Erigeron annuus (L.) Pers. and Solidago canadensis L. antagonistically affect community stability and community invasibility under the co-invasion condition

The effects of co-invasion by three Asteraceae invasive alien species on plant taxonomic and functional diversity in herbaceous ruderal communities in southern Jiangsu, China

Invasive alien species can affect plant taxonomic and functional diversity. Multiple invasive alien species can co-invade the same plant community. However, the effects of such co-invasion on plant taxonomic and functional diversity are currently unclear. Our study aimed to estimate the effects of co-invasion by three Asteraceae invasive alien species (i.e., Conyza canadensis (L.) Cronquist, Conyza sumatrensis (S.F. Blake) Pruski and G. Sancho, and Solidago canadensis L.) on plant taxonomic and functional diversity in herbaceous ruderal communities in southern Jiangsu, China. The effects of these three invasive alien species under seven invasion combinations (including invasion by one invasive alien species, co-invasion by two invasive alien species, and co-invasion by these three invasive alien species) on plant taxonomic and functional diversity were investigated in a comparative field study of herbaceous ruderal communities. Niche differentiation mediated the functional divergence between these three invasive alien species and natives under all invasion combinations. These three invasive alien species significantly increased plant taxonomic diversity (especially plant diversity and richness) and plant functional diversity (especially Rao's quadratic entropies) under all invasion combinations. The relative abundance of invasive alien species was significantly positively associated with plant functional diversity (especially community-weighted mean trait values and Rao's quadratic entropy). The number of invasive alien species was significantly positively associated with plant taxonomic diversity (especially plant diversity and richness) and plant functional diversity (especially Rao's quadratic entropies). Thus, co-invasion by these three invasive alien species may synergistically increase plant taxonomic diversity (especially plant diversity and richness) and functional diversity (especially Rao's quadratic entropies).

Unveiling allelopathic dynamics and impacts of invasive Erigeron bonariensis and Bidens pilosa on plant communities and soil parameters

Invasive alien species are becoming more and more prevalent worldwide, Erigeron bonariensis and Bidens pilosa are two invasive species of Asteraceae in Egypt. To mitigate their detrimental effects and understand their differences in invasiveness, we compared the allelopathic potentials of E. bonariensis and B. pilosa using leachates, decaying residues, and volatilization processes. Notably, the allelopathic variances in leachates were significant, influenced by plant types, concentrations, and response patterns of target plant traits, as indicated by EC50. The relative phytotoxicity of the invasive species decayed residues peaked between 20 and 25 days in the soil, with a positive correlation with concentrations and soil properties. The highest quantities of phenolic acids were chlorogenic acid and caffeic acid reaching (5.41 and 4.39 µg g-1) E. bonariensis and (4.53 and 4.46 µg g-1) B. pilosa, in leachates extracts respectively, while in the soil extract of decayed residues were coumaric acid and ferulic acid measuring (1.66 and 1.67 µg g-1) E. bonariensis and (1.47 and 1.57 µg g-1) B. pilosa, respectively. Using GC/MS analysis, the main volatile components in E. bonariensis were 1, 8 cineole (5.62%), and α-terpinene (5.43%) and iso-Caryophyllene (5.2%) which showed the greatest inhibitory effects. While B. pilosa main constituents were trans-sabinene (5.39%) and Camphene (5.11%), respectively. Finally, the high invasion level displayed from E. bonariensis (0.221) compared with B. pilosa (0.094) which correlated with the stronger allelopathic activities against plant species, and soil properties. Therefore, the allelopathic potentialities of these species are critically relevant to their invasion success.

Biochar may alter plant communities when remediating the cadmium-contaminated soil in the saline-alkaline wetland

It is thought remediating cadmium pollution with biochar can affect plant traits. However, the potential impact of this practice on plant communities is poorly understood. Here, we established natural-germinated plant communities using soil seed bank from a saline-alkaline wetland and applied a biochar treatment in Cd-polluted wetland soil. The outcomes illustrated that Juglans regia biochar (JBC), Spartina alterniflora biochar (SBC), and Flaveria bidentis biochar (FBC) promoted exchangeable Cd transform into FeMn oxide bound Cd. Additionally, most biochar addition reduced species abundance, root-shoot ratio, biomass, diversity, and community stability, yet enhanced community height. Among all treatments, the 5 % SBC demonstrated the most significant reduction in species abundance, biomass, species richness and functional richness. Specifically, it resulted in a reduction of 92.80 % in species abundance, 73.80 % in biomass, 66.67 % in species richness, and 95.14 % in functional richness compared to the CK. We also observed changes in root morphological traits and community structure after biochar addition. Soil pH, salinity, and nutrients played a dominant role in shaping plant community. These findings have implications for biodiversity conservation, and the use of biochar for the remediation of heavy metals like cadmium should be approached with caution due to its potential negative impacts on plant communities.

Identity and Diversity of Invasive Plant Affecting the Growth of Native Lactuca indica

Despite the significant number of studies that have recently focused on plant invasion and invasive plants' success, many uncertainties still exist on the effects of invasive plant identity and diversity on the native plant response under different levels of diversity. A mixed planting experiment was conducted using the native Lactuca indica (L. indica) and four invasive plants. The treatments consisted of 1, 2, 3, and 4 levels of invasive plants richness in different combinations in competition with the native L. indica. Here, the results showed that native plant response depends on the invasive plant identity and invasive plant diversity, which increases the native plant total biomass under 2-3 levels of invasive plant richness and decreases under high invasive plant density. This plant diversity effect was more significant in the native plant relative interaction index, which shows negative values except under a single invasion with Solidago canadensis and Pilosa bidens. The native plant leaf nitrogen level increased under four levels of invasive plant richness, which means more affected by invasive plant identity than invasive plant diversity. Finally, this study demonstrated that native plant response under invasion depends on the identity and diversity of invasive plants.

A method for quantifying relative competitive advantage and the combined effect of co-invasion for two invasive plants

Image 1.

Effects of surrounding landscape on the performance of Solidago canadensis L. and plant functional diversity on heavily invaded post-agricultural wastelands

High invasiveness and well-documented negative impact on biodiversity and ecosystem functioning make Solidago canadensis L. a species of global concern. Despite a good understanding of the driving factors of its invasions, it remains unclear how the surrounding landscape may shape invasion success of this species in human-transformed ecosystems. In our study, we investigated the impacts of different landscape features in the proximity of early successional wastelands on S. canadensis biomass allocation patterns. Further, we examined the relationships between the surrounding landscape, S. canadensis cover, and plant functional diversity, used as a supportive approach for the explanation of mechanisms underlying successful S. canadensis invasion. We found that increasing river net length had positive impacts on S. canadensis rhizome, stem, and total above ground biomass, but negative effects on leaf biomass, indicating that vegetative spread may perform the dominant role in shaping the competitiveness of this invader in riverine landscapes. A higher proportion of arable lands positively influenced S. canadensis above ground and flower biomass; thus promoting S. canadensis invasion in agricultural landscapes with the prominent role of habitat filtering in shaping vegetation structure. Concerning an increasing proportion of settlements, flower biomass was higher and leaf biomass was lower, thereby influencing S. canadensis reproductive potential, maximizing the odds for survival, and indicating high adaptability to exist in an urban landscape. We demonstrated high context-dependency of relationships between functional diversity components and surrounding landscape, strongly influenced by S. canadensis cover, while the effects of surrounding landscape composition per se were of lower importance. Investigating the relationships between the surrounding landscape, invasive species performance, and plant functional diversity, may constitute a powerful tool for the monitoring, controlling, and predicting of invasion progress, as well as the assessment of ecosystem invasibility.

What modulates the impacts of acid rain on the allelopathy of the two Asteraceae invasives?

Most of the allelopathic studies have focused on the independent allelopathy of one invasive plant, but have ignored the co-allelopathy of the two invasives. The variations in the type of acid rain can modulate the invasiveness of invasives via the changes in the allelopathy. Thus, it is vital to elucidate the allelopathy of invasives, particularly the co-allelopathy of the two invasives, under acid rain with different types, to illuminate the mechanisms driving the co-invasion of two invasives under diversified acid rain. However, little progress has been finished in this aspect presently. This study aimed to evaluate the co-allelopathy of two Asteraceae invasives Solidago canadensis L. and Erigeron annuus L. treated with acid rain with different nitrogen-to-sulfur ratios on seed germination and seedling growth of the horticultural Asteraceae species Lactuca sativa L. via a hydroponic experiment. Aqueous extracts of the two Asteraceae invasives generated obvious allelopathy on L. sativa. S. canadensis aqueous extracts caused stronger allelopathy. There may be an antagonistic effect for the co-allelopathy of the two Asteraceae invasives. Nitric acid at pH 5.6 weakened the allelopathy of the two Asteraceae invasives, but the other types of acid rain strengthened the allelopathy of the two Asteraceae invasives. The allelopathy of the two Asteraceae invasives increases with the increasing acidity of acid rain, but the allelopathy of the two Asteraceae invasives decreases with the increasing nitrogen-to-sulfur ratio of acid rain. Accordingly, the species number of invasives, and the acidity and type of acid rain modulated the impacts of acid rain on the allelopathy of the two Asteraceae invasives.

Effect of poplar ecological retreat project on soil bacterial community structure in Dongting Lake wetland

As an important environmental protection measure, the Poplar Ecological Retreat (PER) project aims to restore the ecology of the Dongting Lake (DL, China’s second largest freshwater lake) wetland. And its ecological impact is yet to be revealed. This study selected soil bacterial community structure (BCS) as an indicator of ecological restoration to explore the ecological impact of PER project on DL wetland. Soil samples were collected from reed area (RA, where poplar had never been planted, as the end point of ecological restoration for comparison in this study), poplar planting area (PA), poplar retreat for 1-year area (PR1A) and poplar retreat for 2 years area (PR2A), then their soil properties and BCS were measured. The results showed that the PER project caused significant changes in soil properties, such as the soil organic matter (SOM) and moisture, and an increase in the diversity and richness index of soil BCS. The Shannon-wiener index of RA, PA, PR1A and PR2A were 3.3, 2.63, 2.75 and 2.87, respectively. The number of operational taxonomic units (OTUs) changed similarly to the Shannon-wiener index. The Pearson correlation analysis and redundancy analysis (RDA) showed that the poplar retreat time, SOM and moisture content were the main factors leading to the increase of BCS diversity. All of these indicated that after the implementation of the PER project, the ecology of the lake area showed a trend of gradual recovery.

Defining invasive species and demonstrating impacts of biological invasions: a scientometric analysis of studies on invasive alien plants in Brazil over the past 20 years

Despite biological invasions being widely recognised as an important driver of environmental change, lack of consensus regarding the definition of invasive alien species (IAS) and vagueness around the demonstration of their impacts limits knowledge and research in this field. In this study, a scientometric approach was used to analyse academic documents published between 2002 and 2021 in three databases with reference to invasive alien plants in Brazil. Despite the growing body of scientific literature in the area, only 10% of the publications provided some definition of invasive species. Of the 398 publications analysed, 23.6% found some type of damage caused by the invader and, of these, only 5% addressed economic or social damage. Only 17% of the publications proposed a method for controlling and/or mitigating biological invasions. The absence of clear terminology and the lack of focus on impacts limits understanding of IAS of plants in Brazil. Based on the present findings, future studies on IAS of plants should move towards a consensus on the definition of biological invasion, as well as understand the impact caused by these species. In addition, it is recommended that further scientometric studies should guide future efforts to support objective measures for management and decision-making.

Acid deposition at higher acidity weakens the antagonistic responses during the co-decomposition of two Asteraceae invasive plants

Co-invasion by two invasive plant species (IPS) can occur in the same habitat. Diversified acid deposition may change the co-invasion process by altering litter decomposition and plant-soil feedback signalling. This study examined the co-decomposition of two Asteraceae IPS (Solidago canadensis L. and Bidens pilosa L.) on litter decomposition rate, soil enzyme activities, and soil N-fixing bacterial communities under diversified acid deposition (mixed acid deposition at pH 5.6 and at pH 4.5, sulfuric acid at pH 4.5, and nitric acid at pH 4.5). B. pilosa litter degraded faster than S. canadensis litter. Acid deposition at higher acidity accelerated the decomposition rate of both pure S. canadensis litter and the equally mixed litters from the two Asteraceae IPS. Antagonistic responses may occur during the co-decomposition of the two Asteraceae IPS with mixed acid deposition, regardless of the pH, as well as with nitric acid deposition at pH 4.5; in contrast, there may be neutral responses for the co-decomposition process with sulfuric acid at pH 4.5. The type of acid deposited may be one of the key factors affecting the intensity of the mixing effect affecting the co-decomposition. Acid deposition at higher acidity weakened the antagonistic responses for the co-decomposition of the two Asteraceae IPS compared with the response to weak acids. Together, these results indicate that acid deposition at higher acidity could facilitate the co-invasion of the two Asteraceae IPS mainly through accelerated litter decomposition as well as weakened antagonistic responses for co-decomposition.

Which factor contributes most to the invasion resistance of native plant communities under the co-invasion of two invasive plant species?

Two invasive plant species (IPS) can co-invade the same plant community. As the number of IPS increases under the co-invasion of two IPS, plant taxonomic and functional diversity, community invasibility, community stability, invasion resistance, and invasion intensity and invasiveness of IPS and their interrelationships may be altered. This study aimed to quantify the contribution of plant taxonomic and functional diversity, community invasibility, community stability, and invasion intensity and invasiveness of IPS to the invasion resistance of native plant communities under the co-invasion of the two IPS Erigeron annuus (L.) Pers. and Solidago canadensis L. in eastern China. This study also defined a method to quantify the invasion resistance of native plant communities designated the invasion resistance index. The community-weighted mean trait values of native plants and plant diversity are the factors that are the most critical to determine the invasion resistance of native plant communities. Thus, the invasion resistance of native plant communities primarily depends on the three following factors: the relative abundance of natives, the growth performance of natives, and the diversity of natives. All levels of invasion significantly decrease the invasion resistance of native plant communities. The two IPS antagonistically affect the invasion resistance of native plant communities less under co-invasion compared with their independent invasion.

Plant community and the influence of plant taxonomic diversity on community stability and invasibility: A case study based on Solidago canadensis L

Invasive alien plants (IAPs) can negatively affect plant taxonomic diversity, community stability, and invasibility in the invaded habitats. This study aimed to assess the degree of influence of the IAP Solidago canadensis L. under various levels of invasion (i.e., light, moderate, and heavy invasion based on its relative abundance in the invaded communities) on plant taxonomic diversity, community stability, and invasibility. In addition, we determined the contribution of plant taxonomic diversity to community stability and invasibility under various levels of S. canadensis invasion. The degree of influence of S. canadensis on plant taxonomic diversity and community stability increases as the level of S. canadensis invasion increases. Community invasibility increases as the level of S. canadensis invasion increases. The competitive advantage of S. canadensis is negatively associated with all indexes of plant taxonomic diversity and community stability but positively connected with community invasibility. Community stability is positively related to Shannon's diversity and Simpson's dominance indexes but negatively associated with community invasibility. Inversely, communities were more likely to be invaded when they had less plant taxonomic diversity. Thus, plant communities with lower values of plant taxonomic diversity and community stability are more vulnerable to S. canadensis invasion. Plant diversity causes a greater pressure on community stability than the other indexes of plant taxonomic diversity under various levels of S. canadensis invasion. However, the contribution intensity of the number of plant species to community invasibility is higher than the other indexes of plant taxonomic diversity under various levels of S. canadensis invasion.

The allelopathy of horseweed with different invasion degrees in three provinces along the Yangtze River in China

The effect of allelopathy from invasive alien plants (IAPs) on native species is one of the main factors for their adaptation and diffusion. IAPs can have different degrees of invasion under natural succession and are distributed in numerous regions. Seed germination and seedling growth (SGe-SGr) play a crucial role in population recruitment. Thus, it is critical to illustrate the differences in the allelopathy caused by an IAP with different degrees of invasion in numerous regions on SGe-SGr of native species to describe the primary force behind their adaptation and diffusion. This study assessed the allelopathy of the notorious IAP horseweed (Conyza canadensis (L.) Cronq.) on SGe-SGr of the native lettuce species (Lactuca sativa L.) under different degrees of invasion (light degree of invasion and heavy degree of invasion) in three provinces (Jiangsu, Anhui, and Hubei) along the Yangtze River in China. The allelopathy of horseweed leaf extract on lettuce SGe-SGr remarkably increased with the increased degree of invasion, which may be due to the buildup of allelochemicals generated by horseweed with a heavy degree of invasion compared with a light degree of invasion. A high concentration of horseweed leaf extract resulted in noticeably stronger allelopathy on lettuce SGe-SGr compared to the extract with a low concentration. There are noticeable differences in the allelopathy of the extract of horseweed leaves from different provinces on lettuce SGe-SGr with the following order i.e. Jiangsu > Hubei > Anhui. This may be due to the high latitudes for the three sampling sites in Jiangsu compared with the latitudes for the collection sites in Hubei and Anhui. There are certain differences in the environments among the three provinces. Thus, the allelopathy of horseweed on SGe-SGr of lettuce may have a greater negative impact in Jiangsu compared to the other two provinces.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00962-y.

Invasive species in the grasslands of the Central Caucasus

Biological invasions and grassland transformation are significant problems in pasture ecosystems of the Central Caucasus. The aim was to study the main patterns of invasive processes in grasslands and included identification the main vegetation parameters and abiotic factors affecting the invasion and distribution of alien species (Erigeron annuus, Ambrosia artemisiifolia, and Xanthium albinum) in plant communities. We assessed vegetation parameters of steppe grasslands with the presence of alien species within 122 model plots on plains, in foothills and low mountains (250-1000 m above sea level). We also modeled the current habitats of the species in grasslands of the Central Caucasus by using the Maxent method. The most suitable for invasion and distribution of Erigeron annuus are productive grasslands (NDVI is 0.25 and more) of the foothills and low mountains with a moderately warm humid climate (average annual temperature is 5-10°C; precipitation of the most humid quarter is 240-300 mm). The most suitable for Ambrosia artemisiifolia are medium-productive grasslands (NDVI is 0.25-0.38) of the foothills and low mountains with low vegetation coverage (65-85%) and moderately humid climate (precipitation of the most humid quarter is 225-275 mm). The most suitable for Xanthium albinum at present are dry unproductive disturbed grasslands of plains.

Indigenous plant species and invasive alien species tend to diverge functionally under heavy metal pollution and drought stress

The functional similarity between indigenous plant species (IPS) and invasive alien species (IAS) governs the invasion process of successful IAS because IPS and coexisting IAS suffer alike or even same ecological selection pressures. The aggravated condition created by heavy metal pollution (HMP) and drought stress may generate a noticeable impact on the invasive competitiveness and invasion process of IAS possibly via the variations in the functional similarity between IPS and IAS. Consequently, it is necessary to illumine the functional similarity between IPS and IAS under HMP and drought stress to clarify the mechanisms underlying the successful invasion of IAS. This study aims to estimate the functional similarity between IPS Amaranthus tricolor L. and IAS A. retroflexus L. under the condition with the alone and combined effects of HMP with different kinds (e.g., Cu and Pb) and drought stress [simulated by polyethylene glycol-6000 (PEG) solution]. HMP notably declines A. tricolor growth but has no remarkable effect on A. retroflexus growth. A. retroflexus displays a strong competitive intensity than A. tricolor under HMP. Further, HMP makes a greater stress intensity on A. tricolor growth than A. retroflexus growth. Therefore, HMP can accelerate A. retroflexus invasion. A. retroflexus displays a poor competitive intensity under drought stress. Thus, drought stress can hinder A. retroflexus invasion. However, drought stress causes a greater stress intensity on A. tricolor growth than A. retroflexus growth. Thus, the continued drought stress may converse the adverse effects of drought stress on A. retroflexus invasion potentially. The two Amaranthus species tend to diverge functionally under the combined HMP and drought stress. Further, A. retroflexus shows a strong competitive intensity than A. tricolor under the combined HMP and drought stress. Moreover, the combined HMP and drought stress induces a greater stress intensity on A. tricolor growth than A. retroflexus growth. Thus, the combined HMP and drought stress can facilitate A. retroflexus invasion. Meanwhile, the competitiveness for sunlight acquisition and leaf photosynthetic capacity may play a key role in the successful invasion of A. retroflexus under the combined HMP and drought stress.

Heavy metal pollution improves allelopathic effects of Canada goldenrod on lettuce germination

Large amounts of heavy metals have been released into the environment. Thus, the allelopathic effects of invasive alien species on the germination performance of co-occurring indigenous species may be altered or even heightened with the rapid growth in heavy metal pollution. This study evaluated the impacts of Canada goldenrod (Solidago canadensis L.) leaf extracts at concentrations of 0, 10 or 20 gl 1 on the germination of lettuce under different forms of heavy metal pollution (Cu2+ , Pb2+ or a combination of Cu2+ and Pb2+ ; 35 mgl 1) during incubation in Petri dishes for 10 days. Goldenrod leaf extracts (high concentration) reduced growth of aboveground and belowground parts of lettuce as well as competition for light and soil nutrients. However, low concentrations of goldenrod leaf extracts dramatically improved growth of lettuce roots, competition for light, soil nutrient availability, leaf photosynthetic area and growth competitiveness. The combination of goldenrod leaf extracts and heavy metal pollution was synergistic on most lettuce germination parameters, probably because high concentrations of goldenrod leaf extracts together with heavy metal pollution had a synergistic negative impact on lettuce germination. Consequently, increased levels of heavy metal pollution may favour invasion of invasive alien species while largely suppressing germination of indigenous species.

The mixed silicon and cadmium synergistically impact the allelopathy of Solidago canadensis L. on native plant species Lactuca sativa L

Several invasive alien plants (IAP) can trigger evidently allelopathy on the seed germination and seedling growth (SgSg) of native plant species (NPS). The getting worse condition with heavy metal pollution (e.g., cadmium) can significantly impact SgSg of plant species. Silicon can offset the adverse effects of environmental pressure on the growth and development of plant species. Thus, it is important to evaluate the influences of silicon on the allelopathy of IAP on SgSg of NPS under cadmium stress to better understand the mechanism driving the successful colonization of IAP. This study focuses on the allelopathy of the infamous IAP Solidago canadensis L. (Canada goldenrod; by using leaf extracts) on SgSg of NPS Lactuca sativa L. under the separated and mixed silicon and cadmium addition. S. canadensis triggers notably allelopathy on SgSg of L. sativa and gradually upsurges with increasing leaf extract concentration. Thus, the growth performance of NPS will be gradually reduced with an increasing degree of S. canadensis invasion. Cadmium evidently declines SgSg of L. sativa due to the broken balance of plant species for nutrient absorption. The mixed S. canadensis leaf extracts and cadmium synergistically impact seed germination of L. sativa but antagonistically affect seedling growth of L. sativa. The mixed silicon and cadmium intensify the allelopathy of S. canadensis on SgSg of L. sativa probably due to the increased effective content of cadmium in plant roots under silicon addition. Thus, the mixed silicon and cadmium will be advantageous to the following invasion process of IAP largely via the depressed SgSg of NPS.

Impacts of soil properties and functional diversity on the performance of invasive plant species Solidago canadensis L. on post-agricultural wastelands

Amongst the numerous consequences of the rapid development of agriculture and urbanization, biological invasions are highlighted as having the biggest impact on the functioning of ecosystems. One of the alien plant species, considered in Europe and Asia to be highly invasive, is Solidago canadensis L.; and its impact on the functioning of ecosystems has been studied in numerous respects. However, knowledge about how the physico-chemical parameters of soils and biotic interactions between species shape the performance of S. canadensis in a transformed landscape is still insufficient. The aim of this study was to assess how complex soil abiotic conditions and the functional diversity of co-occurring vegetation shape the performance of S. canadensis on the wastelands abandoned by agriculture. Apart from detailed investigations of soil properties and S. canadensis biomass, to achieve our study aims, we used parameters of functional diversity, which allowed us to identify the main ecological processes determining the community assembly processes. Under higher contents of loamy fractions in soil, but lower functional richness in surroundings, S. canadensis achieved larger cover. Alongside increasing functional richness and dispersion in co-occurring vegetation, this species has demonstrated sturdy attributes when competing for water and nutrients, expressed by a higher production of rhizomes and roots. Under elevated zinc and lead levels, as well as higher functional evenness in the surroundings, the flower biomass decreased, while the biomass of stems increased. Thus, S. canadensis exhibits a highly adaptive capacity to grow in soils contaminated by heavy metals, due to the buffer properties and life strategies allowing the use of resources absorbed in loamy soils. Environmental factors seem to be more responsible for the shaping of the performance and for the colonization success of S. canadensis than biotic interactions with plants occurring in the surroundings.

Litter decomposition process dramatically declines the allelopathy of Solidago canadensis L. on the seed germination and seedling growth of Lactuca sativa L

A variety of invasive alien species (IAS) can trigger distinct allelopathy on the seed germination and seedling growth (SGeSGr) of native plant species (NPS) mainly through the released allelochemicals. However, the decomposition process of IAS litters may affect their allelopathy on SGeSGr of NPS because part of the allelochemicals will be released during the litter decomposition process, especially under heavy metal pollution. This study focuses on the impacts of the litter decomposition process of the notorious IAS Solidago canadensis L. on its allelopathy on SGeSGr of NPS Lactuca sativa L. under cadmium (Cd) pollution. The decomposition process signally declines the allelopathy of S. canadensis litters on SGeSGr of L. sativa likely because partial allelochemicals in S. canadensis litters discharged during the decomposition process. Cd addition noticeably rises the allelopathy of S. canadensis litters on SGeSGr of L. sativa probably because Cd can reduce plant growth largely via the improved lipid membrane permeability and the induced reactive oxygen molecules which is unfavorable to plant cell metabolism. This phenomenon may also be attributed to the weak acid properties of one of the most abundant allelochemicals in S. canadensis litters, i.e., phenolics (particularly polyphenols), can improve the solubility and the toxicity of Cd.