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This study evaluates the phytotoxic potential of methanolic extracts from six Asteraceae species: Wedelia chinensis, Helianthus annuus, Cosmos bipinnatus, Tagetes erecta, Tithonia diversifolia, and Zinnia elegans. The extracts were tested at concentrations of 0.03, 0.1, 0.3, and 1.0 g/mL to assess their inhibitory effects on the radicle and hypocotyl lengths of Echinochloa crus‐galli and Echinochloa colona. The two most potent species, C. bipinnatus and T. diversifolia, were further evaluated using extracts from their roots, stems, and leaves. Among these, C. bipinnatus leaf extracts showed the most significant phytotoxicity and were tested at 20, 40, and 60 days of plant age. At 0.03 g/mL, C. bipinnatus extract inhibited the hypocotyl and radicle lengths of E. colona by 23.01% and 56.45%, and E. crus‐galli by 8.5% and 36.35%, respectively. At 1.0 g/mL, the extract inhibited the hypocotyl lengths of E. colona and E. crus‐galli by 97.54% and 88.15%, and the radicle lengths by 93.52% and 99.99%, respectively. The 60‐day‐old C. bipinnatus leaf extract exhibited the highest inhibitory effect, correlating with the identification of key allelochemicals such as cinnamic acid, caffeic acid, coumaric acid, ferulic acid, 2‐4 dimethohydroxy benzoic acid, and salicylic acid. These findings suggest that the 60‐day‐old C. bipinnatus leaf extracts have strong potential for use in the biological control of these weed species, offering a promising avenue for the development of natural herbicides. [ABSTRACT FROM AUTHOR]

BACKGROUND RESULTS CONCLUSION Borreria latifolia (Aubl.) K. Schum (Rubiaceae) is an annual weed with a strong allelopathic inhibitory effect on malignant weeds in orchards in southern China. This study was carried out to investigate its allelopathic potential and to identify allelochemicals present in B. latifolia.Aqueous extracts of B. latifolia inhibited the germination and radicle growth of Eleusine indica and the radicle growth of Bidens alba in a dose‐dependent manner. However, only the high‐concentration treatment at 50 mg mL−1 delayed the germination of B. alba and Digitaria sanguinalis. Among the root, stem, and leaf aqueous extracts of B. latifolia, the leaf extract had the strongest inhibitory effects on the germination and seedling growth of E. indica, followed by stem extract and then root extract. A total of 47 published allelochemicals, including coumarin, 4‐hydroxybenzoate, salicylic acid, 4‐hydroxycinnamic acid, and vanillic acid, were identified in the leaf extract. Among the five allelochemicals, coumarin was found to be present in the highest concentration in the leaf extract. Furthermore, coumarin exhibited a significantly greater inhibitory effect on E. indica (EC50 = 36.87 mg L−1) than did the other allelochemicals (EC50 = 100.87–156.30 mg L−1).This study indicates that the leaf extracts of B. latifolia and their allelochemicals have excellent potential as bioherbicides and that coumarin is one of the key allelochemicals in B. latifolia. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The elemental allelopathy hypothesis states that the metal‐rich litter of hyper‐accumulating species may have a detrimental impact on neighbouring plants giving a competitive advantage to hyper‐accumulators. Here, we aim to specify the conditions of application of this hypothesis in realistic field conditions, and its relative importance compared to other positive effects found in metalliferous systems.We disentangled the litter‐induced elemental allelopathy and canopy effects of two metallophyte species (Arenaria multicaulis and Hutchinsia alpina) with different levels of leaf Zn and Cd accumulation on two ecotypes of Agrostis capillaris with different levels of metal tolerance. The experiment was conducted in two habitats with contrasting pollution levels in a former mining valley in the Pyrenees (France).The metallophyte species that accumulates more metals (Hutchinsia alpina) showed a strong elemental allelopathy effect on the target with lower metal tolerance in the habitat with lower pollution level, while the metallophyte species that accumulates less metals (Arenaria multicaulis) had no litter effect. Both metallophyte species had positive canopy effects likely due to improvement of micro‐climatic conditions. The drought that occurred during the experiment may have influenced these canopy effects, increasing their importance during the course of the study. For Hutchinsia alpina, the positive canopy effects were stronger than the negative litter effects, resulting in overall positive effects on both target ecotypes.Synthesis. Our results brought a better understanding of the occurrence of elemental allelopathy in metallophyte communities and its relative importance as compared to micro‐climatic facilitation in a global warming context. [ABSTRACT FROM AUTHOR]

A suite of plant traits is thought to make weed populations highly invasive, including vigorous growth and reproduction, superior competitive ability, and high dispersal ability. Using a breeding design and a common garden experiment, we tested whether such an "invasion syndrome" has evolved in an invasive range of Solidago altissima, and whether the evolution is likely to be genetically constrained. We found an overall shift in invasive phenotypes between native North American and invasive Japanese populations. The invasive populations were taller and produced more leaves, suggesting a superior ability to exploit limited resources. The populations also produced more allelopathic compounds that can suppress competitor growth. Finally, invasive populations produced more seeds, which are smaller and are released from a greater height, indicating a potential for superior dispersal ability than the native populations. Quantitative genetics analyses found a large amount of additive genetic variation in most focal traits across native and invasive populations, with no systematic differences in its magnitude between the ranges. Genetic covariances among three traits representing invasion strategies (leaf mass, polyacetylene concentration and seed size) were small. The R metric, which measures the effect of genetic covariances on the rate of adaptation, indicated that the covariance neither constrains nor accelerates concerted evolution of these traits. The results suggest that the invasion syndrome in S. altissima has evolved in the novel range due to ample additive genetic variation, and relatively free from genetic trade‐offs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cover cropping plays an important role in Integrated Weed Management (IWM). Weed suppression of cover crops occurs by competition, physical barrier on the soil and allelopathy. Under favourable growing conditions, cover crops can provide similar weed suppression in the autumn‐to‐spring period as repeated stubble tillage and non‐selective herbicides. The objective of this study was to test if cover crop species with higher allelopathic potential can suppress weeds in the field with less shoot biomass than cover crop species with lower allelopathic effects. Data of cover crop shoot biomass, percentage of weed suppression in the field and reduction of weed seed germination in petri‐dish bioassays treated with cover crop extracts were analysed from 11 experiments. Weed suppression in relation to cover crop biomass was better predicted by a Weibul three‐parameter model than with the Cousens model. Raphanus sativus var. oleiferus, Sinapis alba, Fagopyrum esculentum and Phacelia tanacetifolia needed at least three‐fold more biomass than Avena strigosa for 80% weed suppression. Vicia sativa had the lowest weed reduction of only 62%. Aqueous extracts of A. strigosa had the highest inhibiting effect on weed seed germination followed by R. sativus. The lowest effect was observed for P. tanacetifolia. It is assumed that for A. strigosa allelopathy strongly contributes to weed suppression whereas for P. tanacetifolia and other cover crops, competition plays the major role for weed suppression. The model can help growers and consultants to mix cover crop species for the autumn‐to‐spring period. Under dry conditions, species such as A. strigosa can provide high weed suppression with low biomass. Under moist conditions, rapidly growing cover crops such as S. alba suppress most weeds and deliver high biomass. [ABSTRACT FROM AUTHOR]

Macrophytes may release allelochemicals that suppress competing phytoplankton, although it is unclear how their effectiveness could be influenced by environmental nutrient conditions. To approach this, we conducted a series of bioassays against the bloom‐forming cyanobacterium Microcystis aeruginosa using extracts and exudates from potentially allelopathic macrophytes under varying nutrient conditions.We screened six different tropical macrophytes and identified antialgal effects in both extracts and exudates of Ludwigia adscendens, Persicaria barbata, Pontederia crassipes and Vallisneria spiralis. Growth assays indicated that extract inhibitory effectiveness decreased as nutrient concentration increased from 5% to 50% strength.Focusing on the potent antialgal extract of L. adscendens, we determined that its inhibitory effects were enhanced by specifically reducing the availability of either micronutrient or bicarbonate availability, indicating a role of these nutrients in protecting algal cells from allelochemicals.Bioactivity‐guided fractionation and ultra‐performance liquid chromatography – mass spectrometry analyses of L. adscendens extract indicated that ellagitannins were the major constituent of bioactive extract fractions, suggesting an antialgal mechanism common to other tannic compounds. Novel allelopathic alkaloids and terpenoid compounds also were described, although their mechanisms of action are unknown.Our findings provide evidence that the availability of carbon and micronutrients to cyanobacteria could influence the effects of macrophyte allelochemicals. This interaction between the nutrient environment and allelochemical sensitivity of cyanobacteria can be substantial, and studies or applications involving allelopathic interactions between macrophytes and phytoplankton should consider this. [ABSTRACT FROM AUTHOR]

Since its accidental introduction in 1951, the South African species Eragrostis plana has invaded a large part of the Pampa biome in South America, a highly diverse grassland ecosystem that has coexisted with livestock since its introduction at the beginning of the 17th century. E. plana, a perennial tussock grass with a deep and abundant root system, is resistant to frost and cattle grazing, and a successful competitor for environmental resources. The species is diploid, C4 dispersed endozoochorically, and flowers in late spring and early summer, with optimal germination occurring at 35°C and viability up to 39–40°C. It is allelopathic because it produces several phenols and alkaloids. Extreme soil disturbance or intense grazing favours initial invasion. Nonetheless, grazing exclusion enhances E. plana competition and affects the grassland community and diversity. E. plana is highly tolerant to interspecific competition, especially with grasses exhibiting a similar growth habit. Under water stress, it responds faster by increasing its root system by 66% more than native grass. Moreover, antioxidant system activity increases, and the species recovers quickly through osmolyte production. In non‐invaded fields, avoiding soil disturbance and intensive grazing are key strategies to preserving Biome Pampa. Nonetheless, in fields where the invasion has already occurred, grazing must be maintained, cattle quarantined practiced, along with strategies that reduce cover and prevent the spread of E. plana. Liming and fertilising native grasslands improve their potential to compete with E. plana. The wiper applicator, a device that allows glyphosate herbicide application selectively to E. plana, is an important component of the integrated weed management system, especially with very severe infestations. Establishing strategies to contain or manage E. plana should be a priority to preserve the biodiversity of the Pampa. In the future, innovative options could also help prevent new invasions. [ABSTRACT FROM AUTHOR]

Summary: By modifying the biotic and abiotic properties of the soil, plants create soil legacies that can affect vegetation dynamics through plant–soil feedbacks (PSF). PSF are generally attributed to reciprocal effects of plants and soil biota, but these interactions can also drive changes in the identity, diversity and abundance of soil metabolites, leading to more or less persistent soil chemical legacies whose role in mediating PSF has rarely been considered. These chemical legacies may interact with microbial or nutrient legacies to affect species coexistence. Given the ecological importance of chemical interactions between plants and other organisms, a better understanding of soil chemical legacies is needed in community ecology. In this Viewpoint, we aim to: highlight the importance of belowground chemical interactions for PSF; define and integrate soil chemical legacies into PSF research by clarifying how the soil metabolome can contribute to PSF; discuss how functional traits can help predict these plant–soil interactions; propose an experimental approach to quantify plant responses to the soil solution metabolome; and describe a testable framework relying on root economics and seed dispersal traits to predict how plant species affect the soil metabolome and how they could respond to soil chemical legacies. [ABSTRACT FROM AUTHOR]

Global spread of invasive plant species threatens biodiversity significantly, with a particularly high presence of invasives in the Asteraceae family. This is partly due to their wide use as ornamental plants and their rapid reproduction and allelopathy. The Indian blanket flower (Gaillardia pulchella) is a native North American species widely used as an ornamental plant and has become invasive in other countries. Although it contains bioactive compounds, its allelopathic impact on other plants has been largely unexplored. We conducted in vitro tests on oilseed rape (Brassica napus) germination and early growth to assess blanket flower's allelopathy. Seeds were exposed to aqueous extracts at three different concentrations (10%, 20%, and 40%). The 40% extract significantly inhibited germination during the treatment. All three concentrations inhibited root growth, with the 40% treatment showing this effect from the second day. In contrast, the extracts promoted significantly shoot elongation. Fresh weight of seedlings was not affected by the extract, but the 10% treatment resulted in higher mass. These findings provide evidence of blanket flower's allelopathic effects, shedding light on its invasive potential. [ABSTRACT FROM AUTHOR]

Soil mulches and conditioners have been shown to improve soil moisture conservation, infiltration, and seed germination and survival, but their interactive effects with sporadic rainfall and the existing vegetation have rarely been considered. In an experimental field study, we assessed the effects of soil additives (sawdust and hydrogel) and mulches (river sand and plant debris) on seedling emergence and survival of Astragalus nigricans Barneby, in the rangelands of Mashhad, northeast Iran. We also assessed any effects on soil moisture and temperature several days after rain in July 2017 and May 2018 and weed composition, density, and diversity. The most successful treatment was hydrogel, associated with earlier seedling emergence for A. nigricans, greater seedling survival, and biomass production. Sawdust and sand treatments were useful for root proliferation and seedling emergence in the spring of the first season, but they led to high seedling mortality under drought. Debris of Artemisia khorasanica shoots was the most efficient and consistent treatment for soil moisture conservation and temperature stability in both years, but its possible allelopathic effects led to high seedling mortality and a long delay (41 days) on seedling emergence. Plant debris also negatively affected the density, richness, and diversity of nontarget plant species. Despite differences among different rainfall events, mulch treatments have an important role in regenerating degraded rangelands. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Few studies tried to explore the mitigation effect and underlying mechanisms of biochar and their complex for negative allelopathy from invasive plants, which may provide a new way in the invasive plant management. Herein, an invasive plant (Solidago canadensis)‐derived biochar (IBC) and its composite with hydroxyapatite (HAP/IBC) were synthesized by high temperature pyrolysis, and characterized by scanning electron microscopy, energy dispersion spectrometer, X‐ray diffraction, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. Then, both the batch adsorption and pot experiments were conducted to compare the removal effects of kaempferol‐3‐O‐β‐D‐glucoside (C21H20O11, kaempf), an allelochemical from S. canadensis, on IBC and HAP/IBC, respectively. HAP/IBC showed a stronger affinity for kaempf than IBC due to its higher specific surface area, more functional groups (P‐O, P‐O‐P, PO43−), stronger crystallization [Ca3(PO4)2]. The maximum kaempf adsorption capacity on HAP/IBC was six times higher than on IBC (10.482 mg/g > 1.709 mg/g) via π–π interactions, functional groups, and metal complexation. The kaempf adsorption process could be fitted best by both pseudo‐second‐order kinetic and Langmuir isotherm models. Furthermore, HAP/IBC addition into soils could enhance and even recover the germination rate and/or seedling growth of tomato inhibited by negative allelopathy from the invasive S. canadensis. These results indicate that the composite of HAP/IBC could more effectively mitigate the allelopathy from S. canadensis than IBC, which may be a potential efficient approach to control the invasive plant and improve invaded soils. [ABSTRACT FROM AUTHOR]

The expansion of woody species from their historical ranges into grasslands is a global problem. Understanding the mechanisms that enable species to successfully establish and then re‐encroach following their removal is critical to effectively managing problem species. Legacy effects are a mechanism that could be critical to the reestablishment of woody encroachers following their removal. Legacy effects occur when a species alters the biotic and abiotic environment in a way that affects communities that establish subsequently. In this study, we assess whether the eastern redcedar (Juniperus virginiana), a North American woody encroacher, generates legacy effects that affect communities that establish following removal of this species from an experimental grass community. We conducted a series of experiments to evaluate the effects of J. virginiana, roots on the germination and growth of grasses and to determine if the effects of root‐addition treatments were derived from a microbial or allelopathic origin. Aqueous extracts of J. virginiana roots were found to inhibit the germination of grasses. We found escalating suppression of overall community biomass and the biomass of each individual species with increasing root treatments. Finally, we determined the origin of the observed suppressive effect is unlikely to be of microbial origin. Synthesis: Our results suggest that J. virginiana exudes an allelochemical into soils that inhibits the growth of certain grasses and thus has the potential to have legacy effects on future occupants. We suggest that the inhibition of the development of grasses in areas where J. virginiana has been removed is a mechanism that may favor the reestablishment of J. virginiana. Our results indicate the legacy effects of J. virginiana must be considered when conducting removal and restoration of J. virginiana infested lands. [ABSTRACT FROM AUTHOR]

Background: Roadside grass cuttings are currently considered a waste product due to their association with road sweepings as contaminated waste, therefore, their potential as a biofertilizer is understudied. Aim: This study aimed to determine whether grass liquid fraction (GLF) collected from a roadside verge in Maldegem, Belgium, and pressed using a screw press was suitable as a biofertilizer. Methods: The characterization of the heavy metal content of the GLF was conducted using an ICP‐OES. From May to September 2019, a pot experiment was set up using a randomized block design to compare tomato plant growth, yield, and nutrition for GLF‐treated plants to two commercial fertilizers and tap water as a control. Results: The heavy metal content of the GLF was below the maximum permissible concentrations (MPCs) for organic fertilizers as set out by the European Comission fertilizer regulation 1069/2009 and 1107/2009 (European Comission, 2019). However, despite having a fairly well‐balanced nutrient content (0.1% N, 0.04% P2O5, and 0.2% K2O), GLF had a negative effect on the growth, root weight, and yield of the tomato plants, killing six out of ten plants. GLF also promoted mold growth in the soil of some plants. Since the GLF was uncontaminated, heavy metal toxicity did not cause the negative effect. Conclusions: Previous research showed that liquid fractions from some plants negatively affect the growth of others due to allelopathic chemicals; this, together with the stimulation of fungal growth, could have caused the negative effects observed. Future experiments will investigate the herbicidal property of GLF and possible treatments to potentially recover the nutrients contained within the GLF for application as a biofertilizer. [ABSTRACT FROM AUTHOR]

The impact of a biological invasion on native communities is expected to be uneven across invaded landscapes due to differences in local abiotic conditions, invader abundance, and traits and composition of the native community. One way to improve predictive ability about the impact of an invasive species given variable conditions is to exploit known mechanisms driving invasive species' success. Invasive plants frequently exhibit allelopathic traits, which can be directly toxic to plants or indirectly impact them via disruption of root symbionts, including mycorrhizal fungi. The indirect mechanism - mutualism disruption - is predicted to impact plants that rely on mycorrhizas but not affect non-mycorrhizal plant species. To assess whether invaderdriven mutualism disruption explains observed changes in native plant communities, we analyzed long-term (1998-2018) plant cover data from forest plots across the state of Illinois. We evaluated native plant communities experiencing a range of abundance of invasive allelopathic garlic mustard Alliaria petiolata and varying environmental conditions. Consistent with the mutualism disruption hypothesis, we showed that as garlic mustard abundance increased over time in 0.25 m2 sampling quadrats, the abundance of mycorrhizal plant species decreased, but non-mycorrhizal plant species did not. Over space and time, garlic mustard abundance predicted plant abundances and diversity at the quadrat level, but this relationship was not present at a larger scale when quadrats were aggregated within sites. Garlic mustard's impact on the plant community was highly localized, yet it was as important as abiotic variables for predicting local plant diversity. We showed that garlic mustard abundance was a key predictor of patterns of plant diversity across invasion intensity and environmental heterogeneity in a way that is consistent with mutualism disruption. Our work indicates that the mutualism disruption hypothesis can provide generalizable predictions of the impacts of allelopathic invasive plants that are evident at a broad spatial scale. [ABSTRACT FROM AUTHOR]

Many invasive and some native tree species in North America exhibit strong allelopathic effects that may contribute to their local dominance. Pyrogenic carbon (PyC; including soot, charcoal, and black carbon) is produced by the incomplete combustion of organic matter and is widespread in forest soils. Many forms of PyC have sorptive properties that can reduce the bioavailability of allelochemicals. We investigated the potential for PyC produced by controlled pyrolysis of biomass ("biochar" [BC]) to reduce the allelopathic effects of black walnut (Juglans nigra) and Norway maple (Acer platanoides), a common native tree species and a widespread invasive species in North America, respectively. Seedling growth of two native tree species (Acer saccharinum [silver maple] and Betula papyrifera [paper birch]) in response to leaf‐litter‐incubated soils was examined; litter incubation treatments included leaves of black walnut, Norway maple, and a nonallelopathic species (Tilia americana [American basswood]) in a factorial design with varying dosages; responses to the known primary allelochemical of black walnut (juglone) were also examined. Juglone and leaf litter of both allelopathic species strongly suppressed seedling growth. BC treatments substantially mitigated these effects, consistent with the sorption of allelochemicals; in contrast no positive effects of BC were observed in leaf litter treatments involving controls or additions of nonallelopathic leaf litter. Treatments of leaf litter and juglone with BC increased the total biomass of silver maple by ~35% and in some cases more than doubled the biomass of paper birch. We conclude that BCs have the capacity to largely counteract allelopathic effects in temperate forest systems, suggesting the effects of natural PyC in determining forest community structure, and also the applied use of BC as a soil amendment to mitigate allelopathic effects of invasive tree species. [ABSTRACT FROM AUTHOR]

Much of the evolutionary ecology of toxic algal blooms (TABs) remains unclear, including the role of algal toxins in the adaptive 'strategies' of TAB‐forming species. Most eukaryotic TABs are caused by mixotrophs that augment autotrophy with organic nutrient sources, including competing algae (intraguild predation). We leverage the standing diversity of TABs formed by the toxic, invasive mixotroph Prymnesium parvum to identify cell‐level behaviours involved in toxin‐assisted predation using direct observations as well as comparisons between genetically distinct low‐ and high‐toxicity isolates. Our results suggest that P. parvum toxins are primarily delivered at close range and promote subsequent prey capture/consumption. Surprisingly, we find opposite chemotactic preferences for organic (prey‐derived) and inorganic nutrients between differentially toxic isolates, respectively, suggesting behavioural integration of toxicity and phagotrophy. Variation in toxicity may, therefore, reflect broader phenotypic integration of key traits that ultimately contribute to the remarkable flexibility, diversity, and success of invasive populations. [ABSTRACT FROM AUTHOR]

Allelopathy, that is, plant–plant inhibition via the release of secondary metabolites into the environment, has potential for the management of weeds by circumventing herbicide resistance. However, mechanisms underpinning allelopathy are notoriously difficult to elucidate, hindering real‐world application either in the form of commercial bioherbicides or allelopathic crops. Such limited application is exemplified by evidence of limited knowledge of the potential benefits of allelopathy among end users. Here, we examine potential applications of this phenomenon, paying attention to novel approaches and influential factors requiring greater consideration, with the intention of improving the reputation and uptake of allelopathy. Avenues to facilitate more effective allelochemical discovery are also considered, with a view to stimulating the identification of new compounds and allelopathic species. Synthesis and Applications: We conclude that tackling increasing weed pressure on agricultural productivity would benefit from greater integration of the phenomenon of allelopathy, which in turn would be greatly served by a multi‐disciplinary and exhaustive approach, not just through more effective isolation of the interactions involved, but also through greater consideration of factors which may influence them in the field, facilitating optimization of their benefits for weed management. [ABSTRACT FROM AUTHOR]

This study investigated spatial distribution and effects of Lantana camara invasion on soil properties and vegetation composition in Tugwi‐Mukosi Recreational Park. Supervised classification with the Random Forest classifier was used to map L. camara in the park. The study area was stratified into two categories based on soil type and the extent of L. camara invasion. Stratified random sampling was used in data collection to assess differences in species diversity and soil properties in the park. Results revealed that L. camara covered an area of 1772 ha. Using Random Forest classification, the study obtained an accuracy score of 92.1% and an F1 score of 86.25%. Two‐way ANOVA showed significant effect of L. camara invasion on soil moisture (F = 28.143, p = 0.000), organic matter (F = 13.377, p = 0.003), pH (F = 1272.369, p = 0.000), total nitrogen (F = 51.762, p = 0.000), total phosphorus (F = 5.000, p = 0.045), woody species density (F = 4.987, p = 0.027), basal area (F = 10.393, p = 0.001), grass species richness (F = 196.258, p = 0.000) and grass cover (F = 3.637, p = 0.042). These results suggest that L. camara was modifying the soil and vegetation properties of the ecosystem which has implications on biodiversity. [ABSTRACT FROM AUTHOR]

Biological invasions are a leading ecological issue of the 21st century because of their worldwide contributions to biodiversity loss and degradation of ecosystem services. Answering general questions about the mechanisms facilitating the spread of successful invasives is key to understanding how to manage them moving forward. The success of introduced primary producers has often been attributed to superior competitive ability or to their release from natural enemies that constrained them in their native range. In contrast, nonnative primary producers can successfully invade and establish in new areas by releasing allelochemical compounds into the environment that are toxic to the native flora. The interactive effects of allelopathy and competition remain underexplored. Here, we evaluated the mechanism of invasion by Guinea grass, a globally distributed tallgrass from tropical and subtropical Africa with known allelopathic effects associated with 2‐hydroxyphenylacetic acid (2HPAA). We asked if allelopathy and light availability interact to give Guinea grass a competitive advantage during seedling establishment in its introduced range. We used a fully factorial greenhouse experiment in which allelochemical concentrations and light availability treatments were based on empirical measurements of these variables at an invaded site in South Texas. Seedling recruitment and growth were assessed for three native species and for Guinea grass itself. We also described the metabolome (the complete set of small molecules) of an invasive grass for the first time to facilitate a comparison of the effect of the known allelochemical 2HPAA with that of the whole‐plant chemical extract. Shading and allelochemistry each reduced recruitment and growth by themselves, and a significant interaction of these stressors exacerbated the negative effects in the shade, resulting in short plants, low biomass, and ultimately decreased seedling recruitment. The whole‐plant metabolomic extract had significantly stronger effects than pure 2HPAA, and these negative effects were intensified in the shade. Moreover, the mechanism showcased here demonstrated that resource competition and biochemical interference are not mutually exclusive mechanisms that facilitate the spread of a globally distributed invasive species. [ABSTRACT FROM AUTHOR]

Summary: Plants actively respond to their neighbors by altering root placement patterns. Neighbor‐modulated root responses involve root detection and interactions mediated by root‐secreted functional metabolites. However, chemically mediated root placement patterns and their underlying mechanisms remain elusive.We used an allelopathic wheat model system challenged with 60 target species to identify root placement responses in window rhizobox experiments. We then tested root responses and their biochemical mechanisms in incubation experiments involving the addition of activated carbon and functional metabolites with amyloplast staining and auxin localization in roots.Wheat and each target species demonstrated intrusive, avoidant or unresponsive root placement, resulting in a total of nine combined patterns. Root placement patterns were mediated by wheat allelochemicals and (–)‐loliolide signaling of neighbor species. In particular, (–)‐loliolide triggered wheat allelochemical production that altered root growth and placement, degraded starch grains in the root cap and induced uneven distribution of auxin in target species roots.Root placement patterns in wheat–neighbor interactions were perception dependent and species dependent. Signaling (−)‐loliolide induced the production and release of wheat allelochemicals that modulated root placement patterns. Therefore, root placement patterns are generated by both signaling chemicals and allelochemicals in allelopathic plant–plant interactions. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical model is applied to investigate the effect of density of allelochemicals on plant population involving delay. The model is constructed using a system of nonlinear delay differential equations. In the model, there are three state variables: plant populations (P1 & P2) and density of allelochemical (T). It is assumed that in the presence of density of allelochemicals, plant populations are affected. It further delays the conversion of resource into the density of allelochemicals and hence affects the plant population adversely. This effect is observed by using delay in the competition model. Equilibrium points are calculated. Using the Routh–Hurwitz theorem, certain explicit formulations defining the stability and path of the Hopf‐bifurcation periodic solutions at the positive equilibrium are obtained. Further, the direction of these bifurcating periodic solutions is also studied. Numerical simulation and graphical support are provided for analytical findings using MATLAB. [ABSTRACT FROM AUTHOR]

Eucalyptus plantations outside their native range—either as an income source or aimed at sequestering atmospheric carbon to combat climate change—are increasingly known to reduce local biodiversity and groundwater levels, and to increase soil degradation and erosion. One additional but less understood effect of Eucalyptus on native floras is allelopathy—the chemical inhibition of other plants' germination. Here we investigate the putative allelopathic effects of Eucalyptus globulus on the germination of Polylepis subtusalbida, a keystone species that characterizes a species‐rich and highly threatened woodland habitat in the Bolivian Andes. We carry out controlled greenhouse experiments reflecting local rainfall, field litter quantity, and Eucalyptus leachate concentrations at multiple levels. Our results, based on five replicates with 390 Polylepis seeds each, show that contrary to our expectation Eucalyptus leachates does not affect germination significantly. Our findings suggest that projects aiming to remove Eucalyptus to restore Polylepis woodlands are likely to succeed even without the resource‐consuming removal of leaf litter, and potentially also bark and roots, from the ground after tree felling. [ABSTRACT FROM AUTHOR]

The encroachment of woody plants into grasslands is an ongoing global problem that is largely attributed to anthropogenic factors such as climate change and land management practices. Determining the mechanisms that drive successful encroachment is a critical step towards planning restoration and long‐term management strategies. Feedbacks between soil and aboveground communities can have a large influence on the fitness of plants and must be considered as potentially important drivers for woody encroachment. We conducted a plant–soil feedback experiment in a greenhouse between eastern redcedar Juniperus virginiana and four common North American prairie grass species. We assessed how soils that had been occupied by redcedar, a pervasive woody encroacher in the Great Plains of North America, affected the growth of Andropogon gerardi, Schizachyrium scoparium, Bromus inermis, and Pascopyrum smithii over time. We evaluated the effect of redcedar on grass performance by comparing the height and biomass of individuals that were grown in live or sterilized conspecific or redcedar soil. We found redcedar created a negative plant–soil feedback that limited the growth of the cool season grasses B. inermis and P. smithii, reducing their overall biomass by >60%. These effects were found in both live and sterilized redcedar soils. In live soils, some growth suppression can be attributed to the negative effects of soil microbes. The limitation of grass growth in sterile soils indicates redcedar may exude an allelochemical into the soil that limits grass growth. Our results demonstrate that plant–soil feedback created by redcedar inhibits the growth of certain grass species. By creating a plant–plant interaction that negatively affects competitors, redcedars increase the probability of seedling survival until they can grow to overtop their neighbors. These results indicate plant–soil feedback is a mechanism of native woody plant encroachment which could be important in many systems yet is understudied. [ABSTRACT FROM AUTHOR]

The impacts of invasive alien plant species on native plants are generally well documented, but little is known about the mechanisms underlying their impacts on crop growth. A better understanding of immediate as well as legacy effects and of direct and indirect impacts of invasive alien plant species is essential for an improved management of invaded cropland. We investigated how Lantana camara impacts the growth of two subsistence crops (maize and cassava) through competition for resources, allelopathy and the indirect plant–plant interactions. We carried out two pot experiments using soils from invaded abandoned, invaded cultivated and non‐invaded cultivated crop fields. In the first experiment maize and cassava were grown alone or together with L. camara and half of the pots were treated with activated carbon to suppress allelochemicals. The effect of the soil microbial community on L. camara—crop interactions was assessed in a second experiment using autoclaved soil with 5% of soil from the three soil types. We found that L. camara reduced the growth of maize by 29%, but cassava was not affected. We did not find evidence of allelopathic effects of L. camara. Inoculation of autoclaved soil with microorganisms from all soil types increased biomass of cassava and reduced the growth of maize. Because L. camara only caused impacts when growing simultaneously with maize, the results suggest that removal of L. camara will immediately mitigate its negative impacts on maize. [ABSTRACT FROM AUTHOR]

Allelopathy is an invasion driver, and arbuscular mycorrhizal fungi (AMF) also play an important role in plant invasion. However, little is known about their interactive effects on plant invasion mechanisms. In this study, we have investigated the interactive effects of allelopathy and AMF on competition between the exotic invasive species, Bidens alba, and its native congener, Bidens biternata. A two‐factor (allelopathy, AMF) common garden experiment was conducted using sterilised soil with or without AMF inoculation and with or without activated carbon (AC) addition. The results showed that both AC and AMF had significant effects on the relative yield (RY) of invasive species and competitive aggressivity (AG) between invasive and native species. Both AC and AMF exerted interactive effects on the AG. Activated carbon significantly reduced AG (0.86 vs 0.15%) without AMF, while it had no significant effects on AG with AMF. Moreover, AC significantly reduced the mycorrhizal dependency of the native species (108.06% vs 23.62%) but did not affect the invasive species. The AMF increased the variety of organic compounds in the aqueous extracts of the rhizosphere soil of invasive species, regardless of the competition. Overall, allelopathy significantly increased the mycorrhizal dependency of the native species, while it promoted the competitive ability of the invader regardless of AMF inoculation. Conversely, AMF reduced the facilitation of allelopathy in the AG of the invasive species. These results suggest that AMF play a critical role in improving the resistance of the native species to the invader by mediating allelopathy. [ABSTRACT FROM AUTHOR]

This study examined phytotoxic activities of several Vietnam localised OM rice (Oryza sativa L. OM) cultivars on junglerice (Echinochloa colona (L.) Link), an invasive weed threatening rice production, and identified allelochemicals and their activities for OM 4498, the most allelopathic cultivar. The aqueous MeOH extracts of all rice cultivars inhibited root and shoot growth of junglerice at a concentration as low as 0.01 g ml−1. Inhibitory effects were greatest in OM 380, OM 2395 and OM 4498, with the average effective doses (EDs) of extracts required for 90% inhibition (ED90) on junglerice as low as 0.981, 0.632 and 0.702 g ml−1, respectively. The phytotoxic substances salicylic acid, vanillic acid, p‐coumaric acid, 2,4‐dimethoxybenzoic acid, benzoic acid, p‐hydrobenzoic acid, trans‐cinnamic acid and coumarin were identified in OM 4498 at concentrations ranging from 0.066 to 11.412 mg in 100 g fresh weight of rice tissue. Two of these substances, 2,4‐dimethoxybenzoic acid and coumarin, have never previously been identified in rice. Compared to other compounds, p‐coumaric acid may have the greatest weed‐suppressant potential on junglerice, with the average ED50 being 0.28 mM. The total activities of salicylic acid, vanillic acid, p‐coumaric acid, trans‐cinnamic acid and 2,4‐dimethoxybenzoic acid in an OM 4498 rice plant on junglerice seedlings were 59.60, 0.78, 3.47, 2.52 and 0.61 mM/mM, respectively. The results clearly suggest that OM 4498 rice extract is an excellent source for allelochemicals against junglerice, and this rice cultivar should be considered in rice production areas invaded by junglerice. [ABSTRACT FROM AUTHOR]

Over the decades the presence of aquatic weeds has caused immense biodiversity loss to the ecosystem. The use of herbicides has arisen emergence of herbicide‐resistant weeds and loss of inherent flora and fauna due to the recalcitrant nature of the chemicals used. Hence, there is a need to use nontoxic, ecosustainable, low‐cost, and efficient biological molecules that are analogous to chemical herbicides. Various plants, bacteria, fungi as well a few viruses are reported to secrete allelopathic biomolecules that inhibit the growth and development of weeds. However, majorly fungal pathogens and their metabolites are found to be effective biocontrol agents for the water hyacinth. The present review puts forward major findings and interventions in the biological control of the weed, water hyacinth. The biosynthesis, mechanism of action and factors regulating the activity of bioherbicides are discussed. In addition, the issues associated with the in situ application of these bioherbicides are also conferred focusing on the available mode of applications and formulation used. The major factors include the type and concentration of allelopathic biomolecules, age, type, and morphology of targeted weed, formulation type, mode of application and other physiological and environmental factors. Among various modes for the application of bioherbicides, emulsions are found to be most effective for the control of water hyacinth. Most of the toxicity studies indicated no toxicity of this fungal pathogen to other ecological plant species except water hyacinth. Yet, in‐depth investigations are needed of these allelochemicals and toxins before field applications. Overall, lab‐scale studies have shown promising results and highlighted a few potential fungi that need to be further explored for optimizing their bioherbicidal activity. [ABSTRACT FROM AUTHOR]

In plants, most competition is resource competition, where one plant simply preempts the resources away from its neighbors. Interference competition, as the name implies, is a form of direct interference to prevent resource access. Interference competition is common among animals that can physically fight, but in plants, one of the main mechanisms of interference competition is allelopathy. Allelopathic plants release cytotoxic chemicals into the environment which can increase their ability to compete with surrounding organisms for limited resources. The circumstances and conditions favoring the development and maintenance of allelochemicals, however, are not well understood. Particularly, despite the obvious benefits of allelopathy, current data suggest it seems to have only rarely evolved. To gain insight into the cost and benefit of allelopathy, we have developed a 2×2 matrix game to model the interaction between plants that produce allelochemicals and plants that do not. Production of an allelochemical introduces novel cost associated with both synthesis and detoxifying a toxic chemical but may also convey a competitive advantage. A plant that does not produce an allelochemical will suffer the cost of encountering one. Our model predicts three cases in which the evolutionarily stable strategies are different. In the first, the nonallelopathic plant is a stronger competitor, and not producing allelochemicals is the evolutionarily stable strategy. In the second, the allelopathic plant is the better competitor, and production of allelochemicals is the more beneficial strategy. In the last case, neither is the evolutionarily stable strategy. Instead, there are alternating stable states, depending on whether the allelopathic or nonallelopathic plant arrived first. The generated model reveals circumstances leading to the evolution of allelochemicals and sheds light on utilizing allelochemicals as part of weed management strategies. In particular, the wide region of alternative stable states in most parameterizations, combined with the fact that the absence of allelopathy is likely the ancestral state, provides an elegant answer to the question of why allelopathy seems to rarely evolve despite its obvious benefits. Allelopathic plants can indeed outcompete nonallelopathic plants, but this benefit is simply not great enough to allow them to go to fixation and spread through the population. Thus, most populations would remain purely nonallelopathic. [ABSTRACT FROM AUTHOR]

The application of biochar and plant‐growth‐promoting bacteria (PGPBs) in biocontrol soil‐borne pathogens has garnered worldwide interest recently. However, how agricultural replanting disease is alleviated by a combination of biochar and PGPBs treatment (SYBB) remains largely unexplored. In this study, we investigated the beneficial effects of single biochar addition and the combination of biochar and PGPBs on alleviating replanting disease by altering the rhizosphere microbiome and metabolites. Our field experiment showed that the SYBB treatment had a better alleviating effect on replanting disease than the single biochar addition. The study indicated the dominant effect of deterministic processes on the bacterial community and of stochastic processes on the fungal community under biochar and PGPBs treatment. The combination of biochar and PGPBs tended to convert the stochastic processes of fungal community assembly into deterministic processes. We found SYBB treatment increased the abundance of potentially beneficial Pseudomonas, Lysobacter, Gemmatimonadetes and Nitrospira, and decreasing the abundance of potentially pathogenic Fusarium, Talaromyces and Fusarium oxysporum. Moreover, the SYBB treatment increased the abundances of carbohydrates, fatty acids and plant hormones, and decreased the abundances of amino acids in the rhizosphere soil. Co‐occurrence network analysis indicated that SYBB treatment increased the connections within the microbial communities and drove the alteration of co‐occurrence network among the microbial communities and metabolites, which increased positive correlations in bacteria‐metabolite networks and decreased positive correlations in fungi‐metabolite networks. Spearman correlation analysis showed the abundances of beneficial Streptomyces, Pseudomonas and Lysobacter were significantly and positively correlated to the metabolites most increased under SYBB treatment. The combination of biochar and PGPBs alleviated replanting disease by mediating the change of rhizosphere soil metabolites, and stimulating the proliferation of indigenous and beneficial soil microbes. The research results are intended to provide the basis for new strategies for green and sustainable remediation of soil‐borne pathogens. [ABSTRACT FROM AUTHOR]

Rice plants produced less allelochemicals when growing with neighbours of a closely related cultivar than when growing with less related ones, but produced the highest level when growing with neighbours of the same cultivar. Xu et al., for the first time, showed that kin recognition can also affect the balance between direct competition for resources and allelopathy, and this together may lead to improved weed suppression in rice (Figure 1). GLO:ETF/01dec21:pce14173-fig-0001.jpg PHOTO (COLOR): 1 The directional root growth towards weeds and allelopathic activity (or allelochemical productivity) of rice plants grown with neighbouring rice plants of (a) the same cultivar, (b) a closely related cultivar and (c) a more distant cultivar, and the consequences of suppression effect on weed growth. Among all biotic stress types (i.e., pathogens, pests and weeds), weeds have the largest potential for yield reduction (larger than the other two combined) (Oerke, 2006). [Extracted from the article]

Summary: Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating inter‐specific and intra‐specific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin versus non‐kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behaviour, allelochemical production and resource partitioning in the dominant weed competitor, as well as soil microbial communities. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non‐kin mixtures. The effect was driven by kin recognition that induced changes in root placement, altered weed carbon and nitrogen partitioning, but was associated with similar soil microbial communities. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighbouring collaborators (kin) or competitors and adjust their growth, competitiveness and chemical defense accordingly. This study identified the role of kin recognition in mediating allelopathic rice interference with weeds, and addressed an interesting concept that relatedness allows allelopathic plants to discriminate neighbouring collaborators or competitors and adjust growth, competitiveness and chemical defense accordingly. [ABSTRACT FROM AUTHOR]

Elymus nutans has been widely planted together with other perennial grasses for rebuilding degraded alpine meadow atop the Qinghai‐Tibetan Plateau. However, the rebuilt sown pastures begin to decline a few years after establishing. One of the possible causes for the degradation of sown grassland may come from allelopathy of planted grasses. The purpose of this study was to examine allelopathic potential of Elymus nutans. Three types of aqueous extract from Elymus nutans and its root zone soil were prepared, and 5 highland crops and 5 perennial grasses were used as recipient plants. Elymus nutans exhibited strong allelopathic potential on germination and seedling growth of 5 crops, but different crops or perennial grasses respond to the extract differently. The pieces aqueous extract have stronger inhibition than whole plant extract and root zone soil extract. Hordeum vulgar var. nudum, Avena sativa, and Festuca sinensis were the most affected, while Chenopodium quinoa and Elymus sibiricus were the least affected. Elymus nutans presented less influence on Poa pratensis and Poa crymophylla than on Festuca sinensis. It is recommended that the species combination of mixture for restoration should be considered for allopathic effects on the coseeding to decrease the seeding rate ratio of Elymus nutans. The annual dicot crop seeds of Chenopodium quinoa and Brassica napus can be used as alternative subsequent crop for the seed field of Elymus nutans monoculture. [ABSTRACT FROM AUTHOR]

Although cover crops are widely used for weed suppression in the agroecosystem, little research is available regarding the possibility that the decomposed weed solution may control weeds. In this study, we tested the allelopathic effect of decomposed weed solution on barnyardgrass (Echinochloa crus‐galli). In two separate tests, we found that the solution of decomposed Myosoton aquaticum completely suppressed the germination of barnyardgrass seeds at a concentration of 20 g l‐1. We then isolated and identified the predominant inhibitory substance in the decomposed M. aquaticum solution. The solution was subjected to organic solvent extraction and then separated on a silica gel column before the final identification of its components by high‐performance liquid chromatography‐tandem mass spectrometry (HPLC‐MS/MS). Dihydrocoumarin was isolated from the M2 and M3 fractions using a bioassay‐guided method and was found to be the most active of eleven candidate allelochemical compounds. Dihydrocoumarin is typically used as a food additive. In this study, barnyardgrass germination was completely inhibited when treated with dihydrocoumarin at 1 g l‐1, and its root and shoot growth were significantly inhibited at an application rate of 0.005 g l‐1. Dihydrocoumarin showed highly efficient inhibition of root and shoot growth in barnyardgrass at low concentrations compared with coumarin. These findings show that weeds may be used as cover crops to provide allelochemicals for weed suppression and that dihydrocoumarin has the potential to be used as a bioherbicide. [ABSTRACT FROM AUTHOR]

Despite widespread evidence that biological invasion influences both the biotic and abiotic soil environments, the extent to which these two pathways underpin the effects of invasion on plant traits and performance remains unknown. Leveraging a long‐term (14‐year) field experiment, we show that an allelochemical‐producing invader affects plants through biotic mechanisms, altering the soil fungal community composition, with no apparent shifts in soil nutrient availability. Changes in belowground fungal communities resulted in high costs of nutrient uptake for native perennials and a shift in plant traits linked to their water and nutrient use efficiencies. Some plants in the invaded community compensate for the disruption of nutritional symbionts and reduced nutrient provisioning by sanctioning more nitrogen to photosynthesis and expending more water, which demonstrates a trade‐off in trait investment. For the first time, we show that the disruption of belowground nutritional symbionts can drive plants towards alternative regions of their trait space in order to maintain water and nutrient economics. [ABSTRACT FROM AUTHOR]

In recent decades, phenolic compounds derived from plants have been considered as potential weed inhibitors due to their environmentally friendly properties, which are profitable regarding sustainable development targets. While experiments indicated that phenolic compounds exhibited significant inhibition on weeds via various biological pathways, none of these natural compounds have been efficiently applied in practical agricultural production. This paper provides an overview of the phenolic allelochemicals (and their plant sources) that have been reported to have the most potential for weed growth inhibition as well as their modes of action. The biosynthetic pathway, classification, distribution, release, degradation, extraction, and isolation of these allelochemicals are also discussed. In addition, the advantages and limitations of applying these allelochemicals in weed management and sustainable agricultural development are indicated. Accordingly, there are three promising strategies to deal with the present problems and improve the effectiveness of future studies, including: (a) to discover a new approach combining phenolic allelochemicals and other prospective phytochemicals in the development of natural herbicides; (b) to modify the chemical structure for strengthening the stability and activity of the target compound; and (c) to generate resistant crops against weed stress related to the proliferation of phenolic allelochemicals through genetic engineering approaches. Conceivably, the information on phenolic allelochemicals that is assembled in this paper may provide a useful dataset for future studies on the application of artificial intelligence in the design and production of efficient natural herbicides for weed management and sustainable agricultural development. [ABSTRACT FROM AUTHOR]

Allelopathy plays an important role in the successful invasion of alien invasive plants. Phenolic compounds are one of the primary classes of secondary metabolites with strong allelopathic activities. Polyploidy can cause significant effects on the production and yield of plant secondary metabolites. However, the effect of allelopathic potential of phenolic compounds on the competitiveness of different geographical cytotypes of Solidago canadensis remains unknown. We conducted a common garden field experiment in the invasive habitat of China to compare the competitive ability of native and introduced diploid, tetraploid and hexaploid S. canadensis against intentionally planted local weeds. Results showed that introduced tetraploids and hexaploids outcompeted local plants and formed a monodominant community due to superior competitive ability. Phenolic metabolism analysis showed these populations had a high accumulation of total phenolic compounds in aerial parts and rhizosphere soil throughout three developmental stages, which contributed to significant allelopathic effects on tested weeds. However, diploids and native polyploids showed less allelopathic activities due to the low level of total phenolic content. Together, these results suggest polyploidization is one of the reasons that driving the differentiation of phenolic metabolism in different geo‐cytotypes of S. canadensis, and the allelopathic abilities of introduced polyploids are further enhanced through a post‐introduction adaptive evolution. Polyploidy‐promoted allelopathic potential makes introduced polyploids more competitive against local plants than diploids and native polyploids, which contribute to its successful invasion. [ABSTRACT FROM AUTHOR]

PREMISE: Invasion processes involve several mechanisms, some of which have received little attention. Allelopathy has been invoked as an invasion driver according to the novel weapon hypothesis (NWH), and polyploidization can also be an important factor for invasion success. However, very few studies have addressed both topics together. We analyzed the allelopathic effect of the polyploid Oxalis pes‐caprae, an invader in mediterranean‐climate areas worldwide, from different origins and ploidy levels (native: South Africa; invaded: Chile, Australia, California, and the Mediterranean Basin) on Lactuca sativa as a model species. METHODS: We measured seed germination, initial plant height, and aboveground and belowground biomass of Lactuca grown in field soil mixed with Oxalis material and with or without activated carbon in a common garden experiment. We performed the experiment twice, when Oxalis was vigorous and when senescent. RESULTS: Vigorous plants of Oxalis tended to reduce Lactuca germination, but both vigorous and senescent Oxalis plants increased Lactuca biomass, probably due to an increase in nutrients provided by plant material. The highest increase in Lactuca traits occurred with Oxalis plants from the Iberian Peninsula. Allelopathy only happened when Oxalis was senescent and was especially strong with plants from Chile. CONCLUSIONS: Although we did not find broad evidence for the NWH considering all areas together, we reported differences in the allelopathic potential of Oxalis plants depending on their origin. These results highlight the independent evolution of invasiveness traits in distant introduced ranges and the importance of the invaders' origin when testing hypotheses about invasion drivers. [ABSTRACT FROM AUTHOR]

PREMISE: Sparse understory communities, in association with non‐native tree species, are often attributed to allelopathy, the chemical inhibition of a plant by another. However, allelopathy is a difficult ecological phenomenon to demonstrate as many studies show conflicting results. Eucalyptus globulus, a tree native to Australia, is one of the most widely planted trees around the world. Sparse understories are common beneath E. globulus plantations and are often attributed to allelopathy, but the ecological impacts of E. globulus on native plant communities outside Austrialia are poorly understood. METHODS: To assess allelopathy as a mechanism of understory inhibition, we tested volatile‐ and water‐soluble leaf extracts from E. globulus, Salvia apiana, and Quercus agrifolia on seed germination of California native plants. We also quantified germination rates and early seedling growth of California native plants grown in soil from E. globulus plantations versus soil from an adjacent native plant community. RESULTS: Volatile compounds from E. globulus did not significantly reduce germination for any species. Inhibition from water‐soluble E. globulus compounds was comparable to that of a native tree, Quercus agrifolia (10%). Eucalyptus globulus soil supported germination and early seedling growth of native species equal to or better than coastal scrub soil, although species responses were variable. CONCLUSIONS: In contrast to previous studies, our results fail to support the hypothesis that E. globulus chemically inhibits germination of native species. California native plants germinate and grow well in soils from E. globulus plantations, which may have significant implications for management and restoration of land historically occupied by E. globulus plantations. [ABSTRACT FROM AUTHOR]

The capability of synthetic pesticides to manage weeds, insect pests and pathogens in crops has diminished due to evolved resistance. Sustainable management is thus becoming more challenging. Novel solutions are needed and, given the ubiquity of biologically active secondary metabolites in nature, such compounds require further exploration as leads for novel crop protection chemistry. Despite improving understanding of allelochemicals, particularly in terms of their potential for use in weed control, their interactions with multiple biotic kingdoms have to date largely been examined in individual compounds and not as a recurrent phenomenon. Here, multi‐kingdom effects in allelochemicals are introduced by defining effects on various organisms, before exploring current understanding of the inducibility and possible ecological roles of these compounds with regard to the evolutionary arms race and dose–response relationships. Allelochemicals with functional benefits in multiple aspects of plant defence are described. Gathering these isolated areas of science under the unified umbrella of multi‐kingdom allelopathy encourages the development of naturally‐derived chemistries conferring defence to multiple discrete biotic stresses simultaneously, maximizing benefits in weed, insect and pathogen control, while potentially circumventing resistance. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Allelopathy (i.e. chemical interactions between plants) is known to affect individual performance, community structure and plant invasions. Yet, a quantitative synthesis is lacking. Here, we performed a meta‐analysis of 384 studies that measured allelopathic effects of one species (allelopathy plant) on another species or itself (test plant). Overall, allelopathy reduced plant performance by 25%, but the variation in allelopathy was high. The type of method affected the allelopathic effect: compared to leachates, allelopathy was more negative when residues of allelopathy plants were applied, and less negative when soil conditioned by allelopathy plants was applied. The negative effects of allelopathy diminished with study duration, and increased with concentrations of leachates or residues. Although allelopathy was not significantly related to lifespan, life form or domestication of the interacting plants, it became more negative with increasing phylogenetic distance. Moreover, native plants suffered more from leachates of naturalised alien plants than from leachates of other native plants. Our synthesis reveals that allelopathy could contribute to success of alien plants. The negative relationship between phylogenetic distance and allelopathy indicates that allelopathy might contribute to coexistence of closely related species (i.e. convergence) or dominance of single species. [ABSTRACT FROM AUTHOR]

Allelopathy, a type of interference competition involving exuded chemicals, has been documented for several types of organisms including terrestrial plants, aquatic macrophytes, microbes, and planktonic algae. However, due to the dynamic nature of the aquatic environment it is unclear whether allelopathy is an evolutionarily stable competition mechanism in such a setting. In this research, we consider a cosmopolitan harmful algae species, Prymnesium parvum, for which multiple ecological roles of its produced deleterious chemicals have been suggested, including broadcast allelopathy (chemicals produced and exuded) and micropredation via cell–cell interactions (chemicals produced and held within the cell). To further investigate the ecological role of the deleterious chemicals, bioassays (with phytoplankton and zooplankton target organisms) were conducted using various fractions of a P. parvum culture grown under balanced N:P stoichiometry or imbalanced, P‐reduced stoichiometry. In addition, time‐series counts were generated with cell density enumerations and observations of behavior of a mixed species culture at intervals over a 24‐h period. Our results suggest that the apparent ecological role of the chemicals in a relatively high‐density population shifts depending on system stoichiometry in regard to nitrogen and phosphorus. We show that under balanced N:P conditions, deleterious chemical production is low and cell contact mediates mortality of prey. Differently, under imbalanced, P‐reduced conditions chemical effect is high and mass mortality occurs independent of cell contact. Thus, imbalanced N:P ratios shift the apparent ecological role of the deleterious chemicals from one of micropredation to one of broadcast allelopathy. These differences likely influence bloom dynamics and result in different ecological outcomes for systems affected by blooms. Further, we suggest that these differences indicate the importance of predatory mixotrophic feeding in the evolutionary maintenance of deleterious chemical production and the occurrence of allelopathic effects as a byproduct. [ABSTRACT FROM AUTHOR]

Altered species composition caused by environmental and climatic change can affect the transfer of plant residues among communities. Whereas transferred residues are typically considered a resource in recipient systems, residues of allelopathic species may instead cause interference.Evergreen dwarf shrubs, specifically the allelopathic species Empetrum nigrum are increasing in abundance in response to a warming climate. Empetrum has small, evergreen leaves that can be transferred to other communities when withered and lost from the plant.We hypothesize that Empetrum can have allelopathic effects in the recipient communities of the withered leaves. We call this allochthonous allelopathy as opposed to autochthonous allelopathy, which is well documented in communities where the plant grows.We measured influx of allochthonous Empetrum leaves onto snow‐covered snowbeds, where they are easily identified within the debris. Next, we compared the bioactivity of allochthonous withered leaves with that of green Empetrum leaves. Finally, we conducted an experiment testing the germination and seedling growth of 10 tundra species in snowbed soil supplemented with no (control) and three densities of allochthonous Empetrum leaves.We found Empetrum leaves to be common on the snow cover of snowbeds. We found Empetrum leaves collected on snowbeds to be as bioactive as green leaves. Finally, we found forb species to have reduced germination and all 10 species to have delayed seedling development when growing in snowbed soil supplemented with withered Empetrum leaves. Seedlings under the control treatment were 2.3 times longer and had 3.2 times more leaves in comparison to seedlings grown under the strongest allochthonous leaf treatment.Results from our study imply that Empetrum is allelopathic in recipient systems of its allochthonous leaves. The abundant nature of Empetrum in the tundra suggests that allochthonous allelopathy is a common phenomenon, causing biotic stress in snowbeds and potentially other parts of the tundra. Exemplifying the ability of a plant to interfere in neighbouring communities, our study demonstrates a plant trait that may provide insight to other study systems. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The mechanisms causing invasive species impact are rarely empirically tested, limiting our ability to understand and predict subsequent changes in invaded plant communities. Invader disruption of native mutualistic interactions is a mechanism expected to have negative effects on native plant species. Specifically, disruption of native plant‐fungal mutualisms may provide non‐mycorrhizal plant invaders an advantage over mycorrhizal native plants. Invasive Alliaria petiolata (garlic mustard) produces secondary chemicals toxic to soil microorganisms including mycorrhizal fungi, and is known to induce physiological stress and reduce population growth rates of native forest understory plant species. Here, we report on a 11‐yr manipulative field experiment in replicated forest plots testing if the effects of removal of garlic mustard on the plant community support the mutualism disruption hypothesis within the entire understory herbaceous community. We compare community responses for two functional groups: the mycorrhizal vs. the non‐mycorrhizal plant communities. Our results show that garlic mustard weeding alters the community composition, decreases community evenness, and increases the abundance of understory herbs that associate with mycorrhizal fungi. Conversely, garlic mustard has no significant effects on the non‐mycorrhizal plant community. Consistent with the mutualism disruption hypothesis, our results demonstrate that allelochemical producing invaders modify the plant community by disproportionately impacting mycorrhizal plant species. We also demonstrate the importance of incorporating causal mechanisms of biological invasion to elucidate patterns and predict community‐level responses. [ABSTRACT FROM AUTHOR]

Homegarden, traditional agroforestry system in tropical and subtropical regions, sustains the availability of daily necessities. Mango (Mangifera indica L.) is an essential tree in the homegardens and is used for multiple purposes such as food, folk medicine, fuel, timber, and apiculture. The interaction between mango and weeds or crops has been evaluated in terms of allelopathy and the evidence of the allelopathy accumulated in the literature over two decades. The leaf extracts and leachate of mango inhibited the germination and growth of several other plants species. Soil collected from mango orchard shows growth inhibitory activity. Residues of mango leaves also suppressed the growth of other plant species. Phytotoxic substances such as coumaric, vanillic, caffeic, cinnamic, gallic and protocatechuic acids, and methyl gallate and quercetin‐3‐O‐α‐glucopyranosyl‐(1 → 2)‐β‐D‐glucopyranoside were identified in mango leaves. Those compounds may be released into the soil through the leaf leachate and the decomposition of plant residues and they can inhibit the germination and the growth of neighboring plants as allelopathic substances. Therefore, the allelopathy of mango is potentially useful for the weed management options in homegardens and other agriculture settings to reduce commercial herbicide dependency. [ABSTRACT FROM AUTHOR]

Invasive plants apply new selection pressures on neighbor plant species by different means including allelopathy. Recent evidence shows allelopathy functions as remarkably influential mediator for invaders to be successful in their invaded range. However, few studies have determined whether native and non‐native species co‐occurring with invaders have evolved tolerance to allelopathy. In this study, we conducted germination and growth experiments to evaluate whether co‐occurring native Juncus pallidus and non‐native Lolium rigidum species may evolve tolerance to the allelochemicals induced by Cyanara cardunculus in Australian agricultural fields. The test species were germinated and grown in pots filled with collected invaded and uninvaded rhizosphere soil of C. cardunculus with and without activated carbon (AC). Additionally, a separate experiment was done to differentiate the direct effects of AC on the test species. The soil properties showed invaded rhizosphere soils had higher total phenolic and lower pH compared with uninvaded soils. We found significant reduction of germination percentage and seedling growth in terms of above‐ and belowground biomass, and maximum plant height and root length of native in the invaded rhizosphere soil of C. cardunculus, but little effect on non‐native grass species. Even soil manipulated with AC showed no significant differences in the measured parameters of non‐native except aboveground biomass. Taken together, the results indicate allelochemicals induced by C. cardunculus exert more suppressive effects on native than non‐native linking the coevolved tolerance of those. [ABSTRACT FROM AUTHOR]

Increasing temperatures associated with climate change are shifting plant species to higher latitudes. Soil communities could aid the plants' shift into novel areas by harbouring fewer soil‐borne antagonists or more mutualists that influence the fitness and stress tolerance of the shifting species. Alternatively, they could contain novel antagonists or fewer mutualists. Thus, soil communities could positively or negatively affect plant range expansion, particularly if they influence plants' responses to climate, such as freeze tolerance, that feedback to affect expansion.We used the northward range expansion of the black mangrove, Avicennia germinans, into a system dominated by marsh cordgrass, Spartina alterniflora, in northern Florida, USA to study how the novel soil environment (i.e. S. alterniflora soil) affects mangrove fitness, susceptibility to cold stress and the colonization of mutualist fungi. We quantified abundance of root mutualistic fungi in mixed marsh‐mangrove habitat and conducted a laboratory experiment to test effects of steam‐sterilized and live soils from A. germinans and S. alterniflora on the growth, condition, fungal colonization and freeze tolerance of A. germinans seedlings.In the field, we found two times higher dark septate endophyte (DSE) colonization of A. germinans roots and three times higher fungal spore density in A. germinans soil compared to S. alterniflora roots and soil. In the laboratory experiment, seedlings in steamed S. alterniflora soil treatments had 50%–65% survival after freezing, compared to 0% survival in treatments with live S. alterniflora soil. A. germinans live soil mixed with S. alterniflora steamed soil yielded A. germinans roots with the highest DSE colonization and seedlings with greater shoot biomass and lower root:shoot ratios. S. alterniflora live soil lowered the freeze tolerance of A. germinans, decreased mangrove survival and depressed DSE colonization.Synthesis. S. alterniflora soil could impede A. germinans establishment in salt marsh communities. As climate warming gradually allows A. germinans to displace S. alterniflora, the rhizosphere could become increasingly hospitable to A. germinans. Our work suggests the soil community associated with resident species mediates climatic stressors to affect expansion success. [ABSTRACT FROM AUTHOR]

1. Forested headwater streams are generally considered to be light‐limited ecosystems where primary production is reduced, and the main source of energy and nutrients is composed of allochthonous detritus. We hypothesised that in these ecosystems, the development of primary producers might also be limited by (1) competition for nutrients with leaf‐litter decomposers (e.g. bacteria and fungi), and (2) leaf‐litter leachates or allelopathic compounds produced by aquatic fungi.2. To test these hypotheses, a 48‐day mesocosm experiment was performed in 12 artificial streams containing stream water inoculated with epilithic biofilm suspensions collected from a forested headwater stream. Three different treatments were applied: control without leaf litter (C), microbially conditioned leaf litter added at the beginning of the experiment and left to decompose throughout the experiment (L), or leaf litter renewed three times during the experiment (RL).3. We predicted that (1) the presence of litter, through microbial nutrient immobilisation and allelopathy, would reduce primary production and that (2) this effect would be amplified by litter renewal. We also predicted that nutrient competition would mean that (3) leaf‐litter decomposers will alter primary producer community composition and physiology. These predictions were tested by analysing biofilm development, physiology, stoichiometry, and benthic algal community structure. To distinguish between the effects of nutrient immobilisation and allelopathy, the biofilm responses to leaf‐litter leachates collected after different microbial conditioning durations were also measured in a parallel laboratory experiment.4. Contrary to our expectations, by day 28, primary producer growth was higher in the mesocosms containing leaf litter (L and RL) despite the rapid decrease in dissolved nutrients when leaf litter was present. After 48 days, the lowest phototrophic biofilm development was observed when leaf litter was renewed (RL), whereas phototrophic biofilm development was similar in the C and L treatments. Biofilm stoichiometry indicated that this effect was most probably related to greater nitrogen limitation in the RL treatment. The presence of leaf litter also affected primary producers' photophysiology, which could be attributed to changes in taxonomic composition and to physiological adjustments of primary producers.5. Laboratory measurements showed that despite a strong inhibition of primary producer growth by unconditioned leaf‐litter leachates, microbially conditioned leaf litter had either low or no effects on the development of primary producers.6. These results reveal that leaf‐litter decomposers can have both positive and negative effects on primary producers underlining the need to consider microbial interactions when investigating the functioning of forested headwater streams. [ABSTRACT FROM AUTHOR]

Premise: The ecological implications of hyperaccumulation have been investigated at the organismal level, but are poorly understood at the plant community level. Questions addressed here were: Does the presence of selenium (Se) hyperaccumulators affect Se distribution and concentration in their native soil, and do hyperaccumulators affect overall vegetation properties and species composition? Methods: Plant survey and soil Se mapping were performed at three seleniferous sites in Colorado. In season one, plots with and without hyperaccumulators were compared for (1) bare ground, canopy cover, and species richness; (2) relative species abundance; (3) soil Se distribution and concentration. In season two, a smaller‐scale design was implemented, focusing on areas 3 m in diameter around hyperaccumulators versus nonhyperaccumulators in 44 paired plots on one site. Results: Plots with hyperaccumulators generally showed more bare ground, less canopy cover, higher species richness, and 2–3‐fold higher soil Se levels. These patterns were not consistently significant across all sites; the effects of hyperaccumulators may have been diluted by their low abundance and the relatively large area of survey. In the smaller‐scale study, highly significant results were obtained, showing more bare ground, less canopy cover, and higher species richness in plots with hyperaccumulators; soil Se concentration was also higher in plots with hyperaccumulators. Conclusions: Hyperaccumulators may significantly affect local soil Se concentration and vegetation over at least a 3 m diameter area, or 4× their canopy. These differences may result from the combined positive and negative allelopathic effects observed earlier at the organismal level. [ABSTRACT FROM AUTHOR]