One of the main factors in the successful invasion of invasive plants is their allelopathy on the growth performance (especially seed germination and seedling growth) of neighboring plants. Salt stress, mainly mediated by soil salinization, may affect or even facilitate the process of invasion of invasive plants via their allelopathy. The aim of this study was to evaluate the allelopathy effect of four Asteraceae invasive plants, including Canada goldenrod (Solidago canadensis L.), horseweed (Conyza canadensis (L.) Cronq.), rallway beggaricks (Bidens pilosa L.), and daisy fleabane (Erigeron annuus (L.) Pers.), on seed germination and seedling growth of the horticultural Asteraceae species Lactuca sativa L. under a gradient of salt stress in an hydroponic incubation experiment. Salt stress significantly reduced seed germination and seedling growth of L. sativa. These four invasive plants are known to negatively affect seed germination and seedling growth of L. sativa through their allelopathy. The allelopathy of S. canadensis was stronger than that of the three other invasive plants. Salt stress significantly intensified the allelopathy of the four studied invasive plants (especially S. canadensis), and the facilitation of salt stress on the allelopathy of the four invasive plants (especially S. canadensis) significantly increased with increasing intensity of salt stress. Therefore, the increased level of salt stress may facilitate the process of invasion of the four studied invasive plants (especially S. canadensis) via their increased allelopathy negatively affecting the seed germination and seedling growth of neighboring plant species.

Habitats with different numbers of plant species (S) may exhibit varying levels of invasibility when invaded by invasive plants (IPS). Nevertheless, there are still doubts about the relationship between S and IPS’ invasion intensity as well as the community invasibility. It is also unclear which environmental factor has the greatest influence on the community invasibility, especially in habitats with different S. A cross-plot comparison approach was employed to estimate the differences in IPS’ relative abundance and invasion intensity, the community invasibility, and plant taxonomic diversity along a gradient of S under the invasion of Erigeron annuus (L.) Pers. Plant diversity, dominance, evenness, and richness evidently increased with increasing S. The relative abundance and invasion intensity of E. annuus, as also the mean, maximum, and minimum relative abundances of all plants, and the community invasibility significantly decreased with increasing S. The community invasibility was positively regulated by the relative abundance and invasion intensity of E. annuus, but negatively regulated by plant diversity, dominance, evenness, and richness. Therefore, protecting the diversity of native plants is crucial for enhancing the resistance to IPS’ invasion.

Co-invasion recruited by multiple invasive plants (IPS) has potential to create more complicated and severe ecological threats on the ecological functions of native communities in comparison with mono-invasion of one IPS. Nevertheless, it is still unidentified whether species number of IPS (SIPS) is an vital factor regulating IPS’ invasion intensity and community invasibility under the invasion with a SIPS gradient. This study aims to estimate the influences of plant taxonomic diversity, the intensity of interspecific interactions, and IPS’ invasion intensity on the community invasibility under different invasion conditions with a SIPS gradient. A comparative field survey method was used in Jiangsu (including Zhenjiang, Nantong, Yancheng, and Lianyungang), China. Plant communities with the mono-invasion achieved by different IPS species, the co-invasion achieved by two and three IPS, and the uninvaded communities were measured. The mono-invasion caused by one IPS significantly declined the Margalef’s richness compared to the uninvaded communities. Plant taxonomic diversity, IPS’ invasion intensity, and the community invasibility increased as SIPS increases. IPS’ invasion declined the intensity of interspecific interactions. IPS’ invasion intensity and the total relative coverage contributed most to the community invasibility under the invasion with a SIPS gradient.

The mechanism driving the effects of the species number of plants (S, including native and invasive plants) on the invasion intensity of invasive plants (IPS) and community invasibility under co-invasion has not been fully elucidated. In addition, it is not clear which environmental factor has the strongest influence on the community invasibility under co-invasion across a gradient of S. This study aims to estimate the relationship among S, invasion intensity of IPS, and community invasibility, and the influence of environmental factors on the community invasibility under co-invasion mediated by two IPS across a gradient of S. The present study employed a comparative field survey method in Zhenjiang, Jiangsu, China. The appraised plant communities encompassed a co-invasion mediated by two IPS across a gradient of S ranging from three to eight plant species per community. As S, plant diversity, dominance, evenness, and richness increase, the invasion intensity of IPS and community invasibility significantly decreased. The invasion intensity of IPS was significantly positively correlated to the community invasibility. Thus, the community invasibility may be positively affected by the invasion intensity of IPS, but negatively affected by plant taxonomic diversity under co-invasion mediated by two IPS.

One key factor in the success of invasive alien species is their frequent competitive superiority over native plants. The interspecific competitive distance between invasive and native plants may vary across different communities. This study aimed to evaluate the functional differences between Solidago canadensis L. and native plants, plant taxonomic diversity, the invasion intensity of S. canadensis and the community invasibility under different interspecific competitive distances between S. canadensis and native plants. This study conducted a comparative field investigation in Zhenjiang, China. S. canadensis and native plants exhibited functionally convergence under the invasion scenario with close interspecific competitive distance, whereas they diverged functionally under the invasion scenario with distant interspecific competitive distance. The invasion intensity of S. canadensis and the community invasibility were greater under the invasion scenario with distant interspecific competitive distance than those under the invasion scenario with close interspecific competitive distance. S. canadensis declined the species number, diversity and richness of plants only under the invasion scenario with distant interspecific competitive distance. Key drivers of the invasion intensity of S. canadensis included the sunlight capture capacity and the community-weighted mean trait values, especially under the invasion scenario with distant interspecific competitive distance. Therefore, the interspecific competitive distance between S. canadensis and native plants may be a critical factor affecting the functional differences between S. canadensis and native plants, the effects of S. canadensis on plant taxonomic diversity, the invasion intensity of S. canadensis and the community invasibility.

BACKGROUND AND AIMS:Trait plasticity may be critical to the successful invasion of invasive plant species (IPS). Furthermore, multiple IPS can coexist in a given habitat. Nevertheless, it remains unclear which functional trait's plasticity contributes most to the competitive advantage of IPS under co-invasion scenarios. This study aims to evaluate the differences in trait plasticity, and to assess the contribution of the trait plasticity of multiple IPS to their competitive advantage under co-invasion scenarios mediated by three IPS, namely Erigeron canadensis L., E. sumatrensis Retz. and Solidago canadensis L., in comparison to native plants, in Jiangsu, China. METHODS:The study was conducted by cross-comparing plant communities under different invasion scenarios mediated by a different number of IPS, including plant communities invaded by one, two and three of the IPS listed above and plant communities without any invasion. KEY RESULTS:The three IPS displayed a significantly lower trait plasticity, particularly with regard to plant height, leaf size and green leaf area, in comparison to coexisting native plants, regardless of the invasion scenario. The competitive advantage of these three IPS was greatest when they invaded independently. CONCLUSIONS:The competitive advantage of these three IPS was determined largely by the plasticity of green leaf area and leaf nitrogen content.

Modifications to the invasion process of invasive plants may influence the functional dissimilarity between invasive and native plants, plant taxonomic and functional diversity, and the community invasibility. This study aimed to examine the ecological effects of the invasive tree Rhus typhina L. on the functional dissimilarity between R. typhina and native plants, plant taxonomic and functional diversity, and the community invasibility. Furthermore, this study assessed the contribution of R. typhina functional traits to its growth competitiveness as well as the relationships between the community invasibility and plant taxonomic and functional diversity under R. typhina-mediated invasion. This study employed a comparative field survey method in a wasteland located in a suburban area in northern China. A divergence in functional traits between R. typhina and native plants was observed. The plant supporting capacity and the leaf photosynthetic capacity of R. typhina were found to be significantly greater than those of native plants in the invaded communities. The leaf photosynthetic capacity of R. typhina may be a critical factor in determining its growth competitiveness. A negative correlation was observed between plant diversity and community invasibility in the invaded communities. Rhus typhina was associated with a reduction in plant diversity and richness, but an increase in the community-weighted mean trait values in the invaded communities.

This study outlines the methodologies employed to ascertain the kin recognition ability among different plant individuals proposing the root biomass allocation index (RBAI) and the contribution of the kin recognition ability to plant growth competitiveness, proposing the kin recognition facilitation index (KRFI). This study also proposed a theoretical framework, i.e., the `hypothesis of successful invasion and co-invasion of invasive plants driven by kin recognition' to clarify the successful invasion and co-invasion of invasive plants. This study will provide a robust theoretical foundation for determining the kin recognition ability among different plant individuals and the contribution of the kin recognition ability to plant growth competitiveness.

Invasive plants can disrupt the growth performance of native plants by releasing allelochemicals affecting on litter decomposition. Furthermore, these invaders can establish a plant-soil feedback loop with soil microorganisms, which promotes their continued successful invasion primarily through decomposition process. Consequently, it is of the utmost importance to conduct research that analyzes the impacts of invasive plants' allelopathy on their interaction with soil microorganisms. This study aims to investigate the effects of Amaranthus retroflexus L., an invasive Amaranthaceae plant's allelopathy, on its interaction with soil bacterial communities, compared to the native plant A. tricolor L., and also the impacts of the allelopathy of Amaranthus retroflexus on soil enzyme activities. The research was conducted via an indoor planting experiment in which a gradient of Amaranthus retroflexus leaf litter was added. In particular, Amaranthus retroflexus leaf litter resulted in an increase in pH, electrical conductivity, total nitrogen, and neutral protease activity in soil under certain treatments. The amount of Amaranthus retroflexus leaf litter and the form of incubation condition may be the primary determinants of the composition of bacterial communities in soil and the number of functional gene pathways of soil bacteria involved in the decomposition process (especially the decomposition of carbon-containing substances), rather than the alpha diversity of soil bacteria. Consequently, Amaranthus retroflexus may predominantly modify the composition of bacterial communities in soil and the number of functional gene pathways of soil bacteria involved in the decomposition process, rather than the alpha diversity of soil bacteria, to facilitate its subsequent invasion.

The allelopathy of invasive plants on the growth performance of neighboring species is a crucial factor in their successful invasion. Drought can affect this interference. Numerous invasive plants, including Bidens pilosa L., can be distributed in different regions in China. This study aimed to analyze the allelopathy of the invasive Asteraceae plant B. pilosa (using its aqueous leaf extracts) from two distribution regions (a low-latitude region and a high-latitude region) in southern China on the seed germination and seedling growth of the Asteraceae plant Lactuca sativa L. under drought (simulated using Polyethylene glycol-6000). Bidens pilosa extracts from the low-latitude region induced greater allelopathy on L. sativa than those from the high-latitude region. Drought intensified the allelopathy of B. pilosa extracts on the seed germination and seedling growth of L. sativa. Bidens pilosa extracts from the low-latitude region posed greater allelopathy on L. sativa than those from the high-latitude region under light drought. However, B. pilosa extracts from the high-latitude region exhibited greater allelopathy on L. sativa than those from the low-latitude region under heavy drought. The intensified allelopathy of B. pilosa extracts on the seed germination and seedling growth of neighboring species under drought may be beneficial to its invasion process. Therefore, it is imperative to eradicate B. pilosa as expeditiously as possible in the habitats where seeds of neighboring species are sown to reduce the allelopathy of B. pilosa on the growth performance (particularly the seed germination and seedling growth) of neighboring species, especially under drought.

The leaves of multiple invasive plants can coexist and intermingle within the same environment. As species number of invasive plants increases, variations may occur in decomposition processes of invasive plants, soil nutrient contents, soil enzyme activities, and soil microbial community structure. Existing progress have predominantly focused on the ecological effects of one species of invasive plant compared to native species, with limited attention paid to the ecological effects of multiple invasive plants compared to one species of invasive plant. This study aimed to determine the differences in the effects of mono-and co-decomposition of four Asteraceae invasive plants, horseweed ( (Erigeron canadensis (L.) Cronq.), Guernsey fleabane (E. sumatrensis Retz.), daisy fleabane (E. annuus (L.) Pers.), and Canada goldenrod ( (Solidago canadensis L.), on litter decomposition responses, soil carbon contents, soil enzyme activities, and soil bacterial community structure. Species number of invasive plants did not significantly affect on the decomposition rate of mixed leaves or mixed-effect intensity of co-decomposition. Soil pH and electrical conductivity enhanced as species number of invasive plants increased. Soil carbon contents (including soluble organic carbon content and microbial carbon content), soil enzyme (including polyphenol oxidase, FDA hydrolase, and sucrase) activities, soil bacterial alpha diversity (including the OTU species, Chao1 richness, ACE richness, and Phylogenetic diversity indexes), and the number of pathways of most functional genes of soil bacterial communities closely related to decomposition processes declined as species number of invasive plants increased. Hence, soil pH and electrical conductivity significantly increased with increasing species number of invasive plants, but soil carbon contents, soil enzyme activities, soil bacterial alpha diversity, and the number of pathways of most functional genes of soil bacterial communities closely related to decomposition processes significantly reduced with growing species number of invasive plants.

Invasive plants have the potential to create microenvironmental conditions conducive to their further invasion via the decomposition process. The plant invasion may be influenced by the contamination of heavy metals via the regulation of the decomposition process. This study aimed to elucidate the effects of the mono- and co-decomposition of the leaves of the invasive plant Amaranthus retroflexus L. and the native plant Amaranthus tricolor L. on soil physicochemical properties, soil nutrient contents, soil enzyme activities, and soil bacterial communities treated with the mono- and co-contamination of copper (Cu) and lead (Pb). The leaves of A. retroflexus decomposed slower than those of A. tricolor without the mono- and co-contamination of Cu and Pb. The decomposition rate of the leaves of the two Amaranthus plants exhibited a decline with an increase in the invasion degree of A. retroflexus without the mono- and co-contamination of Cu and Pb. The mono- and co-contamination of Cu and Pb created a negative effect on the decomposition rate of the leaves of A. tricolor, but posed a positive effect on the decomposition rate of the leaves of A. retroflexus. The stress intensity of the mono- and co-contamination of Cu and Pb on the decomposition rate of the leaves of the two Amaranthus plants decreased with increase in the invasion degree of A. retroflexus. Thus, the mono- and co-contamination of Cu and Pb may facilitate the decomposition process of A. retroflexus via the delay in the decomposition rate of A. tricolor. Accordingly, the mono- and co-contamination of Cu and Pb may facilitate the invasion process of A. retroflexus with regard to the nutrient cycling mediated by the decomposition process.

One of the principal reasons for the successful invasion of invasive plants is that these invaders can facilitate the succession of soil microbial communities in their rhizosphere. This study presents a summary of the effects of invasive plants on soil microbial communities. The effects of invasive plants on soil microbial communities encompass both indirect and direct effects. These include changes in the physicochemical properties (e.g., pH, moisture, and electrical conductivity); alterations in enzyme activities related to nutrient (especially nitrogen) cycling, and nutrient (especially nitrogen) availability levels in soil; variations in the growth performance of invasive and native plants, and the species composition of native plant communities; and changes in the alpha diversity, the relative abundance, the metabolic activity, and the community structure of soil microorganisms (especially the dominant microbial species). In general, invasive plants can cause changes in the structure of soil microbial communities (particularly functional microorganisms, such as the mycorrhizal fungi and N-fixing bacteria) in invaded ecosystems in ways that provide positive feedback for their invasiveness and negative feedback for the growth performance of native plants. This review also considers the limitations of existing studies on the effects of invasive plants on soil microbial communities. The results will provide a solid theoretical basis for elucidating the role of the interactive feedback between invasive plants and soil microbial communities in driving the successful invasion of invasive plants.

Multiple invasive plants (IPS) can coexist in the same community. The intensity of interspecific interactions among multiple plants may progressively alter with the differences in the species number of IPS (Si) under different invasion scenarios. However, the correlation between plant taxonomic diversity, Si, the invasion intensity of IPS, the community invasibility and the intensity of interspecific interactions among multiple plants under different invasion scenarios remains unclear. This study aims to estimate the differences in the intensity of interspecific interactions among multiple plants, the taxonomic diversity of plants, the invasion intensity of IPS and the invasibility of the plant community under different invasion scenarios along a gradient of Si. This study used a comparative field survey method in four cities in Jiangsu (including Lianyungang, Yancheng, Nantong and Zhenjiang), China. The species number of plants and plant richness decreased under the mono-invasion achieved by one IP compared to the uninvaded communities. Plant taxonomic diversity was negatively associated with the invasion intensity of IPS and the community invasibility. Plant taxonomic diversity was positively associated with Si. The intensity of interspecific interactions among multiple plants decreased across all invasion scenarios. The intensity of interspecific interactions among multiple plants showed a significant positive association with the ratio of the max and min relative coverage of all plants, but a significant negative association with plant evenness. Therefore, the ratio of the max and min relative coverage of all plants and plant evenness may be the main factor regulating the intensity of interspecific interactions among multiple plants under different invasion scenarios, rather than Si.

The existence of invasive alien plants (IAP) and native plants in the same environment, subjected to analogous selection pressures, renders the functional differences between IAP and native plants a key factor in determining the success of IAP invasion. This study aimed to propose a methodology for the measurement of the community-weighted trait difference between IAP and native plants by calculating the community-weighted trait difference index. A case study was conducted to determine the community-weighted trait difference between the notorious IAP Erigeron canadensis L. and native plants in the middle and lower reaches of the Yangtze River in China. This study was conducted using cross-site comparisons. The degree of invasion of E. canadensis was evaluated using its relative abundance in the invaded communities (including less invaded areas (the relative abundance < 50%) and highly invaded areas (the relative abundance >= 50%)). As the degree of invasion increased, the community invasibility and invasion intensity of E. canadensis increased. E. canadensis and native plants exhibited a higher community-weighted trait similarity in less invaded areas. The higher community-weighted trait similarity between E. canadensis and native plants can enable the realisation of E. canadensis's fast colonisation in a new habitat via pre-adaptation in the early stages of the invasion. E. canadensis and native plants displayed a higher community-weighted trait dissimilarity in highly invaded areas. The higher community-weighted trait dissimilarity between E. canadensis and native plants can facilitate the successful invasion of E. canadensis in a new habitat via stronger competitive advantage compared to native plants in the late stages of the invasion. Thus, E. canadensis and native plants exhibit a stronger community-weighted trait similarity in less invaded areas but display a higher community-weighted trait dissimilarity in highly invaded areas.

Invasive and native plants can coexist in the same ecosystem. Thus, the fallen leaves of invasive and native plants can be mixed, which can lead to co-decomposition. Invasive plants can create microenvironmental conditions conducive to their invasion process by influencing soil physicochemical properties, soil nutrient contents, and soil enzymatic activities through litter decomposition by released metabolites. Heavy metal contamination may affect the litter decomposition of invasive plants. This study was designed to elucidate the effects of the mono- and co-decomposition of the leaves of the invasive aquatic plant Eichhornia crassipes (Mart.) Solms (Common Water Hyacinth) and the native aquatic plant Nymphaea tetragona Georgi (Pygmy Water-Lily) on soil physicochemical properties, soil nutrient contents, and soil enzymatic activities under the mono- and co-contamination of Cu and Pb. This study was conducted over a six-month period using a polyethylene litter bag experiment. The type of heavy metals may be the most significant factor influencing the differences in the decomposition rate between E. crassipes and N. tetragona. The co-contamination of Cu and Pb increased the decomposition rate of the leaves of E. crassipes and the decomposition rate also increased as the invasion degree of E. crassipes increased relative to N. tetragona. The co-decomposition of the leaves of the two aquatic plants showed an antagonistic response under the mono-contamination of Pb and the control, but presented a synergistic response under the mono-contamination of Cu and the co-contamination of Cu and Pb, regardless of the invasion degree of E. crassipes. Soil enzymatic activities, especially the activities of polyphenol oxidase and cellulase, may be a significant factor influencing the litter decomposition of the two aquatic plants. Consequently, heavy metal contamination may affect the invasion process of E. crassipes with regard to the regulation of the released metabolites during the decomposition process, and this is specifically modulated by the type of heavy metals.

The successful colonization of invasive plants (IPs) may be facilitated by their nutrient release during decomposition, which alters soil physicochemical properties, enzyme activities, microbial metabolic processes and the diversity of soil microorganisms. This study aimed to examine the effects of co-decomposition of four Asteraceae IPs (Conyza canadensis, Conyza sumatrensis, Erigeron annuus and Solidago canadensis) along a gradient of invasion and a native plant (Pterocypsela laciniata) on decomposition rate, soil physicochemical properties, soil enzyme activities and the diversity of soil bacterial communities (SBCs). Leaves of C. canadensis with heavy invasion and S. canadensis with light and heavy invasion decomposed more slowly than P. laciniata. Leaves of C. canadensis with full invasion decomposed more rapidly than P. laciniata. Pterocypsela laciniata and C. sumatrensis had synergistic effects on each other's decomposition, whereas P. laciniata and S. canadensis displayed an antagonistic effect. Decomposition of the four IPs increased soil microbial carbon content but reduced soil fluorescein diacetate (FDA) hydrolase activity compared to P. laciniata. Thus, invasion degree and species identity of IPs modulate the effects of the four IPs on the decomposition rate, mixed-effect intensity of co-decomposition, soil microbial carbon content, soil FDA hydrolase activity and SBC structure.

Multiple invasive plants (IPS) with different genetic relationships can form a co-invasion in the same habitat. This study aims to determine the differences in plant taxonomic diversity, IPS’ invasion intensity and community invasibility under different co-invasion scenarios mediated by two IPS with different genetic relationships. This study used a comparative field survey method in Zhenjiang, Jiangsu, China. The analyzed plant communities including the co-invasion mediated by two IPS with different genetic relationships, including those with the same genus, those with the same family but different genera and those with different families. IPS’ invasion intensity, community invasibility and the similarity of ecological niche of two co-invaded IPS under the co-invasion mediated by two IPS with closer genetic relationship were higher than those under the co-invasion mediated by two IPS with farther genetic relationship. There were no significant differences in plant taxonomic diversity under different co-invasion scenarios mediated by two IPS, regardless of the similarity of the genetic relationship of IPS. IPS’ invasion intensity and community invasibility were significantly negatively correlated with plant taxonomic diversity. In summary, the co-invasion mediated by two IPS with closer genetic relationship can lead to stronger invasion intensity and more pronounced community invasibility. However, the similarity of the genetic relationship of IPS may be not a significant factor affecting plant taxonomic diversity under the co-invasion mediated by two IPS.

Alien species from the Asteraceae family frequently invade native plant communities. This study aims to determine how the number of Asteraceae species (i.e., Erigeron canadensis, E. annuus, and Solidago canadensis) in a co-invasion affects plant taxonomic diversity and invasibility in plant communities in China. We found that co-invasions by one or two Asteraceae species decreased plant diversity and increased community invasibility. However, co-invasion by three Asteraceae species increased plant diversity and community invasibility. We also found that plant taxonomic diversity was negatively correlated with total coverage of invasive Asteraceae species. Conversely, community invasibility was positively correlated with total coverage of invasive Asteraceae species. These findings indicate that the number of Asteraceae invasive species positively correlates with total coverage, diversity, dominance, evenness, and invasibility. Our study shows that co-invasion by three IAS may increase plant taxonomic diversity but also community invasibility, which may further facilitate subsequent invasion.

This study aimed to clarify the differences in the decomposition rates, soil carbon and nitrogen contents, soil enzyme activities, and the structure of the soil bacterial community between the four Asteraceae invasive plants (AIPs), Bidens pilosa L., Conyza canadensis (L.) Cronq., Solidago canadensis L., and Symphyotrichum subulatum (Michx.) G.L. Nesom, and the native plant Pterocypsela laciniata (Houtt.) Shih under the artificially modeled nitrogen with four forms (including nitrate, ammonium, urea, and the mixed nitrogen forms with an equal mixture of three individual nitrogen forms). The mixed nitrogen forms significantly increased the decomposition rate of the four AIPs and P. laciniata. The positive effects of the mixed nitrogen forms on the decomposition rate of the four AIPs and P. laciniata were obviously greater than those of individual nitrogen forms. Nitrogen with four forms visibly up- or down-regulated the dominant role of predominant soil bacterial biomarkers, and significantly increased the species number, richness, and phylogenetic diversity of the soil bacterial community, as well as the number of most of the functional gene pathways of the soil bacterial communities involved in the decomposition process. The decomposition rate of the four AIPs was similar to that of P. laciniata. The leaves of C. canadensis decomposed more easily than those of S. subulatum. The decomposition process of the four AIPs caused remarkable changes in the relative abundance of several taxa of the soil bacterial community and soil bacterial beta diversity, and caused apparent up- or down-regulation in the dominant role of predominant soil bacterial biomarkers and the number of several functional gene pathways of the soil bacterial communities involved in the decomposition process.