screening that revealed a high production of allelochemicals, which are secondary metabolites and may have a function like that of natural herbicides. The result showed that the germination of V. faba seeds in both pure and mixed cultures was not significantly affected by low levels of O. vaginalis shoot aqueous extract treatments in pure and mixed cultures, in contrast, those recorded for R. dentatus gradually dropped as levels of O. vaginalis increased in both cultures. Results recorded a significant increase in total phenolics of V. faba shoots and roots under different treatments, except at the high concentrations of crude powder at the donor species level (5 and10%). A reduction in the total phenolic and flavonoid fractions was observed in R. dentatus roots under varying concentration treatments. Conversely, under high concentration treatments, flavonoids decreased in the roots of the mixed culture of R. dentatus but increased in the shoots. In conclusion, allelopathy can be used to suppress weeds in field crops. The study confirmed the use of O. vaginalis into current weed control techniques. O. vaginalis could be explored further for weed suppression in the field.

Benthic cyanobacterial metabolites interact to reduce coral larval survival and settlement.

Benthic cyanobacterial mats (BCMs) are becoming increasingly abundant on coral reefs worldwide. High growth rates and prolific toxin production give them the potential to cause widespread coral recruitment failure through allelopathic effects, but few studies have made the link between their toxicity for coral larvae and in situ toxin concentrations. Here we investigated the allelopathic effects of the benthic cyanobacterium Anabaena sp.1 on larvae of the coral Pocillopora acuta. This cyanobacterium produces several non-ribosomal cyclic lipopeptides of the laxaphycin family with cytotoxic properties. Therefore, we measured the concentration of laxaphycins A and B in Anabaena mats and in the water column and tested their effects on coral larvae. We found that Anabaena crude extract reduces both larval survivorship and settlement and that laxaphycin B reduces settlement. When larvae were exposed to both laxaphycins, there was a reduction in both larval survival and settlement. In the natural reef environment, laxaphycin A and B concentrations increased with increasing proximity to Anabaena mats, with concentrations being consistently above LC50 and EC50 thresholds within a 1 cm distance of the mats. This study demonstrates that laxaphycins reduce the survival and inhibit the settlement of coral larvae at concentrations found near Anabaena mats in situ. It further shows a combined effect between two cyanobacterial metabolites. As BCMs become more common, more of their secondary metabolites might be released in the water column. Their occurrence will lead to a reduction in coral recruitment rates, contributing to the continuing decline of coral reefs and shift in community structure.

The Invasive Mechanisms of the Noxious Alien Plant Species Bidens pilosa.

Bidens pilosa L. is native to tropical America and has widely naturized from tropical to warm temperate regions in Europe, Africa, Asia, Australia, and North and South America. The species has infested a wide range of habitats such as grasslands, forests, wetlands, streamlines, coastal areas, pasture, plantations, agricultural fields, roadsides, and railway sides and has become a noxious invasive weed species. B. pilosa forms thick monospecific stands, quickly expands, and threatens the indigenous plant species and crop production. It is also involved in pathogen transmission as a vector. The species was reported to have (1) a high growth ability, producing several generations in a year; (2) a high achene production rate; (3) different biotypes of cypselae, differently germinating given the time and condition; (4) a high adaptative ability to various environmental conditions; (5) an ability to alter the microbial community, including mutualism with arbuscular mycorrhizal fungi; and (6) defense functions against natural enemies and allelopathy. The species produces several potential allelochemicals such as palmitic acid, p-coumaric acid, caffeic acid, ferulic acid, p-hydroxybenzoic acid, vanillic acid, salycilic acid, quercetin, α-pinene, and limonene and compounds involved in the defense functions such as 1-phenylhepta-1,3,5-trine, 5-phenyl-2-(1-propynyl)-thiophene, 5-actoxy-2-phenylethinyl-thiophene, and icthyothereol acetate. These characteristics of B. pilosa may contribute to the naturalization and invasiveness of the species in the introduced ranges. This is the first review article focusing on the invasive mechanisms of the species.

Mechanisms Underlying Allelopathic Disturbance of Herbicide Imazethapyr on Wheat and Its Neighboring Ryegrass (Lolium perenne).

As representatives of allelopathy, weeds consistently coexist with crops, exhibiting mutual growth inhibition. At the same time, herbicides are usually employed to control weeds. However, few studies have investigated how herbicides will affect allelopathy between crops and their neighboring weeds. Our findings suggested that allelopathic-induced phenotypic variations in ryegrass were reduced in the presence of the herbicide imazethapyr (IM), consistent with the antioxidant system analysis results. Additionally, IM affected the levels of allelochemical hydroxamic acid (Hx) in both plants. Hydroponic experiments revealed that this impact was due to the accelerated transportation of Hx from wheat to ryegrass, driven by ryegrass-secreted jasmonic acid. This study holds paramount significance for comprehending the effects of herbicides on the allelopathic interactions between nontargeted crops and neighboring weeds, contributing to an enhanced understanding of herbicides on plant species interactions.

The allelopathic potential of red macroalga Pyropia haitanensis solvent extracts on controlling bloom-forming microalgae: Insights into the inhibitory compounds.

Various strategies have been explored to mitigate the impact of harmful algal blooms (HABs). While chemical and physical methods have traditionally been employed to regulate microalgal growth, their prolonged adverse effects on the ecosystem are a cause for concern. Recognizing the integral role of macroalgae within the ecosystem, this study reveals the anti-algal properties of solvent-based extracts derived from the red macroalga Pyropia haitanensis as a means of preventing microalgal blooms. In our investigation, we initially assessed the growth-inhibitory effects of methanol and acetone extracts from P. haitanensis on five microalgae known to contribute to bloom-formation. Significantly reduced growth was observed in all microalgal species when inoculated with both methanol and acetone extracts. Further analysis revealed the effectiveness of the methanol extract (ME), and further fractionation with petroleum ether (PE), ethyl acetate (EA), and n-butanol (NB) for testing against Skeletonema costatum and Pseudo-nitzschia pungens. The methanol fractions exhibited strong inhibition, resulting in the complete elimination of both microalgae after 96 hours of exposure to PE, EA, and NB extracts. Gas Chromatography-Mass Spectroscopy (GC-MS) analysis of the ME and its solvent fractions identified 49 confirmed compounds. These compounds are likely potential contributors to the observed inhibition of microalgal growth. In conclusion, our findings suggest that solvent extracts from P. haitanensis possess substantial potential for the control of HABs, offering a promising avenue for further research and application in ecosystem management.

Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages.

Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation.

Influence of ß-Ionone in the Phytotoxicity of the Rhizome of Iris pallida Lam.

Iris pallida Lam., also known as Sweetie Iris, is a perennial ornamental and medicinal plant that produces a wide range of secondary metabolites. The Sweetie Iris was recently reported to have high allelopathic properties with the potential to be explored in sustainable weed management. This study aimed to identify and evaluate the contributions of compounds involved in the inhibitory effects of the rhizome of Sweetie Iris. High-performance liquid chromatography (HPLC) analysis was used to determine the content of ß-ionone in the rhizome of Sweetie Iris. The phytotoxicity of ß-ionone was evaluated on lettuce (Lactuca sativa L.) and other test plants. The content of ß-ionone in the crude extract of Sweetie Iris rhizome was found to be 20.0 mg g-1 by HPLC analysis. The phytotoxicity bioassay showed that ß-ionone had strong inhibitory activity on the growth of lettuce (Lactuca sativa L.) and the other test plants, including Taraxacum officinale, Stellaria media, Eleusine indica, Amaranthus hybridus, Vicia villosa, and Brassica napus. At a concentration of 23.0 µg mL-1, ß-ionone inhibited the growth of all test plant species treated. Therefore, ß-ionone is an active compound among the other allelopathic substances contained in the rhizome of Sweetie Iris.