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Clonal integration facilitates the growth and reproduction of clonal plants by providing the ability to share resources among ramets in heterogeneous environments. The benefits of clonal integration for plant growth may depend on a contrast in resource availability and may encounter costs, especially when a young part of the clone is growing across a border between richer and poorer conditions than the old part. We studied a clonal amphibian plant growing across a border between an aquatic and a terrestrial ecosystem, which typically differ in the availability of resources. We asked whether the young part of the clone is supporting the old part with phosphorus and whether this support has costs. We performed an experiment with Alternanthera philoxeroides where plants grow from water to a terrestrial habitat. The terrestrial habitat had either a low or high phosphorus supply, and the connection between the old and young parts of the clone was either left intact or split. We determined that the young part of the clone growing in a terrestrial habitat supported the old part with phosphorus when growing on a substrate rich in phosphorus. We have found no cost of this resource translocation; on the contrary, whole clones increased not only their accumulation of phosphorus, but also of nitrogen. Our study shows how an amphibian plant may profit from heterogeneous habitats by resource sharing in a clonal network. [ABSTRACT FROM AUTHOR]

Both soil microbes and soil N:P ratios can affect plant growth, but it is unclear whether they can interact to alter plant growth and whether such an interactive effect depends on nutrient levels. Here, we tested the hypothesis that soil microbes can ameliorate the negative effects of nutrient imbalance caused by low or high N:P ratios on plant growth and that such an ameliorative effect of soil microbes depends on nutrient supply levels. We grew individuals of six populations of the clonal plant Solidago canadensis at three N:P ratios (low (1.7), intermediate (15), and high (135)), under two nutrient levels (low versus high) and in the presence versus absence of soil microbes. The presence of soil microbes significantly increased biomass of S. canadensis at all three N:P ratios and under both nutrient levels. Under the low-nutrient level, biomass, height, and leaf number of S. canadensis did not differ significantly among the three N:P ratio treatments in the absence of soil microbes, but they were higher at the high than at the low and the intermediate N:P ratio in the presence of soil microbes. Under the high-nutrient level, by contrast, biomass, height, and leaf number of S. canadensis were significantly higher at the low than at the high and the intermediate N:P ratio in the absence of soil microbes, but increased with increasing the N:P ratio in the presence of soil microbes. In the presence of soil microbes, number of ramets (asexual individuals) and the accumulation of N and P in plants were significantly higher at the high than at the low and the intermediate N:P ratio under both nutrient levels, whereas in the absence of soil microbes, they did not differ significantly among the three N:P ratio regardless of the nutrient levels. Our results provide empirical evidence that soil microbes can alter effects of N:P ratios on plant performance and that such an effect depends on nutrient availability. Soil microbes may, therefore, play a role in modulating ecosystem functions such as productivity and carbon and nutrient cycling via modulating nutrient imbalance caused by low and high N:P ratios. [ABSTRACT FROM AUTHOR]

Aims: The positive effects of spatial heterogeneity in soil nutrients on plant performance have been well documented, but whether such effects depend on the presence of soil biota or the substrate type in which the heterogeneity is manipulated remains largely unknown. Methods: In a greenhouse experiment, we grew the rhizomatous clonal grass Leymus chinensis in three different substrates (i.e., field soil, potting soil, and mixtures of ceramsite and quartz) that were subjected to two different soil nutrient treatments (i.e., a homogeneous treatment and a heterogeneous treatment consisting of low- and high-nutrient soil patches) and inoculated with either live or sterilized soil biota. Results: In the presence of the live soil biota, L. chinensis produced more biomass in the homogeneous than in the heterogeneous treatment, independent of the substrate type. With the sterilized soil biota, however, L. chinensis produced more biomass in the heterogeneous than in the homogeneous treatment. In the heterogeneous treatment consisting of the field soil and the potting soil, L. chinensis produced more biomass in the high-nutrient patches than in the low-nutrient patches. In contrast, it produced more biomass in the low-nutrient patches than in the high-nutrient patches in the heterogeneous treatment consisting of the field soil and the mixture of quartz and ceramsite. Conclusions: Both soil biota and soil substrates can influence the responses of clonal plants to soil nutrient heterogeneity. Our results highlight the vital importance of including soil biota and soil physical properties in studies designed to examine the effects of soil nutrient heterogeneity on plant performance, population dynamics, species coexistence and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Background and Aims Clonal plants dominate many plant communities, especially in aquatic systems, and clonality appears to promote invasiveness and to affect how diversity changes in response to disturbance and resource availability. Understanding how the special physiological and morphological properties of clonal growth lead to these ecological effects depends upon studying the long-term consequences of clonal growth properties across vegetative generations, but this has rarely been done. This study aimed to show how a key clonal property, physiological integration between connected ramets within clones, affects the response of clones to disturbance and resources in an aquatic, invasive, dominant species across multiple generations. Methods Single, parental ramets of the floating stoloniferous plant Pistia stratiotes were grown for 3 weeks, during which they produced two or three generations of offspring; connections between new ramets were cut or left intact. Individual offspring were then used as parents in a second 3-week iteration that crossed fragmentation with previous fragmentation in the first iteration. A third iteration yielded eight treatment combinations, zero to three rounds of fragmentation at different times in the past. The experiment was run once at a high and once at a low level of nutrients. Results In each iteration, fragmentation increased biomass of the parental ramet, decreased biomass of the offspring and increased number of offspring. These effects persisted and compounded from one iteration to another, though more recent fragmentation had stronger effects, and were stronger at the low than at the high nutrient level. Fragmentation did not affect net accumulation of mass by groups after one iteration but increased it after two iterations at low nutrients, and after three iterations at both nutrient levels. Conclusions Both the positive and negative effects of fragmentation on clonal performance can compound and persist over time and can be stronger when resource levels are lower. Even when fragmentation has no short-term net effect on clonal performance, it can have a longer-term effect. In some cases, fragmentation may increase total accumulation of mass by a clone. The results provide the first demonstration of how physiological integration in clonal plants can affect fitness across generations and suggest that increased disturbance may promote invasion of introduced clonal species via effects on integration, perhaps especially at lower nutrient levels. [ABSTRACT FROM AUTHOR]

Several explanations have been proposed for the rapid spread of Solidago canadensis in various environments. Yet, the specific role of soil prokaryotes in this process remains unclear. To understand the prokaryotic role, we conducted a field study in eastern China, where S. canadensis invaded the native plant Humulus scandens. Prokaryotic communities in the soil were studied across three levels of invasion intensity: low, medium, and high (S. canadensis less than 10, about 50, and above 90%, respectively). We found that the S. canadensis invasion decreased the total prokaryotic abundance in the bulk soil (1.61 ± 0.57 × 108 to 5.78 ± 3.65 × 107 copies g−1 DW), but increased the total prokaryotic abundance in S. canadensis (7.72 ± 5.11 × 107 to 1.27 ± 0.71 × 108 copies g−1 DW) and H. scandens rhizosphere (1.11 ± 0.28 × 108 to 1.79 ± 0.68 × 108 copies g−1 DW). S. canadensis invasion enhanced nutrient-releasing microorganisms (Actinobacteria) (p < 0.05) and disease-resistant microorganisms (Nocardioides) (p < 0.05), while decreasing N-cycling microorganisms (Thaumarchaeota and Nitrospirae) (p < 0.05). This study suggests that S. canadensis may enhance its invasion by modulating the species and relative abundance of functional microorganisms in the bulk soil. [Display omitted] • S. canadensis invasion decreased prokaryotic abundance in bulk soil but increased prokaryotic abundance in plant rhizospheres. • S. canadensis promoted plant growth promoting and disease-resistant microorganisms. • S. canadensis invasion decreased nitrifying microorganisms in soil. [ABSTRACT FROM AUTHOR]

The majority of problematic invasive plants exhibit clonal growth, and the clonal traits are widely recognized as critical determinants contributing to their invasiveness. Division of labor represents a crucial advantage associated with clonal growth; therefore, it is reasonable to anticipate that this particular trait may confer a growth advantage upon invasive clonal species in comparison to native ones. To test this hypothesis, we conducted a comparative experiment in the greenhouse involving the highly invasive plant Alternanthera philoxeroides , its native congener A. sessilis , and its native co-occurring Jussiaea repens. We grew clonal fragments of these three stoloniferous plants under negative spatial covariance of light and soil nutrients while either preventing or allowing division of labor through severing or keeping intact their stolon connections. The results showed that stolon connection significantly increased the root mass to shoot mass ratio of basal ramets under low light and high soil nutrient conditions, but greatly decreased it in the apical ramets under high light and low soil nutrient conditions, suggesting induced division of labor in all studied plants. Moreover, the invasive plant A. philoxeroides demonstrated a greater capacity for division of labor than its co-genus and co-occurring native partners, which conferred it with greater growth performance at the whole clonal fragment level. Given that the commonly observed competitive superiority of invasive clonal plants over co-occurring native species due to their high intrinsic growth rates, these findings suggest that the division of labor may confer a competitive advantage upon some invasive clonal plants, thereby facilitating their successful invasion in heterogeneous habitats characterized by a strong negative correlation between light availability and soil nutrient levels. • Division of labor is a critical clonal trait that affects the success of plant invasion. • Invasive plants may benefit from division of labor more than natives. • The division of labor was induced in all studied plants in heterogeneous habitats. • Greater specialization led to more biomass increase in an invasive plant compared to natives. • Division of labor may give invasive plants a competitive edge, aiding their invasion. [ABSTRACT FROM AUTHOR]

Soil microbes may greatly affect plant growth. While plants are commonly associated with diverse communities of soil microbes, complementary roles of different microbial communities that may stimulate synergistic effects on plant growth are not adequately tested. Also, such synergistic effects may vary with environmental conditions such as soil nutrient and water availability. We conducted a greenhouse experiment with a widespread clonal plant Solidago canadensis. The experiment was a factorial design with four levels of soil microbial inoculation (fresh soil inocula from grasslands in northern and southern China that were expected to differ in soil microbial composition, a mixture of the two fresh soil inocula, and a sterilized mixed inoculum control), two levels of nutrient availability (low vs. high), and two levels of water supply (low vs. high, i.e., 1376 vs. 352 mm per year). Irrespective of water supply and nutrient availability, total, aboveground, and belowground mass of S. canadensis were generally higher when the plant grew in soil inoculated with a mixture of soil microbes from the south and north of China (in the mixed inoculum treatment) than when it grew in soil inoculated with soil microbes from only the north or the south or the sterilized control. Such effects of soil microbes on total and aboveground mass were stronger under high than under low nutrient availability and also under high than under low water supply. Our results suggest that interactions of different soil microbial communities can result in a synergistic effect on plant growth and such a synergistic effect depends on environmental conditions. The findings shed light on the importance of plant–microbe interactions during the spreading of some plant species in face of increased atmospheric nutrient deposition coupled with altered rainfall pattern due to global change. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is commonly considered to contribute to the invasion success of invasive species. However, the importance of phenotypic plasticity, nitrogen (N) levels and warming to the invasion of invasive species is unclear. The effects of warming and N addition on the morphology, biomass allocation and biochemistry traits of Solidago canadensis and their plasticity were investigated by conducting a pot experiment. The results showed that the effect of N addition on biomass was improved for S. canadensis; whereas warming displayed no significant effect, their positive synergistic interact effect resulted in the overall significant increase in plant performance. The mean phenotypic plasticity indices (MPPI) of biochemistry and total parameters demonstrated a difference between operations, and the higher value was observed in N interaction with temperature treatments than N addition or warming alone. The observed MPPI indicated the biochemistry parameters > morphological parameters > allocation parameters. The MPPI of biochemistry parameters, morphological parameters and total parameters exhibited significant and positive correlations with N level and MPPI of morphological parameters was also significantly positively correlated with the fitness of S. canadensis. These results indicated that the global warming and N addition would make the invaded habitat more suitable for the growth of invasive S. canadensis, and even may effectively increase the invasion risk of S. canadensis through the enhanced phenotypic plasticity, which is a crucial factor to help species deal with the changing environment. [ABSTRACT FROM AUTHOR]

The Novel Defense Hypothesis predicts that introduced plants may possess novel allelochemicals which act as a defense against native generalist enemies. Here, we aim to test if the chemicals involved in allelopathy in the invasive plant Wedelia trilobata can contribute to higher resistance against generalist herbivore and pathogen enemies by comparing with its native congener W. chinensis in controlled laboratory conditions. The allelopathic effects of the leaf extract from W. trilobata on the generalist enemies were also assessed. We showed that the larvae of two moth species preferred W. chinensis over W. trilobata. The growth rate of larvae feeding on W. trilobata leaves was significantly lower than those feeding on W. chinensis leaves. When detached leaves were inoculated with phytopathogens, the infected leaf area of W. trilobata was significantly smaller than that of W. chinensis. In addition, the leaf extract of W. trilobata also effectively inhibited the growth of the larvae and the mycelial growth of the phytopathogens. Our results indicate that the defenses of invasive W. trilobata against generalist herbivore and pathogen enemies are stronger than that of its native congener, which may be attributed to the allelopathic effects. This study provides novel insights that can comprehensively link the Novel Defense, Behavioral Constraint and Enemy Release hypotheses. These combined hypotheses would explain how invasive plants escape from their natural specialist enemies, where their allelopathic chemicals may deter herbivorous insects and inhibit pathogen infection. [ABSTRACT FROM AUTHOR]

Aims: Resident plants can exert allelopathic effects on introduced exotic plants, and resistance to exotic plant invasions usually increases with diversity and density of the resident plant communities. We hypothesize that allelopathic effects increase with increasing diversity and density of the community, and thereby contribute to the community's resistance against invaders. Methods: To test these hypotheses, we conducted two greenhouse experiments in which we grew five individuals of the exotic invasive plant Solidago canadensis in pots without residents and in artificially assembled resident plant communities either with two levels of diversity (4 or 8 resident plant species) or two levels of density (8 or 32 individuals, representing 8 species). We used activated carbon as the allelopathy-neutralizer treatment in both the diversity and the density experiment. Results: In the absence of activated carbon, S. canadensis grew worse in the presence of residents, and when diversity or density of the residents increased. These negative effects, however, largely disappeared in the presence of activated carbon, and at the highest resident density S. canadensis even performed better with than without activated carbon. Conclusions: Low invasibility of species-rich and dense plant communities is likely to be at least in part associated with increased allelopathy. Our study provides the first evidence that increasing allelopathy could be a mechanism underlying the diversity and density effects on community invasibility. [ABSTRACT FROM AUTHOR]

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

Changes in resource supply ratios affect interspecific competition; however, the effects on the plant invasions are still relatively unknown. To determine the effects of phosphorus (P) availability on the competitive ability of the invasive herb Solidago canadensis in an elevated P environment, we conducted a greenhouse P addition experiment. The invasive herb S. canadensis and the native plant Pterocypsela laciniata were grown in both monoculture and mixture with P addition under an ambient N condition (P + N − ) and under a high N condition (P + N + ), using ambient N and P conditions (P − N − ) as a control. The growth of P. laciniata was significantly inhibited by S. canadensis under the ambient conditions. The P + N − treatment promoted the growth of P. laciniata , but did not promote the growth of S. canadensis . The competition between S. canadensis and P. laciniata was alleviated under the ambient N condition after P addition. The N requirement of P. laciniata was higher than that of S. canadensis , and P. laciniata outcompeted S. canadensis under the P + N + treatment. We concluded that P addition may reduce the competitive ability of the invasive weed S. canadensis , especially under a high N condition. The ratio of N and P might be a critical factor for determining the competitive abilities of the invasive herb S. canadensis and the native plant P. laciniata . [ABSTRACT FROM AUTHOR]

Clonal plants are able to support the growth of their ramets in stressful environments via clonal integration between the ramets. However, it remains unclear whether the developmental status of stressed ramets affects the role of clonal integration. Here, we explored the effects of clonal integration at both the ramet level and the whole clonal fragment level when the apical ramets (younger) and basal ramets (older) were subjected to different concentrations of cadmium contamination. We grew pairs of ramets of Alternanthera philoxeroides , which were connected or disconnected by stolon between them. The apical and basal ramets were either uncontaminated or individually subjected to Cd contamination at concentrations of 5 mg kg−1 and 50 mg kg−1, respectively. Our results showed that clonal integration significantly promoted the growth of apical ramets subjected to Cd contamination. More importantly, under high Cd treatment, clonal integration also had a significant positive effect on the fitness of the whole clonal fragments. However, clonal integration did not affect plant growth when basal ramets were subjected to Cd contamination. Our study reveals the influence of the developmental status of stressed ramets on the role of clonal integration in heterogeneous heavy metal stress environments, suggesting that clonal integration may facilitate the spread of A. philoxeroides in Cd-contaminated habitats. • Ramet developmental status may affect clonal integration in polluted environments. • Integration did not affect the growth of basal ramets subjected to Cd contamination. • Integration greatly alleviated the negative effects of Cd on the apical ramets. • Integration promoted plant growth when apical ramets subjected to high Cd. • Clonal integration may facilitate the spread of A. philoxeroides in polluted habitats. [ABSTRACT FROM AUTHOR]

Anthropogenic nitrogen (N) inputs lead to the increase of phosphorus (P) demand for plants and plant species competition in a N enriched environment may hinge on its ability to utilize soil P sources. In soils, P mostly exists as insoluble phosphate compounds with three mineral elements: iron (Fe), aluminum (Al) or calcium (Ca), and it remains largely unknown whether invasive plant species are able to access such insoluble P sources and its interaction with N enrichment to gain competitive advantage. We determined the morphological traits, growth and nutrient status of an invasive plant Canada goldenrod ( Solidago canadensis L.) cultured in soluble phosphate KHPO (Ortho-P), and insoluble inorganic phosphate AlPO (Al-P), FePO (Fe-P), Ca(OH)(PO) (Ca-P) at three N supply levels. Results showed that S. canadensis was able to selectively utilize P from Al-P but not from Fe-P or Ca-P by increasing root number and length under N additions. The increasing growth in S. canadensis was closely correlated with the increasing foliar P. Ability to utilize insoluble P sources under enriched N environment serves as a competitive advantage for S. canadensis in Al rich soils. Effective control of S. canadensis invasion may need to consider soil P management in the context of atmospheric N deposition as well. [ABSTRACT FROM AUTHOR]

Allelochemicals released by invasive plants contribute to the successful invasion of new habitats. However, the relationship between allelopathic effects and competitive ability of invasive plants has not been characterized. We quantified the neighbor effects of Wedelia trilobata (family: Asteraceae) and the allelopathic effects of its leaf litter on two Asteraceae competitor species (invasive Eupatorium catarium and non-invasive Lactuca sativa) and on its own ramet growth. The seed germination rate and seedling biomass of the two competitor species decreased following treatment with W. trilobata leaf extracts. When co-cultured with W. trilobata, the total biomass of the two competitor species significantly decreased regardless of whether leaf extracts were present. Under low plant density co-culture conditions, W. trilobata leaf extracts enhanced the inhibitory effects on E. catarium. In contrast, W. trilobata leaf extracts promoted the growth of W. trilobata adventitious roots, resulting in increased competitive ability. Therefore, W. trilobata growth was promoted by its own allelochemicals in leaf extracts, whereas the growth of the invasive and non-invasive competitors was inhibited by the same chemicals. These responses facilitated the invasion by W. trilobata. Our study demonstrates that leaf litter of invasive plants may inhibit the growth of neighboring species to enhance the competitive ability of the invasive plants during the early stages of invasion. [ABSTRACT FROM AUTHOR]

The invasive clonal plant Wedelia trilobata contains higher levels of ent-kaurane diterpenes, which are precursors of gibberellins (GAs), and higher rates of clonal growth than its native congener W. chinensis in invaded habitats. We hypothesized that the higher levels of endogenous GAs facilitate greater ramet growth in W. trilobata compared with W. chinensis. We quantified endogenous levels of GA in the two species and compared their growth responses to the changes of endogenous and exogenous GA by using short-term and long-term hydroponics experiments. After a period of homogeneous cultivation, levels of endogenous GA were higher in W. trilobata than in W. chinensis. The reduction of endogenous GAs repressed the emergence of adventitious roots and the growth of W. trilobata in the initial cultivation stage, and inhibited its shoot elongation and biomass. Levels of endogenous GA were positively correlated with the length of shoots and adventitious roots of W. trilobata. Adventitious roots of W. trilobata also emerged earlier and grew faster when treated with exogenous GA. In contrast, exogenous GA treatment inhibited the length of adventitious roots in W. chinensis, and levels of endogenous GA did not correlate with shoot or adventitious root length. Our study suggests that GAs accelerate the rapid clonal growth of W. trilobata, more than that of its native congener W. chinensis, illustrating the relationship between plant hormones and the clonal growth of invasive plants . These findings are important for understanding the mechanisms associated with the invasiveness of clonal plants and their potential management. [ABSTRACT FROM AUTHOR]

Litter decomposition is a crucial biochemical process in terrestrial ecosystems. Litter mixture consisting of litter from multiple plant species may have non-additive decomposition rates relative to litter of single-species. The litter-mixing effect (LME) on the decomposition process in plants has been explored widely. Allelopathic effects from leaf litter of invasive plants may suppress growth in neighbouring species. Yet, few studies have examined the association between the effects of allelopathy on plant invasions and changes in litter decomposition. To test the relationship between allelopathy and LME during litter decomposition, we conducted both field and greenhouse experiments. The allelopathic effect of invasive Solidago canadensis and native Pterocypsela laciniata was tested on lettuce (Lactuca sativa) using litter extracts. We found that overall invasive litter had a strong allelopathic effect before litter decomposition compared with native litter. Litter extracts in the mixed and single treatments showed both additive and non-additive effects on seed germination and seedling growth in lettuce. Invasive and native litter significantly increased total inorganic nitrogen content (NO 3 −-N and NH 4 +-N), and decreased soil pH value, total phenolics, and total flavonoids after litter decomposition under field conditions. Additionally, the effect of litter types on germination and growth varied between the field and the greenhouse. These findings demonstrate a general relationship between plant performance indices and non-additive responses to allelopathy and suggest that the incubation site may be an important factor in successful invasions. • Litter decomposition is a crucial biochemical process in terrestrial ecosystems. • Invasive litter had a strong allelopathic effect before litter decomposition compared with native litter. • The effect of litter types on germination and growth varied between the field and the greenhouse. [ABSTRACT FROM AUTHOR]

• Nitrogen-fixing bacteria (NFB) help Solidago canadensis in response to low N stress. • NFB significantly increased root biomass and improved the development of root system. • NFB adjust higher investment on root system to buffer the poor nitrogen stress. • Interaction with NFB may greatly promote invasiveness of clonal S. canadensis. Nitrogen-fixing bacteria (NFB) converts nitrogen from the air into a nitrogen source to support plants' requirements. However, the importance of NFB for invasive plants under nitrogen (N) limitation is not well understood. In this study, we investigated the response of Solidago canadensis , an invasive clonal plant, to low nitrogen conditions with the colonization of two NFB strains, using a completely sterile culture system. We found that under very low nitrogen, the addition of both NFB strains significantly increased the investment of belowground biomass and total biomass, and greatly promoted the development of the root system (p < 0.05). Importantly, the significant decrease of anthocyanin and significant increase in root volume and root average diameter indicated that NFB reduced nutritional stress and promoted roots under extreme nitrogen deficiency. Our findings suggest that the interaction with NFB may contribute to the invasiveness of S. canadensis through investing more resources into the root system in a resource-poor environment. [ABSTRACT FROM AUTHOR]

Accumulation and utilization of heavy metals from wastewater by biological treatment system has aroused great interest. In the present study, a metal-reducing bacterium Shewanella oneidensis MR-1 was used to explore the biofabrication of ZnS nanocrystals from the artificial wastewater. The biogenic H 2 S produced via the reduction of thiosulfate precipitated the Zn(II) as sulfide extracellularly. Characterization by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscope (FESEM) confirmed the precipitates as ZnS nanocrystals. The biogenic ZnS nanocrystals appeared spherical in shape with an average diameter of 5 nm and mainly aggregated in the medium and cell surface of S. oneidensis MR-1. UV–vis DRS spectra showed ZnS nanoparticles appeared a strong absorption below 360 nm. Thus, the photocatalytic activity of ZnS was evaluated by the photodegradation of rhodamine B (RhB) under UV irradiation. The biogenic ZnS nanocrystals showed a high level of photodegradation efficiency to RhB coupled with a significant blue-shift of maximum adsorption peak. A detailed analysis indicated the photogenerated holes, rather than hydroxyl radicals, contributed to the photocatalytic decolorization of RhB. This approach of coupling biosynthesis of nanoparticles with heavy metal removal may offer a potential avenue for efficient bioremediation of heavy metal wastewater. [ABSTRACT FROM AUTHOR]

The effects of invasive plants on the species diversity of plant communities are controversial, showing either a positive or negative linear relationship. Based on community data collected from forty 5 m×5 m plots invaded by Sphagneticola trilobata in eight cities across Hainan Island, China, we found S. trilobata decreased plant community diversity once its cover was beyond 10%. We demonstrated that the effects of invasive/native plants on the plant diversity of communities invaded by S. trilobata were curvilinear. These effects, which showed peaks under different degrees of vegetation cover, appeared not only for S. trilobata and all invasive plants, but also for all native plants. Invasive plants primarily had negative effects on plant diversity when they became abundant at a much lower cover level (less than 35%), compared with the native plants (over 60%). Thus, it is necessary to distinguish a range for assessing the effects of plants, especially invasive plants. Our results also confirmed that the invasion intensity of invasive alien plants increased with the intensity of local economic development. We highlight and further discuss the critical importance of curvilinear effects of biological invasion to provide ideas regarding the conservation of local biodiversity and the management of invasive plants. [ABSTRACT FROM AUTHOR]

Background and Aims Invasive clonal plants have two reproduction patterns, namely sexual and vegetative propagation. However, seedling recruitment of invasive clonal plants can decline as the invasion process proceeds. For example, although the invasive clonal Wedelia trilobata (Asteraceae) produces numerous seeds, few seedlings emerge under its dense population canopy in the field. In this study it is hypothesized that light limitation and the presence of a thick layer of its own litter may be the primary factors causing the failure of seedling recruitment for this invasive weed in the field. Methods A field survey was conducted to determine the allocation of resources to sexual reproduction and seedling recruitment in W. trilobata. Seed germination was also determined in the field. Effects of light and W. trilobata leaf extracts on seed germination and seedling growth were tested in the laboratory. Key Results Wedelia trilobata blooms profusely and produces copious viable seeds in the field. However, seedlings of W. trilobata were not detected under mother ramets and few emerged seedlings were found in the bare ground near to populations. In laboratory experiments, low light significantly inhibited seed germination. Leaf extracts also decreased seed germination and inhibited seedling growth, and significant interactions were found between low light and leaf extracts on seed germination. However, seeds were found to germinate in an invaded field after removal of the W. trilobata plant canopy. Conclusions The results indicate that lack of light and the presence of its own litter might be two major factors responsible for the low numbers of W. trilobata seedlings found in the field. New populations will establish from seeds once the limiting factors are eliminated, and seeds can be the agents of long-distance dispersal; therefore, prevention of seed production remains an important component in controlling the spread of this invasive clonal plant. [ABSTRACT FROM AUTHOR]

Abstract: The endemic and valuable timber Madhuca hainanensis Chun& F.C. How is a top priority canopy species for conservation in Hainan due to its high risk of extinction. To investigate human impacts on genetic diversity and differentiation on Madhuca hainanensis, we studied the genetic variability and differentiation of 112 individuals from 6 natural wild populations in three regions and different protected areas on Hainan Island, with 15 selected inter-simple sequence repeat (ISSR) markers. High levels of genetic diversity within species (PPB = 96.9%, I = 0.4914, h = 0.3261), while accordingly low levels within-population diversity (PPB = 65.8%, I = 0.3333, h = 0.2206) were detected. Genetic diversity of M. hainanensis mainly exists within populations (G ST = 0.1975). The genetic diversity of protected group was higher than that of un-protected group. The AMOVA results revealed that there was a significant differentiation among regions and among protected and unprotected groups. The Mantel test demonstrated that there was no significant correlation between pair-wise population PhiPT matrix and geographic distance matrix. All above indicated that the genetic differentiation among regions might be due to the serious human activity, but not geographic isolation. We recommend that strict in-situ conservation efforts should be implemented quickly for future management to prevent further deforestation. [Copyright &y& Elsevier]

Abstract: This study investigated the anaerobic decolorization of the dye mixture containing methyl orange (MO) and naphthol green B (NGB) by Shewanella oneidensis MR-1. S. oneidensis MR-1 showed a strong ability to decolorize the dye mixture. MO was easier to get the electrons and inhibited the reduction of NGB, despite of its lower redox potential than NGB. The Mtr respiratory pathway played an important role in this process. Meantime, addition of extracellular electron shuttles accelerated the decolorization. Those results suggest that the decolorization capacity of S. oneidensis MR-1 is associated with the electricity production. The operating parameters, such as electron acceptors, temperature, and pH, were also investigated in this study. Thus, this work may facilitate a better understanding of the extensive nonspecific reduction capacity of exoelectrogens and is beneficial for promoting their application in bioremediation. [Copyright &y& Elsevier]

The anaerobic decolorization of metal-complex dye Naphthol Green B (NGB) by a metal-reducing bacterium, Shewanella oneidensis MR-1, was investigated. S. oneidensis MR-1 showed a high capacity for decolorizing NGB even at a concentration of up to 1000 mg/L under anaerobic conditions. Maximum decolorization efficiency was appeared at pH 8.0 and 40 °C. Addition of iron oxide caused no inhibition to the NGB decolorization, while the presence of ferric citrate, nitrite, or nitrate almost completely terminated the decolorization. Biosynthesis of nanomaterials was observed coupled with the degradation of NGB when thiosulfate was added. The Mtr respiratory pathway was found to be responsible for the decolorization of NGB by S. oneidensis , in which extracellular electron shuttle also plays a positive role in promoting the decolorization. [ABSTRACT FROM AUTHOR]

Microorganisms in subtropical forest soils are responsible for various ecological functions such as decomposing organic matter and driving carbon and nitrogen cycles. It is essential to understand how environmental factors affect microbial community composition and diversity. Prokaryotic communities (including bacteria and archaea) were investigated according to soil layer (0–2 cm and 18–20 cm), forest type (mountain dwarf forest, Guangdong pine forest, and monsoon evergreen broadleaf forest) and season (summer and winter) in Guangdong Nanling National Natural Reserve in China by Miseq sequencing of 16S rRNA genes. This study reveals key factors that shaped prokaryotic community structure and diversity in subtropical forest soils in China. Results show that Acidobacteria and Proteobacteria were the dominant phyla, with a relative abundance of 54.2% and 20.7% respectively. Soil pH, organic matter, total N, hydrolysable N, available P, NO 3 −, and NH 4 + were significantly correlated with prokaryotic community structure and diversity. Soil layer significantly affected prokaryotic community structure and diversity. Forest type significantly influenced prokaryotic community structure but not diversity. Season did not significantly correlate with prokaryotic community structure or diversity. • Acidobacteria and Proteobacteria dominate subtropical forest soils. • Soil pH, SOM, TN, hydrolysable N, available P, NO 3 − and NH 4 + affect prokaryotes. • Soil layer affects prokaryotic community structure and diversity. • Forest type influences prokaryotic community structure but not diversity. • Season does not correlate with prokaryotic community structure or diversity. [ABSTRACT FROM AUTHOR]

• The impacts of key hypotheses are fitted onto an idealized invasion process. • Synergistic interactions during each phase may drive plant invasions. • A number of hypotheses contribute greatly to invasiveness across multiple phases. Plant invasion is among the most serious of global challenges, affecting ecological processes and threatening biodiversity. With alien plant species (APS) continuously invading new environments, understanding the mechanisms involved in the invasion process will provide important insights for the prediction and control of APS. After over 60 years of invasion biology research, numerous hypotheses to explain successful invasions were proposed. However, due to the dynamic nature of invasions, a great deal of overlap exists among hypotheses and no single hypothesis can account for all invasions. Most hypotheses only focus on a single factor (e.g. biotic or abiotic) contributing to invasion at a given single invasion phase. Synthesizing the suite of hypotheses by considering all of them in tandem across the invasion timeline will allow an integrative understanding of plant invasions. In this current review, we integrate the major hypotheses into an idealized invasion process by their importance towards invasion. In this framework, we grouped hypotheses into intrinsic habitat invasibility and invasiveness of the invasive plant, and describe the relationships among hypotheses where enhanced mutualistic interactions with local biota, elevated competitive ability, and new adaptations drive invasion at the establishment phase. Alternate ways to invasive spread are also discussed. The hypotheses were fitted onto the invasion timeline according to their importance during each invasion phase. Our framework presents how the mechanisms suggested by the hypotheses jointly contribute to invasiveness over time. This invasion road map unifies the many disparate but related hypotheses on APS invasions, and highlights the potential targets for future management and research. [ABSTRACT FROM AUTHOR]

• Soil nutrient heterogeneity and parasitic plants can both influence plant growth. • However, little is known about their interactive effects on plant communities. • Cuscuta australis parasitism reduced community biomass by reducing forb biomass. • Such an effect of C. australis was independent of soil nutrient heterogeneity. Soil nutrient heterogeneity and parasitic plants have been well-documented to affect plant growth. However, their interactive effects on plant communities have not been tested yet. We assembled plant communities consisting of eight grassland species of three functional groups in one homogeneous soil and four heterogeneous soils consisting of high and low nutrient patches. The heterogeneous soils were manipulated by combining factorially two patch size treatments (large or small patch) with two patch contrast treatments (high or low contrast). All communities were either infected with the holoparasitic plant Cuscuta australis or not. Seven weeks after infection with C. australis , aboveground biomass of the communities was significantly reduced through suppressing the growth of forbs, but not that of grasses or legumes within the communities. Compared to the homogeneous soil, soil heterogeneity overall did not influence the growth of the communities or that of the component functional groups. However, aboveground biomass of the communities was greater in the heterogeneous soil with high patch contrast than in the heterogeneous soil with low patch contrast. A similar pattern was found for the legumes, but aboveground biomass of the forbs or grasses did not show any difference. Patch size did not influence aboveground biomass of the communities, forbs or legumes within the communities. Aboveground biomass of the grasses was greater in the heterogeneous soil with small patches than in the heterogeneous soil with large patches. The effects of C. australis infection on the relative abundance of the forbs, legumes, and grasses varied from negative, neutral to positive. However, the interaction of C. australis infection with soil nutrient heterogeneity, its patch size or patch contrast had little impact on the growth and functional composition of the communities. Our results suggest that parasitic plant infection can influence plant communities by altering the performance of component functional groups, independent of soil nutrient heterogeneity. [ABSTRACT FROM AUTHOR]

Modifications in soil fertility and microbiota structure driven by invasive plants can initiate a self-promoting mechanism that facilitates their invasion process. This study aimed to resolve how the progression of invasion affects the chemical, biochemical and microbial properties of soil using Conyza canadensis , a widespread and noxious invasive farmland weed, as a model. Different stages of the invasion process were simulated by growing C. canadensis and a non-invasive crop, Lactuca sativa , at different relative densities. Increasing invasion levels (i.e. increasing invader relative densities) resulted in altered properties of the soil, with an overall increase in nutrient supply and enzymatic activities as invasion intensified. Threshold changes in available nitrogen, organic matter and catalase activity in the soil were identified at invasion levels of 69%, 50% and 47%, respectively. Increasing invasion levels also affected the structure of the soil microbiota, with substantial changes occurring in the relative abundance for a number of bacterial and fungal taxa, including some that are relevant to nutrient cycling. Such changes in soil abiotic and biotic composition driven by C. canadensis might lead to positive plant-soil feedbacks that could promote the establishment and spread of the invasive weed. Image 1 • Different invasion levels of Conyza canadensis were simulated in pot trials. • Nutrients contents and enzyme activities increased with the higher invasion levels. • Invasion thresholds were identified for soil nitrogen, organic matter and catalase. • Invasion levels affected some microbes related to nutrient-cycling. • Positive plant-soil feedback might be involved in the spread of weed C. canadensis. [ABSTRACT FROM AUTHOR]

• The root mass fraction (RMF) increased in invasive species respond to N addition. • There was a decrease in RMF of native species respond to N addition. • The potential exclusion of native plants via an increase in RMF of invasive plants. • Biomass allocation in relation to N was explained by the optimal partitioning theory. Nitrogen (N) is one of the most important nutrition controlling plant functioning and ecological stability, which is predicted to increase rapidly in the future. Despite numerous attempts to clarify the effects of N deposition on the growth and physiological processes of plants, the difference in the effects of N deposition on biomass allocation between invasive and native species have not been fully understood. We conducted simulated N deposition experiments on a co-occurring species pair in a greenhouse to examine the plant invasion mechanisms from the patterns in plant biomass allocation. The results showed that the invasive Solidago canadensis and native Artemesia argyi have the similar response trend in N addition, where leaf mass fraction (LMF) significantly decreased and stem mass fraction (SMF) significantly increased. The root mass fraction (RMF) strongly increased in invasive S. canadensis but there was a decrease in native A. argyi respond to N addition. These findings indicated that increased nutrients, such as soil N, may shift the plant allocation structure due to unequal effects of N among different organs and species. And provided an invasion mechanism where a change in the environment leads to the potential exclusion of native competitors via a significant increase in root biomass fraction of invasive plants. We also found that the optimal partitioning theory rather than the allometric partitioning theory, better explains the N-induced changes in biomass allocation strategies in the poor-resource environment. These could lead to an increased competitive ability of invasive plants for resource acquisition and profit from neighboring species, coupled with greater biomass accumulation and higher competitiveness in its new habitat (N addition in poor resource environment) compared to A. argyi , could give S. canadensis a substantial advantage over its co-occurring native species. [ABSTRACT FROM AUTHOR]

Invasive plants are a huge burden on the environment, and modify local ecosystems by affecting the indigenous biodiversity. Invasive plants are generally less affected by pathogens, although the underlying molecular mechanisms responsible for their enhanced resistance are unknown. We investigated expression profiles of three defense hormones (salicylic acid, jasmonic acid, and ethylene) and their associated genes in the invasive weed, Alternanthera philoxeroides, and its native congener, A. sessilis, after inoculation with Rhizoctonia solani. Pathogenicity tests showed significantly slower disease progression in A. philoxeroides compared to A. sessilis. Expression analyses revealed jasmonic acid (JA) and ethylene (ET) expressions were differentially regulated between A. philoxeroides and A. sessilis, with the former having prominent antagonistic cross-talk between salicylic acid (SA) and JA, and the latter showing weak or no cross-talk during disease development. We also found that JA levels decreased and SA levels increased during disease development in A. philoxeroides. Variations in hormonal gene expression between the invasive and native species (including interspecific differences in the strength of antagonistic cross-talk) were identified during R. solani pathogenesis. Thus, plant hormones and their cross-talk signaling may improve the resistance of invasive A. philoxeroides to pathogens, which has implications for other invasive species during the invasion process. [ABSTRACT FROM AUTHOR]