Invasive Alternanthera Philoxeroides Research Articles

Neutral interactions between native Alternanthera sessilis and exotic Alternanthera philoxeroides along a light gradient under tropical climatic conditions

AbstractRiparian ecosystems are under a serious threat of invasion due to the clearance of riparian vegetation, which allows for increased light levels at ground level. This study presents the interactions between native Alternanthera sessilis (L.) R. Br. ex DC and invasive Alternanthera philoxeroides (Mart.) Griseb. during the colonization stage along a light gradient under tropical climate conditions. We conducted a 6 week growth experiment with monocultures of A. philoxeroides and A.sessilis and mixed communities of two species under four light levels (100%, 46%, 26% and 14% of full sunlight). Exposure to full sunlight (nearly 1800 μmol m−2 s−1) resulted in a significantly high biomass accrual in both species. However, biomass accrual did not correlate with the light intensity. At higher shade levels, reduction of lateral spread and shoot/root ratio was observed. Community composition had no influence on biomass accrual or morphological variations. Plasticity index values were approximately same in both species. Total relative yield was approximately two in all shade conditions, indicating that the two species interact neutrally along the light gradient. Therefore, the results of the study indicate that increased light levels will accelerate the proliferation of both species in riparian zones. Nevertheless, increased or decreased shade is unlikely to alter neutral interactions between A. philoxeroides and A. sessilis.

Invasive Plant Alternanthera philoxeroides Benefits More Competition Advantage from Rhizosphere Bacteria Regardless of the Host Source.

The rhizosphere plays a vital role in the exchange of materials in the soil-plant ecosystem, and rhizosphere microorganisms are crucial for plant growth and development. In this study, we isolated two strains of Pantoea rhizosphere bacteria separately from invasive Alternanthera philoxeroides and native A. sessilis. We conducted a control experiment to test the effects of these bacteria on the growth and competition of the two plant species using sterile seedlings. Our findings showed that the rhizobacteria strain isolated from A. sessilis significantly promoted the growth of invasive A. philoxeroides in monoculture compared to native A. sessilis. Both strains significantly enhanced the growth and competitiveness of invasive A. philoxeroides under competition conditions, regardless of their host source. Our study suggests that rhizosphere bacteria, including those from different host sources, can contribute to the invasion of A. philoxeroides by significantly enhancing its competitiveness.

Rare Production of Seeds by Invasive Alternanthera philoxeroides (Alligator Weed) in North America Observed in Terrestrial Populations

Rare Production of Seeds by Invasive Alternanthera philoxeroides (Alligator Weed) in North America Observed in Terrestrial Populations

Effects of simulated acid rain on rhizosphere microorganisms of invasive Alternanthera philoxeroides and native Alternanthera sessilis.

Acid rain not only has serious harm to the environment, but also has the same threat to plants, but the invasive plant Alternanthera philoxeroides still grows well compared to the native plant Alternanthera sessilis under acid rain stress. However, the underlying mechanism of resistance to the acid rain environment in invasive Alternanthera philoxeroides remains unclear. In the current study, we comparatively analyzed the plant physiological characteristics, soil physicochemical properties, and rhizosphere microbial communities of invasive A. philoxeroides and native A. sessilis under different pH condition. The simulated acid rain had a significant inhibitory effect on the morphological and physiological traits of A. philoxeroides and A. sessilis and reduced the soil nutrient content. However, A. philoxeroides was more tolerant of acid rain. Compared with CK, simulated acid rain treatment at pH 2.5 significantly increased the Chao1, ACE, and Shannon indexes of A. philoxeroides microorganisms. Under simulated acid rain treatment at pH 2.5, the fungal flora Chao1, ACE and Shannon index were significantly higher than those of CK by 14.5%, 12.4%, and 30.4%, respectively. The dominant bacterial phyla of soil bacteria were Proteobacteria, Actinobacteria, Bacteroidota, Actinobacteria, Firmicutes, Myxococcota, Chloroflexi, Patescibacteria, Gemmatimonadota, Verrucomicrobiota, and Armatimonadota. The dominant fungi were Ascomycota, Basidiomycota, Rozellomycota, and Olpidiomycota. The bacterial and fungal diversity and structure of A. philoxeroides and A. sessilis showed the greatest difference between the pH 2.5 treatment and CK. Redundancy analysis showed that electrical conductivity (EC) and total phosphorus (TP) were the main factors changing the bacterial communities, and available phosphorus (AP), organic matter (OM), EC, and pH were the main factors changing the fungal communities. This study contributes to the microbial community structure of the invasive plant A. philoxeroides and provides a theoretical basis for studying the invasion mechanism of invasive plants under acid rain.

Invasive Alternanthera philoxeroides has performance advantages over natives under flooding with high amount of nitrogen

Invasive Alternanthera philoxeroides has performance advantages over natives under flooding with high amount of nitrogen

Invasive plant indirectly regulates native plant decomposition by affecting invertebrate communities

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.

Growth prediction of Alternanthera philoxeroides under salt stress by application of artificial neural networking

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-Layer Perceptron (MLP) were used for building a Predicted Neural Model (PNM) using soil parameters such as pH, electrical conductivity (EC), water content, temperature, humidity, and organic content and a growth parameter, i.e. plant height. Quality assessment of the produced PNM is done through ex-post errors, i.e. Relative-Approximation Error (RAE), Root-Mean Square (RMS) error, Mean-Absolute Error (MAE), and Mean-Absolute Percentage Error (MAPE). The MAPE was 2.21% for PNM of A. philoxeroides, which was less than 10%, thus proving that all the obtained results are highly satisfactory. In the next step, the sensitivity analysis assigned the highest rank 1 to salt stress in the model with a quotient value of 1.71, and the rank-2 was assigned to EC of soil with quotient value of 1.51. Therefore, the constructed PNM will provide the basis for building new prediction tools for the growth of invasive species. It will be an important element for prediction of invasiveness of A. philoxeroides in a stressful environment and will also be helpful for the management of invasive species.

Parasitism changes rhizospheric soil microbial communities of invasive Alternanthera philoxeroides, benefitting the growth of neighboring plants

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.

Influence of Soil Nutrient Heterogeneity and Competition on Sprouting and Ramets Growth of Alternanthera philoxeroides

Environmental heterogeneity and plant competition influence plant vegetative sprouting and ramets growth. Many major invasive plants reproduce largely or exclusively by vegetative propagation. The terrestrial invasive Alternanthera philoxeroides mainly regenerates from fleshy roots. Here, it is tested whether resource heterogeneity and intraspecific competition influence the fleshy root sprouting and ramet growth of this species. Four or twelve similar‐sized fleshy roots of A. philoxeroides are grown in two soil substrates that are either homogeneous or heterogeneous but have the same total amount of nutrients. After 6 months, the sprouting and ramet growth traits (i.e., ramet number, leaf traits, biomass and biomass allocation) are analyzed. The fleshy root density significantly affects the sprouting and ramet growth traits, but the soil nutrient heterogeneity does not. The sprouting and ramet growth traits decrease in the treatments with high densities of fleshy roots. These results suggest that intraspecific competition has a greater influence on the root sprouting and ramet growth of the invasive terrestrial A. philoxeroides than soil nutrient heterogeneity. Thus, intraspecific competition can limit the establishment of terrestrial A. philoxeroides.

Invasive plant Alternanthera philoxeroides suffers more severe herbivory pressure than native competitors in recipient communities.

Host-enemy interactions are vital mechanisms that explain the success or failure of invasive plants in new ranges. We surveyed the defoliation of invasive Alternanthera philoxeroides and co-occurring native plants on two islands during different seasons over three consecutive years and measured the leaf nitrogen content and the C/N ratio of each plant species. To evaluate the effects of herbivory on A. philoxeroides, an herbivore exclosure experiment was conducted. We found that the mean defoliation of A. philoxeroides was higher than that of native plants, regardless of whether the dominant species was A. philoxeroides or native plants. A. philoxeroides defoliation increased significantly as the months progressed, whereas the defoliation of the total population of native plants was constant. The leaf nitrogen content was positively correlated with defoliation, and it was highest in A. philoxeroides. Additionally, A. philoxeroides in the herbivore exclusion treatment showed an increase in shoot biomass and total shoot length. Our study revealed that native generalist herbivores prefer the invasive plant to the natives because of the higher leaf nitrogen content. These results support the biotic resistance hypothesis, suggesting that native herbivore species can limit the population spread of invasive plants.

Spatial arrangements affect suppression of invasive Alternanthera philoxeroides by native Hemarthria compressa

It has been hypothesized that differences in spatial arrangements change the relative frequency of intra- and interspecific encounters between plant species. Manipulating spatial arrangement may play a role in invasive plant suppression when native species are used as competitors against introduced species. In this study, a replacement series experiment was performed to investigate the effects of intraspecifically random and aggregated spatial arrangements on interactions between the native plant Hemarthria compressa and the invasive plant Alternanthera philoxeroides, to test the possibility and effectiveness of H. compressa in suppressing A. philoxeroides. When both species were planted in intraspecifically random spatial patterns, H. compressa had a competitive advantage over A. philoxeroides at relative densities of 2:2 and 3:1. However, aggregation increased the strength, and therefore the cost, of intraspecific competition in H. compressa, resulting in lower biomass production, which reduced its effectiveness as an interspecific competitor. As the relative density of H. compressa in mixtures decreased, plants allocated more biomass to belowground parts, but fewer interspecific encounters lowered its inhibitory effects on A. philoxeroides. The results not only confirm that the frequency of conspecific and heterospecific encounters can influence competitive outcomes, but also suggest that a reduction in the degree of spatial aggregation in H. compressa and an increase in its relative densities may be essential to increase the suppression of A. philoxeroides.

Climate warming affects biological invasions by shifting interactions of plants and herbivores

Plants and herbivorous insects can each be dramatically affected by temperature. Climate warming may impact plant invasion success directly but also indirectly through changes in their natural enemies. To date, however, there are no tests of how climate warming shifts the interactions among invasive plants and their natural enemies to affect invasion success. Field surveys covering the full latitudinal range of invasive Alternanthera philoxeroides in China showed that a beetle introduced for biocontrol was rare or absent at higher latitudes. In contrast, plant cover and mass increased with latitude. In a 2-year field experiment near the northern limit of beetle distribution, we found the beetle sustained populations across years under elevated temperature, dramatically decreasing A.philoxeroides growth, but it failed to overwinter in ambient temperature. Together, these results suggest that warming will allow the natural enemy to expand its range, potentially benefiting biocontrol in regions that are currently too cold for the natural enemy. However, the invader may also expand its range further north in response to warming. In such cases where plants tolerate cold better than their natural enemies, the geographical gap between plant and herbivorous insect ranges may not disappear but will shift to higher latitudes, leading to a new zone of enemy release. Therefore, warming will not only affect plant invasions directly but also drive either enemy release or increase that will result in contrasting effects on invasive plants. The findings are also critical for future management of invasive species under climate change.

Effects of N:P Ratio and Nutrient Level on the Competition between Invasive <i>Alternanthera philoxeroides</i> and Native <i>Oenanthe javanica</i>

This study examined the effects of N:P ratio and nutrient level on the competition between invasive Alternanthera philoxeroides and native Oenanthe javanica in terms of morphological and physiological traits and the relative dominance index (RDI). In the experiment, A. philoxeroides was grown in mixture with O. javanica at three N:P supply ratios (1,10,100) combined with three levels of nutrient supply. The results suggested that the morphological and physiological traits of invasive and native species were both significantly affected by N:P ratio and nutrient supply level. The total biomass of both species was maximal under the treatment of lowest N:P ratio and highest nutrient supply, and A. philoxeroides had higher total biomass than O. javanica in every treatment. A. philoxeroides had higher plasticity than O. javanica on total biomass, R/S, SLA, which had sensitive response to the changing nutrient conditions. Meanwhile, the RDI of A. philoxeroides under high nutrient supply was higher than that under low nutrient supply, which showed that high nutrient supply could promote the invasion of A. philoxeroides while P-limitation (high N:P ratio) may prevent the successful invasion of A. philoxeroides under the lower nutrient supply.

Invertebrate community composition differs between invasive herb alligator weed and native sedges

Chemical and/or architectural differences between native and exotic plants may influence invertebrate community composition. According to the enemy release hypothesis, invasive weeds should host fewer and less specialised invertebrates than native vegetation. Invertebrate communities were compared on invasive Alternanthera philoxeroides (alligator weed) and native sedges (Isolepis prolifer and Schoenoplectus tabernaemontani) in a New Zealand lake. A. philoxeroides is more architecturally and chemically similar to I. prolifer than to S. tabernaemontani. Lower invertebrate abundance, richness and proportionally fewer specialists were predicted on A. philoxeroides compared to native sedges, but with greatest differences between A. philoxeroides and S. tabernaemontani. A. philoxeroides is more architecturally and chemically similar to I. prolifer than to S. tabernaemontani. Invertebrate abundance showed taxa-specific responses, rather than consistently lower abundance on A. philoxeroides. Nevertheless, as predicted, invertebrate fauna of A. philoxeroides was more similar to that of I. prolifer than to S. tabernaemontani. The prediction of a depauperate native fauna on A. philoxeroides received support from some but not all taxa. All vegetation types hosted generalist-dominated invertebrate communities with simple guild structures. The enemy release hypothesis thus had minimal ability to predict patterns in this system. Results suggest the extent of architectural and chemical differences between native and invasive vegetation may be useful in predicting the extent to which they will host different invertebrate communities. However, invertebrate ecology also affects whether invertebrate taxa respond positively or negatively to weed invasion. Thus, exotic vegetation may support distinct invertebrate communities despite similar overall invertebrate abundance to native vegetation.

Invasive Alternanthera philoxeroides (alligator weed) associated with increased fungivore dominance in Coleoptera on decomposing leaf litter

Invasive Alternanthera philoxeroides (alligator weed), when controlled by biocontrol agent Agasicles hygrophila, is known to differ from native vegetation in its decomposition dynamics. This study investigated whether this difference would have indirect effects for fungal-feeding Coleoptera. The study tested the hypothesis that fungivores would be more abundant and species rich on A. philoxeroides than on native vegetation. The study also tested the hypothesis that fungivores would be more affected than other functional groups. The study was conducted in a northern New Zealand lake. Litterbags were placed beneath A. philoxeroides and two native sedge species (Schoenoplectus tabernaemontani and Isolepis prolifer). Coleoptera communities were examined from the litterbags. Fungivorous Coleoptera were more abundant and species rich beneath A.philoxeroides than beneath either sedge species. No other functional groups differed between cover types. Fungivorous Coleoptera also comprised a greater proportion of total Coleoptera catch from litterbags beneath A.philoxeroides cover than from beneath native sedge cover. Four of the six fungivorous Coleoptera species collected in the study were present beneath A.philoxeroides cover. Of these, the two most abundant species (on native, one exotic) were both from the family Corylophidae. Alternanthera philoxeroides invasion is thus associated with altered Coleoptera communities in this ecosystem.

Effects of resource availability on tolerance of herbivory in the invasive Alternanthera philoxeroides and the native Alternanthera sessilis

Sun Y, Ding J & Frye MJ (2010). Effects of resource availability on tolerance of herbivory in the invasive Alternanthera philoxeroides and the native Alternanthera sessilis. Weed Research 50, 527–536. Summary Resource availability is known to affect herbivore selectivity and the ability of plants to respond to herbivores. However, little information is available for the performance of invasive plants subject to insect herbivory and limited resources availability. We conducted a glasshouse experiment using both the invasive Alternanthera philoxeroides and its native congener Alternanthera sessilis, to compare the effects of resource availability on plant tolerance to herbivory. The results suggest that water availability affects plant tolerance to herbivory, such that stressful water conditions promoted greater herbivore tolerance for A. philoxeroides and decreased herbivore tolerance for A. sessilis. The addition of fertiliser also affected the plant’s ability to respond to herbivory. Fertilised plants of both species generated more biomass and had greater tolerance to herbivory than unfertilised plants. Adding fertiliser appeared to increase the compensation capacity to herbivory for A. philoxeroides. In unfertilised conditions, moisture had no effect on A. philoxeroides tolerance to herbivory, and plants performed better under drought conditions. The results of this study may help to further our understanding of why biological control efforts against A. philoxeroides have been successful in some aquatic environments, but not others. Our study suggests that control of A. philoxeroides in high-moisture and nutrient poor environments should be more effective than control under nutrient rich and low-moisture soils. Understanding the mechanism of invasive plant compensation under different environmental conditions will be important for improving and predicting management efficiency.

The Structural Adaptation of Aerial Parts of Invasive Alternanthera philoxeroides to Water Regime

Alternanthera philoxeroides has successfully invaded diverse habitats with considerably various water availability, threatening biological diversity in many parts of the world. Because its genetic variation is very low, phenotypic plasticity is believed to be the primary strategy for adapting to the diverse habitats. In the present paper, we investigated the plastic changes of anatomical traits of the aerial parts of A. philoxeroides from flooding to wet then to drought habitat; the results are as follows: A. philoxeroides could change anatomical structures sensitively to adapt to water regime. As a whole, effects of water regime on structures in stem were greater than those in leaf. Except for principal vein diameter and stoma density on leaf surfaces, all other structural traits were significantly affected by water regime. Among which, cuticular wax layer, collenchyma cell wall, phloem fiber cell wall, and hair density on both leaf surfaces thickened significantly with decrease of water availability, whereas, pith cavity and vessel lumen in stem lessened significantly; wet habitat is vital for the spread of A. philoxeroides from flooding to drought habitat and vice versa, because in this habitat, it had the greatest structural variations; when switching from flooding to wet then to drought habitat, the variations of cuticular wax layer, collenchyma cell wall, phloem fiber cell wall, pith cavity area ratio, diameter of vessel lumen, and hair density on both leaf surfaces, played the most important role. These responsive variables contribute most to the adaptation of A. philoxeroides to diverse habitats with considerably various water availability.

Clonal integration affects growth, photosynthetic efficiency and biomass allocation, but not the competitive ability, of the alien invasive Alternanthera philoxeroides under severe stress.

Many notorious alien invasive plants are clonal, but little is known about some roles and aspects of clonal integration. Here, the hypothesis is tested that clonal integration affects growth, photosynthetic efficiency, biomass allocation and competitive ability of the exotic invasive weed Alternanthera philoxeroides (Amaranthaceae). The apical parts of Alternanthera were grown either with or without the lawn grass Schedonorus phoenix (tall fescue) and their stolon connections to the basal parts grown without competitors were either severed or left intact. Competition greatly reduced the maximum quantum yield of photosystem II (F(v)/F(m)) and growth (biomass, number of ramets and leaves, total stolon length and total leaf area) of the apical Alternanthera, but not the biomass of S. phoenix. Stolon connections significantly increased F(v)/F(m) and growth of Alternanthera. However, such effects on growth were smaller with than without competition and stolon connections did not alter the relative neighbour effect of Alternanthera. Stolon connections increased Alternanthera's biomass allocation to roots without competition, but decreased it with competition. Clonal integration contributed little to Alternanthera's competitive ability, but was very important for Alternanthera to explore open space. The results suggest that the invasiveness of Alternanthera may be closely related to clonal integration.

Invasive Alternanthera philoxeroides: biology, ecology and management

喜旱莲子草Alternanthera philoxeroides原产于南美洲,属于苋科Amaranthaceae莲子草属Alternanthera。一百多年来,该物种通过压舱水或军马饲料被传播到北美洲、大洋洲、欧洲,以及东南亚和中国等地,成为暖温带-热带湿润气候区淡水生态系统的重要外来入侵种。本文结合对喜旱莲子草在原产地的分布状况的考察、原产地和入侵地喜旱莲子草的比较研究,以及入侵生态学研究的最新成果,对该物种在原产地的地理分布和种内变异、生活史特征、入侵机制和控制策略等方面进行评述,以提高我国科研人员对这一外来入侵种的认识,为科学管理和控制提供依据。