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An innovative shoe bolt connection for precast concrete (PC) structures that features resilience is proposed in this study. In this connection, a steel washer plate that could be easily replaced after an earthquake serves as the “fuse” element, and the bolt passing through the horizontal joints serves as the self-centring element. To validate the reliability of the proposed connection, quasi-static tests were conducted on two PC shear wall specimens. One specimen was designed with a conventional wall shoe bolt connection (S-1). The other specimen was designed with the proposed connection (S-2). The crack pattern, failure mode, hysteresis curve, skeleton curve, ductility and energy dissipation capacity of the specimens were studied. Furthermore, finite element (FE) analysis was conducted to reproduce the test and facilitate an in-depth understanding on the mechanism of the specimens. The test and analysis results indicated that S-1 exhibited brittle failure, while the failure of S-2 was governed by concrete crushing and fuse plate yielding and reflected a remarkable self-centring capacity; only minor shear slips of the horizontal joints occurred, even for the specimen S-1 with a smaller axial load ratio, indicating that the joints had enough shear resistance; the proposed three-dimensional FE model could predict the skeleton curve and the failure mode of the specimens with acceptable accuracy; for the specimen with proposed connection, the failure mode was significantly influenced by the thickness of the fuse plate.

Exploring how functional traits vary and covary is important to understand plant responses to environmental change. However, we have limited understanding of the ways multiple functional traits vary and covary within invasive species.We measured 12 leaf traits of an invasive plant Chromolaena odorata, associated with plant or leaf economics, herbivore defense, and drought resistance on 10 introduced populations from Asia and 12 native populations from South and Central America, selected across a broad range of climatic conditions, and grown in a common garden.Species' range and climatic conditions influenced leaf traits, but trait variation across climate space differed between the introduced and native ranges. Traits that confer defense against herbivores and drought resistance were associated with economic strategy, but the patterns differed by range. Plants from introduced populations that were at the fast-return end of the spectrum (high photosynthetic capacity) had high physical defense traits (high trichome density), whereas plants from native populations that were at the fast-return end of the spectrum had high drought escape traits (early leaf senescence and high percentage of withered shoots).Our results indicate that invasive plants can rapidly adapt to novel environmental conditions. Chromolaena odorata showed multiple different functional trait covariation patterns and clines in the native and introduced ranges. Our results emphasize that interaction between multiple traits or functions should be considered when investigating the adaptive evolution of invasive plants.

Aims Plant-soil feedback (PSF), which may vary across space and time, is considered an important mechanism in biological invasion. However, it is still unclear how PSF change during biological invasion in heterogeneous environmental background.Methods Here, we measured the effects of soil microbial communities on the invasive species Ageratina adenophora and soil fungal communities at 24 sites with different invasion periods in two forest gaps with contrasting soil environmental backgrounds. The dominance of A. adenophora (cover and aboveground biomass) and diversity of native species at these sites were evaluated.Results In the lightly disturbed forest gaps, A. adenophora showed strong a positive response to their soil biota relative to sterilized soil (total PSFs), but a negative response to their own soil biota relative to other species’ soil biota (specific PSFs), which increased over their residence time. However, in the severely disturbed forest gaps, the invader had strong positive specific PSFs, which were maintained over a long invasion history. Higher resistance against soil pathogens may contribute to long-term maintenance of positive specific PSFs. Correspondingly, the diversity, richness of native species and dominance of A. adenophora did not significantly change during biological invasion in the lightly disturbed gap whereas in the severely disturbed gap, native species declined, and A. adenophora dominance increased after a long invasion.Conclusions These findings indicate that changes in PSFs may contribute to changes in the dominance and impact of invasive species in forest, and also highlight the need to consider the habitat context when studying PSFs.

Global changes such as atmospheric CO2 enrichment often facilitate exotic plant invasions and alter soil arbuscular mycorrhizal fungi (AMF) community. However, it is still unclear whether the effects of CO2 enrichment on exotic plant invasions are associated with its effects on root-AMF symbiosis of invasive and native plants. To address this issue, the annual invasive plant Xanthium strumarium and two phylogenetically related annual natives were compared under ambient and elevated CO2 concentrations for three consecutive years. Atmospheric CO2 enrichment increased AMF colonization rates for the species only in few cases, and the invader did not benefit more from CO2 enrichment in terms of AMF colonization. Under ambient CO2 concentration, however, the invader had a higher AMF colonization rate than the natives in the first year of the study, which disappeared in the second and third year of the study due to the increase of AMF colonization rates in the natives but not in the invader. The influences of species, CO2 concentrations and planting year on AMF colonization were associated with their effects on both soil nutrient and AMF community, and the former may be more important as it also influenced the latter. Our results indicate that the invader could more quickly form symbiosis with soil AMF, contributing to adaptation and occupation of new habitats, and that it is necessary to consider the roles of AMF and the effects of time when determining the effects of global changes such as atmospheric CO2 enrichment on exotic plant invasions.

Efforts to concurrently test for enemy release of both above- and belowground enemies for invasive plants in non-native range are limited. Moreover, direct evidence for the causal link between enemy release and performance is rare for invasive plants. Thus, we sought to investigate if above- and/or belowground enemies are involved in the enemy release mechanisms at various life stages of a temperate invader and their consequences on plant community properties. We conducted field surveys of enemy damage and plant performance, and plant-soil feedback experiments in the glasshouses using Ambrosia trifida in both its non-native and native ranges across the seed, seedling, and adult life stages. Field surveys showed that seeds of A. trifida were more severely damaged by aboveground enemies in the native relative to the non-native range, while the difference in leaf damage between ranges was small. Plant-soil feedback experiments showed that release from belowground enemies was also important, as seed germination and plant growth were significantly reduced in soils from the native range compared with soils from the non-native range. Consistent with the above results, A. trifida was larger, produced more seeds, had higher density, and exerted stronger impacts on co-occurring native plants in the non-native relative to the native range. Our results demonstrated that release from both above- and belowground enemies at various life stages contributed to the invasion success of A. trifida in its non-native range and highlighted the importance of considering both above- and belowground enemy release when studying plant invasions.

Aims Riparian corridors play vital roles in the maintenance of biodiversity. Nonetheless, plant species diversity and vegetation coverage in riparian corridors are seriously threatened by increasing pressure owing to livestock consumption and anthropogenic disturbance; even the stability of river courses has been threatened. The establishment of enclosures is a widely used strategy to restore degraded grassland ecosystems, but its impact on degraded herbaceous riparian vegetation and soil properties remains unclear. The aim of this study was to evaluate whether species composition, richness, diversity, and soil properties can be recovered by the enclosure. Methods Twenty long-term monitoring sample plots were set in the Liaohe main stream river, Liaohe main stream river was enclosed for grazing and farmland exclusion in 2012. The height, coverage and individual numbers of plant were recorded for species richness and diversity evaluation from 2012 to 2017; soil nutrients were measured for comparative analysis in 2012 and 2017. We examined the effects of the establishment of enclosures on plant species diversity and soil properties from 2012 to 2017 in the riparian corridors of the Liaohe River system in China. Important Findings Plant species richness and diversity significantly increased from 2012 to 2017. The dominance of Asteraceae plants increased, while the abundance of Gramineae plants decreased over time. The difference in abundance increased each year since enclosure was implemented in 2012. The concentrations of phosphorus and potassium in the soil significantly decreased as a result of the combined effects of vegetation restoration and prohibition of farming practices following the establishment of enclosures. There was also a lag time related to the response of soil organic matter to the establishment of enclosures. In conclusion, our study provides new evidence regarding the response of species diversity, species composition and soil properties following riparian vegetation restoration efforts through enclosure development.

The evolution of increased competitive ability (EICA) hypothesis states that, when introduced in a novel habitat, invasive species may reallocate resources from costly quantitative defense mechanisms against enemies to dispersal and reproduction; meanwhile, the refinement of EICA suggests that concentrations of toxins used for qualitative defense against generalist herbivores may increase. Previous studies considered that only few genotypes were introduced to the new range, whereas most studies to test the EICA (or the refinement of EICA) hypotheses did not consider founder effects. In this study, genetic and phenotypic data of Chromolaena odorata populations sampled across native and introduced ranges were combined to investigate the role of postintroduction evolution in the successful invasion of C. odorata. Compared with native populations, the introduced populations exhibited lower levels of genetic diversity. Moreover, different founder effects events were interpreted as the main cause of the genetic structure observed in introduced ranges. Three Florida, two Trinidad, and two Puerto Rico populations may have been the sources of the invasive C. odorata in Asia. When in free of competition conditions, C. odorata plants from introduced ranges perform better than those from native ranges at high nutrient supply but not at low nutrient level. The differences in performance due to competition were significantly greater for C. odorata plants from the native range than those from the introduced range at both nutrient levels. Moreover, the differences in performance by competition were significantly greater for putative source populations than for invasive populations. Quantities of three types of secondary compounds in leaves of invasive C. odorata populations were significantly higher than those in putative source populations. These results provide more accurate evidence that the competitive ability of the introduced C. odorata is increased with postintroduction evolution.

High-phenotypic plasticity has long been considered as a characteristic promoting exotic plant invasions. However, the results of the studies testing this hypothesis are still inconsistent. Overlooking the effects of species resource requirements and environmental resource availability may be the main reasons for the ambiguous conclusions. Here, we compared phenotypic plasticity between five noxious invasive species with different nutrient requirements (evaluated using the soil nutrient status of their natural distribution ranges) and their phylogenetically related natives under five nutrient levels. We found that species with high-nutrient requirements showed greater plasticity of total biomass than species with low-nutrient requirements, regardless of their status (invasive or native). Invasives with high-nutrient requirements had greater growth plasticity than their related natives, which may contribute to their invasiveness under high-nutrient environments. However, compared with the related natives, a higher growth plasticity may not help exotic species with low-nutrient requirements to invade nutrient-rich habitats, and exotic species with high-nutrient requirements to invade nutrient-limited habitats. In contrast, invasives with low-nutrient requirements exhibited lower growth plasticity than their related natives, contributing to their invasiveness under nutrient-limited habitats. Functional traits showed growth-related plasticity in only 10 cases (3.8%), and there was no functional trait whose plastic response to soil nutrients was beneficial to exotic plant invasions. Our study indicates that low-growth plasticity could also promote exotic plant invasions, high plasticity may not necessarily lead to invasiveness. We must test the adaptive significance of plasticity of functional traits when studying its biological roles.

Exotic plant invasions are generally assumed to negatively impact biodiversity of recipient communities. However, experimental evidence for this assumption is little, especially in developing countries. In addition, there is hardly applicable method to control invasive plants. Enemy release is often hypothesized to facilitate exotic plant invasions, thus re-association with natural enemies of invasive ranges may inhibit invasions of exotic plants, and these enemies may have the potential to be used as biological control agents for these invaders. To address above problems, we determined abundance of the invasive plant Xanthium strumarium, its impacts on co-occurring native plants, and abundances of three herbivores and their impacts on the invader at five sites in the rice tract of Punjab, Pakistan. Relative abundance of the invader varied greatly among the study sites, ranging from 3.5% to 50.4%. The invader significantly reduced abundance of co-occurring native plants at all study sites, and their richness and evenness at some sites with high abundances of the invader. The polyphagous insects Phenacoccus solenopsis, Podisus maculiventris and Spodoptera frugiperda were all found on the invader (not on crops) at all study sites, which significantly reduced growth of the invader. The abundance of P. solenopsis on the invader was much higher than those of P. maculiventris and S. frugiperda. The abundances of the herbivores were significantly higher at sites with high relative to low relative abundances of the invader. Our study indicates that natural enemies may accumulate on invasive plants with the increase of their abundance and/or invasion time, inhibiting further invasions, and provides evidence for enemy release hypothesis. More studies are needed to determine whether these herbivores, especially P. solenopsis, could be used as biological control agents for the invader.

Phenotypic plasticity index (PI), the slope of reaction norm (K) and relative distances plasticity index (RDPI), the most commonly used estimators, have occasionally been found to generate different plasticity rankings between groups (species, populations, cultivars or genotypes). However, no effort has been made to determine how frequent this incongruence is, and the factors that influence the occurrence of the incongruence. To address these problems, we first proposed a conceptual framework and then tested the framework (its predictions) by reanalyzing 1248 sets of published data. Our framework reveals inherent conflicts between K and PI or RDPI when comparing plasticity between two groups, and the frequency of these conflicts increases with increasing inter-group initial trait difference and/or K values of the groups compared. More importantly, the estimators also affect the magnitude of the inter-group plasticity differences even when they do not change groups' plasticity rankings. The above-mentioned effects of plasticity estimators were confirmed by our empirical test using data from the literature, and the conflicts occur in 203 (16%) of the 1248 comparisons between K and indices, indicating that a considerable proportion of the comparative conclusions on plasticity in literature are estimator-dependent. The frequency of the conflicts is influenced by phylogenetic relatedness of the groups compared, being lower when comparing within relative to between species, but not by specific types of environments, traits and species. Our study indicates that care is needed to select estimator when comparing groups' plasticity, and that the conclusions in relevant literature should be treated with great caution.

Invasive plants are often genetically different from their native conspecifics. In the introduced range, the evolution of functional traits or plasticity might occur as an adaptive response to novel environmental pressures. Chromolaena odorata originates from the Americas, but now is a noxiously invasive species in some other tropical and subtropical areas. In this study, plant growth, morphology, photosynthesis and plasticity were compared between C. odorata plants from five introduced and five native populations under three light intensities (low, medium and full light). Compared to native C. odorata, introduced conspecifics had higher height under medium and full light, but lower root to shoot biomass ratio across all light conditions, and lower leaf N under medium light. This indicates genetic differences between native and introduced C. odorata. Furthermore, plasticity was higher for introduced C. odorata plants than for native conspecifics under various light environments. Our results indicate that biomass reallocation (from belowground into aboveground) and stronger plasticity could contribute to successful invasion of introduced C. odorata in frequently disturbed environments.

Quantifying the magnitude of phenotypic plasticity to compare among species, populations, cultivars, or genotypes is important for revealing the ecological and evolutionary significance of plastic responses to various abiotic and biotic factors. Commonly used plasticity estimators have occasionally been found to generate different species’ plasticity rankings. However, we do not know how frequent this incongruence is or the factors that influence the occurrence thereof; nor do we know which plasticity estimator is more reliable. We first addressed these problems using a theoretical framework, revealing inherent conflicts between the reaction norm slope and plasticity indices, and the conditions affecting these conflicts. We then empirically tested the effects of the estimators on interspecific plasticity differences by reanalyzing 1248 sets of relevant data, confirming the predictions derived from our theoretical framework. Finally, we show through theoretical analyses that the reaction norm slope is more reliable than plasticity indices for interspecific comparisons.

Invasive cocklebur (Xanthium strumarium) is characterized by its excellent genetic and ecological plasticity, ability to spread in agriculture crops. There is a dire need to locate useful management strategies to control this invasive weed at diversified latitudinal gradients. In ecology, there is weak evidence that the damage caused by the natural enemy varies with latitudes. Therefore, we investigated this evidence with the help of transect quadratic ecological sampling method which was conducted randomly at ten different sites of Northeast China. Overall, significantly high infestation of gall-forming insect (Epiblema strenuana) was observed onXanthiumleaves (21.16%) at 41.51279°N, followed by 40.2241°N latitude. Similarly, there was a significantly high abundance ofEpiblemainfestation (7.3) with high damage (3.88%) at 41.51279°N and 40.12749°N latitude. Likewise, the fungal abundance (5.6) of rust i.e.Puccinia xanthii(presenting 16.23% attack) was dominated significantly at 41.51279°N. Hence, high pathogen infection rate (8.97%) was detected at 40.2241°N. On the other hand growth parameters, i.e. plant height (cm), stem diameter (mm) vary with latitude and longitudinal trends. In our experiment, of plant natural enemy interaction provides the evidence-based indication theEpiblemaabundance, was diversified at 41.51279°N, andP. xanthiiinfection was most frequent at 40.22411°N latitudes. This study provides an evidence-based indication that natural enemy pressure varies with latitude, however this investigations gave valuable information that insect and phytopathological fungus having biological control potential againstXanthium strumariuminvasive weed. Secondly, phytochemical qualitative and chemical signaling through Gas Chromatography-mass spectrometry (GC-MS) executed the presence of flavonoids, phenols, saponins, alkaloids, terpenoids, nitrogen (N), sulpher (S), silicon (Si) containing compounds in both treated and controlled leaves that defend againstPuccinia xanthii. Fascinatingly, allX. strumariumpopulations collected from different latitudes possess similar compositions. In interaction mechanism, plant known to omit volatile organic compounds in response to attack of natural herbivores. The leave chemical profiling suggested that the influence of fungus attack on invasive weed brought different changes in chemical infrastructure of leave and these chemicals also play a vital role in the food web. After attack of these biological control agents, plants exhibits passionate compound reprogramming within the leaf naturally that act upon in defense systems.Author summaryThe study was conducted to observe the environmental impact on the trend of insect, invasive weed and pathogens.There was a significant dominance of gall-forming insect on invasiveXanthiumweed at all locations.Puccinia xanthiiinfected more than 16% plantationPlant growth had significant variation at various longitudes and latitudes.The abundance of insect was positively linked with different environmental factors andXanthiumplant.The results of GC-MS suggested thatPuccinia xanthiiinfected (treatment) leaves covered maximum area (%) compared to control treatments due to breakdown of the chemical compounds that proved our hypotheses that volatile organic compounds altered infrastructures of the leave chemistry that led to activeness of plant defensive chemicals resulted invasion success.

Xanthium strumarium is yearly weed local to North America and is presently an obtrusive species. The intrusive weed can contend with local decent variety may turn into a hazardous weed for the agrarian profitability and rangeland biological systems. The present examination researched the challenge of intrusive and local weed populaces inside two straight out variables in matched quadratic rings (treatment/invasive with control/non-invasive). The present investigation was led at four unique areas of northeast China to discover competition of Xanthium strumarium on 40 paired matched vegetations in same condition and living space conditions. The number of species (NOS) occurred in quadratic ring; abundance (A); Simpsons Diversity Index (SDI); Margalef’s Richness Index (MRI) compared between invasive and non-invasive quadrates by t-test was recorded significant (PXanthium strumarium. Rarefaction bend with respect to coefficient of determination (R2) explored in the overviewed network (0.86) proposed that there is a solid positive polynomial connection between various weed families. Greatest difference list (87.06%) recorded in Huailai province followed by Yangyuan (44.43%), Zhangjiakou (40.13%) and at Fushun (29.02%). Significant (PXanthium strumarium compete with native weeds diversity created significant threat to the natural diversity. Most extreme thickness of weed species gave cautioning that the predominant edaphic and natural states of the uneven regions are profoundly favorable for the dispersion and development of the weed in future.

Empirical evidence of enemy release is still inconsistent for invasive alien plant species, although enemy release is the key assumption for both the enemy release hypothesis (ERH) and the evolution of increased competitive ability hypothesis (EICA). In addition, little effort has been made to test this assumption in terms of defense investment using a multi-species comparative approach. Using a phylogenetically controlled within-study meta-analytical approach, we compared leaf herbivore damage, structural defenses and nutrients between 47 pairs of invasive versus native and/or non-invasive alien plants in China. The invasive relative to the co-occurring native or non-invasive (native and non-invasive alien) plants incurred lesser leaf herbivore damage, had lesser leaf concentrations of cellulose, hemicellulose, lignin and carbon, lesser leaf density and carbon or lignin to nitrogen ratio but greater nutrients, which may facilitate success of the invasive plants. The lesser structural investment did not result in lesser leaf construction costs for the invaders, which may be associated with their greater leaf nitrogen concentration. However, the invasive plants were not significantly different from the non-invasive alien plants in any trait. Our results provide strong evidence for ERH, also are consistent with EICA, and indicate that enemy release may be an important factor in alien plant invasions.

Identity recognition (competition or altruism depending on genetic relationship) in plants was reported more infrequently than in animals. Few studies found identity recognition can help reducing competition between kin plants, and increasing population fitness. The exotic invasive plants usually form dense monoculture distribution, but native plants rarely distribute similarly. It might due to the invader had higher identity recognition ability, which could reduce intraspecific competition and enhance overall population fitness. In this study, we compared identity recognition ability between invasive Eupatorium adenophorum and two native congeners (Eupatorium fortunei and Eupatorium lindleyanum) in different nutrient condition and planting density. The results indicated that all three species did not show identity recognition ability in low and intermediate density condition. However, in high density condition, invasive E. adenophorum shew higher identity recognition ability than two native congeners. Recognition could alleviate intraspecific competition of invasive E. adenophorum through reducing carbon accumulation and RMF, but increasing the height to enhance light use efficiency. This strategy might contribute to high population fitness of E. adenophorum when it grew in high densities. This is the first study to explore the relationship between identity recognition and exotic plant invasion.

Fe2O3 is one of promising negative materials for supercapacitors (SCs), because of its low cost and high theoretical value of specific capacitance. However, the inferior conductivity and insufficient ionic diffusion rate of Fe2O3 will seriously hinder the electrochemical performance of Fe2O3, resulting in limiting its practical application in SCs. Herein, a sea urchin-like 3D Fe2O3 was synthesized via hydrothermal methods. And then, the 2D Ti2C3Tx MXene nanosheets with high conductivity closely self-assemble on the surface of Fe2O3 to provide efficient pathways for the rapid electrons transport. In addition, the sea urchin-like structure of Fe2O3 can facilitate the rapid diffusion of the electrolyte to accelerate faradaic reaction. The optimized Fe2O3/MXene composite as electrode material exhibits a high specific capacitance of 486.3 F g−1 at current density of 1 A g−1, and excellent cycling stability with 95.7% capacity retention after 5000 charge/discharge cycles. Furthermore, an asymmetric supercapacitors (ASCs) device was assembled by using Fe2O3/MXene composite as anode and MnO2 as cathode, showing a high energy density of 32.2 Wh kg−1 at the power density of 900.6 W kg−1, and remarkable long-term durability (95.7 % capacitance retention after 5000 cycles). This work demonstrates an effective approach of integrating the sea urchin-like Fe2O3 with 2D MXene nanosheets to fabricate Fe2O3/MXene composite for high-performance SCs.

Summary Soil microbes are important in mediating allelopathic interactions between invasive and native plants in the field. However, it was not known how these interactions vary in the process of biological invasions and the effects of soil microbes; this knowledge may facilitate understanding the dynamics and mechanisms of biological invasions and managing invaded ecosystems. We conducted competition and seed germination experiments to determine the allelopathic effects of Ageratina adenophora in soils from 42 sites with varying abundances of the invasive plant. Then we isolated the microbes that could degrade the allelochemicals of the invasive plant and tested their functions. In both experiments, the allelopathic effects of the invasive plant were much stronger in soils from non-invaded sites than in soils from invaded sites. Activities of the allelochemical-degrading microbes were higher and degradation of the allelochemicals of the invasive plant was faster in soils from invaded sites than in soils from non-invaded sites. In living soils from 30 sites with increasing abundance of A. adenophora, the allelopathic effects of the invasive plant decreased and degradation of the allelochemicals and activity of the allelochemical-degrading microbes gradually increased. Two bacterial strains were isolated from the soils. Inoculation of Arthrobacter sp. ZS, which was isolated from soil invaded by A. adenophora, greatly increased the degradation of the allelochemicals, thereby decreasing its allelopathic effects. Synthesis and applications. Our results indicate that soils may accumulate microbes that can degrade allelochemicals in the process of biological invasions, gradually reducing the allelopathic effects of invasive species. The effects of soil microbes should be considered when studying dynamics and mechanisms of biological invasions. Application of allelochemical-degrading microbes may facilitate ecological restoration of invaded or newly disturbed ecosystems by alleviating allelopathic inhibition of invasive plants on native plants.

Exotic plant species can benefit from altering soil microbial communities; however, the knowledge of the mechanisms through which this occurs is limited. The exotic species, Eupatorium adenophorum is a perennial plant that is aggressively invading southern China. Its invasiveness is attributed partially to its ability to release secondary chemicals that affect native plant species. Nevertheless, their effect on soil bacterial communities has rarely been explored. Here, we used natural fresh leaf and root leachate of E. adenophorum, and two pure, phytotoxic chemicals amorpha-4,7(11)-dien-8-one, and 6-hydroxy-5-isopropyl-3,8-dimethyl-4a,5,6,7,8,8a-hexahydraphthalen-2(1H)-one to evaluate: (a) short-term (3 days) effects of secondary chemicals on soil bacterial communities in mixed forests and (b) long-term (6 months) effects of leaf leachate on soil bacterial communities in three habitats. Additionally, the composition and diversity of soil bacterial communities were explored with high throughput sequencing using IlluminaMiSeq. In the short-term experiments, all treatments affected soil bacterial communities, but leaf leachate most significantly reduced soil bacterial richness and diversity. In the long-term experiments, leaf leachate altered bacterial communities in all soil samples, and reduced bacterial richness and diversity in soils from the forest and wasteland, but increased bacterial richness and diversity in soils from roadside. Redundancy analysis indicated that changes in bacterial communities were associated with soil organic carbon, nitrogen content, and pH. These results indicate that the water-dissoluble secondary chemicals of E. adenophorum, especially from its leaves, have an impact on soil bacterial communities, though the degree of the impact depends on soil ecotype.

The root economics spectrum (RES), a common hypothesis postulating a tradeoff between resource acquisition and conservation traits, is being challenged by conflicting relationships between root diameter, tissue density (RTD) and root nitrogen concentration (RN). Here, we analyze a global trait dataset of absorptive roots for over 800 plant species. For woody species (but not for non-woody species), we find nonlinear relationships between root diameter and RTD and RN, which stem from the allometric relationship between stele and cortical tissues. These nonlinear relationships explain how sampling bias from different ends of the nonlinear curves can result in conflicting trait relationships. Further, the shape of the relationships varies depending on evolutionary context and mycorrhizal affiliation. Importantly, the observed nonlinear trait relationships do not support the RES predictions. Allometry-based nonlinearity of root trait relationships improves our understanding of the ecology, physiology and evolution of absorptive roots., Kong et al. use a global trait dataset of 800 plant species to examine the root economics spectrum in relation to root diameter, tissue density and root nitrogen concentration. Nonlinear trait relationships were observed, suggesting allometry-based nonlinearity in root trait relationships.

Multiple mechanisms may act synergistically to promote success of invasive plants. Here, we tested the roles of three non-mutually exclusive mechanisms-founder effects, post-introduction evolution and phenotypic plasticity-in promoting invasion of Chromolaena odorata. We performed a common garden experiment to investigate phenotypic diversification and phenotypic plasticity of the genetically impoverished invader in response to two rainfall treatments (ambient and 50% rainfall). We used ancestor-descendant comparisons to determine post-introduction evolution and the QST-FST approach to estimate past selection on phenotypic traits. We found that eight traits differed significantly between plants from the invasive versus native ranges, for two of which founder effects can be inferred and for six of which post-introduction evolution can be inferred. The invader experienced strong diversifying selection in the invasive range and showed clinal variations in six traits along water and/or temperature gradients. These clinal variations are likely attributed to post-introduction evolution rather than multiple introductions of pre-adapted genotypes, as most of the clinal variations were absent or in opposite directions from those for native populations. Compared with populations, rainfall treatments explained only small proportions of total variations in all studied traits for plants from both ranges, highlighting the importance of heritable phenotypic differentiation. In addition, phenotypic plasticity was similar for plants from both ranges although neutral genetic diversity was much lower for plants from the invasive range. Our results showed that founder effects, post-introduction evolution and phenotypic plasticity may function synergistically in promoting invasion success of C. odorata.

Xanthium orientale subsp. italicum (Moretti) Greuter is an annual herbaceous plant in the Asteraceae family, native to North America. It was first found in Beijing, China, in 1991. Since then, it has spread into many provinces such as Heilongjiang, Jilin, Liaoning, Hebei, Shandong, Xinjiang, and so on. Furthermore, it has been listed as one of the dangerous quarantine weeds in China (4). This noxious invasive weed has a strong ability to acclimatize to new environments. X. orientale subsp. italicum can usually be found in alluvial flatlands, riverbanks, wastelands, roadsides, pastures, as well as farmlands. The presence of this plant decreases the native biodiversity and influences the production of agriculture and stockbreeding. In August 2013, a rust disease was first observed on X. orientale subsp. italicum in Dalian, Liaoning Province, northeast China. Various sized lesions were found on approximately one third of the leaves of each infected plant. These lesions were yellow in the early stage of infection; gradually the center of each lesion turned brown, and eventually the infected lesions became necrotic and ruptured. The small (on average 4 mm in diameter) and dark brown raised telia appeared in the center of the lesions on the lower leaf surface. The teliospores were brown, clavate, two-celled, and measured 42 to 58 × 12 to 21 μm. Teliospores had a conical top, constricted septa, and a persistent pedicel (22 to 70 μm in length). The walls of the teliospores were smooth, 0.8 to 1.2 μm thick at the side and 4 to 8 μm thick at the apex. The size, color, and morphology of the teliospores fit the description of Puccinia xanthii (1,3). A pathogenicity test was conducted by the method of detached leaf inoculation (2). We collected 48 healthy leaves from six individuals of X. orientale subsp. italicum plants, eight from each individual. Teliospores from disease samples were suspended to 1 × 105 spores per ml with sterile water and then smeared on 24 leaves (four per individual); the remaining leaves were inoculated with sterile water as control. Each of the leaves was put on a moist filter paper in a petri dish, and was cultured in a chamber with a 12-h photoperiod at 25°C. Seven days later, dark brown raised telia were observed on all inoculated leaves but not on control ones. The teliospores were removed from the sorus on inoculated leaves, and according to the morphology confirmed to be those of P. xanthii. The rust caused by P. xanthii has been documented in different hosts in many other countries such as Spain, France, Italy, former Yugoslavia, Australia, the United States, and South Africa. In addition, the rust fungus was found to infect X. orientale subsp. italicum in eastern Hungary (1). To our knowledge, this is the first report of P. xanthii attacking the invasive plant X. orientale subsp. italicum in China. It is important to study the potential of using this rust fungus as a biological control agent of X. orientale subsp. italicum. This work was supported by the Project of the National Natural Science Foundation of China (31270582). References: (1) I. Dávid et al. Plant Dis. 87:1536, 2003. (2) Z. D. Fang. Research Methods of Plant Disease, 1998. (3) J. A. Parmelee. Can. J. Bot. 47:1391, 1969. (4) F. H. Wan et al. Biological Invasion: Color Illustration of Invasive Alien Plants in China, 2012.

Invasive plants are exotic species that escape control by native specialist enemies. However, exotic plants may still be attacked by locally occurring generalist enemies, which can influence the dynamics of biological invasions. If invasive plants have greater defensive (resistance and tolerance) capabilities than indigenous plants, they may experience less damage from native herbivores. In the present study, we tested this prediction using the invasive plant Eupatorium adenophorum and two native congeners under simulated defoliation and generalist herbivore insect (Helicoverpa armigera and Spodoptera litura) treatments. E. adenophorum was less susceptible and compensated more quickly to damages in biomass production from both treatments compared to its two congeners, exhibiting greater herbivore tolerance. This strong tolerance to damage was associated with greater resource allocation to aboveground structures, leading to a higher leaf area ratio and a lower root: crown mass ratio than those of its native congeners. E. adenophorum also displayed a higher resistance index (which integrates acid detergent fiber, nitrogen content, carbon/nitrogen ratio, leaf mass per area, toughness, and trichome density) than its two congeners. Thus, H. armigera and S. litura performed poorly on E. adenophorum, with less leaf damage, a lengthened insect developmental duration, and decreased pupating: molting ratios compared to those of the native congeners. Strong tolerance and resistance traits may facilitate the successful invasion of E. adenophorum in China and may decrease the efficacy of leaf-feeding biocontrol agents. Our results highlight both the need for further research on defensive traits and their role in the invasiveness and biological control of exotic plants, and suggest that biocontrol of E. adenophorum in China would require damage to the plant far in excess of current levels.

Different species have differential physiological requirements and ecological strategies, and the resident species and resource type may affect invasiveness of alien plants. Resource pulse is an important factor influencing the invasion status of alien plants. Here, we tested the effects of irradiance and nutrient pulse on the competitiveness of the invasive plant Chromolaena odorata when cultured with two resident plants, Abelmoschus manihot and Xanthium sibiricum. Our results suggest that the response of competitiveness to a resource pulse (nutrient and irradiance) depended on species identity – Chromolaena odorata was more competitive with Abelmoschus manihot than with Xanthium sibiricum under resource pulse. Moreover, Chromolaena odorata has higher advantage than resident species in competitive conditions but not in monoculture conditions. This study provided information for controlling the future spread of invasive C. odorata.

The roles of photosynthesis-related traits in invasiveness of introduced plant species are still not well elucidated, especially in nutrient-poor habitats. In addition, little effort has been made to determine the physiological causes and consequences of the difference in these traits between invasive and native plants. To address these problems, we compared the differences in 16 leaf functional traits related to light-saturated photosynthetic rate (Pmax ) between 22 invasive and native plants in a nutrient-poor habitat in northeast China. The invasive plants had significantly higher Pmax , photosynthetic nitrogen- (PNUE), phosphorus- (PPUE), potassium- (PKUE) and energy-use efficiencies (PEUE) than the co-occurring natives, while leaf nutrient concentrations, construction cost (CC) and specific leaf area were not significantly different between the invasive and native plants. The higher PNUE contributed to higher Pmax for the invasive plants, which in turn contributed to higher PPUE, PKUE and PEUE. CC changed independently with other traits such as Pmax , PNUE, PPUE, PKUE and PEUE, showing two trait dimensions, which may facilitate acclimation to multifarious niche dimensions. Our results indicate that the invasive plants have a superior resource-use strategy, i.e. higher photosynthesis under similar resource investments, contributing to invasion success in the barren habitat.

Successful invasion by exotic plant species can modify the abundance and composition of soil microbial communities. Eupatorium adenophora and Chromolaena odorata are exotics that have become highly invasive plants in China. Several studies have investigated mechanisms of their successful invasions including phenotypic plasticity, genetic differentiation, and allelopathy, but little is known about their effects on soil microorganisms. Moreover, whether soil microbial community changes could cause feedback effects on these plant species is also not known. We seek a belowground microbiological mechanism supporting successful invasions by these exotic plants. In this study, two invasive (E. adenophora and C. odorata) and two native plant species (Eupatorium japonicum and Eupatorium heterophyllum) were used to compare the soil feedback (on plant growth) before and after soil sterilization and from plant-root exudates. Bacterial and fungal biomass and community composition were also examined. We found that soil sterilization significantly increased biomass of native species and did not affect the invasive species’ biomass. After root exudates from these plants had acted on the soil biota for 10 months, soil sterilization significantly decreased the growth of E. adenophora and C. odorata and continued to significantly increase the biomass of two native species. Denaturing gradient gel electrophoresis revealed that these four plant species modified fungal rather than bacterial communities in soil. Higher abundance of Paraglomus sp. in soil with C. odorata is likely to provide C. odorata roots with more soil nutrients. Considered together, these results strongly suggest that invasive E. adenophora and C. odorata created a belowground feedback that may be a mechanism contributing to their success as invasive species.

Xanthium strumarium L. var. canadense (Mill.) Torr. & A. Gray (Canada cocklebur; Asteraceae), an annual herb native to North America, has been widely naturalized in Eurasia (Yin et al. 2012). This introduced plant was first recorded in Beijing in 1991 and now has spread into many provinces in China such as Hebei, Shandong, Liaoning, Jilin, Heilongjiang, Guangdong, Guangxi, and Xinjiang. This invasive, noxious weed generally invades disturbed habitats such as wastelands, riverbanks, roadsides, meadows, and croplands, causing serious ecological and economic impacts in China (Zhao et al. 2014). To determine its distributions and natural enemies in Liaoning Province, we carried out field surveys in the summer of 2016. On August 7, dodder was first found on Canada cocklebur at three disturbed sites (N 41°49′15.41″ to 41°49′20.81″, E 123°34′56.37″ to 123°35′05.41″, 54 to 57 m above sea level) along the Xinkai River in Shenyang (with temperate continental monsoon climate), Liaoning Province, Northeast China. At each site we found a nearly circular patch of Canada cocklebur (3, 5, and 8 m in diameter, respectively) that was parasitized by dodder. Cocklebur parasitized by the dodder showed wilting and senescent leaves, stunted growth, and few or no fruit produced. The dodder wrapped around petioles and stems of the invasive weed, and it occasionally spread onto cooccurring native plants such as Setaria viridis (L.) Beauv. and Humulus scandens (Lour.) Merr. Where the dodder penetrated the cocklebur stem tissues, brownish black lesions developed with small cracks. Based on its inflorescence, bracts, calyces, pedicles, flowers, capsule, ovary, and seed, the dodder was identified as Cuscuta australis R. Br. (Wu 1979; Zhao et al. 2015). The morphological identification was confirmed by molecular evidence. We measured the base sequence of the internal transcribed spacer (ITS) region of ribosomal DNA of the dodder (amplified with S2F-S3R as primers) and found that it (deposited into GenBank; accession no. MH370812) was 99.75% similar to that of C. australis in GenBank (AY554398). Our dodder was 96.47% similar to the nearest relative, C. epithymum (AY554400.1) (Revill et al. 2005). Dodder is distributed worldwide from temperate to tropical regions. It has been found parasitizing other invasive plants such as Ambrosia artemisiifolia (Zhao et al. 2015). To our knowledge, this is the first report of C. australis parasitizing Canada cocklebur in China. The dodder produced 228 to 2,985 seeds (1.05 to 1.22 mm in length) on each infested host and reduced aboveground biomass of the cocklebur by 68.70 to 80.69% and fruit production by 87.59 to 97.21% in the field (data not shown). The dodder and other natural enemies such as Puccinia xanthii (Zhao et al. 2014) may mitigate the impacts of the invasive cocklebur in China.

Invasive plants generally escape from specialist herbivores of their native ranges but may experience serious damage from generalists. As a result, invasive plants may evolve increased resistance to generalists and tolerance to damage. To test these hypotheses, we carried out a common garden experiment comparing 15 invasive populations with 13 native populations of Chromolaena odorata, including putative source populations identified with molecular methods and binary choice feeding experiments using three generalist herbivores. Plants from invasive populations of C. odorata had both higher resistance to three generalists and higher tolerance to simulated herbivory (shoot removal) than plants from native populations. The higher resistance of plants from invasive populations was associated with higher leaf C content and densities of leaf trichomes and glandular scales, and lower leaf N and water contents. Growth costs were detected for tolerance but not for resistance, and plants from invasive populations of C. odorata showed lower growth costs of tolerance. Our results suggest that invasive plants may evolve to increase both resistance to generalists and tolerance to damage in introduced ranges, especially when the defense traits have low or no fitness costs. Greater defenses in invasive populations may facilitate invasion by C. odorata by reducing generalist impacts and increasing compensatory growth after damage has occurred.

To explore the traits contributing to invasion success of Eupatorium adenophorum, a noxious invasive perennial forb throughout the subtropics in Asia, Oceania, Africa, and USA, we compared the differences in ecophysiology and phenology between the invader and native E. japonicum under eight treatment combinations of two irradiances and four nitrogen additions in a two-year shadehouse experiment. The invader had significantly higher mass-based light-saturated photosynthetic rate (P max) than its native congener in all treatments, contributing to higher photosynthetic nitrogen-, phosphorus-, and energy-use efficiencies. The higher P max of the invader was associated with its higher nitrogen concentrations in the photosynthetic apparatus, which resulted from higher leaf nitrogen allocation to photosynthesis. The invader had higher specific leaf area and stomatal conductance at most of the treatments, also contributing to its higher P max. The invader was not constrained by the negative correlation between leaf lifespan and specific leaf area or P max. Leaf lifespan and total leaf area of the invader were greater than those of the native. From November to March the native congener was leafless, whereas the invader maintained a large area of leaves with relatively high P max. Biomass accumulated in these months accounted for more than 40 % of the total biomass of the invader. Our results indicate that both the ability to capture and utilize resources efficiently and the ability to use resources when they are unavailable to natives contribute to invasion success of E. adenophorum and emphasize the importance of exploring multiple, non-mutually exclusive mechanisms for invasions.

The eccentric discharge of stored solids in squat silos has caused many failures, especially that in metal silos. However, these failures are poorly interpreted by specialists. In particular, the lateral pressure distribution on vertical wall couldn’t be accurately recognized. In order to set out the method to calculate static lateral pressure, the appearance of stored solids in silos after eccentric discharge is researched. In this study, based on the overall balance method (OBM), the method for calculating lateral static pressure in squat silos after eccentric discharge is proposed. Four cases are listed according to different discharge stages. Calculative formulae are deducted for each case. This method is also focusing on unsymmetrical distribution characteristic of the lateral pressure. Two calculative examples are listed and the results of which illustrate the necessity of lateral pressure calculation in squat silos.

Enemy release hypothesis predicts that alien plants that escape from their natural enemies suffer lower enemy regulation in their introduced ranges than in native ranges. An extension of this theory suggests that if enemy release plays a crucial role in invasive success, then in the introduced range, invasive plants should also suffer lower local enemy impact than native residents (local enemy release hypothesis, LERH). In order to test LERH, we compared invasive Eupatorium adenophorum with two native congeners (E. heterophyllum and E. japonicum) in terms of damage by leaf enemies at two natural field sites and two manipulated sites. We also determined enemy impact on carbon assimilation at two manipulated sites. In each site, E. adenophorum was only damaged by herbivores, while in native congeners, leaf scabs or (and) leaf rolls was found in addition to herbivory damage. In both manipulated sites, the total enemy impact on carbon assimilation was lower for E. adenophorum than for native congeners; this observation was consistent with LERH. The results of this study indicate that a short co-existence time with generalist enemies (behavior constraint) might be the main contributor to the lower enemy impact on E. adenophorum.