Research Progress on the use of Plant Allelopathy in Agriculture and the Physiological and Ecological Mechanisms of Allelopathy

Potential Effect of Root Exudates from Ten Crops on Promoting Stress Tolerance in Alfalfa (Medicago sativa) Seedlings

Allelopathy plays a major role in agricultural production, influencing plant protection, crop yield, and crop rotation systems. This study investigated the effects of root exudates on 3105c alfalfa (Medicago sativa) seeds and seedlings to identify crops with strong and weak allelopathic potential. The results revealed that corn (Zea mays L.) (T1) exhibited the strongest allelopathic effects, whereas soybean (Glycine max (Linn.) Merr.) (T10) exhibited the weakest effects. T1 promoted seed germination by increasing radicle length and the simple vitality index. Both T1 and T10 promoted 3105c seedling growth and enhanced antioxidant capacity, albeit through different mechanisms. T1 primarily increased antioxidant capacity by elevating ascorbate and dehydroascorbate levels while reducing malondialdehyde content. In contrast, T10 enhanced antioxidant capacity by increasing soluble sugar and protein levels via hydroxyl free radical inhibition. These findings demonstrate that the allelopathic properties of corn effectively promote alfalfa growth by enhancing seed germination and improving physiological stress resistance.

Nonlocal models in biology and life sciences: Sources, developments, and applications

Mathematical modeling is one of the fundamental techniques for understanding biophysical mechanisms in developmental biology. It helps researchers to analyze complex physiological processes and connect like a bridge between theoretical and experimental observations. Various groups of mathematical models have been studied to analyze these processes, and the nonlocal models are one of them. Nonlocality is important in realistic mathematical models of physical and biological systems when local models fail to capture the essential dynamics and interactions that occur over a range of distances (e.g., cell-cell, cell-tissue adhesions, neural networks, the spread of diseases, intra-specific competition, nanobeams, etc.). This review illustrates different nonlocal mathematical models applied to biology and life sciences. The major focus has been given to sources, developments, and applications of such models. Among other things, a systematic discussion has been provided for the conditions of pattern formations in biological systems of population dynamics. Special attention has also been given to nonlocal interactions on networks, network coupling and integration, including brain dynamics models that provide an important tool to understand neurodegenerative diseases better. In addition, we have discussed nonlocal modeling approaches for cancer stem cells and tumor cells that are widely applied in the cell migration processes, growth, and avascular tumors in any organ. Furthermore, the discussed nonlocal continuum models can go sufficiently smaller scales, including nanotechnology, where classical local models often fail to capture the complexities of nanoscale interactions, applied to build biosensors to sense biomaterial and its concentration. Piezoelectric and other smart materials are among them, and these devices are becoming increasingly important in the digital and physical world that is intrinsically interconnected with biological systems. Additionally, we have reviewed a nonlocal theory of peridynamics, which deals with continuous and discrete media and applies to model the relationship between fracture and healing in cortical bone, tissue growth and shrinkage, and other areas increasingly important in biomedical and bioengineering applications. Finally, we provided a comprehensive summary of emerging trends and highlighted future directions in this rapidly expanding field.

Via Air or Rhizosphere: The Phytotoxicity of Nepeta Essential Oils and Malus Dihydrochalcones

Many specialized metabolites found in plants have significant potential for developing environmentally friendly weed management solutions. This review focuses on the phytotoxic effects of volatile terpenes and phenolic compounds, particularly nepetalactone, an iridoid monoterpenoid from Nepeta species, and phloretin, a dihydrochalcone predominantly found in the genus Malus. We highlight current findings on their herbicidal effects, including morphological, physiological, and biochemical responses in target plants. These results underscore their potential for developing sustainable herbicides that could control weeds with minimal environmental impact. We also discuss their soil persistence and methods to enhance their solubility, chemical stability, and bioavailability. Additionally, the possible effects on non-target organisms, such as pollinators, non-pollinating insects, and soil microbiota, are considered. However, further research and a deeper understanding of their long-term ecological impact, along with a resistance development risk assessment, is essential for the potential development of bioherbicides that could be applied in sustainable weed management practices.

Allelopathy and potential allelochemicals of Ligularia sagitta as an invasive plant

Allelopathy is the main chemical means in the invasion process of exotic plants and one of the key factors in grassland degradation. In this experiment, we investigated the effects of ethyl acetate phase extract (EAE), n-butanol phase extract (BE) and aqueous phase extract (AE) from the aboveground (stems and leaves) and roots of Ligularia sagitta on seed germination and seedling growth of four Gramineae forages (Poa pratensis L. Festuca ovina L. Elymus nutans Griseb. Agropyron cristatum (L.) Gaertn.) in their sympatric domains and one Legosuminae forage (Medicago sativa L.). The chemical components in each phase extract of L. sagitta were determined with UHPLC-MS/MS non-targeted metabolomics, and the differential compounds were screened using Orthogonal Partial Least Squares-Discriminant Analysis (OPLS-DA). Within a set concentration range, EAE significantly inhibited seed germination and seedling growth of four Gramineae forages. BE and AE acted mainly in the seedling growth stage and did not significantly inhibit forage seed germination. P. pratensis was most sensitive to L. sagitta extracts; at 2.0 mg/mL of EAE from roots, germination energy and germination rate of P. pratensis seeds were 0. L. sagitta extracts inhibited the growth of M. sativa seedlings and did not inhibit its seed germination. A total of 904 compounds were identified with UHPLC-MS/MS, among which 31, 64, 81 and 66 metabolites displayed different accumulation patterns in the four comparison groups (R.EAE vs. R.BE, R.EAE vs. R.AE, SL.EAE vs. SL.BE, SL.EAE vs. SL.AE), respectively. In particular, 9 compounds were found to be common up-regulated differential metabolites in the four comparison groups and were enriched in EAE. Additionally, N,N-dimethylaniline, Caffeic acid, 4-Hydroxybenzoic acid, 4-Hydroxybenzaldehyde and cis-9-Octadecenoic acid as potential allelochemicals in L. sagitta. The results of this study support efforts at finding alternative control plants for the restoration of poisonous grass-type degraded grasslands.

Phytotoxic Activity Analysis of 2-Methoxyphenol and 2,6-Di-tert-butyl-4-methylphenol Present in Cistus ladanifer L. Essential Oil

The evaluation of the wide variety of allelochemicals present in allelopathic plants allows the detection of safer bioherbicides with new mechanisms of action. This study tested two phenolic compounds of Cistus ladanifer essential oil (2-Methoxyphenol and 2,6-Di-tert-butyl-4-methylphenol), which are commercially available. At 0.01 mM, these compounds, both separately and in combination (1/1), inhibited up to over 50% of germination, cotyledon emergence and seedling growth of Lactuca sativa for the tests conducted on paper. Against Allium cepa, cotyledon emergence and seedling growth were inhibited at 0.5 mM. When the tests were carried out in the soil, the mixture of the two study compounds significantly inhibited the germination of L. sativa and A. cepa when applied at 0.5 and 1 mM, respectively, and seedling growth inhibition was greater for the latter in the paper tests. The greatest inhibitions were observed, with the highest concentrations analysed. Although there was no statistically significant difference among treatments, 2-Methoxyphenol seemed to affect germination and cotyledon emergence to a greater extent, whereas 2,6-Di-tert-butyl-4-methylphenol had a greater impact on seedling size. The effect of the mixture was greater than that of both compounds separately.

Allelopathic effects of six alfalfa varieties at three stubbles on the germination, seedling and root growth of green foxtail and barnyardgrass

Alfalfa (Medicago sativa) is known to release allelopathic substances to affect the germination and growth of other plants, which have the potential to be applied in controlling weeds. Green foxtail (Setaria viridis) and barnyardgrass (Echinochloa crus-galli), as malignant weeds worldwide, also pose a serious threat to alfalfa in northern China. In this study, the sensitivity of the two weeds to the extracts from the first, second, and third stubbles of six varieties were investigated to further reveal the allelopathic interference of different varieties of alfalfa on notorious weeds. The germination rate, the length and fresh weight of seedlings, the length and fresh weight of roots were measured to elucidate the allelopathy of alfalfa extracts on the two weeds. The results suggested that: (1) The allelopathy of six alfalfa varieties tested showed obvious intraspecific differences, the inhibition of Zhongmu No.3 on green foxtail and barnyardgrass was weaker than other varieties, with the values of synthetical allelopathic effect (SAE) were -0.55 and -0.29, respectively. (2) The inhibitory effect of alfalfa extracts on green foxtail was enhanced with the increase of stubbles, while the differences between three stubbles on barnyardgrass were not clear, especially between the first and second stubbles. (3) Compared with barnyardgrass (SAE = -0.39 ~ -0.29), green foxtail (SAE = -0.65 ~ -0.52) was generally more susceptible to the extracts. (4) The inhibitory effect of alfalfa extracts on root was stronger than seedling in the same weed. For example, the third stubble extracts of Baoding variety inhibited 88.00% of the roots at the concentration of 0.01 g mL-1, but did not affect the seedlings of green foxtail. The study may help to comprehensively reveal the allelopathic effect of different alfalfa varieties in the first three stubbles on green foxtail and barnyardgrass, providing scientific evidence for weed control based on natural plant extracts in the future.

Plant-microbe interactions: PGPM as microbial inoculants/biofertilizers for sustaining crop productivity and soil fertility

Plant-microbe interactions play pivotal roles in sustaining crop productivity and soil fertility, offering promising avenues for sustainable agricultural practices. This review paper explores the multifaceted interactions between plants and various microorganisms, highlighting their significance in enhancing crop productivity, combating pathogens, and promoting soil health. Understanding these interactions is crucial for harnessing their potential in agricultural systems to address challenges such as food security and environmental sustainability. Therefore, the introduction of beneficial microbes into agricultural ecosystems by bio-augmentation reduces the negative effects of intensive, non-sustainable agriculture on the environment, society, and economy, into the mechanisms underlying the application of plant growth promoting microbes as microbial inoculants/biofertilizers; their interactions, the factors influencing their dynamics, and the implications for agricultural practices, emerging technologies and strategies that leverage plant-microbe interactions for improving crop yields, soil fertility, and overall agricultural sustainability.

Invasive Plants' Root Extracts Display Stronger Allelopathic Activity on the Germination and Seedling Growth of a New Zealand Native Species than Extracts of Another Native Plant or Conspecifics

The release of allelochemicals is one of the contributing factors to the success of invasive plants in their non-native ranges. It has been hypothesised that the impact of chemicals released by a plant on its neighbours is shaped by shared coevolutionary history, making natives more susceptible to "new" chemicals released by introduced plant species (novel weapons hypothesis). We explored this hypothesis in a New Zealand system where the two invasive plants of European origin, Cytisus scoparius (Scotch broom) and Calluna vulgaris (heather) cooccur with natives like Chionochloa rubra (red tussock) and Leptospermum scoparium (mānuka). We characterised the chemical composition of root extracts of broom, heather, red tussock and mānuka using gas chromatography-mass spectrometry and then investigated the influence of aqueous root extracts at different concentrations (0.1%, 1%, 5%, 50% and 100% v/v) on mānuka seed germination and seedling growth (root and shoot length and biomass), using deionised water as control. The results show clear distinctions in the chemical composition of the four plants' root extracts, with 4-O-methylmannose dominating the broom extract and (E)-pinocarveol the heather extract, while 16-kaurene and methyl palmitate were abundant in both mānuka and tussock extracts. We found a significant effect of invasive plant (heather and broom) root extracts on mānuka germination at all concentrations tested, and adverse effects on seedling growth and biomass only at higher concentrations (≥ 5%). Broom displayed stronger allelopathic effects than heather at the highest concentration (100%). For extracts of conspecific and other native species (mānuka and red tussock) allelopathic effects were only observed at very high concentrations (50 and 100%) and were generally weaker than those observed for invasive plants. These results show that while both native and invasive plants produce chemicals with allelopathic potential, native species are likely to be more vulnerable to the allelopathic effects of species they did not co-evolve with, supporting the novel weapons hypothesis. However, this study also highlights differences in allelopathic potential between invasive species.

Sustainable control of invasive plants: Compost production, quality and effects on wheat germination

Invasive plant species pose significant ecological threats worldwide, affecting the stability and biodiversity of local ecosystems. As a result of their control, a considerable amount of plant biomass is produced, which can be used to produce various value-added products. Five different composts were prepared from three invasive plant species found in Latvia - Reynoutria japonica, Solidago canadensis, Lupinus polyphyllus. The stages of composting have been investigated and recommendations for process optimization have been made based on the quality characterization of the final compost. The quality of the prepared invasive plant biomass composts has been evaluated based on the main plant nutrient concentration, humic substance concentration, and mineral contents. The allelopathic lupin alkaloid concentration throughout the composting process has been evaluated and shows a consistent reduction. Obtained compost quality complies with the EU regulations for fertilizing products and soil amendments thus it can be considered equivalent to industrially produced compost and vermicompost. Seed germination tests confirm that compost prepared from invasive plants is suitable for plant growth and comparable to commercial composts. Based on pilot-scale composting results, recommendations for invasive plant composting have been suggested.

Assessment of nutrient cycling in an intensive mariculture system

Rapid mariculture expansion has raised concerns about coastal eutrophication. This study assesses nutrient cycling in Sansha Bay, China, a eutrophic semi-enclosed bay with intensive mariculture. A two-endmember mixing model showed significant additions of dissolved inorganic nitrogen (DIN; 6.9 ± 4.1 μmol L-1) and phosphorus (DIP; 0.45 ± 0.29 μmol L-1) in May 2020, mainly from mariculture. Estimated N and P inputs from fish farming were 7789 ± 361 tons and 1497 ± 91 tons in spring, respectively, with N mainly in dissolved form and P in particulate form. And, trash fish feed caused higher nutrient release than formulated feed. Of the feed input, 52.8 ± 4.7 % of DIN and 33.0 ± 3.7 % of DIP were released into environment, exceeding riverine input and offshore exchanges. Co-culturing kelp and oysters removed 1079 ± 11 tons of N and 156 ± 8 tons of P. Therefore, adjusting feed types and planning co-cultivation strategies could alleviate eutrophication resulting from mariculture expansion.

Ecophysiological Trade-Off Strategies of Three Gramineous Crops in Response to Root Extracts of Phytolacca americana

The invasive Phytolacca americana L. poses a significant threat to local agroforestry ecosystems due to its allelopathic toxicity. However, the ecophysiological response mechanisms of crops to allelochemicals remain unclear. This study investigated the seedling growth, physiological, and biochemical responses of three gramineous crops to the root extracts of P. americana and identified potential allelochemicals of the invader. The germination and seedling growth of three crops were inhibited by extracts differently, with high-concentration extracts causing more severe inhibition on seedling roots in hydroponic (>57%) than soil culture experiments (>18%). This inhibition may be related to representative secondary metabolites such as fatty acyls, alkaloids, and phenols. Despite the significant inhibition of high-concentration extracts on seedling growth, the levels of soluble sugar, soluble protein, and antioxidant enzymes increased synergistically. Under allelopathic stress, three species enhanced antioxidant enzyme activities and metabolite contents at the cost of reducing their shoot, root biomass, and root/shoot ratio. This may be an ecophysiological growth-defense strategy to bolster their resistance to allelopathy. Interestingly, transgenic rice exhibited greater sensitivity to allelochemicals than wild-type rice, resulting in more pronounced growth inhibition and increased levels of most metabolites and antioxidant enzymes. This study highlights the adaptive strategies of three gramineous crops to the allelopathy of invasive P. americana.

Allelopathic Molecular Mechanisms of the Two Main Allelochemicals in Sweet Potato

Sweet potato (Ipomoea batatas L.) is one of the most important global food crops. This crop exhibits excellent allelopathic potential against various weeds, but its allelopathic mechanism at the molecular level is unclear. Therefore, metabolomic and transcriptomic analyses were performed to explore the allelopathic effects, metabolic pathway, and associated genes for two major compounds with allelopathic activity, palmitic acid and linoleic acid. The sweet potato variety Ningshu 25 was employed in the current study. The results showed that palmitic acid and linoleic acid had strong allelopathic effects on seed germination, plant growth, antioxidant enzyme activity, and chlorophyll content of two weeds Digitaria sanguinalis and Bidens pilosa. The content of the two targeted metabolites was affected by different environmental conditions and was significantly increased under low temperature (15 °C). Five metabolic pathways involved in the two targeted metabolites of fatty acids were found: fatty acid biosynthesis, fatty acid elongation, fatty acid degradation, biosynthesis of cutin, suberine, and wax, and the linoleic acid metabolism pathway. The synthesis of palmitic acid is significantly enriched in the biosynthesis pathways of fatty acids, cutin, suberine, and wax, and the synthesis of linoleic acid is significantly enriched in the linoleic acid metabolism pathway. Under different environmental conditions, there were three key genes expressed-g4988, g11881, and g19673-located in the biosynthesis pathways of cutin, suberine, and wax; four key genes expressed-g31191, g60956, g49811, and g59542-located in the biosynthesis pathway of fatty acids; and six key expressed genes-g26575, g24787, g23517, g57649, g58562, and g4314-located in biosynthesis pathway of linoleic acid, respectively. Our study advances understanding of the molecular mechanisms behind allelopathic traits in sweet potato and provides a set of candidate genes for use in improving allelopathic potential in sweet potato germplasm resources.

Conserved perception of host and non-host signals via the a-pheromone receptor Ste3 in Colletotrichum graminicola

Understanding the interactions between fungal plant pathogens and host roots is crucial for developing effective disease management strategies. This study investigates the molecular mechanisms underpinning the chemotropic responses of the maize anthracnose fungus Colletotrichum graminicola to maize root exudates. Combining the generation of a deletion mutant with monitoring of disease symptom development and detailed analysis of chemotropic growth using a 3D-printed device, we identify the 7-transmembrane G-protein coupled receptor (GPCR) CgSte3 as a key player in sensing both plant-derived class III peroxidases and diterpenoids. Activation of CgSte3 initiates signaling through CgSo, a homolog to the Cell Wall Integrity Mitogen-Activated Protein Kinase (CWI MAPK) pathway scaffold protein identified in other filamentous fungi, facilitating the pathogen's growth towards plant defense molecules. The NADPH oxidase CgNox2 is crucial for peroxidase sensing but not for diterpenoid detection. These findings reveal that CgSte3 and CWI MAPK pathways are central to C. graminicola's ability to hijack plant defense signals, highlighting potential targets for controlling maize anthracnose.

Molecular responses of seaweeds to biotic interactions: A systematic review

Seaweed farming is the single largest aquaculture commodity with >30 million tonnes produced each year. Furthermore, the restoration of lost seaweed forests is gaining significant momentum, particularly for kelps in warming temperate areas. Whether in aquaculture settings, following restoration practices, or in the wild, all seaweeds undergo biotic interactions with a diverse range of co-occurring or cocultured organisms. To date, most research assessing such biotic interactions has focused on the response of the organism interacting with seaweeds, rather than on the seaweeds themselves. However, understanding how seaweeds respond to other organisms, particularly on a molecular scale, is crucial for optimizing outcomes of seaweed farming or restoration efforts and, potentially, also for the conservation of natural populations. In this systematic review, we assessed the molecular processes that seaweeds undergo during biotic interactions and propose priority areas for future research. Despite some insights into the response of seaweeds to biotic interactions, this review specifically highlights a lack of characterization of biomolecules involved in the response to chemical cues derived from interacting organisms (four studies in the last 20 years) and a predominant use of laboratory-based experiments conducted under controlled conditions. Additionally, this review reveals that studies targeting metabolites (70%) are more common than those examining the role of genes (22%) and proteins (8%). To effectively inform seaweed aquaculture efforts, it will be crucial to conduct larger scale experiments simulating natural environments. Also, employing a holistic approach targeting genes and proteins would be beneficial to complement the relatively well-established role of metabolites.

Isolation of Allelochemicals from Rhododendron capitatum and Their Allelopathy on Three Perennial Herbaceous Plants

Rhododendron capitatum community expansion is a major threat to alpine meadow. Allelopathy is an important mediator in managing relationships between plants in natural ecosystems. However, allelopathy and specific allelochemicals of R. capitatum have not been studied yet. In this study, the allelopathy of the foliage litter of R. capitatum was explored on Elymus nutans, Poa pratensis and Medicago ruthenica, and the chemical composition and their allelopathy were studied. The results showed that the aqueous extract of the foliage litter of R. capitatum had an allelopathy of "low concentration promotion and high concentration inhibition" on the germination of E. nutans, P. pratensis, and M. ruthenica. Organic acids, fatty acids, terpenes, phenols, and phenolic acid compounds were identified, with Zanamivir (77.81%), alpha-linolenic acid (18%), Kaurenoic acid (23.50%), 4-hydroxyphenylglycolic acid (21.54%), and Quinic acid (28.24%) having the highest relative content, and all five compounds showed significantly inhibitory effects on seed germination and seedling growth of E. nutans, P. pratensis, and M. ruthenica, which further suggests that the five compounds are the critical allelochemicals for negative allelopathy of R. capitatum. These results highlight the crucial role of inhibitory allelopathy produced by R. capitatum in the establishment and expansion of its populations.

Biotechnological frontiers in harnessing allelopathy for sustainable crop production

Allelopathy, the phenomenon in which plants release biochemical compounds that influence the growth and development of neighbouring plants, presents promising opportunities for revolutionizing agriculture towards sustainability. This abstract explores the role of biotechnological advancements in unlocking the potential of allelopathy for sustainable crop production and its applications in agriculture, ecology, and natural resource management. By combining molecular, genetic, biochemical, and bioinformatic tools, researchers can unravel the complexities of allelopathic interactions and their potential for sustainable crop production and environmental stewardship. The development of novel management methods for weed control is getting a lot of attention with the introduction of new genetic technologies such as Gene drive, Transgene technologies, Gene silencing, Marker-assisted selection (MAS), and Clustered regularly interspaced short palindromic repeats (CRISPR-Cas9). By strengthening competitive characteristics these tools hold great promise for boosting crops' ability to compete with weeds. Considering recent literature, this review highlights the genetic, transcriptomics, and metabolomics approaches to allelopathy. Employing allelopathic properties in agriculture offer sustainable benefits like natural weed management, pest management, and reduced chemical pollution, but challenges include environmental factors, toxicity, regulatory hurdles, and limited resources. Effective integration requires continued research, regulatory support, and farmer education​. Also, we aimed to identify the biotechnological domains requiring more investigation and to provide the basis for future advances through this assessment.

Selective biotic stressors' action on seed germination: A review

In the realm of plant biology and agriculture, seed germination serves as a fundamental process with far-reaching implications for crop production and environmental health. This comprehensive review seeks to unravel the intricate web of interactions between some biotic stressors and seed germination, addressing the pertinent issue of how these stressors influence seed germination. Different chemicals produced by interacting plants (different parts), fungi, bacteria, or insects can either promote or inhibit seed germination. Releasing chemicals that modulate signaling pathways and cellular processes significantly disrupt essential cellular functions. This disruption leads to diverse germination outcomes, introducing additional layers of complexity to this regulatory landscape. The chemicals perturb enzyme activity and membrane integrity, imposing unique challenges on the germination process. Understanding the mechanisms- how allelochemicals, mycotoxins, or bacterial toxins affect seed germination or the modes of action holds promise for more sustainable agricultural practices, enhanced pest control, and improved environmental outcomes. In sum, this review contributes to a fundamental exposition of the pivotal role of biotic stressors in shaping the germination of seeds.

Toxicological assessment of invasive Ageratina adenophora on germination and growth efficiency of native tree and crop species of Kumaun Himalaya

The present study was designed to assess the allelopathic potential of invasive weed Ageratina adenophora leaf extracts on seed germination and seedling development efficiency of native tree [viz. Quercus leucotrichophora A. Camus (Oak) and Pinus roxburghii Sarg. (Pine)] and crop [(Triticum aestivum L. (Wheat) and Lens culinaris Medik. (Lentil)] species of Kumaun Himalaya. Pot experiments were conducted in the glasshouse of the Botany Department, D.S.B. Campus, Kumaun University Nainital, following a Completely Randomized Block Design (CRBD) with three treatments (C1-25%, C2-50%, and C3-100% of aqueous leaf extract) and one control, each with five replicates. The experiment lasted one year for tree species and continued until the seed maturation phase for crop species. Parameters such as seed germination proportion, root and shoot measurements, biomass, and crop productivity traits were recorded accordingly. Our bioassay results indicated that the inhibitory effect of leaf extracts on the measured traits of the selected native species was proportional to the applied extract concentrations of A. adenophora. Overall, lentil among crops and oak among tree species exhibited more inhibition compared to wheat and pine, respectively. At the highest concentration, reductions of 44%, 34%, 36%, and 24% in biomass production capacity were recorded for wheat, lentil, pine, and oak, respectively, while wheat and lentil productivity decreased by up to 33% and 45%, respectively. These results suggest that water-soluble allelochemicals produced by A. adenophora may impede the establishment of selected crop and tree species in agroecosystems and forest ecosystems invaded by this weed species. However, further studies on the characterization of phytochemicals and their specific role in seed germination and growth are warranted. Furthermore, the allelopathic potential of A. adenophora can be explored for the preparation of biopesticides and nature-friendly option to improve soil health, crop productivity, and reduce environmental pollution and management of this invasive weed.

Phytotoxicity and Identification of Active Compounds from Elaeocarpus floribundus Blume Plant for Controlling Weeds

Phytotoxic compounds isolated and identified from different plants have the ability to use as plant-based herbicides. Phytotoxic chemicals may be essential to weed management and environmental protection in order to reduce the indiscriminate use of synthetic pesticides. It has been reported that Elaeocarpus floribundus plant possesses phytotoxic compounds. The leaf extracts of this species demonstrated significant growth inhibition against the tested plants (dicot plant lettuce and plant monocot timothy) and inhibition was dose- and species-dependent pattern. Two phytotoxic compounds were separated using different purifications methods and identified as compounds 1 and 2. All phytotoxic compounds displayed potent growth limitation against the tested species (cress). The compound concentrations needed for the inhibition of 50% growth (IC50 value) of tested species ranged from 1.06 to 8.53 µM (micromolar). Findings of this research suggest that these compounds might be responsible for the phytotoxicity of Elaeocarpus floribundus plant. The results of this study may be helpful for the development of natural herbicide to control weeds.

Effects of Phloretin on Seedling Growth and Histochemical Distribution of Phenols, Polysaccharides and Lipids in Capsella bursa-pastoris (L.) Medik

The present study evaluates the phytotoxic effects of phloretin, a prevalent secondary metabolite of apple trees, on the broadleaf weed Capsella bursa-pastoris (L.) Medik. known for its resistant myxospermous seeds that form a long-lasting soil bank. The results indicate a significant, dose-dependent inhibitory effect of phloretin on the growth and morphological parameters of weed seedlings grown in vitro. Although the applied phloretin concentrations (250-1000 µM) were not lethal to the C. bursa-pastoris seedlings after two weeks, the metabolism of the seedlings was impaired, resulting in an accumulation of lipid droplets in the root tips and root hairs. Histochemical analysis shows deposits of phenols in the root epidermal cells, which are probably aggregates of phloretin or its metabolic derivatives. The accumulation of pectin in the cell walls of root border cells in phloretin-treated seedlings indicates an attempt to reduce the uptake of phloretin and reduce its concentration in the cells. Inhibition of shoot growth associated with chlorosis and reduced photosynthetic pigment content is a consequence of seedling exposure to phloretin. This study provides a basis for further evaluation of phloretin as a new bioherbicidal compound and for elucidating the mechanism underlying its phytotoxic activity.

Turning glucosinolate into allelopathic fate: investigating allyl isothiocyanate variability and nitrile formation in eco-friendly Brassica juncea from South Korea

Leaf mustard (Brassica juncea L.) is explored for its biofumigant properties, derived from its secondary metabolites, particularly allyl isothiocyanate (AITC), produced during the enzymatic breakdown of glucosinolates like sinigrin. The research examines eight leaf mustard cultivars developed in Yeosu city, South Korea, focusing on their genetic characteristics, AITC concentration and nitriles formation rates from glucosinolates. Results indicate that the allelopathic effects, largely dependent on AITC concentration and enzymatic activity, vary across cultivar. Sinigrin and AITC constitute 79% and 36%, respectively, of glucosinolate and its hydrolysis products. The cultivar 'Nuttongii' demonstrates significant potential for inhibiting weeds, exhibiting the highest AITC concentration at 27.47 ± 6.46 µmole g-1 These outcomes highlight the importance of selecting mustard cultivars for biofumigation based on their glucosinolate profiles and hydrolysis product yields. The study also identifies a significant genetic influence on AITC and nitrile formation, suggesting that epithiospecifier protein modulation could enhance both allelopathic and other beneficial effects. Collectively, the research underscores the promise of mustard as a sustainable, environmentally friendly alternative to traditional herbicides.

Pre-treatment of Cucurbita maxima 'Hokkaido orange' by Viscum album aqueous extracts in search of allelopathic potential

Viscum album L. (VA) is a unique plant with regard to its biological content. It is rich in many different metabolites with high potential in various spheres of human activity. We conducted a pilot study with 5 VA aqueous extracts of different host-tree species for pre-sowing treatment of Cucurbita maxima 'Hokkaido orange' seeds. We set the following objectives consisting of hypotheses (1) H01 is based on different effects of tested VA extracts depending on host trees and time of pre-treatment; (2) H02 focuses on the allopathic properties of the tested extracts affecting the plant growth and development by dose-response relationship; (3) A01 considers highly biologically active compounds of VA extracts also containing allelochemicals that can be used to regulate plant growth processes and create eco-friendly and resilient cities. The analysis of the stimulatory allelopathy index for 7 parameters demonstrates the direct effect of VA extracts in 62.3% of cases. The variability of the broad spectrum of effects of VA extracts of different host trees on the ontogenesis of C. maxima plants shows the presence of potential allelochemicals, resulting from the vital products of the host-parasite relationship. These effects are not fully explained by total polyphenol content and antioxidant activity as in previous studies of other mistletoe species. The authors consider this work a pilot study that expands the areas of application of VA extracts and knowledge about potential sources of allelochemicals.

Review of Allelopathy in Green Tides: The Case of Ulva prolifera in the South Yellow Sea

The proliferation of large green macroalgae in marine environments has led to the occurrence of green tides, particularly in the South Yellow Sea region of China, where Ulva prolifera has been identified as the primary species responsible for the world's largest green tide events. Allelopathy among plants is a critical factor influencing the dynamics of green tides. This review synthesizes previous research on allelopathic interactions within green tides, categorizing four extensively studied allelochemicals: fatty acids, aldehydes, phenols, and terpenes. The mechanisms by which these compounds regulate the physiological processes of green tide algae are examined in depth. Additionally, recent advancements in the rapid detection of allelochemicals are summarized, and their potential applications in monitoring green tide events are discussed. The integration of advanced monitoring technologies, such as satellite observation and environmental DNA (eDNA) analysis, with allelopathic substance detection is also explored. This combined approach addresses gaps in understanding the dynamic processes of green tide formation and provides a more comprehensive insight into the mechanisms driving these phenomena. The findings and new perspectives presented in this review aim to offer valuable insights and inspiration for researchers and policymakers.

Metabolomic and transcriptomic analyses highlight metabolic regulatory networks of Salvia miltiorrhiza in response to replant disease

BACKGROUND

Salvia miltiorrhiza, a well-known traditional Chinese medicine, frequently suffers from replant diseases that adversely affect its quality and yield. To elucidate S. miltiorrhiza's metabolic adaptations to replant disease, we analyzed its metabolome and transcriptome, comparing normal and replant diseased plants for the first time.

RESULTS

We identified 1,269 metabolites, 257 of which were differentially accumulated metabolites, and identified 217 differentially expressed genes. Integrated transcriptomic and metabolomic analyses revealed a significant up-regulation and co-expression of metabolites and genes associated with plant hormone signal transduction and flavonoid biosynthesis pathways in replant diseases. Within plant hormone signal transduction pathway, plants afflicted with replant disease markedly accumulated indole-3-acetic acid and abscisic acid, correlating with high expression of their biosynthesis-related genes (SmAmidase, SmALDH, SmNCED, and SmAAOX3). Simultaneously, changes in hormone concentrations activated plant hormone signal transduction pathways. Moreover, under replant disease, metabolites in the local flavonoid metabolite biosynthetic pathway were significantly accumulated, consistent with the up-regulated gene (SmHTC1 and SmHTC2). The qRT-PCR analysis largely aligned with the transcriptomic results, confirming the trends in gene expression. Moreover, we identified 10 transcription factors co-expressed with differentially accumulated metabolites.

CONCLUSIONS

Overall, we revealed the key genes and metabolites of S. miltiorrhiza under replant disease, establishing a robust foundation for future inquiries into the molecular responses to combat replant stress.

Exploring the Potential of Myrcia Genus Essential Oils: A Review of Biological Activities and Recent Advances

The present study provides a comprehensive analysis of the chemical composition of essential oils from species of the Myrcia genus and their applications. The compiled results highlight the chemical diversity and biological activities of these oils, emphasizing their potential importance for various therapeutic and industrial applications. The findings reveal that Myrcia essential oils present a variety of bioactive compounds, such as monoterpenes and sesquiterpenes, which demonstrate antimicrobial activities against a range of microorganisms, including Gram-positive and Gram-negative bacteria, as well as yeasts. Furthermore, this study highlights the phytotoxic activity of these oils, indicating their potential for weed control. The results also point to the insecticidal potential of Myrcia essential oils against a range of pests, showing their viability as an alternative to synthetic pesticides. Additionally, species of the genus Myrcia have demonstrated promising hypoglycemic effects, suggesting their potential in diabetes treatment. This comprehensive synthesis represents a significant advancement in understanding Myrcia essential oils, highlighting their chemical diversity and wide range of biological activities. However, the need for further research is emphasized to fully explore the therapeutic and industrial potential of these oils, including the identification of new compounds, understanding of their mechanisms of action, and evaluation of safety and efficacy in different contexts.

Vacuum fractional distillation of Cunila galioides Benth. essential oil: chemical composition and biological activities of raw oil and its fractions

This work aimed to rectify Cunila galioides essential oil and evaluate the raw oil and the fractions' antifungal, allelopathic, and antioxidant activities. The results showed that the raw essential oil and the bottom fraction were primarily composed of linalyl propionate (42.9 wt.% and 60.2 wt.%). The top fraction was composed mainly of limonene (45.7 wt.%). The antioxidant activity changed with the radical and the fraction. The bottom had a weaker antifungal effect than the raw oil and the top. Nevertheless, the essential oil and the fractions had a similar antifungal activity at 0.50 % v/v and higher. Similar behavior was observed for the allelopathic tests. No difference occurred between the raw oil and the fractions, with reduced germination percentages and speed at 0.25 % v/v and complete inhibition at 0.50 % v/v. The oil can be rectified, and the fractions may be used without harming their biological activity.

Can allelopathic potentialities of Mediterranean plant species reduce the spread of invasive plant species, Acacia dealbata and Ailanthus altissima?

Beyond ecological and health impacts, invasive alien plant species can generate indirect and direct costs, notably through reduced agricultural yields, restoration, and management of the invaded environment. Acacia dealbata and Ailanthus altissima are invasive plant species that cause particularly significant damage to the railway network in the Mediterranean area. The allelopathic properties of Mediterranean plant species could be used as nature-based solutions to slow down the spread of such invasive plant species along railway borders. In this context, a mesocosm experiment was set-up: (i) to test the potential allelopathic effects of Cistus ladanifer, Cistus albidus, and Cotinus coggygria leaf aqueous extracts on seed germination and seedling growth of A. dealbata and A. altissima; (ii) to evaluate whether these effects depend on the extract dose; and finally, (iii) to estimate whether these effects are modified by soil amendment. Leaf aqueous extracts of the three native plant species showed negative effects on both seed germination and seedling growth of the two invasive species. Our results show that the presence of allelochemicals induces a delay in seed germination (e.g., A. dealbata germination lasted up to 269% longer in the presence of high-dose leaf aqueous extracts of C. coggygria), which can lead to a decrease in individual recruitment. They also highlight a decrease in seedling growth (e.g., high-dose C. coggygria leaf aqueous extracts induced a 26% decrease in A. dealbata radicle growth), which can alter the competitiveness of invasive species for resource access. Our results also highlight that compost addition limits the inhibitory effect of native Mediterranean plants on the germination of invasive alien plants, suggesting that soil organic matter content can counteract allelopathic effects on invasive alien plants. Thus, our findings revealed that the allelopathic potential of certain Mediterranean plant species could be a useful tool to manage invasive plant species.

Optimizing Allelopathy Screening Bioassays by Using Nano Silver

Nano solutions are widely used in medicine and also have the potential to be used when performing allelopathy screening studies. The present experiment aimed to test the effectiveness of colloidal nano silver Silver-Amber© with nanoparticles of 20 nm (>20 mg/L at a purity level of 99.99%) as a carrier of allelochemicals in laboratory conditions. The influence of eleven concentrations of Silver-Amber© (0.10, 0.20, 0.39, 0.78, 1.56, 3.13, 6.25, 12.5, 25.0, 50.0 and 100.0% v/v) on the germination and initial development of test plant Lactuca sativa L. in 0.75% agar medium was studied. Data revealed that when increasing the quantitative ratio of Silver-Amber©, an inhibitory effect on seed germination (from 37.8 to 94.3%) and on the plant growth (from 54.0 to 98.9%) appeared. Lower concentrations (0.63 to 0.04 ppm) had an indifferent to statistically unproven stimulatory effect on the germination and initial development of L. sativa (GI ranged from 88.7-94.6%). Therefore, nano silver can be used as carrier of allelochemicals in allelopathic studies in laboratory conditions.

Unveiling allelopathic dynamics and impacts of invasive Erigeron bonariensis and Bidens pilosa on plant communities and soil parameters

Invasive alien species are becoming more and more prevalent worldwide, Erigeron bonariensis and Bidens pilosa are two invasive species of Asteraceae in Egypt. To mitigate their detrimental effects and understand their differences in invasiveness, we compared the allelopathic potentials of E. bonariensis and B. pilosa using leachates, decaying residues, and volatilization processes. Notably, the allelopathic variances in leachates were significant, influenced by plant types, concentrations, and response patterns of target plant traits, as indicated by EC50. The relative phytotoxicity of the invasive species decayed residues peaked between 20 and 25 days in the soil, with a positive correlation with concentrations and soil properties. The highest quantities of phenolic acids were chlorogenic acid and caffeic acid reaching (5.41 and 4.39 µg g-1) E. bonariensis and (4.53 and 4.46 µg g-1) B. pilosa, in leachates extracts respectively, while in the soil extract of decayed residues were coumaric acid and ferulic acid measuring (1.66 and 1.67 µg g-1) E. bonariensis and (1.47 and 1.57 µg g-1) B. pilosa, respectively. Using GC/MS analysis, the main volatile components in E. bonariensis were 1, 8 cineole (5.62%), and α-terpinene (5.43%) and iso-Caryophyllene (5.2%) which showed the greatest inhibitory effects. While B. pilosa main constituents were trans-sabinene (5.39%) and Camphene (5.11%), respectively. Finally, the high invasion level displayed from E. bonariensis (0.221) compared with B. pilosa (0.094) which correlated with the stronger allelopathic activities against plant species, and soil properties. Therefore, the allelopathic potentialities of these species are critically relevant to their invasion success.

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.

New Perspective on the Use of α-Bisabolol for Weed Control

The indiscriminate use of synthetic herbicides reduces its effectiveness. Bioherbicides produced with metabolites emerge as an alternative to managing weeds. We aimed to analyze the phytotoxic potential of the essential oil of Vanillosmopsis arborea (EOVA) and the α-bisabolol molecule, its main component. We evaluated the effects of EOVA and α-bisabolol at different concentrations on the germination, growth, antioxidant metabolism, and photosynthesis of different species. EOVA and α-bisabolol showed promising phytotoxic effects on the germination and initial growth of the weed Senna occidentalis, inhibiting the activity of the antioxidant enzymes and increasing lipid peroxidation. α-Bisabolol reduced the weed seedling growth by inducing oxidative stress, which suggests a greater role in postemergence. Moreover, in the weed postemergence, both EOVA and α-bisabolol caused damage in the shoots, reduced the chlorophyll content, and increased lipid peroxidation besides reducing photosynthesis in S. occidentalis. Overall, we suggest the promising action of α-bisabolol and EOVA as bioherbicides for weed control.

Rhizosphere: Role of bacteria to manage plant diseases and sustainable agriculture-A review

General plant diseases as well as soil-borne pathogens severely reduce agricultural yield. The rhizosphere (the region of the soil that includes and surrounds the roots) is an important niche for microbial diversity in particular phytobeneficial bacteria including plant growth-promoting rhizobacteria (PGPR) which have been used for a very long time to combat plant diseases. Pathogen control and crop productivity can both be improved through the use of PGPR several mechanisms, including iron-based nutrition, antibiotics, volatile substances, enzymes, biofilm, allelochemicals, and so on. Their modes of action and molecular mechanisms have improved our comprehension of how they are used to control crop disease. Therefore, there is a lot of literal information available regarding PGPR, but this review stands out since it starts with the fundamentals: the concept of the rhizosphere and the colonization process of the latter, particularly because it covers the most mechanisms. A broad figure is used to present the study's findings. The advantages of using PGPR as bioinoculants in sustainable agriculture are also mentioned.

Interspecific competition affects spore germination and gametophore development of mosses

Background

Interactions between moss species in their earliest growth stages have received little attention. To what extent interspecific competition or priority effects influence spore germination, protonemal development and gametophore emergence is unknown. We evaluated such effects in pairwise interaction between six common bryophyte species: Atrichum undulatum, Bryum argenteum, Ceratodon purpureus, Funaria hygrometrica, Hypnum cupressiforme, Leptobryum pyriforme.

Methods

Interspecific interactions were assessed in vitro. Spores were sterilized and sown on agar plates in three treatments: 1) as single species cultures (controls), 2) as pairwise species cultures inoculated simultaneously, and 3) with a time lag of 20 days between species. Data on time needed for spore germination, germination rate, the time needed for gametophore differentiation, number of gametophores per germinated spore and average diameter of colonies were collected. We also performed spore germination tests in single-species cultures at the start and end of the study, as well as tests for density-dependency at spore germination and gametophore formation.

Results

We observed strong pairwise interactive effects when sowing spores of different species simultaneously or with a delay of 20 days. The results indicate that spore germination is often inhibited by interspecific competition. The first species has an advantage as compared to the later colonizing species, i.e., an apparent priority effect. Interspecific interactions were also evident during gametophore development and included both inhibition and facilitation.

Conclusion

We found pronounced differences in the relative performance of species in interaction with other species during spore germination and gametophore formation. Allelopathic effects are the most probable explanation for these observations. Our results under sterile lab conditions are likely to reflect processes that occur in the wild, governing biotic filtering and bryophyte community assembly during primary and secondary colonization.

Reproducible growth of Brachypodium in EcoFAB 2.0 reveals that nitrogen form and starvation modulate root exudation

Understanding plant-microbe interactions requires examination of root exudation under nutrient stress using standardized and reproducible experimental systems. We grew Brachypodium distachyon hydroponically in fabricated ecosystem devices (EcoFAB 2.0) under three inorganic nitrogen forms (nitrate, ammonium, and ammonium nitrate), followed by nitrogen starvation. Analyses of exudates with liquid chromatography-tandem mass spectrometry, biomass, medium pH, and nitrogen uptake showed EcoFAB 2.0's low intratreatment data variability. Furthermore, the three inorganic nitrogen forms caused differential exudation, generalized by abundant amino acids-peptides and alkaloids. Comparatively, nitrogen deficiency decreased nitrogen-containing compounds but increased shikimates-phenylpropanoids. Subsequent bioassays with two shikimates-phenylpropanoids (shikimic and p-coumaric acids) on soil bacteria or Brachypodium seedlings revealed their distinct capacity to regulate both bacterial and plant growth. Our results suggest that (i) Brachypodium alters exudation in response to nitrogen status, which can affect rhizobacterial growth, and (ii) EcoFAB 2.0 is a valuable standardized plant research tool.

Phytochemistry, allelopathy and anticancer potentiality of Withania somnifera (L.) Dunal (Solanaceae)

Abstract Withania somnifera is a wild plant that shows great activity and safety against several human diseases. The current research explored the plant's chemical composition and allelopathic effects on Rumex dentatus (recipient plant). Moreover, anticancer activity is also tested against four types of human cancer cell lines. Chemical analysis of W. somnifera showed a high percentage of saponins and tannins, while glycosides, alkaloids, and flavonoids occurred in the second order. Results of the allelopathic experiments revealed significant inhibition of the R. dentatus plumule and radicle lengths as well as their relative dry weights. In addition, significant reductions in some primary metabolites of R. dentatus, like non-reducing and total sugar as well as soluble proteins, were determined. Cytotoxic potentiality of W. somnifera was also proved against four different cancer lines, namely; human hepatocellular carcinoma cell line (HepG2), human non-small cell lung cancer cell line (A549), human breast cancer cell line (MCF7), and colon cancer cell line (CaCo2) with IC50 value of about 38, 19, 27, and 24 ��g/ml, respectively.

Allelochemicals: A source for developing economically and environmentally friendly plant growth regulators

Allelochemicals are specific secondary metabolites that can exhibit autotoxicity by inhibiting the growth of the same plant species that produced them. These metabolites have been found to affect various physical processes during plant growth and development, including inhibition of seed germination, photosynthesis, respiration, root growth, and nutrient uptake, with diverse mechanisms involving cell destruction, oxidative homeostasis and photoinhibition. In some cases, allelochemicals can also have positive effects on plant growth and development. In addition to their ecological significance, allelochemicals also possess potential as plant growth regulators (PGRs) due to their extensive physiological effects. However, a comprehensive summary of the development and applications of allelochemicals as PGRs is currently lacking. In this review, we present an overview of the sources and categories of allelochemicals, discuss their effects and the underlying mechanisms on plant growth and development. We showcase numerous instances of key phytohormonal allelochemicals and non-phytohormonal allelochemicals, highlighting their potential as candidates for the development of PGRs. This review aims to provide a theoretical basis for the development of economical, safe and effective PGRs utilizing allelochemicals, and emphasizes the need for further research in this area.

Allelopathy and allelobiosis: efficient and economical alternatives in agroecosystems

Chemical interactions in plants often involve plant allelopathy and allelobiosis. Allelopathy is an ecological phenomenon leading to interference among organisms, while allelobiosis is the transmission of information among organisms. Crop failures and low yields caused by inappropriate management can be related to both allelopathy and allelobiosis. Therefore, research on these two phenomena and the role of chemical substances in both processes will help us to understand and upgrade agroecosystems. In this review, substances involved in allelopathy and allelobiosis in plants are summarized. The influence of environmental factors on the generation and spread of these substances is discussed, and relationships between allelopathy and allelobiosis in interspecific, intraspecific, plant-micro-organism, plant-insect, and mechanisms, are summarized. Furthermore, recent results on allelopathy and allelobiosis in agroecosystem are summarized and will provide a reference for the future application of allelopathy and allelobiosis in agroecosystem.

Anthraquinone as emerging contaminant: technological, toxicological, regulatory and analytical aspects

Anthraquinone (anthracene-9,10-dione) is a multifaceted chemical used in the paper industry, in the production of synthetic dyes, in crop protection against birds and is released from fossil fuels. Additionally, the anthraquinone scaffold, when substituted with sugars and hydroxyl groups is found in plants as metabolites. Because of these multiple applications, it is produced on a large scale worldwide. However, its toxicological aspects have gained interest, due to the low limits in the foods defined by legislation. Worrying levels of anthracene-9,10-dione have been detected in wastewater, atmospheric air, soil, food packaging and more recently, in actual foodstuffs. Recent investigations aiming to identify the anthracene-9,10-dione contamination sources in teas highlighted the packaging, leaves processing, anthracene metabolism, reactions between tea constituents and deposition from the environment. In this context, this review seeks to highlight the uses, sources, biological effects, analytical and regulatory aspects of anthracene-9,10-dione.

Graphical Abstract

Persistence of Root Exudates of Sorghum bicolor and Solidago canadensis: Impacts on Invasive and Native Species

Root exudates of the invasive Solidago canadensis and the cereal crop Sorghum bicolor (L.) Moench cv. 'Hybridsorgo' were tested for allelopathic interactions against native and invasive plant species in a controlled environment. After the surface was sterilized, the seeds of two invasive species (Bromus sterilis and Veronica persica) and two native species (Youngia japonica and Rumex acetosa) were germinated and transplanted into the soil (1:1 mixture of coco peat and sand) that had been conditioned for one month by the cultivation of Solidago canadensis and Sorghum bicolor, both in combination or as unplanted controls. After an additional eight weeks of growth, morphometric measurements of the shoot and root, including foliar characteristics and above- and below-ground biomass accumulation, were performed. The results revealed significant inhibitory effects of root exudates released by Sorghum bicolor and Solidago canadensis on native species' productivity and physiology. The invasive species exhibited variable growth responses, with Veronica persica showing reduced shoot and root expansion, but Bromus sterilis revealed increased shoot and root biomass allocation and nutrition under the exudate treatments. Exudates from Solidago canadensis and Sorghum bicolor together showed synergistic negative effects on native species, while they promoted growth and nutrition in Veronica persica. Taken together, the differential species responses indicate that the tested native species were more sensitive to the allelopathic compounds than the invasive species, which is in line with the theory of novel weapons. The legacy effects of root exudates of both Sorghum bicolor and Solidago canadensis could promote invasive establishment through imposing allelochemical interference competition against native plant species. Understanding the specific allelopathic mechanisms may help with the development of integrated strategies for managing invasive species.

Inhibition of continuous cropping obstacle of celery by chemically modified biochar: An efficient approach to decrease bioavailability of phenolic allelochemicals

The accumulation of allelochemicals released by plants is commonly found in continuous monocropping systems. These chemicals, such as phenolic acids, were shown to be the major sources of autotoxin or pathogen accumulation in soils, leading to a direct or indirect continuous cropping obstacle. In this study, three types of agricultural residuals, i.e., rice husk, tea waste, and wood meal, were chosen as feedstocks. Biochar samples were prepared from these feedstocks to examine their abilities to remove gallic acid, a representative phenolic acid. Biochar, which was prepared from wood meal soaked with H3PO4 (1:1.5, w/w) and pyrolyzed at 400 °C (symbolized as WP400), exhibited the highest adsorption capacities of gallic acids and other phenolic acids. The mechanisms of phenolic acid removal by WP400 were evaluated via experimental and spectroscopic investigations to elucidate the notable adsorption capacity of WP400. The adsorption of gallic acids was pH-dependent and followed a pseudo-second-order kinetic model. The combination of high surface area, the existence of O-containing groups, and the enhancement of H bonds between CC groups and phenolic acids may contribute to the high adsorption capacity of WP400. In a pot experiment, we found that celery growth was promoted with the addition of 0.3% (w/w) WP400 to soils that were continuously monocropped with celery. A large decrease in the water-soluble phenolic compound by more than 40% may be responsible for the results. However, WP400 scavenged nitrate, and this study showed that the synergistic actions of WP400 and nutrients exhibited the greatest efficiencies in mitigating the continuous cropping obstacles of celery.

Multiple invasive species affect germination, growth, and photosynthesis of native weeds and crops in experiments

Alien plant species regularly and simultaneously invade agricultural landscapes and ecosystems; however, the effects of co-invasion on crop production and native biodiversity have rarely been studied. Secondary metabolites produced by alien plants may be allelopathic; if they enter the soil, they may be transported by agricultural activities, negatively affecting crop yield and biodiversity. It is unknown whether substances from different alien species in combination have a greater impact on crops and wild plants than if they are from only one of the alien species. In this study, we used a set of common garden experiments to test the hypothesis that mixed extracts from two common invasive species have synergistic effects on crops and weeds (defined as all non-crop plants) in European agricultural fields compared to single-species extracts. We found that both the combined and individual extracts had detrimental effects on the seed germination, seedling growth, biomass, and photosynthetic performance of both crops and weeds. We found that the negative effect of mixed extracts was not additive and that crop plants were more strongly affected by invasive species extracts than the weeds. Our results are important for managing invasive species in unique ecosystems on agricultural land and preventing economic losses in yield production.

Allelopathic Mechanisms in Camellia oleifera-Arachis hypogaea L. Intercropping

Tree-crop intercropping is of great significance in food security, land protection, and sustainable agriculture. However, the mechanisms of allelopathy between plant species during intercropping are still limited. This study focuses on the allelopathic effects in the intercropping between Camellia oleifera and Arachis hypogaea L. in southern China. We use different parts of the C. oleifera extract to evaluate their impact on peanut seed germination. The results showed that it has inhibitory effects on peanut germination and growth, with the fruit shell having the strongest inhibitory effect. Three main allelopathic substances affecting A. hypogaea germination and growth were identified using gas chromatography-mass spectrometry (GC-MS) analysis, namely, 2,4-di-tert-butylphenol, hexanal, and benzaldehyde. Transcriptomics and metabolomics analyses revealed their effects on glutathione metabolism pathways and specific gene expression. In summary, this study reveals the allelopathic interaction mechanism between C. oleifera and A. hypogaea, which helps to better understand the role of allelopathy in intercropping practices between trees and crops.

The Bio-herbicidal potential of some wild plants with allelopathic effects from Tabuk Region on selected local weed species

Weeds are considered one of the most serious problems limiting global agricultural production. As a result, chemical herbicides have been extensively used for weed control. However, overuse of synthetic herbicides, has resulted in public concerns over the effect of herbicides on the health of the ecosystems and humans. In the food system, innovative approaches are needed to foster sustainable practices that preserve biodiversity, conserve habitats, and mitigate climate change factors. Thus, alternatives are required to control the weeds. This study aimed to determine the impact of some wild plants' (Citrullus colocynthis, Euphorbia retusa, Retama raetam, Artemisia monosperma, Tamarix gallica, and Artemisia judaica) allelopathic potentials (at rates of 0, 15, 25, 35, and 50 g/L) on seed germination of selected local weeds (Portulaca oleracea, Amaranthus retroflexus, and Chloris barbata) collected from different locations in Tabuk region, Saudi Arabia. GC-MS analysis was used to evaluated the main compounds in the wild plants under study. The experimental design was completely randomized block design (CRBD) with three replicates. According to the results, phytochemical screening of the wild plants using GC-MS analysis showed a wide range of phytochemicals. Amaranthus retroflexus exhibited the highest germination rate in the control group. In addition, applying 5 g/L and 20 g/L of Citrullus colocynthis extracts had no discernible effect on the rate of germination of A. retroflexus seed; however, they were able to reduce the germination rate as compared to the control. As the extract concentration of Artemisia monosperma rose to 20 g/L, the germination rate of A. retroflexus dropped. Neither 35 g L-1 nor 50 g L-1 of A. monosperma extract inhibited the germinate of A. retroflexus. The germination rate of Portulaca oleracea decreased with increasing extract concentration of C. colocynthis. The extract of C. colocynthis at 50 g/L had the lowest rate. The germination rate of Chloris barbata decreased with increasing extract concentration of C. colocynthis. The highest germination rate of C. barbata was observed in control, followed by 5g/L, while no germination was observed at 20, 35, and 50 g/L of C. colocynthis extracts. A. retroflexus's root length shrank when the extract concentration of C. colocynthis rose. A. retroflexus's control sample had the most extended root length, followed by 5 and 20 g/L, respectively. C. colocynthis at 35 and 50 g/L showed no root elongation as this treatment inhibited radicle protrusion. High concentration of d-Glycero-d-galacto-heptose and pentane in C. colocynthis aqueous extract may be the cause of C. colocynthis' ability to inhibit Chloris barbata germination. The entire C. barbata plant length decreased when treated with 5 g/L of C. colocynthis extract. No growth was seen at any of the higher C. colocynthis concentrations (20, 35, and 50 g/L). The present work revealed that cultivating allelopathic crops like the selected studied wild plants from the Tabuk region has a promising future as an antagonistic species in a biological weed control program or combined with integrated weed management in agricultural food production.

Potential of Artemisia dubia Wall Biomass for Natural Crop Protection

The Green Deal strategy has the very ambitious goal of transforming the European Union into the first climate-neutral continent by 2050. For the agricultural sector, one of the main challenges is to reduce the use of synthetic fertilizers and pesticides. Crop protection measures aim to maintain and ensure certain standards of yield and quality, which are generally achieved by the control of pests, diseases, and weeds. One of the possibilities to reduce the use of pesticides could be allelopathic plants, which are not only potential sources of allelochemicals but also renewable biomass sources. The aim of this study was to analyze the productivity of Artemisia dubia Wall and evaluate the allelopathic effects of biomass on crops and weeds. It was determined that the biomass productivity of A. dubia varied from 2 to 18 t ha-1, depending on how many times it is cut during the growing season and the fertilizer rate. A. dubia has allelopathic properties, which were verified using an aqueous extract and can completely suppress the germination of Taraxacum officinale seeds. Young plants harvested in the middle of summer were characterized by the highest number of phenolic compounds. This shows the strong allelopathic effect of A. dubia biomass on other plants.

Synergistic effects of grass competition and insect herbivory on the weed Rumex obtusifolius in an inundative biocontrol approach

Outcomes of weed biological control projects are highly variable, but a mechanistic understanding of how top-down and bottom-up factors influence the success of weed biological control is often lacking. We grew Rumex obtusifolius, the most prominent native weed in European grasslands, in the presence and absence of competition from the grass Lolium perenne and subjected it to herbivory through targeted inoculation with root-boring Pyropteron spp. To explore whether the interactive effects of competition and inundative biological control were size-dependent, R. obtusifolius was planted covering a large range of plant sizes found in managed grasslands. Overall, competition from the grass sward reduced aboveground biomass and final root mass of R. obtusifolius about 62- and 7.5-fold, respectively, and increased root decay of R. obtusifolius from 14 to 58%. Herbivory alone increased only root decay. However, grass competition significantly enhanced infestation by Pyropteron spp. and, as a consequence, enhanced the impact of herbivory on aboveground biomass and final root mass. The synergistic effect was so strong that R. obtusifolius plants grown from initially smaller roots did no longer develop. Inoculating R. obtusifolius with Pyropteron species in grasslands should be further pursued as a promising inundative biological control strategy in the weed's native range.

Decoding the Multifaceted Potential of Artemisia monosperma: Comprehensive Insights into Allelopathy, Antimicrobial Activity, and Phytochemical Profile for Sustainable Agriculture

Weeds present a significant hazard to crop production, necessitating the development of effective and sustainable strategies for weed management. Although synthetic herbicides are effective, concerns about their environmental and health impact have been raised. This study investigates the allelopathic potential, antimicrobial activity, and phytochemical profile of Artemisia monosperma. Extracts from A. monosperma proficiently impede the growth of Chenopodium murale and Amaranthus viridis, while exhibiting varying effects on crops Solanum lycopersicum and Cucumis sativus. Leaf and seed extracts demonstrate the most significant inhibition of weed growth. Interestingly, the leaf extract at a concentration of 50% inhibited weed growth in pot experiments without affecting crop growth. Moreover, extracts from A. monosperma exhibit noteworthy antifungal and antibacterial activity, with the root extract demonstrating the strongest inhibition. The root extract inhibited the mycelial growth of Colletotrichum musae by 63% as compared to control. The leaf extract exhibited the highest levels of phenolic acids, in particular gallic acid, amounting to 116.30 ppm. This study emphasizes the multifaceted potential of A. monosperma as a sustainable solution for weed management and proposes its use in crop protection. Further investigation of its practical applications and optimization of extraction methods can aid in its integration into contemporary agricultural systems, promoting both crop yield and environmental sustainability.

Teline monspessulana Can Harm the Chilean Native Tree Nothofagus obliqua: Effects on Germination and Initial Growth

Teline monspessulana is highly invasive in several countries around the world. This species pressurizes and displaces several native and endemic tree species in south-central Chile such as Nothofagus obliqua, the native species of greatest timber interest. We determined the effects induced by allelochemical stress of T. monspessulana on N. obliqua germination and initial growth. Germination was evaluated under in vitro conditions and in natural substrate obtained from sites inhabited by N. obliqua and from nearby areas invaded by T. monspessulana. Controls irrigated with tap water and treatments with aqueous extracts of aerial organs of the invasive species were used. Morphometric and morphological variables were evaluated, and the composition of alkaloids and phenols from the plant organs used for the aqueous extracts was determined. The substrates were also chemically characterized. Allelochemicals synthesized by T. monspessulana caused germination and growth inhibition and tissue-level alterations, as well as leaf and root damage in N. obliqua seedlings. In the aerial organs of T. monspessulana, the quinolizidine alkaloids aphylline, caulophylline, anagyrine, and sophocarpine were mainly detected. In addition, 21 phenolic compounds were identified, including gallic acid, vanillic acid, chlorogenic acid, p-coumaric acid, and quercetin. The phytotoxic potential of T. monspessulana can compromise the natural multiplication of N. obliqua and its survival from its first phenological stages. This interdisciplinary study model facilitated the clarification of the plant-plant relationship mediated by allelochemicals. The model can be replicated to investigate other interspecific interactions between invasive and native species.

Ecosystem health and malfunctions: an organisational perspective

A recent idea of "ecosystem health" was introduced in the 1970s and 1980s to draws attention to the fact that ecosystems can become ill because of a reduction of properties such as primary productivity, functions and diversity of interactions among system components. Starting from the 1990s, this idea has been deeply criticized by authors who argued that, insofar as ecosystems show many differences with respect to organismic features, these two kinds of systems cannot share a typical organismic property such as health. In recent years, an organisational approach in philosophy of biology and ecology argued that both organisms and ecosystems may share a fundamental characteristic despite their differences, namely, organisational closure. Based on this kind of closure, scholars have also discussed health and malfunctional states in organisms. In this paper, we examine the possibility of expanding such an organisational approach to health and malfunctions to the ecological domain. Firstly, we will see that a malfunction is related to a lower effectiveness in the functional behaviour of some biotic components with respect to other systemic components. We will then show how some introduced species do not satisfactorily interact in an organisational closure with other ecosystem components, thus posing a threat to the self-maintenance of the ecosystem in which they are found. Accordingly, we will argue that an ecosystem can be said to be healthy when it is a vital environment organisationally grounded on its intrinsic capacity to ensure, under favourable conditions, appropriate functional behaviours for ecosystem components and ecosystem self-maintenance.

Effects of Algicidal Macrophyte Metabolites on Cyanobacteria, Microcystins, Other Plankton, and Fish in Microcosms

To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type.

The Aqueous Extract of Brassica oleracea L. Exerts Phytotoxicity by Modulating H2O2 and O2- Levels, Antioxidant Enzyme Activity and Phytohormone Levels

Allelopathic interactions between plants serve as powerful tools for weed control. Despite the increasing understanding of the allelopathic mechanisms between different plant species, the inhibitory effects of B. oleracea on weed growth remain poorly understood. In this study, we conducted experiments to demonstrate that B. oleracea extract can suppress the germination of Panicum miliaceum L.varruderale Kit. seeds as well as of the roots, shoots and hypocotyl elongation of P. miliaceum seedlings. Furthermore, we observed that B. oleracea extract reduced the levels of hydrogen peroxide and superoxide anion in the roots while increasing the activities of catalase and ascorbate peroxidase. In the shoots, B. oleracea extract enhanced the activities of superoxide dismutase and peroxidase. Moreover, the use of the extract led to an increase in the content of phytohormones (indole-3-acetic acid, indole-3-acetaldehyde, methyl indole-3-acetate, N6-isoPentenyladenosine, dihydrozeatin-7-glucoside, abscisic acid and abscisic acid glucose ester) in P. miliaceum seedlings. Interestingly, the aqueous extract contained auxins and their analogs, which inhibited the germination and growth of P. miliaceum. This may contribute to the mechanism of the B. oleracea-extract-induced suppression of P. miliaceum growth.