Aims Leaf traits are closely related to plant light use efficiency and photosynthesis. They can indicate plant adaptation strategies to the environment. Spartina alterniflora is a major alien invasive plant in many coastal wetlands, and it seriously threatens coastal wetland ecosystems in China. Tidal flooding is one of the main limiting factors for the growth and distribution of S. alterniflora in coastal wetlands. However, there has been very little research directly examining the pattern and adaptation mechanism of leaf traits of S. alterniflora along a tidal gradient.

Methods In this study, a tidal elevation control platform was established in Zhangjiang Estuary, Fujian. We studied the response pattern and driving factors of leaf functional traits (length, width, length width ratio, area, dry mass, and specific leaf area) of S. alterniflora to the tidal gradient (relative elevation).

Important findings The results showed that: (1) The leaf length, leaf width, leaf area, and leaf dry mass of S. alterniflora decreased with increasing elevation, whereas the leaf length width ratio increased with increasing elevation. (2) The specific leaf area of S. alterniflora and elevation showed a hump-shaped relationship. (3) The effects of inundation frequency, soil porewater salinity, and soil water content on leaf traits were different. The leaf length, leaf width, leaf area, and leaf dry mass of S. alterniflora increased with increasing inundation frequency and soil water content, but decreased with increasing soil porewater salinity; the leaf length width ratio of S. alterniflora decreased with increasing inundation frequency and soil water content, but increased with increasing soil porewater salinity; the specific leaf area of S. alterniflora increased first and then decreased with increasing inundation frequency, and increased with increasing soil water content. In summary, the patterns and main driving factors of leaf traits of S. alterniflora differed along a tidal gradient, and this finding may be due to differences in the effects of leaf traits on plant physiological processes. Thus, S. alterniflora can adapt to changes in tidal elevation by adjusting leaf traits and their trade-offs. This study provides a new perspective for understanding and predicting the ecological adaptation of S. alterniflora to sea level rise in coastal wetlands.

Aims Exotic plants invasions impact both function and stability of ecosystems. Compared with native plants, invasive plants are generally characterized by stronger stress resistance and resource utilization abilities. Nitrogen deposition, as an important issue of global change, can directly increase soil nitrogen availability and promote plant invasions. Soil microorganisms, including both fungi and bacteria, play an important role in regulating soil nutrient availability and nutrient uptake, both of which are highly associated with successful invasion of plants. However, the effects of soil fungi and bacteria on the growth of invasive plants from different origins under nitrogen deposition background remain unclear.

Methods To understand the effects of soil fungi and bacteria on the growth of invasive plants from different provenances with nitrogen addition, both original and invasive Triadica sebifera were chosen as model plant populations. Soil bacterial inhibitor (streptomycin) and fungal inhibitor (iprodione) were applied to regulate the activity of soil bacteria and fungi communities. Nitrogen deposition was simulated by nitrogen addition treatment to understand the growth response of T. sebifera with different population origins as affected by different soil microbial communities under the context of nitrogen deposition.

Important findings The results showed that, invasive provenance of T. sebifera presented substantial growth advantage in terms of plant height, leaf number and biomass compare with that of native provenance. Soil bacterial and fungal inhibitor applications significantly reduced aboveground biomass of T. sebifera. Moreover, the growth of T. sebifera is more dependent on soil bacteria. Nitrogen addition and its interaction with soil bacteria and fungi significantly affected both the growth and resource allocation of T. sebifera, which could have enhanced the competitive ability of T. sebifera for resources during range invasion process, and should be focused in future studies.

Aims Many factors can influence the invasiveness of alien plants, and among them endophytes may play a key role. Thus, the aim of this study is to investigate the effects of endophytic nitrogen-fixing bacteria on the growth strategy of invasive plants.

Methods We grew the invasive plant Sphagneticola trilobata and its native congener S. calendulacea infected by endophytic nitrogen-fixing bacteria or not under two nitrogen levels (low and high) and compared their growth and total nitrogen content.

Important findings The endophytic bacteria Kosakonia sp. WTB-JS007, isolated from S. trilobata, had different effects on the growth strategy of the two species (S. trilobata and S. calendulacea) and such an effect did not depend on the nitrogen levels. Under the low nitrogen level, inoculation with WTB-JS007 showed no significant effect on the growth or total nitrogen content of S. calendulacea, but significantly increased aboveground biomass (by 30.48%), promoted stolon length, decreased belowground biomass (by 56.58%), and enhanced total nitrogen content (by 47.51%) of S. trilobata. Similarly, under the high nitrogen level, endophytic bacteria stimulated the aboveground growth of S. trilobata, but had no effect on that of S. calendulacea. These results suggest that endophytic nitrogen-fixing bacteria can differently affect the growth, biomass allocation and nitrogen uptake of invasive and its co-occurring native plant species. Such a difference in the growth strategy can facilitate the rapid growth and expansion of the aboveground part of invasive plants and thus promote their invasiveness.

Aims The interspecific interactions between plants are vital for species survival. For biological invaders, stronger competitive ability allows them to invade successfully when appearing with indigenous species, which is considered as an important mechanism underlying successful invasion. However, environmental changes may alter interspecific interactions, thus impacting invasion consequences. In this study, we aimed to explore the effect of acid rain, which is a seriously environmental problem worldwide, on the interactions between a Chinese invader common ragweed (Ambrosia artemisiifolia) and its accompanying indigenous forb (Bidens bipinnata) to further explore the role of an environmental disturbance in biological invasions.

Methods In March 2021, we performed a de Wit replacement competitive experiment with A. artemisiifolia and B. bipinnata at the campus of Beijing Normal University; meanwhile we also simulated acid rain through providing different concentrations of solutions (pH = 3, 4, 5, 7). Plant height after 24, 34, 45 days, final plant height, and aboveground biomass were determined for each individual plant. Relative neighbor effect (RNE) and replacement diagrams were used to estimate interspecific competition.

Important findings When the two species were planted separately, the medium level of an acid solution (pH = 4) promoted their early growth, and the high level of an acid solution (pH = 3) significantly inhibited their early growth but did not affect the final plant height. When grown together, the ragweed showed a decrease in plant height in the presence of the high level of an acid solution (pH = 3) after 34 and 45 days, but this negative effect disappeared at harvest. The plant height of bidens applied with the high level of an acid solution (pH = 3) decreased significantly at harvest compared with the control treatment. The RNE of bidens on ragweed was not significant under all the treatments, while the RNE of ragweed on bidens was significant without acid application or under the condition of acid treatments at a lower proportion of bidens. Replacement diagrams showed that the bidens had an advantage over ragweed when applied with the low level of an acid solution (pH = 5) at higher proportions, and the ragweed had an enhanced advantage over bidens when applied with the high level of an acid solution (pH = 3). Our study suggests that acid rain might affect the growth of ragweed and bidens as well as their interactions, and acid rain with low pH may boost the competitive advantage of invasive ragweed.

On the basis of a brief discussion of the definitions of alien plants, we summarized the investigation and research status of China’s naturalized alien plants, and made corrections of the data regarding naturalized alien plants on two papers in 2019 and 2021.

Under global change, the variations of resources such as nutrients and water are not stabilized and often occur in the form of pulses with low frequency, large amplitude, and short duration. The existing evidence suggests that resource pulses have the potential to disrupt the inherent equilibrium of plant communities, and thereby play a critical role in another important component of global change, plant invasion. To date, studies on the impacts of global change on plant invasion have mainly focused on the constant changes of resources, but have ignored the resource fluctuation, in particular the role of resource pulses. Here, we present a literature review concerning the effects of resource pulses on plant invasion, including causes, types and impacts of resource pulses. Then we discuss the importance of resource pulses in plant invasion. Furthermore, our review puts forward some fields that are worthy to be paid more attention in the future, such as the importance of attributes and types of resource pulses, their interactive impacts on and potential mechanisms in plant invasion.

Aims Due to fast-growing and high drought stress tolerance, Leucaena leucocephala has been widely used for afforestation in degraded tropical forests worldwide, but it is also a global invasive exotic species. Studies have shown that fast-growing can help L. leucocephala successfully invade subtropical forests. In this study, we aimed to investigate whether fast-growing and high drought stress tolerance can help L. leucocephala invade tropical rain forests.
Methods The pioneer community of tropical rain forest which had been invaded by L. leucocephala in the Baopoling Mountain, Sanya, China was the research object. Through the t-test, we compared the differences in key functional traits that were related to growth rate (photosynthesis rate, stomatal conductance and transpiration rate) and drought stress tolerance (leaf turgor loss point) in both wet and dry seasons between L. leucocephala and eight dominant native species of pioneer community of tropical rain forest. And the principal component analysis (PCA) was used to investigate whether these functional traits can best discriminate between Leucaena leucocephala and the eight dominant native species.
Important findings Leucaena leucocephala could be invariably growing fast (photosynthesis rate, stomatal conductance and transpiration rate much higher than native species) from wet to dry seasons and had higher drought stress tolerance (leaf turgor loss point much lower than native species) in the dry season. The results of PCA showed that these functional traits could significantly discriminate between L. leucocephala and the eight dominant native species. Therefore, invariable fast-growing from wet to dry season and high drought stress tolerance in the dry season make L. leucocephala successfully invade pioneer communities of tropical rain forests. In the future, these functional traits can be used to select many native species to perform biological control of L. leucocephala in other tropical forests.

Mycorrhizal fungi symbiosis is an important strategy for plant to uptake soil nutrients. Alien plants could thwart the symbiotic relationship between native plants and mycorrhizal fungus, and thus suppress the growth of native plants, which is an important mechanism for alien plant invasion, and has been increasingly emphasized in recent studies. In the present review, we summarized several key aspects of such mycorrhizal-related mechanism of plant invasion: 1) the impacts of alien plants on mycorrhizal fungi of native plants (i.e. mycorrhizal colonization rate, internal structures of mycorrhizal hyphae, amount of external hyphae, mycorrhizal and non-mycorrhizal composition, and mycorrhizal network); 2) mechanisms of alien-plant impacts on mycorrhizal fungi of native plants, including ecological mechanisms such as resource competition, allelopathy and edaphic fertility, as well as their molecular mechanisms; 3) variations of the above mentioned alien-plant impacts and related mechanisms at different durations of plant invasion. Despite thwarting mycorrhizal fungi of native plants is an important mechanism for alien plant invasion, researches on such mechanism are still scarce comparing to other mechanisms such as natural enemy release and new weapon hypothesis. Therefore, we proposal several research areas that need to be focused on in future studies: 1) how do global changes affect the alien-plant-invasion impacts on mycorrhizal fungi of native plants; 2) what are the relationships among different mechanisms including the mycorrhizal-related mechanism; 3) how does the mycorrhizae-related mechanism change at large spatio-temporal scales.

Aims Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with most terrestrial plants, contributing to the nutrient uptake of host plants. While little is known on how rhizospheric microorganisms affect the relationships between AMF and host plants under nutritional stress. We hypothesize that AMF may compete for nutrients with host plants in extremely nutrient-limited environments, such as nitrogen deficient habitats, and nitrogen-fixing bacteria will alleviate the competition.
Methods In order to test our hypotheses, we grew Solidago canadensis plants under nitrogen deficient treatments. We inoculated plants with AMF and a nitrogen-fixing bacterium to test the relationships among the host plant and microorganisms.
Important findings Under the lowest nitrogen level (0.025 mmol·L^-1 N of ammonium nitrogen), the growth of S. canadensis was more restricted with AMF colonization, suggesting competition between AMF and the host. However, with the inoculation of nitrogen-fixing bacterium, AMF colonization was promoted and plant growth was increased. These results indicate that nitrogen-fixing bacteria could moderate the competition for nutrients between AMF and their host under nitrogen deficiency. This study improves our understanding of the invasion mechanisms of alien plants, where they interact with different microorganisms under extreme nutrient stress.

Aims Invasive plants are a subset of naturalized plants, and naturalization is a fundamental precondition for plant invasion and so compiling a complete inventory of naturalized alien species is necessary for predicting and hence preventing such invasion.
Methods Based on field investigations and various literature reports, we compiled a nationwide list of the naturalized plant species of China.
Important findings The results showed that there are 1 099 naturalized plants belonging to 112 families and 578 genera in China, 70% of them were introduced intentionally and were of American origin, followed by those with European origins, herbs were prevalent among naturalized species. Compositae, Gramineae and Leguminosae were the three most dominant families. Spatially, species diversity and density decreased from the southeast coast to inland northwest. Latitude and gross domestic product is the primary driver of this pattern, however, colonial history, distribution of botanical gardens and the number of surveys may also affect formation. In temporal terms, species diversity is currently in a period of rapid growth and will continue for 20 to 30 years. Social and economic development, human disturbance, land use and global change are the main drivers. This study enriches the background information about naturalized plants and improves our knowledge on threats associated with plant invasions in China. The gained information can be used to provide arguments for efforts on control and management of alien plants or conservation of native biodiversity in the country.

Aims Solidago canadensis, an invasive herbaceous species, has a strong capacity of potassium enrichment, that may relate to its influence on soil microbial community. Rhizosphere potassium-soluble bacteria can convert mineral potassium into soluble forms being able to be used by plants. It is not known how invasion of S. canadensis may affect diversity and potassium-solubilizing activity of the potassium-solubilizing bacteria. Methods We compared S. canadensis and its coexisting native plant Imperata cylindrica in the reclaimed Hangzhou Bay wetland, Zhejiang Province. We compared the potassium contents of soil and the plant tissues of S. canadensis and Imperata cylindrica which coexists with the invasive species, the effect of potassium supply level on biomass accumulation of plants, and the quantity, diversity and potassium-soluble activity of the rhizosphere potassium-solubilizing bacteria. Important findings The potassium contents in stem and leaf of S. canadensis were significantly higher (1.59 and 7.33 times respectively) than that of I. cylindrica, the contents of available potassium in the 0-10 cm soil layer where the two species grew were significantly different, but not in the 10-20 cm soil layer. Potassium application experiments showed significant biomass increase in both S. canadensis and I. cylindrica, and tissue potassium concentrations as well. Potassium-dissolving medium culture results showed that the number of potassium-‌solubilizing bacteria of S. canadensis rhizosphere was 2.51 times higher than that of I. cylindrica. The strains with potassium-dissolving rings were identified, and the amount of released potassium was determined. Among the 15 strains of potassium-solubilizing bacteria isolated from the rhizosphere soil of S. canadensis, nine efficiently dissolved potassium, and the content of K ⁺ in the treatment solution was 85.11%-192.54% higher than that in the control. Strain H2-20 had the strongest ability with the dissolved K ⁺ of 10.657 mg·L ^-1. The potassium- solubilizing effect of rhizosphere potassium-solubilizing bacteria of S. canadensis was significantly higher than that of I. cylindrica. According to 16S rDNA identification, the 15 strains of bacteria associated with S. canadensis were of 11 genera, and 6 of them had been reported to have the potassium-solubilizing ability. Our results suggest that potassium-solubilizing bacteria in the rhizosphere of S. canadensis is abundant, and may play an important role in potassium enrichment.

Aims Exotic plant invasion has been a global eco-environmental issue, which declines biodiversity and influences ecosystem structure and function. Over the past decades, more and more studies showed that influences of exotic plant invasion on soil nitrogen (N) cycles, and soil N availabilities can facilitate the success and aggravation of invading plants.
Methods Based on differences in soil N contents between invaded and uninvaded areas in natural ecosystems at the same study sites, this study explored magnitudes and ecophysiological mechanisms of soil N variations under exotic plant invasion.
Important findings Based on the data integrated from 107 papers, we found that contents of soil total N, ammonium-N, nitrate-N, inorganic N, microbial biomass N under exotic plant invasion were increased by (50 ± 14)%, (60 ± 24)%, (470 ± 115)%, (69 ± 25)%, (54 ± 20)% respectively relative to those under no invasion. The increment in the soil nitrate-N pool was highest, suggesting higher nitrification rate, which potentially promoted plant nitrate-N utilization and the coexistence of nitrate-preferring species. The increment of soil nitrate-N pool under invasion was higher in the temperate zone than the subtropical zones significantly. Invasion of N₂-fixing plants caused obviously larger increments of soil total N and nitrate-N contents compared to invasion of non-N₂-fixing plants. The invasion of woody and evergreen invasive plants caused larger increments of soil total N than herbaceous and deciduous plants, respectively. The increases in soil ammonium-N under invasion did not differ substantially among different life forms and showed no clear relationship with the percentage of N₂-fixing plants. Differently, soil nitrate-N showed much larger increments under invasion and showed positive linear relationship with the percentage of N₂-fixing invasive plants. The N₂-fixing function, litter quality and quantity of invasive plants are important factors regulating soil N mineralization and nitrification under invasion. This study provides novel insights into the mechanisms underlying the success and aggravation of plant invasion and into the relationships between soil N dynamics and plant functional traits in ecosystems under exotic plant invasion.

Invasive alien plants not only influence plant community composition, biodiversity and ecosystem structure and function, but also have severe impacts on soil nitrogen transformation processes. The effects of invasive alien plants on nitrogen (N) cycling have been one of the hot topics in invasion ecology. Litter decomposition and its nutrient release play an important role in nutrient cycling. In addition, invasive alien plants have the potential to influence soil N transformation through allelopathy. All these processes are tightly related to soil microbes. Therefore, this review mainly focuses on litter decomposition and its nutrient release, and allelopathy to understand the effects of plant invasion on soil N transformation. Changes in soil N transformation and soil microbes (esp. Ammonia oxidizing bacteria and Ammonia oxidizing archaea) due to plant invasion, as well as the feedbacks of these changes to further invasion of alien plants were discussed. Finally, the interactions between arbuscular mycorrhizal fungi and plant invasion were reviewed.

Aims Darwin’s naturalization conundrum describes the paradox that the relationship of exotic species to native residents could either promote or hinder invasion success through opposing mechanisms: niche pre-adaptation or competitive interactions. Previous Darwin’s naturalization studies have showed invasion success could vary at stages, sites, and spatial and phylogenetic scales. Our objective was to assess the effects of exotic-native species relationship on invasion process of exotic plant species in China, where related research is still lacking.
Methods Generalized linear mixed models were used to examine relationship between exotic-native species relationship and performance of exotic species at different spatial scale (provincial, municipal and community) and invasion stages (naturalization, dispersal and invasion). At community scale, we measured environmental factors of communities we investigated to control the effect of habitat heterogeneity among them.
Important findings At the provincial and municipal scales, exotic species closely related to native flora were more likely to be naturalized and distributed, which is more consistent with the expectation of the pre-adaptation hypothesis. On the community scale, the exotic-native species relationship was not related to establishment and abundance of exotic species in the community. The results suggested that exotic species did not strongly compete with their close native relatives in communities, but were better adapted to areas where their close relatives had lived. Considering their high potential of naturalization and invasion, special attention should be paid to those exotic species that closely related to the native flora in the management of invasive species.

Aims Exotic plant invasions are important components of global change, threatening both the stability and function of invaded ecosystems. Shifts in competitive ability of invasive plants versus their native congeners have been documented. Enhanced UV-B radiation and nitrogen (N) deposition might interact with soil biota communities impacting the invasion process of exotic plant species. To understand the potential effects by UV-B and N with soil biota on plant growth would enhance our understanding of the mechanisms in plant invasions in the context of global change.
Methods We conducted a full-factorial pot experiment in the native range (China) of Triadica sebifera invading US to investigate how UV-B radiation, N and soil biota together determined their seedling growth.
Important findings The results showed that UV-B radiation, N and soil sterilization together impacted the growth of T. sebifera seedlings. UV-B radiation induced changes in biomass allocation with larger leaf biomass observed in response to UV-B radiation. In addition, N increased aboveground biomass and decreased root biomass simultaneously. Soil biota imposed positive effects on growth of T. sebifera, and the addition of N amplified these positive effects. The negative effects by UV-B radiation on growth of T. sebifera showed no response to N addition. Plant height, leaf biomass and total biomass of the invasive T. sebifera populations out- performed those of the native ones. In addition, invasive T. sebifera populations weakened the dependence of root/shoot ratio and root biomass on local soil microorganisms than native populations, but enhanced that of leaf area ratio.

Aims Stoichiometric homeostasis is an important mechanism in maintaining ecosystem structure, function, and stability. The invasion of exotic species, Spartina alterniflora, has largely threatened the structure and function of native ecosystems in the Minjiang River estuarine wetland. However, how S. alterniflora invasion affect plant stoichiometric homeostasis is largely unknown. This could enhance our understanding on wetland ecosystem stability and expand the applications of ecological stoichiometry theory.
Methods Nitrogen (N) and phosphorus (P) contents of plant organs and soils in the S. alterniflora, Cyperus malaccensis var. brevifolius, and S. alterniflora-C. malaccensis var. brevifolius mixture were measured, and the homeostatic index (H) was calculated according to the stoichiometric homeostasis theory.
Important findings Our results showed that the invasion of S. alterniflora significantly increased soil N:P ratio (p < 0.05), but did not affect soil N or P contents. The N and P contents of leaf and stem were the highest for S. alterniflora, and those of the stem were the highest for C. malaccensis var. brevifolius. At the ecosystem level, the average of homeostatic index (H) of N (H_N, 25.31) was larger than those of P (H_P, 10.33) and N:P (H_N:P, 2.50). At the organ level, root H_N was significantly larger than stem H_N (p < 0.05) and sheath H_N:P was greater than root H_N:P (p < 0.05), while there was no significant difference for H_P among root, stem, leaf, and sheath (p > 0.05). As for species, root H_N of S. alterniflora was significantly larger than that of C. malaccensis var. brevifolius in the mixture community (p < 0.05). In the monoculture, stem H_N:P of S. alterniflora was significantly higher than that of C. malaccensis var. brevifolius (p < 0.05). Furthermore, root H_N, leaf H_N and sheath H_N of S. alterniflora in the mixed community was significantly larger than that of S. alterniflora in the monoculture (p < 0.05), suggesting that S. alterniflora invasions increased their stoichiometric homeostasis. Meanwhile, the stoichiometric homeostasis of invasive and native plants were influenced by multiple factors, such as nutrients, organs, vegetation, and invasion. However, larger homeostasis was found in S. alterniflora than in C. malaccensis var. brevifolius in some particular organs either in mixture or monoculture communities. Therefore, the successful invasion of S. alterniflora may result from higher homeostatic index than the native species, C. malaccensis var. brevifolius.

Aims The extensive use of herbicide to control invasive plants would change the relationship between alien and neighboring plants. In order to provide data for rational use of herbicide and a theoretical reference for further studies on the ecological effects of glyphosate, we explored the variation of the relationship between an invasive plant Solidago canadensis and a native plant Imperata cylindrica when they were sprayed glyphosate.
Methods A replacement series experiment was conducted from June to August 2016 in Wetland Ecosystem Research Station of Hangzhou Bay, State Forestry Administration, to examine the effects of glyphosate at seven concentration levels (0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 mL·L^-1) on the growth and interspecific competition of S. canadensis and I. cylindrica.
Important findings (1) Glyphosate treatment significantly inhibited the growth of S. canadensis and I. cylindrica (p < 0.05). During the test, cumulative growth of height and leaf number of S. canadensis were apparently reduced with the increase of glyphosate concentration, but the leaf number of S. canadensis treated with 0.3- 1.5 mL·L^-1 glyphosate was re-growing with time, while the one treated with 1.8 mL·L^-1 was mostly dead. The withering rate of tiller and green leaf of I. cylindrica also significantly increased with the increase of glyphosate concentration, and the growth indices of this plant treated with 0.3-0.6 mL·L^-1 were also re-growing with time. (2) Glyphosate treatment significantly affected interspecific competition (p < 0.05), which diminished as the glyphosate concentration increased. (3) Interspecific competition has significant influence on the biomass allocation of S. canadensis (p < 0.05). When facing competition, S. canadensis would allocate more organic matter to root and thus increase the ratio of root to shoot. Competition only inhibited the tiller number and total biomass of I. cylindrica, but insignificantly affected its ratio of root to shoot. (4) The interaction between glyphosate treatment and S. canadensis-I. cylindrica interspecific relationship also significantly influenced the biomass of S. canadensis and I. cylindrica (p < 0.05), but insignificantly affected the root/shoot ratio of two plants. Different plants have different tolerance to glyphosate stress. Compared with native plant I. cylindrica, S. canadensis has stronger tolerance to glyphosate. Low-concentration glyphosate could decrease the competitive intensity between S. canadensis and I. cylindrica, which may disturb the structure and dynamics of plant communities.

Aims The cordgrass Spartina alterniflora is one of the highly successful invasive plants in coastlines worldwide. Although the S. alterniflora invasion is threatening mangroves and the increasing heavy metal pollution of oceans and coasts are of growing concerns, especially in China, the effects of S. alterniflora invasion on the enrichment of sedimental heavy metals in mangrove wetlands are not known. The objectives of this study are to determine the effects of S. alterniflora invasion on enrichment of sedimental heavy metals in the mangrove wetland and the underlying mechanisms.
Methods We investigated differences in the contents of sedimental heavy metals, including As, Cd, Cr, Cu, Ni, Pb, Zn, and Mn, for two pairs of comparisons (unvegetated shoal vs S. alterniflora monoculture and Avicennia marina monoculture vs A. marina + S. alterniflora mixture), and their relationships with environmental factors in Zhanjiang Mangrove National Natural Reserve, Guangdong, China.
Important findings Spartina alterniflora invasions in mangrove wetlands increased the contents of sedimental heavy metals, with the effects being significant on Cr, Ni, Cu, Zn, and Mn. The intermediate level of pollution was only detected in the sedimental Cd. The presence of S. alterniflora resulted in enrichment in the sedimental heavy metals in the mangrove wetland in Zhanjiang, but not to the degree of concerns for contaminations. The contents of sedimental organic matter, total C, total N, total S and total K were strongly related to the contents of sedimental heavy metals in the invaded mangrove wetland. Ultimately, the dense above-and below-ground architectures of the invasive S. alterniflora likely play a predominant role in causing enrichment of sedimental heavy metals.

Aims How alien invasive plants and co-occurring native plants utilize nutrients is one of major issues in invasion ecology. Foliar nitrogen (N) and phosphorus (P) contents and stoichiometry can elucidate the uptake ability and limitation status of nutrients in plants, which provides basic knowledge for understanding the invading ability and co-occurrence or disappearance of plants.
Methods Based on typical alien invasive plants (Chromolaena odorata, Ageratina adenophora) and native plants in southwestern China, this study focused on strategies of N and P utilization among invasive plants and native plants under different invasion conditions. The species compositions, aboveground biomass, leaf N and P contents and leaf N:P were investigated for plants in plots with no invasion and with different invasion extents (estimated by the plot-based percentage of invaders’ biomass in total community) at Mt. Kongming in Xishuangbanna region, Yunnan Province, China.
Important findings The species number decreased significantly with the invasion extent of both C. odorata and A. adenophora, although the aboveground biomass was greatly enhanced. Leaf N and P contents did not differ between the two studied invaders, but they showed significantly higher N and P levels than both co-occurring and only native species (p < 0.05). Besides, leaf N and P contents of invaders increased with the invasion extent, and leaf N of native plants also showed an increasing trend with the invasion extent. When the influence of invasion was checked for the same species, leaf P contents decreased, whereas leaf N and N:P increased for most native plants under invasion. Based on the absolute foliar N and P contents, N:P values, we inferred that native plants were still limited by N, although N availability might be enhanced by invasion. Both invasive plants had leaf N:P values lower than 10, suggesting a higher P uptake relative to N uptake. All above results highlighted a higher N and P uptake of typical alien invasive plants in southwestern China.

Aims Soil nitrogen (N) availability is the most limiting factor for terrestrial plant growth, and global N deposition can improve the soil N availability. Fast growth may be a general trait of successful invaders, so learning how N addition affected the growth and competitive ability of three Centaurea stoebe populations is conductive to forecasting the plant invasion risk under N deposition.
Methods We conducted an experiment simulating N deposition at Chengdu, in which three populations from the invasive forb C. stoebe and one native species Poa pratensis were subjected to two treatments: N addition and ambient. In our study, C. stoebe populations and P. pratensis were planted alone or together, and we determined plant height, leaf area and biomass.
Important findings In the absence of competition, N addition promoted the growth of C. stoebe populations, thereby improving their invasive potential to a certain extent. So under the condition of competition, we found that N addition obviously enhanced the competitive effects of C. stoebe on P. pratensis, particularly interspecific root competition. The competitive ability of different populations performed similarly in response to N addition. These results preliminarily suggest that N deposition may increase the potential invasion risks of C. stoebe populations by improving their competitive ability.

To examine our current understanding on biological invasions in mangrove forests, relevant information from literature was reviewed and several key points were summarized based on the database of ISI Web of Science and the information analysis software HistCite. First, most of the studies have focused on the invasion of plant species in mangrove forests, and little attention are paid to other organisms. Secondly, there is an obvious bias on the locations of study sites, with most being situated in the southern and southeastern coasts of China (especially in the Pearl River Estuary and west of the Leizhou Peninsula) and the southeastern coast and Hawaiian Islands of the United States. Thirdly, that whether Sonneratia apetala can result in invasion is still a hot but controversial topic. Introduction of this species should be cautious. Forth, Spartina alterniflora and Mikania micrantha are the most notorious invaders around the world; both possess fast growth rate, high reproductive and competitive capacity, and strong allelopathic effects. They have invaded mangrove forests and caused severe ecological consequences, and apparently deteriorated the microhabitat and changed the benthic organisms’ community. Fifth, Rhizophora mangle has invaded Hawaiian Islands as an exotic mangrove species, modified the sedimentary environment, and enriched the benthic organisms, but the impacts are yet to be considered at the global scale. In general, studies on biological invasions in mangrove forests are still at the infant stage and we know little about the underlying mechanisms of the invasions. Specific strategies are lacking for controlling the invasion. The state of invasion and corresponding impacts should be continually focused in future studies. Exploration of the mechanisms and controlling strategies of invasion in mangroves should be launched as soon as possible. The assessment of the effects of biological invasion on ecological services of mangroves should also be emphasized. Finally, a sound management system for the control of biological invasions in mangrove forests is urgently needed.

Bamboos (Poaceae: Bambusoideae) have posed a serious threat to native ecosystems, though they play an important role socially and economically. Here we review recent research progresses on bamboo expansion with emphasis on process, consequence and mechanism. Based on the review it is considered that (1) the bamboo expansion process can be divided into four stages including underground extension, aboveground sprouting, exclusive competition, and absolute dominance; (2) Bamboo expansion will likely lead to drastic shifts in community structure and composition, biodiversity, soil properties (physical, chemical and microbial), ecological processes and functions, and local landscape; and (3) bamboos, with many inherent superiorities of rapid growth, clonal reproduction, phenotypic plasticity and collaboration, could gradually invade into adjacent communities especially derived forests, by means of shading, physical damage, litterfall, nutrient competition and allelopathy. Disturbances to neighboring communities are likely to facilitate bamboo expansion. Therefore, bamboo expansion is a typical example of local biological invasion brought about by interactions among inherent superiority, resource opportunity and disturbance by human or nature (wind, snow-ice, etc.). At a time of rapid global changes, we are confronted with new challenges from biological invasion. We recommend that priorities for future studies should be directed at understanding the responses and adaptions of bamboo to global environmental changes, bamboo-broadleaved/coniferous forest interface characteristics, bamboo expansion process and pattern, ecological risk evaluation, management and control strategies of bamboo expansion, and proper utilization of bamboo resources. This overview suggests that more attentions should be paid to native invasive species aside from alien species.

Aims In order to explore the main reasons and the invasive processes of water hyacinth (Eichhornia crassipes) in the dike-pond district in southern China, we reviewed and comprehensively analysed the historical documents and files on the water hyacinth concerning the latest research progress on its invasion ecology.
Methods We obtained the data through searches and reviews of relevant historical documents and files.
Important findings We found that water hyacinth invaded water networks and channels of the Hangzhou- Jiaxing-Huzhou plain from 1911, and was a common aquatic plant in the Pearl River Delta region since 1911. The dike-pond system was a typical organic cycling farming system in the two regions between 1911 and 1980, when farmers generally used water hyacinth as organic fertilizer. Although local government extended cultivation techniques for water hyacinth from the late 1950s to the 1980s and farmers increased water hyacinth production in large scales, the species was still contained. However, the dike-pond ecological farming systems between the Changjiang River Delta and the Zhujiang River Delta were widely abandoned because of the rapid urbanization and industrialization, and the water environments of the wetlands deteriorated since 1980. These are the main reasons for the situation of aggressive water hyacinth invasion in southern China.

Aims The invasive alien plant Solanum rostratum has different phenotypes in different distribution areas in China. Our objectives were to determine the reason for the phenotype variation and to find typical traits of the phenotype variation.
Methods Seeds of S. rostratum collected from nine areas of distribution in China were sowed in a common garden. We investigated 10 phenotypic traits and used one-way ANOVA, principal component analysis, UPGMA cluster analysis and correlation analysis to analyze results.
Important findings Inter-population variation was significant in all morphological characters (p < 0.01), indicating that the phenotypic variation had a genetic foundation. The coefficient of variation of reproductive organs (CV = 18.2%) was higher than that of vegetative organs (CV = 9%). Analysis of CV and the principal component analysis of phenotypic traits both indicated that the traits of radius, corolla diameter, internode space and plant height were the main factors accounting for the phenotypic variations. According to UPGMA cluster analysis, the nine populations could be divided into three groups. These cluster results were not due to geographic distances. Altitude had greater influence on phenotypic traits than longitude and latitude.

Selection on defense strategies of plant species may be different in direction and magnitude among sites, because of differences in the herbivore communities in which plant populations are embedded. This may be the case for some invasive species, which are often introduced without coevolved specialists, but suffer generalist damage comparable to their native ones. We review recent advances in the adaptive evolution of defense strategies in Chinese tallow (Triadica sebifera) and other invasive plant species. We focus particularly on resistance and tolerance, direct and indirect resistance, and constitutive and induced resistance to understanding the effects of herbivores on invasive plant success. Furthermore, we evaluate the effects of changes in defense strategies on the efficiency of biological control. We also propose future research on defense strategies of invasive plant species.

Aims Understanding the impacts of invasive plants on the dynamics of native plants in invaded communities is important for the control of the invasives. Our objectives were to analyze the dynamics of native plants in communities invaded by Solidago canadensis.
Methods We selected native plant communities that had experienced different densities of S. canadensis invasion. Four different invasive stages (based on S. canadensis densities of 0, 5-7, 11-13 and >18 ind. plant∙m^-2) were determined, and 10 plots were randomly distributed in each invasive stage. The plant height, density and aboveground biomass of native species in each plot were measured. The niche breadths and niche overlap coefficients of seven common native species were determined for each plot. Nitrate nitrogen (N), ammonia N, available phosphorus (P), total P and total N of soil were measured, as was total N of plant tissue for the seven common native species.
Important findings Solidago canadensis had more N accumulation than all seven common native species. The invasion of S. canadensis significantly decreased native species richness. With greater intensification of S. canadensis invasion, niche breadth significantly increased for native species with higher plant tissue total N but significantly decreased for native species with lower plant tissue total N, and the average value of niche overlap coefficients of each native species decreased. The invasion of S. canadensis significantly increased soil nitrate N, but decreased soil ammonia N, available P, total P and total N. Results indicated that the ability to accumulate nitrogen determined the dynamics of native plant species when communities were invaded by S. canadensis.

Aims Invasive plants can alter soil physicochemical properties by changing the soil microbial community (which is closely related to plant growth and development) and thus further promote the invasion process. Our objectives were to (a) compare changes in soil bacterial diversity with cultivation of four replacement plants (Sorghum bicolor × S. sudanense, Helianthus annuus, Medicago sativa and Lolium perenne) mixed with Flaveria bidentis in different growth period and (b) determine the responses of the soil bacterial community to F. bidentis invasion and replacement.
Methods Total soil bacterial DNA was extracted by PowerSoil^® DNA Isolation Kit, 16S rRNA V3 fragments were amplified with bacterial universal primers, and purified fragments were cloned into pGEM-T-Easy vector. Sequence results were aligned on NCBI.
Important findings Soil bacterial diversity was decreased in F. bidentis monoculture and was lower than in the soils of the monocultures of the four replacement plants and in the soils of the replacement plants and F. bidentis. There were Hsignificant differencesH in soil bacterial 16S rRNA denaturing gradient gel electrophoresis (DGGE) fingerprinting patterns between the mixed- and monoculture soils. Also, there were characteristic bacterial communities with each mixed culture soil on different dates. The Shannon diversity index of soil bacteria peaked in July and decreased starting in August, and this change was synchronous with plant growth. Soil bacterial diversity was reduced following the invasion of F. bidentis, and that the diversity level was increased by cultivating replacement plants with F. bidentis. Therefore, we proposed that soil bacteria play an important role in F. bidentis invasion and control.

Aims Wind dispersal of cypsela is the prevailing natural dispersal pattern in Asteraceae alien invasive species, but few studies have addressed the relationship between the characteristics of cypsela adapted to wind-dispersal and invasiveness. Our objective is to study the relationship between wind-dispersal traits and invasiveness to provide insight into invasion mechanisms and control of alien invasive species.

Methods We selected ten wind-dispersed Asteraceae invasive species with cypselas, observed morphological traits of cypsela such as pappus number, pappus length, barb number on pappus and 1000-grain weight of cypsela and measured vertical settlement velocity in still air and horizontal dispersal distance in moving air. Correlations between morphological traits of cypsela and settlement velocity and horizontal dispersal distance were analyzed in relation to invasive range.

Important findings We categorized the ten Asteraceae invasive species into three classes with strong, medium and weak dispersal-wind potential according to morphological traits of cypsela. Correlation analysis showed that pappus traits and weight of cypsela significantly affected both the settlement velocity and the horizontal dispersal distance. The settlement velocity was significantly affected by both pappus length (r = -0.483, p < 0.001) and barb numbers on pappus (r = -0.282, p = 0.002). Factors most affecting horizontal dispersal distance were cypsela weight and pappus length. Settlement velocity and horizontal dispersal distance were negatively correlated (r = -0.806, p = 0.005). The occurrence of these Asteraceae invasive species was significantly negatively correlated with settlement velocity (r = -0.721, p = 0.019) and significantly positively correlated with horizontal dispersal distance (r = 0.927, p = 0.000), suggesting that the horizontal dispersal distance better reflected invasiveness. Agratum conyzoides and Galinsoga parviflora with high invasiveness should be primary targets for invasive species management in Nanjing, China based on our results.

Aims The invasive plant Coreopsis lanceolata can reproduce sexually and clonally, but the relative importance of these remains largely unknown. Our objective was to determine if reproductive characteristics affect the invasiveness of C. lanceolata.

Methods We observed the flowering dynamics of inflorescence, self-compatibility, germination traits of seed and clonal reproductive traits of C. lanceolata.

Important findings Most C. lanceolata flowered and fruited between April and November. The florescence of a single capitulum persisted approximately 5 to 6 days, and the fruits matured after 18 days. Bagged capitula showed there were no seed set in single capitulum, and they were geitonogamous, which indicated self-incompatibility. The pollen-ovule (P/O) ratio was 103 549.40 ± 7 162.44. There was high pollen viability during flowering, and pollinator movement ensured endogamy, which improved the rate of out-crossing. Under natural conditions, the germination percentage is >50%, and germination occurs within 2-3 days. Coreopsis lanceolata has strong asexual capacity; there were many phalanx ramets from roots during the growing season, and the guerrilla ramets only occurred beginning in the last ten days of August, which is beneficial to C. lanceolata in excluding other species and forming mono-culture populations. These results suggest that the invasiveness of C. lanceolata is closely related to its reproductive traits.

Chromolaena odorata, native to Central and South America, is a worldwide perennial invasive alien weed. It has spread into most of the humid tropical and subtropical regions of Africa, Asia, Oceania and Micronesia. Moreover, C. odorata continues to spread rapidly, posing a serious threat to crops, forestry, indigenous vegetation and biodiversity conservation. It has captured extensive attention because of its serious impacts on environment and socioeconomic development. In order to restrict its range expansion and eliminate its adverse impacts, it is necessary to elucidate the mechanisms underlying successful invasion of C. odorata, for which introduction status and invasion routes should be known. We reviewed the research on this weed, including its biological characteristics, geographic distribution, invasion consequences and control, especially its introductions, invasion routes throughout the world and mechanisms of successful invasion. We presented prospects for research on the ecophysiology and molecular biology of C. odorata, emphasizing that study of the genetic basis of adaptive evolution may facilitate elucidating mechanisms underlying its successful invasion.