Concentrations Of Allelochemicals Research Articles

Hormesis and Antagonism in Low-Dose Phalaris Allelochemicals during Microcystis Control

Aquatic ecosystems face significant challenges globally from cyanobacterial blooms. Phalaris arundinacea (Reed Canary Grass) is used in artificial wetlands and found in natural wetlands. We investigated whether allelochemicals released from Phalaris root exudates inhibit Microcystis aeruginosa growth. We conducted experiments to disentangle the effect of the root exudates from living plants on resource competition and the potential role of microbiota in controlling Microcystis growth. We found that allelochemicals from root exudates and their inhibitory effect decayed over time. Results from filtration experiments and microscopic observations indicated that the removal of microorganisms (≥ 0.22 µm) allowed for the growth of Microcystis, suggesting that protists and rotifers may control Microcystis growth. We also tested commercial allelochemicals at environmentally relevant concentrations (≤ 1000 µg Lˉ¹) against Microcystis. Concentrations of 1000 µg Lˉ¹ of anthraquinone, gallic acid, gramine, hordenine, linoleic acid, naringuin, stigmasterol, tannic acid, 4-nitroindol-5-carboxaldehyde and the mixture of the nine allelochemicals inhibit Microcystis (≥ 87%). The minimum effective concentration was determined to be 100 µg Lˉ¹ for most allelochemicals, except for anthraquinone, which had a hormetic effect stimulating Microcystis growth by up to 70% compared to the controls. Our findings indicate that allelochemicals could be used to control Microcystis, but it is essential to establish the effective allelochemical minimum inhibitory concentrations from biofilters, wetlands, or macrophytes to assess their potential for managing Microcystis, other cyanobacteria, and microalgae. The increasing global use of artificial wetlands to control cyanobacterial blooms justifies further investigation into allelochemical concentrations, including decaying trends over time and hormetic effects.

Allelopathy and arbuscular mycorrhizal fungi interactions shape plant invasion outcomes

The novel weapon hypothesis suggests that allelopathy is an important mechanism for exotic plants to successfully invade native plant communities. Allelochemicals from exotic plants affect both native plants and arbuscular mycorrhizal fungi (AMF) in soil. To explore these effects, we conducted pot experiments using a native plant community comprising of Chenopodium album L., Vitex negundo L., Rhus chinensis Mill., and Acer truncatum Bunge. We incorporated AMF strains (Funneliformis mosseae, Glomus versiforme, and Rhizophagus intraradices in a 1:1:1 volume ratio) into a soil mixture comprising equal volumes of autoclaved field soil and grass ash at five concentrations (0 g L–1, CK; 10 g L–1, LRE; 20 g L–1, NRE; 30 g L–1, MRE; and 40 g L–1, HRE) to investigate the allelopathy of Rhus typhina L. root and its interactions with AMF on the native plant community. Our results indicated that low concentrations of allelochemicals promoted the relative growth rate and leaf nitrogen content in the native plant community, which was attributed to the increased environmental stress that improved the degree of leaf photosynthetic capacity and organic synthesis rate in the native communities. Moreover, allelochemicals with toxicity decreased the colonization rates of AMF. Meanwhile, the presence of allelopathic effects induced a decrease in leaf nitrogen, and allelopathy altered the effects of AMF on the native community. Specifically, the high concentration of allelochemicals altered the positive effect of AMF on the total aboveground biomass of the native plant community to a negative effect, likely by decreasing colonization rates or affecting soil physicochemical properties and the composition of the mycorrhizal communities. Consequently, it is necessary to consider the effects of AMF when testing the roles of allelopathy or the novel weapons hypothesis in biological invasions. Graphical abstract

Allelopathic effects of aqueous extracts from uncomposted and composted Mexican devil (Ageratina adenophora) plants on forest fungal growth and soil nitrogen and phosphorus mobilization

AbstractMexican devil [Ageratina adenophora (Spreng.) R.M. King & H. Rob.], a globally invasive weed with destructive effects on forests, has spread to numerous countries. To elucidate the inhibition of tree growth by A. adenophora, a study was conducted using the fungi (Lactarius deliciosus, Ceriporia lacerata, and Fomitopsis palustris) involved in the recycling of carbon and nutrients in forests. The focus was on investigating soil nitrogen and phosphorus availability in response to aqueous extracts from uncomposted and aerobically composted A. adenophora (EUA and ECA, respectively). The samples of composted A. adenophora from different sites exhibited a significant reduction in the concentration of allelochemicals 4,7-dimethyl-1-(propan-2-ylidene)-1,4,4a,8a-tetrahydronaphthalene-2,6(1H, 7H)-dione and 6-hydroxy-5-isopropyl-3,8-dimethyl-4a,5,6,7,8,8a-hexahydronaphthalen-2(1H)-one. This reduction more than 94% when compared with the concentration of these allelochemicals in CA. The EUA solutions at 5 and 10 mg L−1 (oven-dried plant biomass base) minimized L. deliciosus and C. lacerata growth, and significantly decreased F. palustris growth on the soil surface and within the soil. However, soil with ECA had no effect or promoting effect on the fungal growth. Compared with CK (only fungal inoculation in tested soil), the EUA solution reduced soil nitrogen and phosphorus, while ECA had the opposite effect; soil pH was increased by 0.01 to 0.08 under EUA treatment, while it decreased by 0.5 to 0.41under ECA treatment. Nitrogen and phosphorus availability were positively correlated with protease and phosphatase activity (r = 0.723 to 0.944), while available phosphorus was inversely correlated with pH in tested soils (r = -(0.809 to 0.978)). As such, the EUA solution decreased soil nitrogen and phosphorus supplies by inhibiting the liberation of proteases, phosphatases, and protons, which may lead to poor growth or even mortality of three fungal species. The in situ aerobically composted A. adenophora residues left behind may directly supply fungal species with nutrients and indirectly increase soil nutrient availability via the promotion of nitrogen and phosphorus mobilization.

The role of signaling compounds in enhancing rice allelochemicals for sustainable agriculture: an overview.

Plant phytotoxin synthesis is influenced by intricate signaling networks like jasmonic acid (JA) and salicylic acid (SA). These compounds not only induce allelochemical production but also aid weed suppression and plant immunity. (-)-Loliolide, JA, SA, and their derivatives trigger rice allelochemical synthesis and gene expression. Enhancing allelochemical synthesis in crops offers an alternative, reducing reliance on traditional herbicides for effective weed management. Rice (Oryza sativa L.) serves as a crucial staple food crop, nourishing over half of the global population, particularly in South Asia. Within rice plants, various secondary metabolites are produced, contributing to its nutritional value and providing energy to consumers. Over the last 5 decades, researchers have investigated 276 distinct types of secondary metabolites found in rice plants. These metabolites predominantly include phenolic acids, flavonoids, steroids, alkaloids, terpenoids, and their derivatives. The role of these secondary metabolites is to regulate the growth and development of the rice plant. In this research paper, we have focused on the allelopathic potential of rice, which involves its active defense strategy to suppress other species in its vicinity. This defense mechanism is regulated by plant signaling compounds. These signaling compounds enable rice plants to recognize and detect competitors, pathogens, and herbivores in their environment. As a response, the rice plants elevate the production of defensive secondary metabolites. One crucial aspect of rice allelopathy is the phenomenon of neighbor detection. Rice plants can sense the presence of neighboring plants and respond accordingly to establish their competitive advantage and ensure their survival. This paper specifically highlights the impact of exogenously applied signaling compounds, namely Methyl salicylate (MeSA) and Methyl Jasmonate (MeJA), on paddy rice. The aim is to provide deeper insights into the signaling mechanisms involved in rice allelopathy and how the exogenous application of signaling compounds influence the induction and regulation of defensive secondary metabolites in rice plants. Comprehensive analysis of various researchers' studies clearly reveals that the application of these elicitor compounds noticeably augments the allelopathic potential of rice, resulting in heightened accumulation of phenolic acid compounds. Expansion in more enlistment of phenolics may be because of expansion in the activities of enzymes, such as cinnamate 4-hydroxylase (C4H) and phenylalanine ammonia-lyase (PAL), the two main enzymes of the phenylpropanoid pathway, which are associated with allelopathic crop plants, and along this, they recognize the presence of weeds and react by expanding allelochemical focuses. Consequently, substantial endeavors have been dedicated in recent times to discover and characterize plant-derived signaling molecules. In bioassays conducted by Patni et al. in 2019, both competitive and non-competitive rice genotypes exhibited elevated phytotoxicity against Echino colona following treatment with MeSA. MeSA-treated rice plants displayed accelerated growth, increased yield, and concurrently demonstrated weed-suppressing properties. Published studies from 1976 to 2021 are reviewed in this paper. The study indicates that signaling compounds induce allelochemical concentrations, enhancing allelopathic activity. This insight may lead to development of novel herbicides for effective sustainable weed management.

Aquatic plant allelochemicals inhibit the growth of microalgae and cyanobacteria in aquatic environments.

Excess nitrogen and phosphorus nutrients in the aquatic environment result in the growth of algal cells and water eutrophication, which adversely affect the aquatic environment and human health. Therefore, discovering a safe and efficient algae suppression method is necessary to ensure the ecological safety of water. Recently, the allelopathic effects of aquatic plants on algae have attracted extensive attention from researchers. This review demonstrates the current research hotspot of allelopathic algal inhibition in aquatic plants and lists the common aquatic plant species and allelochemicals. In addition, the inhibition mechanism of allelochemicals from aquatic plants on algae is systematically discussed. Moreover, the key factors affecting the inhibition of allelopathy in algae, such as pH, temperature, algal cell density, and concentration of allelochemicals, are summarized. The present utilization modes of allelochemicals on algae are also presented. Finally, the problems existing in the study of allelopathic algal inhibition of aquatic plants are highlighted, and suggestions for further research are proposed.

Allelopathic Effects of Caffeic Acid and Its Derivatives on Seed Germination and Growth Competitiveness of Native Plants (Lantana indica) and Invasive Plants (Solidago canadensis)

Allelopathy has garnered considerable attention, but the effects of different allelochemicals on invasive plants remain unclear. This study addressed the knowledge gap surrounding allelopathy and its impact on native and invasive plant species. We focused on the impact of caffeic acid and its derivatives on the growth and competitiveness of the native Lantana indica and the invasive plant Solidago canadensis. We selected three allelochemicals, caffeic acid, methyl caffeic acid, and ethyl caffeic acid, for evaluation at two concentrations (0.1 mM and 1.0 mM). Three planting methods were employed: (1) a single species of S. canadensis, (2) a single species of L. indica, and (3) a combination of S. canadensis and L. indica. In addition, a control group was also included. Results revealed that high concentrations (1 mM) of methyl caffeate (MC) and ethyl caffeate (EC) significantly reduced seed germination rate, seed germination index, and seed germination speed index of L. indica compared to a low concentration (0.1 mM). Plant height, stem diameter, biomass, and root length in the control group (CK) of S. canadensis were significantly higher than those in the treated groups. However, with increasing allelochemical concentration, L. indica’s relative competitiveness gradually decreased. These findings provide insights into the concentration-dependent effects of allelopathic compounds on the growth of L. indica and S. canadensis. By analyzing how these allelochemicals influence the growth and competitiveness of native and invasive plants, the study sheds light on the dynamics of allelochemical interactions between these species. This knowledge can be pivotal for understanding plant competition dynamics in ecosystems and could inform strategies to control invasive species or promote native plant growth.

Adding insult to injury: Light competition and allelochemical weapons interact to facilitate grass invasion

AbstractBiological 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.

The First Evidence of Gibberellic Acid's Ability to Modulate Target Species' Sensitivity to Honeysuckle (Lonicera maackii) Allelochemicals.

Invasive species employ competitive strategies such as releasing allelopathic chemicals into the environment that negatively impact native species. Decomposing Amur honeysuckle (Lonicera maackii) leaves leach various allelopathic phenolics into the soil, decreasing the vigor of several native species. Notable differences in the net negative impacts of L. maackii metabolites on target species were argued to depend on soil properties, the microbiome, the proximity to the allelochemical source, the allelochemical concentration, or environmental conditions. This study is the first to address the role of target species' metabolic properties in determining their net sensitivity to allelopathic inhibition by L. maackii. Gibberellic acid (GA3) is a critical regulator of seed germination and early development. We hypothesized that GA3 levels might affect the target sensitivity to allelopathic inhibitors and evaluated differences in the response of a standard (control, Rbr), a GA3-overproducing (ein), and a GA3-deficient (ros) Brassica rapa variety to L. maackii allelochemicals. Our results demonstrate that high GA3 concentrations substantially alleviate the inhibitory effects of L. maackii allelochemicals. A better understanding of the importance of target species' metabolic properties in their responses to allelochemicals will contribute to developing novel invasive species control and biodiversity conservation protocols and may contribute to applications in agriculture.

Effects of Allelochemicals on Root Growth and Pod Yield in Response to Continuous Cropping Obstacle of Peanut

Continuous cropping (CC) obstacle is a major threat in legume crops production; however, the underlying mechanisms concerning the roles allelochemicals play in CC obstacle are poorly understood. The current 2-year study was conducted to investigate the effects of different kinds and concentrations of allelochemicals, p-hydroxybenzoic acid (H), cinnamic acid (C), phthalic acid (P), and their mixtures (M) on peanut root growth and productivity in response to CC obstacle. Treatment with H, C, P, and M significantly decreased the plant height, dry weight of the leaves and stems, number of branches, and length of the lateral stem compared with control. Exogenous application of H, C, P, and M inhibited the peanut root growth as indicated by the decreased root morphological characters. The allelochemicals also induced the cell membrane oxidation even though the antioxidant enzymes activities were significantly increased in peanut roots. Meanwhile, treatment with H, C, P, and M reduced the contents of total soluble sugar and total soluble protein. Analysis of ATPase activity, nitrate reductase activity, and root system activity revealed that the inhibition effects of allelochemicals on peanut roots might be due to the decrease in activities of ATPase and NR, and the inhibition of root system. Consequently, allelochemicals significantly decreased the pod yield of peanut compared with control. Our results demonstrate that allelochemicals play a dominant role in CC obstacle-induced peanut growth inhibition and yield reduction through damaging the root antioxidant system, unbalancing the osmolytes accumulation, and decreasing the activities of root-related enzymes.

Simulating effects of agricultural intensification and climate change: Nitrogen fertilisation and drought stress decrease insect herbivore performance

Abstract Biodiversity is globally under pressure, and the current decline in insect biomass and diversity is likely caused by human activities. Key drivers of biodiversity loss include agricultural intensification and anthropogenic climate change. Nevertheless, a thorough understanding of potential interactions between both factors and the mechanisms underlying insect declines, in general, is still lacking. Here, the authors investigate the combined effects of nitrogen fertilisation and drought, as applied to host plants, on the preference and performance of the butterfly Lycaena tityrus. Individuals performed best on plants having received medium nitrogen levels, while performance was reduced by either a lack of or strong fertilisation, the former potentially caused by nitrogen limitation and the latter by increased concentrations of toxic allelochemicals. Female oviposition preference though was positively related to nitrogen fertilisation, resulting in a mismatch between preference and offspring performance at high nitrogen levels. Plant drought stress additionally reduced herbivore performance, and females appeared to suffer more from low‐quality food than males. Our results indicate that increasing nitrogen fertilisation, as applied in intensive agriculture, may substantially reduce host‐plant quality for insect herbivores, which may be exaggerated in the course of climate change due to the more frequent occurrence of droughts. Our study thus contributes to a better understanding of the mechanisms underlying human‐driven insect declines in agricultural landscapes and beyond.

P450 gene family mediates allelochemical detoxification and tolerance to alkaloids in cactophilic Drosophila

AbstractCacti are characterized by the extensive production of a broad variety of toxic metabolites as an anti‐herbivore strategy but nevertheless cactophilic Drosophila spp. (Diptera: Drosophilidae) feed and breed on decaying cacti. The family of cytochrome P450 is a group of enzymes involved in the detoxification metabolism, which are critical for the adaptation of phytophagous insects, especially populations of Drosophila exploiting cacti. In this context, Drosophila buzzatii Patterson & Wheeler and Drosophila koepferae Fontdevila & Wasserman (Drosophilini), constitute an excellent model for the study of the genetic basis of tolerance to cacti allelochemicals. These closely related species allow testing to what extent a relatively small set of genes can explain host use patterns and their role in the divergent evolution of specialization. We evaluated the role of the P450 genes in the adaptation of these species to the use of one of their hosts, the columnar cactus Trichocereus terscheckii (Parm.) Friedrich & GD Rowley (Cactaceae). Experimentally evolved strains exhibiting different degrees of cactus specialization were exposed to artificial rearing media enriched with cactus allelochemicals and piperonyl butoxide (PBO), an inhibitor of P450 family activity. Our analyses showed a significant viability reduction in the presence of PBO, in the non‐tolerant strains of both species as well as in the strain historically subjected to mild concentrations of allelochemicals (the soft strain) of D. koepferae. We confirmed the key role of P450 genes for the evolution of cactus specialization but also found evidence for the evolution of other detoxification pathways.

Bioavailability of Allelochemicals in Soil Environment Under Climate Change: Challenges and Perspectives

Weed management is an important component in sustainable agriculture. The current agriculture is changing with climate change. Allelopathy has been recognized as a component of integrated weed management over the years. The allelopathic ideas have been used in various facets of allelopathic implications. Some of these include use of cover crops, plant residues, plant extracts, crop cultivars and others. And it is being challenged under climate change factors such as increased atmospheric CO2, temperature rise, erratic rainfall patterns and others. The relevance of allelopathy has been highly discussed due to the lack of phytotoxic concentrations of allelochemicals under field conditions. Crop residues from existing crop or rotational crops can provide selective weed suppression through their physical presence on the soil surface and/or through the release of allelochemicals. Brassica nigra, Avena fatua, Fagopyrum esculentum, Secale cereale, Sorghum bicolor, Triticum aestivum and other cover crops have been used in weed management on a limited basis. Some of the allelochemicals such as DIBOA, DIBOA-glycoside, dhurrin, isoflavonoids, isothiocyanate, juglone, momilactone, scopoletin, and sorgoleone have been reported to play a role in weed management under field conditions. The living and dynamic soil system influences the fate and functions of allelochemical activity. The bioavailability of allelochemicals in the soil is dependent on soil processes such as adsorption, leaching and degradation by abiotic and biotic factors. These processes and other related soil conditions are greatly influenced by several underlined climatic variables. Future allelopathic research should be focused on persistence and availability of allelochemicals in soil environment. The bioavailability of allelochemicals under field conditions with climate change associated rising atmospheric CO2, rising temperature and intensity and erratic rainfall must be established for its effective practical role in weed management. Currently, we face challenges and opportunities in using allelopathy as a part of weed management strategies in today’s agriculture.

Improving weed control in sustainable agro-ecosystems: Role of cultivar and termination timing of rye cover crop

Alternative strategies to control weeds are required at the field level to reduce herbicides and derived pollution. As cover crop, rye (Secale cereale L.) is adopted mainly because of its allelopathic weed control, which takes place through a strong inhibition of germination and seedling growth in several types of grass and broad-leaved weeds. The present study consisted of: i) a field trial, focused on the evaluation of biomass production and allelochemical concentration in the biomass, and in situ weed control at 30 days after termination (with two termination timings: T1 - heading phase and T2 - 10 days later) of 8 rye varieties; ii) a pot experiment, focused on the inhibition effect of mulches derived by those 8 rye varieties on four summer weeds: velvetleaf (Abutilon theophrasti Med.), lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and common purslane (Portulaca oleracea L). Results showed that biomass production was the highest with Protector, closely followed by Primizia, Sito 70, Hellvus, Forestal, and Hymonta. In any case, rye mulching always reduced the weed biomass, especially with Fasto and Forestal. The allelochemical concentration in the biomass was the highest with Fasto and Forestal and decreased on average from T1 to T2 (–38% for total benzoxazinoids and –57% for isovitexin). Conversely, the rye biomass production increased (on average +77%), passing from T1 to T2. We also found that the reduction of weed biomass, compared with the control, is highly correlated with the allelochemical content in rye biomass in the case of T1 termination, while with the biomass production in the case of T2. In pots, a strong inhibitory effect on seedling growth due to rye mulching was observed for C. album (–76%), A. retroflexus (–56%), and P. olearcea (–84%), while not for A. theophrasti. We concluded that, regardless of the variety, adopting rye as a cover crop may be considered as a suitable practice to reduce weed pressure at the field level. Among all the varieties tested, Forestal and Protector showed the most significant weed suppression potential, due to the high amount of allelochemicals production for Forestal and high biomass production for Protector. Highlights - One month after rye termination, the weed biomass under mulching is reduced by 4 times, compared with the control. - When rye is terminated early, the allelochemical content in rye tissues reduces the weed biomass production. - When rye is terminated late, the weed biomass production is reduced by the amount of rye biomass. - Lambsquarters, redroot pigweed and purslane growth is inhibited by rye mulching, while velvetleaf is not affected.

Allelopathic activity of Acer negundo L. leaf litter as a vector of invasion species into plant communities

The article shows the results of the influence of different concentrations of allelochemicals of Acer negundo L. leaf litter, germination energy, absolute germination of seeds and plant growth. The seeds of Raphanus sativus L. and Avena sativa L. were used as model objects. Active substances contained in leaf litter A. negundo, have a selective inhibitory effect on the germination of seeds and the growth of seedlings of monocotyledonous and dicotyledonous plants. The allelopathic effect of the fall is not a limiting factor for the germination of seeds of herbaceous plants of the above-ground cover of the studied plantation.

Understory plant species diversity and allelochemicals in rhizosphere soils of Eucalyptus grandis plantations with different densities

To explore the influencing factors of understory plant species diversity of Eucalyptus grandis, we examined understory plant species diversity and phenolic allelochemicals in the rhizosphere soils of four-year-old and eight-year-old E. grandis plantations with different densities (1200, 1600, 2000 ind·hm-2) in Danling County of Sichuan Province. The results showed that a total of 45 plant species were recorded, belonging to 33 families and 44 genera. With the increases of stand age and decreases of stand density, plant species richness increased and their importance values were evenly distributed. Phanerophytes was the dominant life form across all stands. Shannon index and Margalef index of shrub in the four-year-old E. grandis plantations increased significantly at the density of 1600 ind·hm-2. All herbage plant diversity index except for Margalef index in four-year-old ones and Pielou index in eight-year-old plantations increased significantly with the decreases of density. Shannon index and Margalef index of shrub in 1200 ind·hm-2 were significantly higher in eight-year-old E. grandis stands than those in four-year-old ones. Five phenolic allelochemicals in the rhizosphere soils of E. grandis plantations were identified. In four-year-old stands, salicylic acid concentrations decreased significantly at the density of 1600 ind·hm-2. The concentrations of chrysin in four-year-old stands reduced significantly with the decreases of density. The concentrations of salicylic acid in eight-year-old stands increased significantly with the decreases of tree density. Salicylic acid concentrations in 2000 ind·hm-2 were significantly higher in four-year-old stands than that in eight-year-old ones, but the result was opposite in stands with density of 1600 ind·hm-2. The concentrations of chrysin in stand with density of 1200 ind·hm-2 were significantly higher in eight-year-old stands than that in four-year-old ones. Rundancy analysis (RDA) result showed that soil pH, bulk density, and the concentrations of soil organic matter, total nitrogen, total phospho-rus, and allelochemicals were the main environmental factors influencing understory plant species diversity. Therefore, prolonging rotation period and reducing stand density would improve micro-environmental condition of forests and buffer the allelopathy of E. grandis, which could facilitate the development of understory vegetation.

Biogeographic differences in the allelopathy of leaf surface extracts of an invasive weed

Allelopathy, the release of chemicals by plants that inhibit the germination and growth of competing species, can be an important trait for invasive success. However, little is known about potential biogeographical differences in allelopathy due to divergent regional eco-evolutionary histories. To test this, we examined the allelochemical potential of the highly invasive species Centaurea solstitialis from six world regions including native (Spain, Turkey) and non-native ranges (Argentina, Chile, California and Australia). Seeds from several populations in each region were collected and grown under common garden conditions. Allelopathic potential and chemical composition of three leaf extract concentrations of C. solstitialis from each region: 0.25%, 0.5% 0.75% (w/v−1) were assessed on the phytometer Lactuca sativa. The main allelochemicals present in the leaf-surface extract were sesquiterpene lactones that varied in major constitutive compounds across regions. These leaf extracts had strong inhibitory effects on L. sativa seed germination and net growth. Summed across regions, the 0.25% concentration suppressed germination by 72% and radicle elongation by 66%, relative to the controls. At the 0.5% concentration, no seeds germinated when exposed to extracts from the non-native ranges of Argentina and Chile, whereas germination and radicle growth were reduced by 98% and 89%, respectively, in the remaining regions, relative to controls. Germination and seedling growth were completely inhibited at the 0.75% concentration extract for all regions. Some non-native regions were characterized by relatively lower concentrations of allelochemicals, suggesting that there is biogeographical variation in allelopathic expression. These findings imply that rapid selection on the biochemical signatures of an exotic invasive plant species can be highly region-specific across the world.

Identification and Quantification of Allelochemicals from Selected Sweet Potato (<i>Ipomoea batatas</i> (L.) Lam.) Cultivars

Allelopathic compounds have the potential to inhibit the growth and development of other organisms in a diverse manner ranging from shifting nutrients and enhancing their growth to inflicting diseases. In addition, these compounds influence seedling growth and seed germination of various crops. The goal of this study was to identify and quantify different allelochemicals in various sweet potato cultivars through high-performance liquid chromatography techniques. Selected sweet potato slips (weight: 2.0 - 2.5 grams/slip) were propagated in separate glass tubes filled with 10.0 mL distilled water. Water extract from each glass tube was collected after 2, 4, and 6 weeks after transplanting (WAP) to identify and quantify allelochemical compounds by comparing their peaks with the retention time of standards. Results show that the concentration of allelochemicals in water extract was increased from 2 to 4 WAP but remained constant in the sixth week. Quantitative analysis revealed that the amount of chlorogenic acid was higher in all sweet potato cultivars compared to other allelochemicals. Some sweet potato cultivars, A5 and A39, exhibited higher allelopathy (18.28 - 19.37 ppm/slip) and reduced the height and biomass of Palmer amaranth the most due to the presence of increased concentration of combined allelochemicals, while other cultivars produced lesser allelochemicals (10.90 ppm/slip) and did not reduce the growth of the weed species. Allelopathic sweet potato cultivars high in chlorogenic acid production can effectively suppress Palmer amaranth with minimal dependence on chemicals to manage weeds and harmful pests under sustainable agricultural system.

Comparison Study of Allelochemicals and Bispyribac-Sodium on the Germination and Growth Response of Echinochloa crus-galli L.

The phytotoxic effects of two allelochemicals (trans-cinnamic acid and syringaldehyde) at different concentrations (1000, 100, 10, and 1 µM) on seed germination, seedling growth, and physiological and biochemical changes of Echinochloa crus-galli L. were tested by comparison to a commercial herbicide ‘Nominee’ (that is, 100 g/L bispyribac-sodium). trans-Cinnamic acid and the herbicide inhibited seed germination completely at 100 µM, whereas for syringaldehyde, complete inhibition required 1000 µM. However, with 100 µM syringaldehyde, the seed germination of the test species was 53% of the control. Allelochemicals and the herbicide delayed seed germination and significantly affected the speed of germination index (S), speed of cumulative germination index (AS), and coefficient of germination rate (CRG). The roots were more affected when nutrients were not added to the growth bioassay. In general, with the increasing concentration of allelochemicals from 100 to 1000 µM, the inhibitory effects increased. Via microscopy analysis, we found leaf blade wilting and necrosis at concentrations above 100 µM in allelochemical-treated plants. Roots of E. crus-galli treated with 1000 µM allelochemicals had black points on root nodes but had no root hairs. The anatomy of roots treated with allelochemicals (1000 µM) showed contraction or reduction of root pith cells as well as fewer and larger vacuoles compared to the control. The allelochemicals also showed remarkable effects on seedling growth, SPAD index, chlorophyll content, and free proline content in a pot culture bioassay, indicating that trans-cinnamic acid and syringaldehyde are potent inhibitors of E. crus-galli growth and can be developed as herbicides for future weed management strategies.

Carbon (δ13C) and Nitrogen (δ15N) Stable Isotope Composition Provide New Insights into Phenotypic Plasticity in Broad Leaf Weed Rumex acetosa under Allelochemical Stress

Phenolic compounds, hydroquinone and cinnamic acid derivatives have been identified as major allelochemicals with known phytotoxicity from allelopathic plant Acacia melanoxylon R. Br. Several phenolic compounds such as ferulic acid (FA), p-hydroxybenzoic acid (pHBA) and flavonoid (rutin, quercetin) constituents occur in the phyllodes and flowers of A. melanoxylon and have demonstrated inhibitory effects on germination and physiological characteristics of lettuce and perennial grasses. However, to date, little is known about the mechanisms of action of these secondary metabolites in broad-leaved weeds at ecophysiological level. The objective of this study was to determine the response of Rumex acetosa carbon isotope composition and other physiological parameters to the interaction of plant secondary metabolites (PSM) (FA and pHBA) stress and the usefulness of carbon isotope discrimination (Δ13C) as indicative of the functional performance of intrinsic water use efficiency (iWUE) at level of plant leaf. R. acetosa plant were grown under greenhouse condition and subjected to PSM stress (0, 0.1, 0.5, 1.0, and 1.5 mM) for six days. Here, we show that FA and pHBA are potent inhibitors of Δ13C that varied from 21.0‰ to 22.9‰. Higher pHBA and FA supply enhanced/retard the Nleaf and increased the Cleaf while ratio of intercellular CO2 concentration from leaf to air (Ci/Ca) was significantly decreased as compared to control. Leaf water content and leaf osmotic potential were decreased following treatment with both PSM. The Ci/Ca decreased rapidly with higher concentration of FA and pHBA. However, iWUE increased at all allelochemical concentrations. At the whole plant level, both PSM showed pronounced growth-inhibitory effects on PBM and C and N concentration, root fresh/dry weight, leaf fresh/dry weight, and root, shoot length of C3 broad leaf weed R. acetosa. Carbon isotope discrimination (Δ) was correlated with the dry matter to transpiration ratio (transpiration efficiency) in this C3 species, but its heritability and relationship to R. acetosa growth are less clear. Our FA and pHBA compounds are the potent and selective carbon isotope composition (δ13C) inhibitors known to date. These results confirm the phytotoxicity of FA and pHBA on R. acetosa seedlings, the reduction of relative water content and the induction of carbon isotope discrimination (Δ) with lower plant biomass.

Exploring the Herbicidal and Hormetic Potential of Allelopathic Crops Against Fenoxaprop-Resistant Phalaris minor

ABSTRACT: Recent increases in the development of herbicide resistance in Phalaris minor worldwide demand alternative non-chemical strategies to control this weed. A series of experiments were conducted under laboratory and greenhouse conditions to explore the herbicidal potential of four allelopathic crops, including maize, rice, sorghum and sunflower, at different concentrations of aqueous extracts (2.5% and 5%), residues (1%, 2% and 4%) and mulches (4, 8, and 12 ton ha-1) against fenoxaprop-resistant P. minor. Aqueous extracts, residues and mulches provided 86-100%, 73-100% and 16-40% control of this resistant weed biotype, respectively. The dry biomass reduction due to aqueous extracts, residues and mulches was 48-100%, 48-100% and 20-54%, respectively. Mulches also caused 17-41% reduction in the seed production potential of P. minor. Lower concentrations of allelochemicals showed hormesis (positive effect) against some emergence and growth traits of P. minor. The phytotoxic chemicals of these four crops have a strong herbicidal potential against herbicide-resistant P. minor, and can be used as an organic alternative to control herbicide resistant P. minor, thus ensuring a sustainable wheat production.