Cirsium vulgare (Asteraceae) is a newly emerged invasive species in Yunnan Province, China, and its phytotoxic potential has not yet been studied. This study was conducted to explore potential allelopathic effects of C. vulgare and to identify its flavonoid and phenolic acid compounds. Four aqueous extracts (roots, stems, leaves, and flower/fruit heads) of C. vulgare exhibited high inhibitory activity against the germination and seedling growth of Bidens pilosa and Digitaria sanguinalis. The inhibition rates of germination rate, germination index, root length, shoot length, and biomass of both species increased significantly with increasing concentrations, with B. pilosa being more inhibited than D. sanguinalis. Extracts from leaves and flower/fruit heads yielded the strongest inhibition, followed by stem extracts, with the lowest impact from root extracts. Flavonoids (65.41%) and phenolic acids (23.1%) collectively comprised 88.51% of all identified compounds. Thirty-eight flavonoid compounds and thirty phenolic acid compounds were selected for further analysis, representing 53.97% and 71.91% of the total content of flavonoids and phenolic acids, respectively. Many of the flavonoids and phenolic acids identified have been previously reported as known allelochemicals with possible allelopathic effects. This was the first study to show that the allelopathic potential of C. vulgare may aid its invasion and expansion.

ABSTRACT Alternanthera pungens Kunth is considered to be less invasive compared to its exotic congener A. philoxeroides (Mart.) Griseb. However, in recent 10 years, it has spread rapidly in Yunnan Province, China. To better understand the species' invasion and distribution, we simulated the potential distribution of A. pungens in China using a MaxEnt model under the current climate scenario and several future climate scenarios, with varying emissions and time frames. The model achieved excellent prediction performance, with A. pungens having an area under the curve value and true skill statistics value of 0.979 and 0.910, respectively. Temperature seasonality and mean temperature of coldest quarter were the greatest predictive environmental variables, with a cumulative contribution of more than 85.3% and a cumulative permutation importance of more than 89.8%. The suitable geographic region of A. pungens is concentrated in southern China. Under the current climate scenarios, projected areas ranked as highly and moderately suitable for A. pungens accounted for 0.31% and 1.03% of the Chinese mainland area, respectively. Under future climate scenarios, the suitable areas for A. pungens in China will expand northwards, with a maximum projected growth rate of 41.4% in the 2070s. This study was the first to show that A. pungens is predicted to expand its range in China in the future. Early warning and monitoring of A. pungens should be pursued, with greater vigilance in southern China to prevent its further spread and invasion.

Acmella radicans (Jacq.) R.K.Jansen (Asteraceae) is a widespread and troublesome weed in Yunnan Province, China and information about its seed germination biology is scant. A series of experiments were conducted to explore the effects of various environmental factors (temperature, light, pH, NaCl, soil water content, and burial depth) on germination and seedling emergence of A. radicans under controlled conditions. The optimum temperature for maximum germination (85.0

Using multiple species in native plant communities may improve control efficiency compared with single-species use. We conducted field investigations to assess the effects of Artemisia argyi, Portulaca oleracea, and their mixtures on the growth and reproduction of Mikania micrantha, followed by a greenhouse de Wit replacement series to compare different combinations of M. micrantha, A. argyi, and P. oleracea in terms of multispecies competition, phytoallelopathy, and photosynthesis. Field investigation showed that compared with M. micrantha monoculture (Group D), aboveground biomass, total stem length, flower biomass, inflorescence biomass, seed biomass, and seed number of M. micrantha increased in the P. oleracea community (Group B), though only seed number was significantly higher (p < 0.05). In contrast, in the A. argyi community (Group A) and the mixed community of A. argyi and P. oleracea (Group C), all these indicators decreased significantly (p < 0.05), in the order: Group C < Group A < Group D < Group B. This indicates that the mixed community (Group C) most strongly suppressed M. micrantha growth and reproduction. The effects of A. argyi, P. oleracea, and their mixture on the growth of M. micrantha in the greenhouse experiments mirrored the trends observed in field investigations. Calculated indices (relative yield, relative yield total, competitive balance index, and change in contribution) of A. argyi, P. oleracea, and their mixed population on M. micrantha demonstrated a higher competitive ability and higher influence of the combination of the two species compared with either A. argyi or P. oleracea alone. The interspecific phytoallelopathy experiment demonstrated strong allelopathic potential of A. argyi versus M. micrantha (p < 0.05) but showed no significant effect on P. oleracea. The net photosynthetic rate (Pn) of M. micrantha was generally lower in communities with both competitors compared with single-species communities. Our results suggest that, compared with a single plant population, the mixed population of A. argyi and P. oleracea exhibited a markedly enhanced ecological control capability through increased relative competitive ability, strengthened allelopathic inhibition, and markedly reduced photosynthetic efficiency of M. micrantha.

Acmella radicans (Jacquin) R.K.Jansen is an annual herb native to Central America. In China, it is becoming increasingly invasive and often co-occurs with the native congener A. paniculata (Wall. ex DC.) R.K.Jansen in some habitats. In order to understand the invasion mechanism of A. radicans, we investigated the growth parameters of both the invasive A. radicans and the native congener, A. paniculata, under different light conditions (5%, 25%, 50%, 75%, and 100% of light availability) using potted plants in a glasshouse. Light level, plant species, and their interaction were significant, with plant species generally having a greater effect than light level. Acmella radicans and A. paniculata showed great phenotypic plasticity to various light intensities and had a similar trend with increased shade. The plasticity indices of all parameters of A. radicans, except for branch length and inflorescence number, were greater than those of A. paniculata under the same light intensity. The physiological parameters for A. radicans under both favorable (high light intensity) and unfavorable (low light intensity) conditions showed less inhibition than those of A. paniculata. All these responses indicated that A. radicans had greater phenotypic plasticity and higher adaptability to low light, which may contribute to its invasion success.

Research on the potential distribution of invasive plants and their biological control agents under climate change is critical for informing strategies in invasive species management. The rust fungus Puccinia spegazzinii shows significant potential as a biological control agent for the invasive weed Mikania micrantha. The MaxEnt (Maximum Entropy) model was used to simulate the distribution of M. micrantha and P. spegazzinii under current and future climate scenarios. The models achieved excellent prediction performance, with M. micrantha and P. spegazzinii having area under the curve values of 0.921 and 0.978 respectively, and true skill statistics values of 0.886 and 0.902 respectively. Precipitation is the primary factor influencing the distributions of M. micrantha, while P. spegazzinii is determined by both temperature and precipitation. The suitable areas for the two species are concentrated in southern China, with M. micrantha exhibiting broader adaptability compared to P. spegazzinii. Under future climate scenarios, the suitable areas for M. micrantha in China will expand northward, with a maximum projected growth rate of 84.6 % in the 2070 s, whereas P. spegazzinii exhibits a contracting trend (with a projected reduction of 40.8 % in the 2050 s). Under the current climate scenario, the overlapping suitable areas between the two species account for 25.2 % of the total suitable area for M. micrantha and 100 % of that for P. spegazzinii and both remain relatively stable under future climate scenarios. This work can provide guidance for the application of biological control, and serves as a valuable reference for developing early warning and management response strategies for invasive species in China.

The allelopathic effects have not previously been studied for Acmella radicans (Jacquin) R. K. Jansen, a new invasive species recorded for Yunnan Province, China. In the current study, the allelopathic potential of root, stem, leaf, flower, and fruit head aqueous extracts from A. radicans on two important vegetable crops, Brassica rapa (field mustard) and Chrysanthemum coronarium (garland daisy), was explored in the laboratory. All four plant part aqueous extracts had some inhibitory effects on B. rapa and C. coronarium in terms of seed germination and seedling growth. Increasing concentrations of aqueous extracts of A. radicans reduced many indicators significantly, including germination rate, the seed germination index, root length, stem length, and biomass of B. rapa and C. coronarium. Generally, the most inhibited parameter was root length, followed by shoot length and biomass, with the lowest being seed germination. In terms of allelopathic response index, flowers and fruit heads yielded the strongest inhibition, followed by leaves and stems, with the lowest impact from root extracts. Root extracts had positive effects at 0.0125–0.025 g·mL−1. The inhibition rates for A. radicans extracts on B. rapa were generally higher than those of C. coronarium. It is concluded that A. radicans has allelopathic potential on vegetable crops with the overall inhibition rates ranked in the order flower and fruit head > leaf > stem > root. This was the first study to show that the allelopathic potential of A. radicans against crops may be strongly linked to its invasion and expansion.

BACKGROUND:Weeds resistant to herbicides pose significant challenges in crop production, making early resistance monitoring crucial for timely control of resistant weeds. Prolonged use of ACCase-inhibiting herbicides, like pinoxaden, has led to the evolution of high-level resistance in weed populations over time. American sloughgrass (Beckmannia syzigachne), is a noxious grass weed, that severely impacts the yield and quality of wheat and rapeseed crops. RESULTS:To accurately and rapidly detect the mutations in the target gene of B. syzigachne, we developed a novel rapid detection method based on the CRISPR-Cas12b/sgRNA system to evaluate the target mutation at amino acid position 1781 of the ACCase gene. By optimizing various reaction conditions, the novel detection system can assess target-site resistance of B. syzigachne to pinoxaden within 40 min at a constant temperature of 54 °C. This novel system exhibits excellent specificity, high sensitivity, simplicity in procedure, also with time-efficient and high throughput. CONCLUSION:This study presents an efficient method based on the CRISPR-Cas12b system for rapidly detecting the target-site resistance, which will facilitate the precise management of resistant weeds. © 2025 Society of Chemical Industry.

Acmella radicans (Jacquin) R.K. Jansen is a new invasive species recorded in Yunnan Province, China, and little is known about its allelopathic potential and allelochemicals. In this study, the allelopathic effects of the essential oil (EO) of A. radicans on seed germination and seedling growth of four common plants, Brassica napus, Brassica rapa ssp. chinensis, Digitaria sanguinalis, and Lolium multiflorum, were explored. The results showed that the seed germination index, germination rate, root length, stem length, and biomass of B. napus and B. rapa ssp. chinensis were significantly inhibited at all EO concentrations of A. radicans, but there was a ‘low-promotion and high-inhibition effect’ on the root length of D. sanguinalis and L. multiflorum at low concentrations of 0.5 μL·mL−1 and 0.5–1.0 μL·mL−1, respectively. With increasing concentrations of EO, the inhibition rates of seed germination and seedling growth of four common plants gradually increased, and D. sanguinalis and L. multiflorum were the most inhibited, followed by B. rapa ssp. chinensis, and the least inhibited was B. napus. Thirty-two components were identified using GC–MS, representing 99.07% of the EO in A. radicans. The major components were 2-tridecanone (30.46%), caryophyllene oxide (19.18%), 4,8,11,11-tetramethylbicyclo[7.2.0]undec-3-en-5-ol (7.84%), β-caryophyllene (7.67%), and widdrol (4.7%). Among the compounds we identified, (E,E)-2,4-decadienal, 2-tridecanone, γ-cadinene, δ-cadinene, (E)-α-cadinol, spathulenol, caryophyllene oxide, and widdrol have been previously reported as having possible allelopathic effects. Our study was the first to show that A. radicans could potentially release allelochemicals to influence neighboring plants during its invasion and expansion.

To examine the effects of the recent Acmella radicans invasion on plant community and diversity in invaded habitats, the composition, density, species richness, diversity indices, and evenness index of the soil seed bank community of two different habitats (wasteland and cultivated land) in Yunnan Province, China, were analyzed through field sampling and greenhouse germination tests. A total of 28 species of plants belonging to 15 families and 28 genera, all annual herbs, were found in the soil seed bank. Seed densities and species number in the seed bank tended to be greater in April than in October; cultivated land also featured higher seed densities and species numbers compared to wasteland. With increased A. radicans cover, the seed bank population of A. radicans also significantly increased, but the seed bank populations of many other dominant species (e.g., Ageratum conyzoides and Gamochaeta pensylvanica) and native species (e.g., Laggera crispata and Poa annua) clearly declined. The germination of A. radicans seeds was concentrated during the period from the 4th to the 5th weeks. Vertically, the seed number of A. radicans was significantly different among the 0-5 cm, 5-10 cm and 10-20 cm layers that accounted for 80.7-90.6%, 9.4-16.1% and 0.0-3.2% of the total seed density in wasteland, respectively; and in cultivated land, A. radicans accounted for 56.8-64.9%, 26.7-31.8% and 8.1-13.5% of the total seed density, respectively. With reduced A. radicans cover, the species richness, Simpson index, Shannon-Wiener index, and Pielou indices of the weed community generally increased, and most diversity indices of weed communities in cultivated land were lower than in wasteland under the same cover of A. radicans. The results indicate that the invasion of A. radicans has negatively affected local weed community composition and reduced weed community diversity, and that these negative impacts in cultivated land may be enhanced by human disturbance. Our study was the first to elucidate the influence of A. radicans invasion on soil seed bank community characteristics in invaded habitats, providing a better understanding of its invasion and spread mechanisms in order to aid in developing a scientific basis for the prevention and control of this invader.

Acmella radicans (Jacquin) R.K. Jansen is a new invasive species record for Yunnan Province, China, as of 2017 and little is known about its invasion mechanisms. To better understand its invasive strategies, we investigated the growth, physiological and soil nutrient use parameters of the invader under combined conditions of light (25%, 50%, 75%, and 100% of light availability) and soil water content (full, high, medium, and low soil water content) in the glasshouse. The results showed that light level, soil water content and their interaction had a significant effect on all plant morphological, physiological and soil nutrient parameters for A. radicans (P < 0.05). For the most part, plant height, total branch length, leafstalk length, leaf area, inflorescence number, seed number, leaf biomass, stem biomass, aboveground biomass, and total biomass of A. radicans were significantly increased with increased shading rate and soil water content and were generally greater at intermediate light levels and intermediate to high soil water levels. Under high-irradiance conditions, the chlorophyll content was greatly reduced compared to other treatments. We also observed that leafstalk length, leaf area, Pn, chlorophyll a, and chlorophyll b of A. radicans were markedly increased with increased shading rate and soil water content, and were generally highest under intermediate irradiance and soil water conditions, but many plant physiological parameters also exhibited relatively high values under waterlogging conditions. The concentrations of organic matter, available N and available K of A. radicans soils at high-irradiance and full-high soil water content treatments and medium-irradiance and high-medium soil water content treatments were often less than those of other treatments indicated that hypothetically soil absorption was increased by moderate shading and high soil water. This was the first study demonstrating that A. radicans thrives best under moderate light conditions in combination with high soil water. Furthermore, we surmised that its higher phenotypic and physiological plasticity contributes to its invasion success.

Abstract Background Growing allelopathic crops to control invasive weeds is considered as an environmental friendly, and economically sustainable approach, understanding the reasons are essential for current and future green control of invasive weeds. Phalaris minor Retz. is one of the most troublesome invasive weeds worldwide. Our previous studies found that rapeseed(Brassica juncea)exhibited strong inhibitory effects of this weed in agroecosystems, but it is unknown whether allelopathic effects are involved in this process. In this study, we assessed the allelopathic effects of B. juncea to P. minor, then, allelochemicals were separated and identified from its leaves, further, biological activity and physiological responses by some individual compounds were investigated. Results Our results showed that water extracts from roots, stems, and leaves of B. juncea have strong allelopathic potential which can significantly inhibit the seedling growth of P. minor, and leaves have the strongest allelopathic inhibitory effects. Different solvents extracts from leaves water extracts of B. juncea significantly inhibited seed germination and seedling growth of P. minor at higher concentration (20 mg/mL), but no significantly inhibited at lower concentration (1.25 mg/mL), allelopathic effects of different solvents extracts were ranked in order from petroleum ether (strongest), ethyl acetate (moderate), N-butyl alcohol, and residual water (least). The petroleum ether extracts of B. juncea affected the protective oxidase activity and chlorophyll content, resulting in a significant increase of malondialdehyde (MDA) content and a significant reduced superoxide dismutase (SOD) activity and chlorophyll content of P. minor. Twenty-one components were identified by GS-MS, with proportion of 96.47% of petroleum ether extracts of B. juncea. The major components were erucic acid (EA) (19.08%), palmitic acid(PA) (14.16%), dibutyl phthalate(DP) (13.19%), ethyl palmitate(EP) (12.31%), linoleic acid(LA) (9.43%), and oleic acid(OA) (6.24%), among which components PA, EP, and LA exhibited strong inhibitory activity against P. minor. Conclusions Overall, these relults suggested that B. juncea has strong allelopathic inhibitory effect on P. minor, and PA, EP and LA were major compounds of petroleum ether extract of B. juncea and exhibited strong inhibitory activity against P. minor, suggested that B. juncea can be used for ecological control and developing environmentally friendly herbicides to control P. minor.

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

BACKGROUND ACMELLA RADICANS: (Jacquin) R.K. Jansen is a new invasive species record for Yunnan Province, China. Native to Central America, it has also been recently recorded invading other parts of Asia. To prevent this weed from becoming a serious issue, an assessment of its ecological impacts and potential distribution is needed. We predicted the potential distribution of A. radicans in China using the MaxEnt model and its ecological impacts on local plant communities and soil nutrients were explored. RESULTS: Simulated training using model parameters produced an area under curve value of 0.974, providing a high degree of confidence in model predictions. Environmental variables with the greatest predictive power were precipitation of wettest month, isothermality, topsoil TEB (total exchangeable bases), and precipitation seasonality, with a cumulative contribution of more than 72.70% and a cumulative permutation importance of more than 69.20%. The predicted potential suitable area of A. radicans in China is concentrated in the southern region. Projected areas of A. radicans ranked as high and moderately suitable comprised 5425 and 26,338 km2, accounting for 0.06 and 0.27% of the Chinese mainland area, respectively. Over the 5 years of monitoring, the population density of A. radicans increased while at the same time the population density and importance values of most other plant species declined markedly. Community species richness, diversity, and evenness values significantly declined. Soil organic matter, total N, total P, available N, and available P concentrations decreased significantly with increasing plant cover of A. radicans, whereas pH, total K and available K increased. CONCLUSION: Our study was the first to show that A. radicans is predicted to expand its range in China and may profoundly affect plant communities, species diversity, and the soil environment. Early warning and monitoring of A. radicans must be pursued with greater vigilance in southern China to prevent its further spread.

Introduction:In natural systems, diverse plant communities tend to prevent a single species from dominating. Similarly, management of invasive alien plants may be achieved through various combinations of competing species.Methods:We used a de Wit replacement series to compare different combinations of sweet potato (Ipomoea batatas (L.) Lam), hyacinth bean (Lablab purpureus (L.) Sweet) and mile-a-minute (Mikania micrantha Kunth) through measures of photosynthesis, plant growth, nutrient levels in plant tissue and soil, and competitive ability.Results:Cultured alone sweet potato and hyacinth beans exhibited higher total biomass, leafstalk length, and leaf area than mile-a-minute. In mixed culture, either sweet potato or hyacinth bean or both together significantly suppressed the mile-a-minute parameters, i.e., plant height, branch, leaf, adventitious root, and biomass (P<0.05). Based on a significantly lower than 1.0 relative yield of the three plant species in mixed culture, we showed intraspecific competition to be less than interspecific competition. Calculated indices (relative yield, relative yield total, competitive balance index, and change in contribution) demonstrated a higher competitive ability and higher influence of either crop compared to mile-a-minute. The presence of sweet potato and hyacinth bean, especially with both species in combination, significantly reduced (P<0.05) mile-a-minute's net photosynthetic rate (Pn), antioxidant enzyme activities (superoxide dismutase, peroxidase, catalase, and malondialdehyde), chlorophyll content, and nutrient content (N, P, and K). In soil with mile-a-minute in monoculture soil organic matter, total and available N, total and available K, and available P were significantly greater (P<0.05) than in soil with sweet potato grown in monoculture, but less than in soil with hyacinth bean grown in monoculture soil. Nutrient soil content was comparatively reduced for plant mixtures. Plant height, leaf, biomass, Pn, antioxidant enzyme activities, and plant and soil nutrient contents of sweet potato and hyacinth bean tended to be much greater when grown with two crops compared to in mixture with just sweet potato or hyacinth bean.Discussion:Our results suggest that the competitive abilities of both sweet potato and hyacinth bean were greater than that of mile-a-minute, and also that mile-a-minute suppression was significantly improved via a combination of the two crops compared to either sweet potato or hyacinth bean alone.

研究旨在掌握入侵杂草——加拿大一枝黄花在云南省的发生发展情况,并提出对其防控策略,防止进一步的传播扩散.于2020年5月—2022年5月通过走访调查,分析和研究加拿大一枝黄花在云南省的入侵分布情况.结果表明,该入侵植物在云南尚处于零散点状发生状态,个别地区有入侵农田的情况发生,且这些发生点是以有意引入或无意传播途径为主.加拿大一枝黄花在云南多地发生,且有蔓延发展的趋势,应加强管控并及时防除.

[目的]研究替代物种与选择性除草剂,以实现对紫茎泽兰安全、高效和绿色的防控.[方法]采用植物间竞争试验法测定替代物种(高丹草、非洲狼尾草和黑麦草)和除草剂对紫茎泽兰的防效及其互作效应.[结果]高丹草、非洲狼尾草和黑麦草的竞争力依次强于紫茎泽兰.随着3种替代物种密度比例增加,紫茎泽兰的株高、分枝、根冠比、叶面积比均受到显著抑制,当替代物种与紫茎泽兰密度比为5:1时,高丹草、非洲狼尾草和黑麦草对紫茎泽兰的替代控制效果分别为55.1％、46.9％和40.3％.除草剂氨氯吡啶酸、三氯吡氧乙酸、氯氟吡氧乙酸和二氯吡啶酸的毒力测定表明,二氯吡啶酸相对最高,LC90为902.1 g·hm-2,但三氯吡氧乙酸对替代物种的安全性相对最好,对高丹草、非洲狼尾草和黑麦草选择性指数分别为3.75、2.79和2.67.高丹草和非洲狼尾草与紫茎泽兰种植密度比例为3:1时,结合二氯吡啶酸和三氯吡氧乙酸,非洲狼尾草和二氯吡啶酸结合表现拮抗作用,与三氯吡氧乙酸结合表现加成作用;高丹草和二氯吡啶酸结合表现加成作用,与三氯吡氧乙酸结合表现增效作用,在同等取得90％防效的情况下,可减少三氯吡氧乙酸用量20.0％～35.0％(即210.0～370.0 g·hm-2).[结论]合理的替代物种结合除草剂应用可实现互作增效,可作为紫茎泽兰综合防控的重要措施.

Sweet potato [Ipomoea batatas (L.) Lam] is grown as important cash and food crop worldwide and has been shown to exhibit allelopathic effects on other plants. However, its metabolome has not been studied extensively, particularly with respect to the production of phytotoxic bioactive secondary products. In this study, the chemical composition of petroleum ether extract of sweet potato was characterized, and the morphological and physiological effects of some individual components against four invasive alien weeds Bidens pilosa L., Galinsoga parviflora Cav., Lolium multiflorum Lam., and Phalaris minor Retz. were determined. Twenty-one components were identified by GS-MS, constituting 96.08% of petroleum ether extract in sweet potato. The major components were palmitic acid (PA) (17.48%), ethyl linoleate (EL) (13.19%), linoleic acid (LA) (12.55%), ethyl palmitate (EP) (11.77%), ethyl linolenate (ELL) (8.29%) oleic acid (5.82%), ethyl stearate (4.19%), and 3-methylphenol acetate (3.19%). The five most abundant compounds exhibited strong inhibition activity against the four invasive weeds tested. The highest inhibition rates were seen for LA, followed by PA and EP, respectively. Catalase (CAT), malondialdehyde (MDA), and peroxidase (POD) content of L. multiflorum were increased by the three allelochemicals, i.e., LA, PA and EP, but superoxide dismutase (SOD), chlorophyll-a and chlorophyll-b levels declined. Overall, the combined impact of all five compounds could be quite effective in suppressing the invasive weeds of concern.

Using crops to control invasive weeds is an important approach for the long-term management of invasive species in agroecosystems. Nitrogen application can improve the yield and quality of crops, but may shift interactions of invasive weeds and crops, potentially affecting grass control ability. To explore the yield of a crop and its control efficacy of invasive weed under different nitrogen conditions, we studied the competitive effects of the high-value crop rapeseed (Brassica napus L.) on growth and photosynthetic characteristics of invasive species littleseed canarygrass in the field experiments. The results showed that the rapeseed yield and its control efficacy on littleseed canarygrass were significantly affected (p < 0.05) under different N regimes, and the control efficacy of littleseed canarygrass by rapeseed increased first and then decreased with the increase of basal nitrogen rates, while increasing topdressing N rates increased control efficacy of littleseed canarygrass by rapeseed. In fact, yield and weed control efficacy of rapeseed was most ideal when both basal and topdressing N was 90 kg·ha−1. We also found that N significantly impacted the competitive ability of rapeseed toward littleseed canarygrass, and rapeseed had the highest competitive ability when both basal and topdressing N was 90 kg·ha−1. With the increase of basal nitrogen rates, competitive balance index (CB) of rapeseed increased initially but decreased beyond an optimal level. CB continually increased with increasing topdressing N rates. Our research also showed level and period of N application had a significant effect (p < 0.01) on the photosynthetic rate (Pn) and chlorophyll content (Chl) of both rapeseed and littleseed canarygrass. Under the same N application regime, the Pn and Chl of littleseed canarygrass were higher than that of rapeseed in December, while the Pn and Chl of rapeseed was higher than that of littleseed canarygrass in February. Our study indicated that photosynthetic characteristics of rapeseed and littleseed canarygrass in different growth stages differ in their sensitivity to N regimes, creating a dynamic competitive relationship. Together, our results demonstrated that optimal application of fertilizer N could help rapeseed produce higher yields and greater weed control efficacy, suggesting that future modeling or experimental studies on utilizing crops to control invasive weeds should carefully consider both timing and placement of N.

本研究通过盆栽试验和生物测定试验,分别研究了 9个不同农艺性状的甘薯品种对三叶鬼针草Bidens pi-losa和粗毛牛膝菊Galinsoga quadriradiata的竞争作用和化感作用.结果表明,'烟薯25''宁薯10号'和'西瓜红普薯'等6个品种的竞争平衡指数(CBa)大于0,其中'宁薯10号'的竞争优势最强,对三叶鬼针草的株高和根长的抑制率分别为62.29％和63.31％;生物测定中仅有'17234'和'宁薯10号'两个品种表现出明显的化感作用,其中'17234'的化感作用指数(AD最大,对粗毛牛膝菊的株高和根长的抑制率分别为74.32％和82.58％.结合甘薯品种的竞争作用与化感作用进行聚类分析和综合评价,'宁薯10号'的CBa和AI分别达0.74和0.63以上,为竞争作用和化感作用均较强的抗(耐)性品种;'烟薯25,虽然对两种入侵杂草的CBa分别达到0.85和0.70,但其AI＜0.1,表现为具有竞争优势的非化感品种;尽管'17234'的CBa＜0,但其AI＞0.67,说明其为强化感作用的品种.结果表明,甘薯对入侵杂草的抗(耐)性决定于其自身的竞争作用、化感作用或两者的共同作用.这为进一步利用甘薯不同品种对入侵杂草的种间关系实施替代控制提供了科学基础.