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Biological invasions are a great threat to biodiversity. Invasive plants targeted for control with introduced biological control agents are also exposed to indigenous herbivores in the invaded range. The density of native herbivores may affect the interactions between biological control agents and those native herbivores. We conducted a common-garden experiment to examine the interactive effects between a native natural enemy, the root-knot nematode Meloidogyne incognita (Kofold & White), and the leaf beetle Agasicles hygrophila Selma & Vogt, an introduced biological control agent of the invasive alligator weed, Alternantera philoxeroides (Mart.) Griseb., and its native congener Alternantera sessilis (Linn.) DC. We also manipulated the density of the two herbivores to examine the role of herbivore density in modulating plant–herbivore interactions. We found that (1) the performance of A. hygrophila on A. philoxeroides was inhibited by the nematode regardless of nematode initial density, (2) A. philoxeroides plants subject to herbivory by two beetles had more leaves and fine roots under the high nematode density than those not exposed to nematodes, and (3) the stem diameter of A. philoxeroides subject to herbivory by one beetle was smaller under the moderate nematode density than for plants not exposed to nematodes. However, under the high initial nematode density, both the native and introduced plants had fewer root-knots when co-exposed to herbivory by one beetle than when co-exposed to plants with two beetles. Under the high initial nematode density, A. philoxeroides produced more aboveground biomass but less root biomass than did plants not exposed to nematodes. However, A. sessilis plants exposed to the high initial nematode density produced more root biomass but produced similar aboveground biomass than did plants not exposed to nematodes. These findings suggest that the biological control efficiency of biological control agents may be potentially affected by other herbivores such as nematodes from the soil, and herbivores’ densities may determine the nature of the interactive impacts among multiple herbivores on invasive plants.

We investigated the antibacterial activity of alligator weed (Alternanthera philoxeroides) organic extracts against three bacterial phytopathogens (Erwinia carotovora, Ralstonia solanacearum and Xanthomonas axonopodis). The extracts were prepared by soaking the dry powder of leaf, stem and root of A. philoxeroides into methanol, n-hexane, chloroform and ethyl acetate. The disk diffusion method was used to determine the antibacterial activity at 100 mg/mL extract concentration. The n-hexane extract of A. philoxeroides leaves showed the maximum inhibition zone diameter (IZD)= 28.1 mm against R. solanacearum, while, the corresponding value for the positive control (Penicillin) was 48 mm IZD. There was no antibacterial activity of negative control, dimethyl sulfoxide (DMSO). Gas Chromatography Mass-Spectrometry (GC-MS) analysis revealed the presence of acetic acid, 2-(2-methoxycarbonylamino-5-nitrophenylthio)-, methyl ester, at the highest concentration (31.9 %), followed by 1, 4-benzenediol, 2, 5-bis (1,1-dimethylethyl)- (15.06 %),. It was concluded that the observed biological activity in this study may be due to the presence of these compounds.

Although it is well-documented that invasion of invasive plants is promoted with allelopathic effects by inhibiting the growth and phenotypic performance of native plants, little is known conversely. In this study, the allelopathy effects of a native plant, Humulus scandens (Lour.) Merr., on a typical invasive species Alternanthera philoxeroides (Mart.) Griseb., was investigated by exposing A. philoxeroides seedlings to three chemical solvent extracts (i.e., petroleum ether extract (PE), ethyl acetate extract (EE), and n-butanol extract (NE) of H. scandens root (HR). The three chemical extracts inhibited the growth, stem length, node number, leaf number, leaf area, and root number, and increased malondialdehyde (MDA) content of A. philoxeroides seedlings, which indicated that the extracts inhibited the plant growth by damaging the membrane system of leaves. And the synthetical effect of allelopathy (SE) index indicated that EE had the greatest inhibition on the growth of A. philoxeroides. Fifty compounds were identified from the three extracts of HR using GC–MS analysis, among which 5 compounds (dibutyl phthalate, stigmasta-3,5-diene, 2,6-Di-tert-butylphenol campesterol, and neophytadiene) were identified from H. scandens root extracts for the first time. And n-hexadecanoic acid exists in all three extracts. The findings of the present study provide a novel method to potentially control the invasion of A. philoxeroides. However, field monitoring under natural conditions would be necessary to confirm in practice the results obtained with the bioassays.

Background and Aims Plant invasions can change soil microbial communities and affect subsequent invasions directly or indirectly via foliar herbivory. It has been proposed that invaders promote uniform biotic communities that displace diverse, spatially variable communities (the biotic homogenization hypothesis), but this has not been experimentally tested for soil microbial communities, so the underlying mechanisms and dynamics are unclear. Here, we compared density-dependent impacts of the invasive plant Alternanthera philoxeroides and its native congener A. sessilis on soil fungal communities, and their feedback effects on plants and a foliar beetle. Methods We conducted a plant–soil feedback (PSF) experiment and a laboratory bioassay to examine PSFs associated with the native and invasive plants and a beetle feeding on them. We also characterized the soil fungal community using high-throughput sequencing. Key Results We found locally differentiated soil fungal pathogen assemblages associated with high densities of the native plant A. sessilis but little variation in those associated with the invasive congener A. philoxeroides, regardless of plant density. In contrast, arbuscular mycorrhizal fungal assemblages associated with high densities of the invasive plant were more variable. Soil biota decreased plant shoot mass but their effect was weak for the invasive plant growing in native plant-conditioned soils. PSFs increased the larval biomass of a beetle reared on leaves of the native plant only. Moreover, PSFs on plant shoot and root mass and beetle mass were predicted by different pathogen taxa in a plant species-specific manner. Conclusion Our results suggest that plant invasions can rapidly increase the similarity of soil pathogen assemblages even at low plant densities, leading to taxonomically and functionally homogeneous soil communities that may limit negative soil effects on invasive plants.

The purpose of this study was to develop an independent multi-criteria model to predict the growth of invasive Alternanthera philoxeroides under salt stress. Artificial neural-networks with Multi-L...

The cyanobacteria Microcystis flos-aquae can cause harmful algal blooms in waterbodies, which threaten the normal functioning of aquatic ecosystems and human health. Some plant extracts are considered as promising algaecides. In this study, the effects of ten plant extracts (Cinnamomum camphora, Ginkgo biloba, Firmiana platanifolia, Salix babylonica, Euphorbia humifusa, Erigeron annuus, Solidago canadensis, Alternanthera philoxeroides, Thalia dealbata and Eichhornia crassipes) against M. flos-aquae were investigated. The results showed that all ten plant extracts had a significant inhibitory effect on M. flos-aquae growth after 96 h (P < 0.01). The inhibition rates of S. babylonica, E. humifusa, S. canadensis and A. philoxeroides were over 70.00%. Furthermore, the E. humifusa extract had the best inhibitory effect on the photosynthesis of M. flos-aquae, with the effective quantum yield of photosystem II and maximal relative electron transport rate decreasing by 97.50% and 97.00%, respectively, after 96 h. Additionally, the E. humifusa extract was found to be non-toxic to non-target organisms such as Brachydanio rerio and Vallisneria spiralis within 96 h. This study contributes to the existing knowledge and data of freshwater cyanobacteria blooms, and provides insights for their control and the restoration of freshwater systems affected by cyanobacteria blooms.

Alternanthera philoxeroides (Mart.) Griseb. (Alternanthera philoxeroides) is an important herbage species, which could provide high-quality feed for livestock and poultry breeding. This paper is the first to report the A. philoxeroides's chloroplast genomes, which were detected by de novo sequencing. The results showed that the length of A. philoxeroides' chloroplast genome sequence was 152,255 bp, including a large single-copy (LSC) region (84,670 bp), a small single-copy (SSC) region (17,343 bp), and two inverted repeat (IR) regions (25,121 bp). Alternanthera philoxeroides' chloroplast genome encoded 132 genes including 8 rRNA, 38 tRNA, and 86 protein-coding genes. After phylogenetic and cluster analysis, A. philoxeroides was closest to Amaranthaceae, and the relationship between Amaranthus and Achyranthes was closest.

Parasitic plants represent a peculiar and highly specialized group and are important members of terrestrial ecosystems. Although much is known about how parasitic plants influence growth, reproduction, physiology, and metabolism of host plants, their possible role as modulators of microbial community properties remains largely unexplored. Using next-generation sequencing of the bacterial 16S rRNA gene and fungal rRNA internal transcribed spacer, we analyzed the effects of parasitism on both composition and diversity of soil microbial communities in the rhizosphere of an invasive species Alternanthera philoxeroides parasitized by Cuscuta australis, and feedback effects of parasitism-altered soil microbes on the growth of the host (A. philoxeroides) and on the co-existing native Trifolium repens. Cuscuta australis parasitism increased alpha-diversity and changed the composition of both bacterial and fungal community in the rhizospheric soil of A. philoxeroides. Alternanthera philoxeroides produced significantly less plant biomass when grown in soils inoculated with microbial communities of A. philoxeroides parasitized by C. australis compared to non-parasitized soils and control soils, whereas T. repens produced significantly more biomass grown in soils inoculated with microbial communities of A. philoxeroides parasitized by C. australis. Inoculation with soil microbial communities of A. philoxeroides not parasitized by C. australis increased the competitiveness of A. philoxeroides to neighboring T. repens, whereas, inoculation with soil microbial communities of A. philoxeroides parasitized by C. australis reduced the competitiveness of A. philoxeroides. These results suggest that plant parasitism-induced changes in soil microbiome can negatively affect host plant growth, and positively affect the growth of the native neighbor plants, via shift of the competitive hierarchy between the host and co-existing native plants.

AimsRecent studies have revealed heritable phenotypic plasticity through vegetative generations. In this sense, changes in gene regulation induced by the environment, such as DNA methylation (i.e. epigenetic changes), can result in reversible plastic responses being transferred to the offspring generations. This trans-generational plasticity is expected to be especially relevant in clonal plants, since reduction of sexual reproduction can decrease the potential for adaptation through genetic variation. Many of the most aggressive plant invaders are clonal, and clonality has been suggested as key to explain plant invasiveness. Here we aim to determine whether trans-generational effects occur in the clonal invader Alternanthera philoxeroides, and whether such effects differ between populations from native and non-native ranges.MethodsIn a common garden experiment, parent plants of A. philoxeroides from populations collected in Brazil (native range) and Iberian Peninsula (non-native range) were grown in high and low soil nutrient conditions, and offspring plants were transplanted to control conditions with high nutrients. To test the potential role of DNA methylation on trans-generational plasticity, half of the parent plants were treated with the demethylating agent, 5-azacytidine.Important FindingsTrans-generational effects were observed both in populations from the native and the non-native ranges. Interestingly, trans-generational effects occurred on growth variables (number of ramets, stem mass, root mass and total mass) in the population from the native range, but on biomass partitioning in the population from the non-native range. Trans-generational effects of the population from the native range may be explained by a ‘silver-spoon’ effect, whereas those of the population from the non-native range could be explained by epigenetic transmission due to DNA methylation. Our study highlights the importance of trans-generational effects on the growth of a clonal plant, which could help to understand the mechanisms underlying expansion success of many clonal plants.

The successful invasion of alligator weed (Alternanthera philoxeroides) into both aquatic and dry terrestrial environments has been attributed to its phenotypic plasticity and high rates of growth and vegetative propagation. Here, we evaluated whether the anatomical structures of alligator weed make it well adapted to colonize the aquatic-terrestrial transition zone. Anatomical and histochemical analysis revealed an impermeable apoplastic barrier that consists of a cuticle and an endodermis of the adventitious root and stem in both aquatic and terrestrial environment; stem and root possess a periderm in the terrestrial environment; and the root has a lignified cortex and hypodermis in the aquatic environment. A supernumerary cambia produces secondary vascular bundles, parenchyma and adventitious buds. Dilated parenchyma cells exist in the aged terrestrial roots. Aerenchyma tissue and pith cavities in the roots and stems produce air spaces, and the aquatic roots possess large aerenchyma compared with intercellular aerenchyma of terrestrial roots. In summary, phenotypic plasticity of anatomical characters, such as impermeable apoplastic barriers, air spaces, and reproductive supernumerary cambia, may be evidence that alligator weed is well adapted to the aquatic–terrestrial transition zone.

The plant–herbivore interaction is one of the most fundamental interactions in nature. Plants are sessile organisms, and consequently rely on particular strategies to avoid or reduce the negative impact of herbivory. Here, we aimed to determine the defense strategies against insect herbivores in the creeping invasive plant Alternanthera philoxeroides. We tested the defense response of A. philoxeroides to herbivory by a leaf-feeding specialist insect Agasicles hygrophila and a polyphagous sap-feeding insect Planococcus minor. We also tested the mechanisms triggering defense responses of A. philoxeroides by including treatments of artificial leaf removal and jasmonic acid application. Furthermore, we examined the effect of physiological integration on these defense strategies. The combination of artificial leaf removal and jasmonic acid application produced a similar effect to that of leaf-feeding by the real herbivore. Physiological integration influenced the defense strategies of A. philoxeroides against herbivores, and increased biomass allocation to aboveground parts in its apical ramets damaged by real herbivores. Our study highlights the importance of physiological integration and modular plasticity for understanding the consequences of herbivory in clonal plants.

Clonal integration, i.e. resource sharing between interconnected ramets, can help clonal plants tolerate abiotic stress. However, few studies have directly examined the ecological significance of clonal integration in the ability of clonal plants to tolerate biotic stress such as herbivory. We grew clonal fragments of an invasive clonal plant Alternanthera philoxeroides, each consisting of an apical part (relatively young) and a basal part (relatively old), at two levels (low and high) of soil nitrogen (N). For each fragment, the apical part was subjected to either no herbivory or herbivory for 2 weeks by a specialist insect, Agasicles hygrophila, and was either connected with or disconnected from the basal part not subjected to herbivory. Herbivory in the apical part severely reduced leaf growth (leaf mass, leaf number or leaf area) and ramet production of both apical and basal parts, and increased root to shoot ratio of the apical part. Irrespective of herbivory and soil N, stem connection between the apical and the basal part decreased root to shoot ratio of the apical part, but did not change its growth measures. Meanwhile, connection increased stem N concentration of the apical part growing under high-N supply and decreased stem carbon (C) concentration of the apical part under low-N supply. By contrast, connection increased root to shoot ratio of the basal part, but reduced its leaf and ramet production. Connection also increased leaf and stem C concentrations of the basal part under low-N supply. Thus, clonal integration can be beneficial for the early development of young A. philoxeroides ramets, but not for their local adaptation to herbivory damage by A. hygrophila.

Se informa de la presencia de la especie exótica invasora Alternanthera philoxeroides en el río Guadalquivir, en Sevilla (España, S. de la Península Ibérica). El hallazgo corresponde a la primera cita para Andalucía y se añade a las otras dos que ya existían para la Península Ibérica. Palabras clave: especies exóticas, corología, flora vascular, Península Ibérica, plantas acuáticas, río Guadalquivir. We report the presence of the invasive alien species Alternanthera philoxeroides in the river Guadalquivir, in Seville (Spain, Southern Iberian Peninsula). This finding is the first record for Andalusia and it is added to the other two that have been already published for the Iberian Peninsula.

Herbivorous insects use plant volatile compounds to find their host plants for feeding and egg deposition. The monophagous beetle Agasicles hygrophila uses a volatile (E)-4,8-dimethyl-1,3,7-nonanetriene (DMNT) to recognize its host plant Alternanthera philoxeroides. Alternanthera philoxeroides releases DMNT in response to A. hygrophila attack and nerolidol synthase (NES) is a key enzyme in DMNT biosynthesis; however, the effect of A. hygrophila on NES expression remains unclear. In this study, the A. philoxeroides transcriptome was sequenced and six putative NES genes belonging to the terpene synthase-g family were characterized. The expression of these NES genes was assayed at different times following A. hygrophila contact, feeding or mechanical wounding. Results showed that A. hygrophila contact and feeding induced NES expression more rapidly and more intensely than mechanical wounding alone. This may account for a large release of DMNT following A. hygrophila feeding in a previous study and subsequently facilitate A. hygrophila to find host plants. Our research provides a powerful genetic platform for studying invasive plants and lays the foundation for further elucidating the molecular mechanisms of the interaction between A. philoxeroides and its specialist A. hygrophila.

Invasive plants may have variable effects depending on their interactions with native species, yet few studies have examined the phenomenon of the invasive plant-mediated priming effect. To investigate the priming of invasive species on native leaf litter decomposition, we allocated two native leaf species of contrasting recalcitrance (Neosinocalamus affinis and Ficus virens) in single and double species mixtures with and without invasive Alternanthera philoxeroides, and then incubated them for 65 days in a eutrophic shallow lake. Invasive plant addition promoted decomposition of F. virens and a mixture of two native plants, with positive priming effects of 25.47 % for F. virens and 30.49 % for the mixture based on mass loss, respectively. However, the decomposition of N. affinis was inhibited, with a negative priming of −16.55 %. In total, the associated faunal communities comprised 15 microinvertebrate taxa, 10 meioinvertebrate taxa, and 11 macroinvertebrate taxa. Among these, sarcodina (omnivores) were shared components colonizing all plant materials, while ciliates (filter-collectors) and cladocerans (filter-collectors) mostly colonized the mixture of native species and mixture × A. philoxeroides materials. The abundances of rotifers (filter-collectors) and chironomids (gather-collectors) were the highest in F. virens × A. philoxeroides materials. Compared to the faunal assemblage without A. philoxeroides treatments, the invertebrate richness and abundance, microalgae abundance and microbial respiration were more than one times higher with A. philoxeroides treatments. Our findings indicate that the priming effect can be induced by invasive A. philoxeroides, invertebrate community played an important role in this process.

Many researchers have surveyed damages caused by natural enemies of invasive plants in both native and introduced ranges to test the enemy release hypothesis. In this study, we report our findings on the physiological and morphological impacts of a co-evolved specialist insect (Agasicles hygrophila) and two generalist insects (Atractomorpha sinensis and Hymenia recurvalis) in introduced ranges on an invasive plant, Alternanthera philoxeroides, in both field trials and controlled environments. The resistance of A. philoxeroides against the generalists and the specialist was also studied. We obtained consistent results in both the field trials and the controlled treatments: both the generalists and the specialist decreased leaf biomass, photosynthesis, leaf nitrogen content, and total leaf non-structural carbohydrate content in A. philoxeroides. However, the specialist decreased leaf mass, photosynthesis, and leaf nitrogen content more acutely than the generalists. Moreover, A. philoxeroides increased both leaf lignin and cellulose concentrations upon the generalists’ attack but only increased cellulose concentration in response to the specialist. Our results showed that even under the same population density, the co-evolved specialists from original ranges caused more severe morphological and physiological damage to A. philoxeroides than the generalists in introduced ranges. This revealed that invasive plants released some herbivory stress before their co-evolved specialists were introduced, which may contribute to the superior performance of invasive plants in introduced regions.

Resource sharing between the connected ramets of clonal plants through physiological integration can increase the tolerance of plants to environmental stress. However, the role of physiological integration in the translocation of heavy-metal pollutants between different habitats receives little attention, especially in the aquatic-terrestrial ecotones. An amphibious clonal plant Alternanthera philoxeroides was used to simulate plant expansion from unpolluted soil to a chromium (Cr)-polluted water environment. Basal older ramets growing in unpolluted soil were connected or disconnected with apical younger ramets of the same fragments in polluted environments at different Cr concentrations. Harvested basal ramets were also used for decomposition tests for the loss of residual mass and release of Cr to soil. With increasing Cr concentration there was reduction in biomass of the apical ramets, especially those separated from the basal parts. Cr was detected in the basal ramets with connection to apical parts. The decomposition of plant litter from the basal ramets connected with polluted apical parts might release retained Cr to unpolluted soil. The amount and chemical forms of Cr in the plant litter changed over time. It is concluded that Cr could be transferred from polluted aquatic to unpolluted terrestrial habitats through amphibious clonal plants.

Responses to both submergence and de-submergence are important for evaluating flood tolerance of plants. Clonal integration (resource translocation between connected ramets within clones) has been shown to increase flood tolerance of amphibious clonal plants. However, no study has truly separated the effects of clonal integration during de-submergence from those during submergence. We grew 40 clonal fragments of the amphibious plant species Alternanthera philoxeroides, each consisting of two ramet systems, under half-submerged conditions (one ramet system submerged and the other un-submerged) for 30 d and then de-submerged for 20 d. To evaluate the effects of clonal integration during submergence, stolon connection between the two ramet systems was either severed or not on day 1, and 10 replicates of the fragments of each treatment were harvested on day 30. To evaluate the effects of clonal integration after de-submergence, the remaining 20 clonal fragments with connected stolons during submergence were de-submerged; half of them were subjected to stolon severing on day 31 and the remaining 10 fragments were not. All the 20 fragments for de-submergence were harvested on day 50. After 30 d of submergence, stolon connection between the submerged and the un-submerged ramets significantly increased growth, biomass allocation to roots and photosynthetic capacities of the submerged ramets, and also increased growth and photosynthetic capacities of the un-submerged ramets. Consequently, clonal integration significantly increased growth of the apical ramets, the basal ramets and the whole fragments. However, after 20 d of de-submergence, stolon connection did not significantly affect growth or photosynthetic capacities of either de-submerged or un-submerged ramets. The results suggest that clonal integration plays different roles during submergence and de-submergence. It increases performance of submerged ramets during submergence by translocation of photosynthates from un-submerged ramets, but plays little roles during de-submergence.

Disturbance has been considered to exert positive, neutral or negative effects on the invasion of exotic plants. Disturbance may enhance the invasion success of alien invasive species by both increasing their performance and alleviating the harmful effects caused by disturbance via tolerance and resistance, especially in the late phases of the invasion process. However, the tolerance and resistance of invasive plant clonal populations to disturbance has been mostly neglected. In the present study, we explored the phenotypic responses of clonal populations of the invasive plant Alternanthera philoxeroides and three co-occurring non-invasive clonal species, i.e., Alternanthera sessilis, Myriophyllum aquaticum and Jussiaea repens, to different levels of fluctuating flood disturbances using a mesocosm experiment. Different functional traits related to morphology, biomass allocation and physiology were used to evaluate plant performance. We found that A. philoxeroides coped with fluctuating flooding by performing phenotypic maintenance that affected ramet number, stolon length, specific leaf area, leaf mass ratio, chlorophyll content, nitrogen content and non-structural carbohydrate content; additionally, the plant experienced variations in stolon diameter, stolon mass ratio, root mass allocation and maximum fluorescence. In addition, Alternanthera philoxeroides demonstrated several similarities with the three non-invasive species in terms of the observed phenotypic responses to different disturbance statuses. Furthermore, Alternanthera philoxeroides showed respective advantages in tolerance compared to A. sessilis, photosynthetic capacity compared to M. aquaticum and especially J. repens, and resistance to submergence compared to all three non-invasive species. Overall, tolerance and resistance facilitated the successful invasion of A. philoxeroides in disturbed habitats. Furthermore, the native constructive species J. repens was severely harmed by fluctuating flooding; thus, fluctuating flooding could create an empty niche that promotes the expansion of the clonal populations of A. philoxeroides.

The ability to tolerate novel herbivores is widely considered to influence plant invasion success. For clonal plants that have reduced capacity to evolve in response to novel herbivores, legacy effects of herbivory on parental plants might be translated to offspring ramets, resulting in pre-adaptation to tolerate herbivory for new vegetative growth. Using the invasive clonal plant Alternanthera philoxeroides, we first exposed plants to herbivory by Planococcus minor, a widespread and generalist piercing-sucking insect. Herbivory decreased above- and below-ground plant biomass by approximately 50% with a concomitant 134% increase in root N concentration but no changes in concentrations of soluble sugars, starch or non-structural carbohydrates related to herbivory tolerance. Offspring ramets were then exposed to herbivory by three different herbivore species: (1) P. minor, (2) the specialist leaf-beetle Agasicles hygrophila, and (3) the stenophagous tortoise-beetle Cassida piperata. There was no evidence of interactive effects between herbivory on parental plants and herbivory on offspring plants on growth, biomass allocation patterns, or physiological responses, suggesting that pre-adaptation to herbivory did not occur in A. philoxeroides with these herbivores. There were, however, species-specific herbivore tolerance responses. In the offspring generation, herbivory by A. hygrophila strongly suppressed growth and biomass allocation, but patterns were generally weaker for other herbivores. Tolerance effects could be explained by stimulatory effects of grazing by C. piperata and P. minor on taproot biomass along with idiosyncratic increases of starch and non-structural carbohydrate concentration in some storage organs. Our results highlight the importance of A. hygrophila in controlling the aboveground spread of A. philoxeroides. However, herbivory by other species was largely tolerated and accompanied by increased allocation to underground storage organs and altered physiological reserves, both of which could allow this invasive plant to tolerate herbivory and successfully invade new areas in the face of new herbivore pressure.

Plants with clonal growth may suffer from great fragmentation risk due to frequent disturbance. Meanwhile, storage capacity of clonal organs (stolon or rhizome) is important for survival and growth of clonal fragments. However, few studies have compared the difference in the regeneration capacity of clonal fragments between invasive clonal plants and congeneric native species. More studies between invasive plants and their congeneric native species are needed to provide insight into traits that contribute to invasiveness. Single-node fragments with stolon internode of different length were used to investigate the effects of stolon storage on survival and growth of three stoloniferous invasive plants (Wedelia trilobata, Alternanthera philoxeroides and Hydrocotyle vulgaris) and their congeneric native species (Wedelia chinensis, Alternanthera sessilis and Hydrocotyle sibthorpioides). Soluble sugar, starch and soluble protein contents of stolon internode per unit length were significantly greater in the three invasive plants than in their congeneric native species. During the experiment, regeneration of clonal fragments was not observed in A. sessilis. With increasing of stolon internode length, accumulative emergence rate of clonal fragments and biomass of their regenerated ramets significantly increased in the other five species. Accumulative emergence rate of clonal fragments and biomass of their regenerated ramets were significantly greater in invasive plant H. vulgaris than in its congeneric native species. A similar pattern was observed in the clonal fragments with stolon internode of long and medium length for Wedelia species pair. In the experiment, regeneration capacity of clonal fragments varied with species and stolon internode length. Clonal fragments of stoloniferous invasive plants benefit more from stolon storage than their congeneric native species. It is suggested that clonal storage may be an important trait for invasiveness of stoloniferous invasive plants. Therefore, intentional fragmentation should be carefully employed to manage stoloniferous invasive plants and avoid the dispersal of generative clonal fragments.

Este artículo presenta los resultados del estudio morfo-anatómico e histoquímico de los órganos subterráneos de cuatro especies de Dicotiledóneas palustres usados en la medicina popular rioplatense. Las especies estudiadas son: Alternanthera philoxeroides, Eryngium pandanifolium, Ludwigia peploides y Senecio bonariensis. El objetivo de este estudio fue caracterizar las raíces y rizomas por sus atributos histológico-estructurales e identificar compuestos químicos que faciliten la diferenciación de los taxones a partir de muestras enteras o fragmentadas. Se analizó material fresco recolectado en el área de estudio, se incorporaron ejemplares al herbario (LPAG), Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata. Material de rizomas y raíces fue fijado en líquido conservador. Se realizaron cortes y preparaciones histológicas, las que fueron estudiadas con microscopio óptico. Mediante técnicas histoquímicas se identificaron almidón, mucílagos, sustancias lipofílicas y taninos. Los caracteres diagnósticos estructurales fueron: el tipo de parénquima cortical; desarrollo secundario de la estructura vascular; presencia de tejidos secretores y tipos de cristales. Se generó una tabla comparativa de los compuestos histoquímicos hallados y una clave dicotómica con los caracteres de rizomas y raíces, datos que constituyen una herramienta de valor en el control de calidad botánica., The paper presents morphology- anatomy and histochemical data of the underground organs of four marshy species of Dicotyledons used in the Rio de la Plata folk medicine. They are: Alternanthera philoxeroides, Eryngium pandanifolium, Ludwigia peploides y Senecio bonariensis. The aim of this study was to obtain structural characteristics of the rhizome and roots, and identified chemical compounds that allow differentiation of taxa, facilitating the identification of whole or fragmented samples of organs used in folk medicine. Fresh material was collected in the study area. Specimens were prepared and included in the LPAG herbarium, Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata. Rhizomes and roots samples were fixed in conservation liquid. Slides were made and analyzed with a light microscope. Histochemical analysis to recognize starch, mucilage, lipophilic substances, and tannins were performed. The diagnoses structural features were: cortical parenchyma type; secondary vascular tissue development; presence of secretory tissue, and crystal types. A comparative table with histochemical results and a dichotomous key using micrographic rhizome and root characters were generated to get a valuable tool to establish authenticity of botany quality control., Laboratorio de Morfología Comparada de Espermatófitas

Clonal integration can contribute to the invasiveness of amphibious plant, Alternanthera philoxeroides, but whether this differs between life-forms and whether such difference is underlying their biological control efficacy have scarcely been addressed. We aimed to determine whether clonal integration differs between life-forms and whether terrestrial form with lower biological control efficacy shows greater capacity of clonal integration in response to defoliation. In a greenhouse experiment, we subjected terrestrial and aquatic A. philoxeroides to four levels of experimental defoliation, i.e., 0 (control), 20% (mild), 50% (moderate), and 80% (heavy) leaf clipping, with the stolon connections being either severed or intact. The results showed that clonal integration greatly improved the growth and clonal propagation of both life-forms, especially under heavier defoliation. The shoot/root ratios of both life-forms were significantly increased by clonal integration under heavy defoliation. Moreover, higher level of resource sharing and greater division of labor promoted the terrestrial form to perform better than the aquatic form. These results supported our hypotheses that terrestrial A. philoxeroides can benefit from clonal integration more than aquatic form under herbivory, which may be an alternative mechanism accounted for the low efficacy of biological control of A. philoxeroides in the terrestrial habitats.

The aims of this study were to measure the concentrations of nutrients and pollutants in peri-urban wetlands, to analyze the plant morphology of the most representative macrophyte species, and to determine their potential use as biomonitors. Four wetlands in the Middle Paraná River floodplain evidencing contamination or anthropogenic impact were studied. The studied species were Typha domingensis Pers., Eichhornia crassipes (Mart.) Solms., Alternanthera philoxeroides (Mart.) Griseb., and Pistia stratiotes L. Besides, the same plant species from an uncontaminated wetland considered as control were studied. A. philoxeroides showed the highest total phosphorus (TP) concentration in leaves throughout the study, while the other species showed a higher TP concentration in roots than in leaves. Since metal concentration in A. philoxeroides tissues was always higher than in sediment, further studies focused on its phytoremediation capacity should be carried out. T. domingensis exhibited the highest Zn concentrations in roots followed by Pb, and E. crassipes presented the highest values of Pb concentrations in roots. The aerial part height of the plants from peri-urban wetlands was significantly higher than that of the plants from the control, while the root length was significantly lower. The root length of P. stratiotes showed a negative correlation with soluble reactive phosphorus (SRP) concentration in water. All the root anatomical parameters of T. domingensis and E. crassipes showed a positive correlation with nitrate and ammonium concentrations in water. The studied macrophytes evidenced a high tolerance, enabling them to grow and survive in peri-urban wetlands that receive pollution from different sources. The use of aquatic and wetland plants as contaminant bioindicators and bioaccumulators in the Middle Paraná River floodplain is completely feasible.

Alternanthera philoxeroides is an alien invasive species, which can cause substantial damage to the local ecosystem by secreting allelochemicals. The objective of the present study was to appraise the effects of root extracts of the invasive plant Alternanthera philoxeroides on soil enzyme and native microbial community. Urease activity was measured using the phenol sodium hypochlorite colorimetric method, sucrase activity was determined by 3, 5-dinitrosalicylic acid colorimetric method, catalase activity was determined using the KMnO4 titration method and alkaline phosphatase activity was determined by the disodium phenyl phosphate colorimetric method. The soil microbial community was investigated by pyrosequencing of the 16S rRNA gene. Results showed that the alkaline phosphatase, sucrase and urease activities were all significantly lower than that of the control treatment. The structure of the soil microbial community in the treatments with root extracts addition clearly differed from that of t...

Most work on clonal growth in plants has focused on the advantages of clonality in heterogeneous habitats. We hypothesized (1) that physiological integration of connected ramets within a clone can also increase plant performance in homogeneous environments, (2) that this effect depends on whether ramets differ in ability to take up resources, and (3) that only ramets with relatively low uptake ability benefit. We tested these hypotheses using the perennial amphibious herb Alternanthera philoxeroides. We grew clonal fragments and varied numbers of rooted versus unrooted ramets, connection between the apical and basal parts of fragments, and availability of nitrogen. Patterns of final size and mass of fragments did not support these hypotheses. By some measures, severance did reduce the growth of more apical ramets and increase the growth of less apical ones, consistent with net apical transfer of resources. Rooting of individual ramets strongly influenced their growth: second and third most apical ramets each grew most when they were the most apical rooted ramet, and this pattern was more pronounced under higher nitrogen levels. This adds to the evidence that signalling between ramets is an important aspect of clonal integration. Overall, the results indicate that physiological integration between ramets within clones in homogeneous environments can alter the allocation of resources between connected ramets even when it does not affect the total growth of clonal fragments.

The availability of nitrogen and phosphorus is an important factor determining the growth and competitive dominance of invasive plants. To clarify the influence of nutrient availability on the performance of alien species, we conducted a greenhouse experiment in which the invasive plant Alternanthera philoxeroides was planted as a monoculture or in mixed culture with noninvasive species ( Oenanthe javanica or Iris pseudacorus ) under combined conditions of various nutrient level (low, medium, and high) and N/P ratio (1, 10, and 100). Nutrient level and N/P ratio both affected the growth of A. philoxeroides and the effects were similar in mixed culture and monoculture. Increased nutrient level significantly increased the total biomass and total stolon length of A. philoxeroides under all N/P ratios. At low nutrient level, N/P ratio had little influence on the total biomass and total stolon length of A. philoxeroides . At medium and high nutrient levels, however, increased N/P ratios inhibited the growth of A. philoxeroides . Nutrient level rather than N/P ratio affected the relative dominance index (RDI) of A. philoxeroides , with increased nutrient levels enhancing the competitive dominance of A. philoxeroides . Furthermore, the RDI of A. philoxeroides in mixed culture with I. pseudacorus was consistently higher than that of A. philoxeroides when grown with O. javanica . Therefore, our results indicate that nutrient enrichment (such as over-fertilization and eutrophication) would aggravate the already serious impact of biological invasions and that the identity of resident plant species might also affect the competitive dominance of exotic plants.

Clonal integration and fragmentation are potentially competing advantages of clonal growth. Clonal fragmentation can increase the dispersal of ramets, but it prevents physiological integration, which can increase the growth of clones and may increase their competitive effect on other plant species. We tested whether fragmentation can reduce the competitive effect of invasive clonal plants within mixed communities and whether this effect of fragmentation is greater under conditions in which the competitive effect of a clonal plant is greater. We constructed wetland communities each consisting of four common, co-occurring, mainly aquatic plant species under flooded and unflooded conditions, and compared the growth of the species with and without intact or fragmented groups of ramets of the widespread, amphibious, invasive clonal plant Alternanthera philoxeroides . We measured the community-level competitive effect of A. philoxeroides on the four aquatic plant species. Fragmentation reduced mass accumulation of A. philoxeroides , but did not reduce its competitive effect, either under flooded or under unflooded conditions. One explanation is that A. philoxeroides was able to maintain production of new ramets when fragmented. Clonal plants may thus mitigate trade-offs between the potential ecological advantages of physiological integration and fragmentation by maintaining rates of vegetative reproduction after fragmentation, even when total growth is reduced.

多数恶性入侵水生植物都是克隆植物，阐明克隆整合属性对其潜在入侵性的影响对了解其入侵机制具有重要意义.以喜旱莲子草（Alternanthera philoxeroides）为研究对象，研究其克隆整合（匍匐茎连接）对入侵本地黄花水龙（Ludwigia peploides）种群时的光合性能、生长、竞争力和资源分配的影响，探讨克隆整合对该植物入侵性的贡献.结果表明，竞争显著降低了喜旱莲子草的光系统Ⅱ最大量子产量、总生物量、分株数和总匍匐茎长；但克隆整合却显著促进了竞争环境中喜旱莲子草的生长，提高了其光合特性、根冠比以及对本地物种的竞争力，因而有利于其入侵性的增强.

Anthropogenic activities and natural causes contribute to the increase of the area and degree of degraded saline wetlands in arid/semi‐arid and coastal regions. The objective of this study was to determine the salt tolerance of seven aquatic plant species during asexual reproduction and at continued growth stage. The species were exposed to five salinity treatments from 0.3 (control) to 20 dS/m during the 30 day experiment. Data were collected on asexual reproduction and growth, chlorophyll content index in leaves, Na+ and K+ concentrations and total nitrogen (TN) and total phosphorus (TP) concentrations in above‐ground biomass (AGB) and below‐ground biomass (BGB). The results of this study showed that: 1) the increase of salinity (especially at a salinity level of EC≥15 dS/m) generally inhibited the capacity for asexual reproduction and reduced the chlorophyll content index in leaves; 2) total dry biomass of plants was significantly and negatively related to asexual reproduction of plants; 3) species‐specific salt tolerance mechanisms were shown as indicated by the Na+ and K+ concentrations and Na+/K+ ratios in different parts of plants; and 4) the absorption of TN and TP were inhibited at high salinity level (i.e., EC=20 dS/m) in AGB and BGB of most tested plant species. Salinity may enhance plant uptake of TN and TP under certain condition (e.g., EC at 5, 10 and 15 dS/m). In general, giant reed (Arundo donax) and alligator weed (Alternanthera philoxeroides) showed better asexual reproduction and growth capacity under high salt stress, and they should be considered as potential plant species to be used in the restoration of degraded saline wetlands and/or in treatment wetlands for decontaminating saline wastewater.

Alternanthera philoxeroides (Mart.) Griseb. is an invasive herbaceous amphibious weed species in China. A pyralid moth Herpetogramma basalis (Walker) was discovered feeding on A. philoxeroides through field surveys and may be a potentially useful biocontrol agent. To determine the host range of H. basalis and evaluate its potential to control A. philoxeroides, no-choice and multiple-choice tests were conducted. Herpetogramma basalis fed on target weeds and 29 nontarget plant species. In addition to the target weed A. philoxeroides, H. basalis developed to adult on eight other nontarget species. Herpetogramma basalis survived to adulthood successfully on A. philoxeroides and less successfully on several other Amaranthaceae species. In multiple-choice studies, H. basalis showed a strong oviposition preference for A. philoxeroides over Amaranthus tricolor L. (Centrospermae: Amaranthaceae). Amaranthus tricolor was the only crop plant that supported the complete development of H. basalis. We cautiously recommend H. basalis for the biological control of A. philoxeroides in China.

Ramella, L. (2016). Nomenclature, typifications and new synonymes in the family Amaranthaceae of the Flora of Paraguay. Candollea 71: 311–326. In Spanish, English and Spanish abstracts. DOI: http://dx.doi.org/10.15553/c2016v712a16 Two nomenclatural novelties are validated: Alternanthera paronychioides subsp. chacoensis (Morong) Pedersen and Alternanthera paronychioides subsp. pilosa (Moq.) Pedersen. Seventeen lectotypes are designated: Alternanthera adscendens Suess., Alternanthera philoxeroides f. angustifolia Suess., Alternanthera philoxeroides var. lancifolia Chodat, Gomphrena celosioides var. aureiflora Stuchlik, Gomphrena celosioides f. suberecta Stuchlik, Gomphrena decumbens var. albiflora Stuchlik, Gomphrena decumbens var. aureiflora Stuchlik, Gomphrena decumbens var. roseiflora Stuchlik, Gomphrena regeliana f. grandifolia Chodat, Pfaffia brachiata Chodat, Pfaffia iresinoides var. angustifolia O. Stutzer, Pfaffia luzuliflora var. paniculata O. Stutzer, Pfaffia luzuliflora subsp. squarrosa ...

Exotic plant invasions may alter ecosystem carbon processes, especially when native plants are displaced by plants of a different functional group. Forb invasions into grasslands are common, yet little is known about how they impact carbon cycling. We conducted a field study over 2 years from April 2010 to March 2012 in China to examine changes in soil respiration (Rsoil) following invasion of exotic perennial forb species (Alternanthera philoxeroides or Solidago canadensis) into an annual grassland dominated by a native annual graminoid (Eragrostis pilosa). Measurements of Rsoil were taken once a week in stands of the native annual graminoid or one of the forb species using static chamber-gas chromatograph method. Aboveground litterfall of each of the three focal species was collected biweekly and litter decomposition rates were measured in a 6-month litterbag experiment. The monthly average and annual cumulative Rsoil increased following invasion by either forb species. The increases in cumulative Rsoil were smaller with invasion of Solidago (36%) than Alternanthera (65%). Both invasive forbs were associated with higher litter quantity and quality (e.g., C:N ratio) than the native annual graminoid. Compared to the native annual graminoid, the invasive forbs Alternanthera (155%) and Solidago (361%) produced larger amounts of more rapidly decomposing litter, with the litter decay constant k being 3.8, 2.0 and 1.0 for Alternanthera, Solidago and Eragrostis, respectively. Functional groups of the invasive plants and the native plants they replaced appear to be useful predictors of directions of changes in Rsoil, but the magnitude of changes in Rsoil seems to be sensitive to variations in invader functional traits.

Some clonal plants can spread their ramet populations radially, and soil heterogeneity and clonal integration may greatly affect the establishment of these types of populations. We constructed Alternanthera philoxeroides populations with a radial ramet aggregation, allowing old ramets of clonal fragments to concentrate in central pots and younger ramets to root in peripheral pots. The peripheral pots were supplemented either with three different levels (high, medium and low) of soil nutrients to simulate a heterogeneous soil environment, or only one medium level of soil nutrients to simulate a homogeneous environment. Stolon connections between the central older ramets and the peripheral younger ramets were left intact or severed to test the effect of clonal integration. The maintenance of stolon connection could induce the division of labor between different-aged ramets, by increasing the root investment in central ramets and the above-ground growth in peripheral ramets. The maintenance of stolon connection could improve the growth of the central and peripheral ramets, clonal fragments and even the whole population. However, the positive consequence in peripheral ramets and whole fragments was only detected in the high-nutrient patch of heterogeneous treatment. In sum, in the population with the radial ramet aggregation, clonal integration can play a key role in the rapid recruitment of young ramets of A. philoxeroides fragments, as well as the expansion of the whole population. The magnitude of clonal integration also became more obvious in the peripheral young ramets and whole fragments that experienced high-nutrient patches.

Plant invasions may result in novel plant-herbivore interactions. However, we know little about whether and how invasive plants can mediate native above- and belowground herbivore interactions. In this study, we conducted greenhouse experiments to examine the interaction between a native defoliating beetle, Cassida piperata, and a native root-knot nematode, Meloidogyne incognita, on the invasive alligator weed, Alternanthera philoxeroides. We also included their native host A. sessilis in the experiments to examine whether the patterns of above- and belowground herbivore interaction vary with host plants (invasive vs. native). We analyzed total carbon and nitrogen in leaves and roots attacked by M. incognita and C. piperata. M. incognita slightly negatively affected feeding by C. piperata on A. philoxeroides, and the leaf area damaged decreased as the number of M. incognita increased. M. incognita had a negative impact on total leaf nitrogen, but had no impact on total leaf carbon. M. incognita egg production on A. philoxeroides roots decreased as the amount of damage caused by C. piperata increased. Herbivory by C. piperata did not affect total root carbon or nitrogen. M. incognita and C. piperata did not affect each other on the native plant A. sessilis. These results suggest that invasive plants can mediate native above- and belowground herbivore interactions. The knowledge of how invasive plants affect those interactions is crucial for better understanding the impacts of biological invasions on native above- and belowground organisms.