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A novel leaky wave endfire filtering antenna based on spoof surface plasmon polaritons (SSPPs) is proposed. The structure of leaky wave antenna consists of multiple radiating elements and one double-sided parallel strip line (DSPSL), and the filtering performance is realized by adding stubs with via holes. The structure with a periodic arrangement of the radiating elements has similar dispersion curves of SSPPs, which has low-pass transmission characteristic and also can radiate energy to the free space. According to the measured results, a peak gain of 8.65 dBi at a center frequency of 7.7 GHz and a bandwidth of 36.36% can be achieved for the leaky wave endfire filtering antenna based on SSPPs. The out-of-band rejection is over 13 dB. [ABSTRACT FROM AUTHOR]

In this article, a novel differential bandpass filter based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. It consists of a pair of double-layer SSPPs using double-sided parallel-strip line (DSPSL), a pair of single-layer SSPPs, and a 180° phase inverter. The transmission characteristics of the proposed SSPPs’ structure are analyzed by the differential-mode and common-mode method, and also applied to design the differential filter. To validate the design concept, a differential filter sample has been designed, fabricated, and measured. The simulated and measured results indicate a 3-dB fractional bandwidth of 25.5% (frequency 5.5 GHz), and a wide 20-dB common-mode suppression from 2.9 to 8 GHz can be achieved for the differential filter. [ABSTRACT FROM AUTHOR]

In this paper, a novel filtering antenna based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. Double-sided parallel-strip line (DSPSL) is used to realize the wideband property for the double-layer SSPPs. Filtering performance can be realized by adding via holes and ring resonators in the double-layer SSPPs. The simulated and measured results indicate the high gain of 9.38 dBi and bandwidth of 10.44% can be achieved for the antenna with via holes and ring resonators, the out-of-band rejection is over 17 dBi. Meanwhile, the gain variations are less than 1 dBi in the whole frequency band. Good agreements can be observed between the measured and simulated results, which indicate good potential applications in the communication systems and integrated circuits. [ABSTRACT FROM AUTHOR]

Darwin's naturalisation hypothesis posing that phylogenetic distance of alien species to native residents predicts invasion success, and Elton's diversity–invasibility hypothesis posing that diversity of native communities confers resistance to invasion, are both rooted in ideas of species coexistence. Because the two hypotheses are inherently linked, the mechanisms underlying them may interact in driving the invasion success. Even so, these links and interactions have not been explicitly disentangled in one experimental study before.To disentangle the links between the two hypotheses, we used 36 native grassland herbs to create greenhouse mesocosms with 90 grassland communities of different diversities, and introduced each of five herbaceous alien species as seeds and seedlings. We used phylogeny and four functional traits (plant height, specific leaf area, leaf size, and seed mass) to calculate different measures of phylogenetic and functional distance and diversity. Specifically, we tested how the alien–native distance (phylogenetic or functional) and the native diversity (phylogenetic or functional) affected each other in their effects on germination, seedling survival, growth, and reproduction of the aliens.Overall, our results supported both hypotheses. Multivariate functional distance based on four traits jointly had stronger positive effects than phylogenetic distance and the univariate ones based on each trait separately. Moreover, the aliens were more successful if they were more competitive by being taller and having larger leaves with a lower SLA than the native residents. Univariate functional diversity based on each trait separately had stronger negative effects than phylogenetic and multivariate functional diversity. Most importantly, we found that the effects of alien–native phylogenetic and multivariate functional distance became stronger as diversity increased. Our analyses with single traits also showed that the strength of the effects of both alien–native hierarchical functional distances (indicative of competitive inequalities) and absolute functional distances (indicative of niche differences) increased at higher diversities, where competition is more severe.Synthesis. Our study explicitly demonstrates for the first time how the mechanisms underlying the two classical invasion hypotheses interact in driving invasion success in grassland communities. This may help to explain some of the puzzling results of studies testing either of the two hypotheses. This study explicitly demonstrates how the mechanisms underlying the two classical invasion hypotheses, Darwin's naturalisation hypothesis and Elton's diversity–invasibility hypothesis, interact in driving the success of alien species in experimental grassland communities. Our findings could help explain some of the puzzling results of studies testing either of the two hypotheses. [ABSTRACT FROM AUTHOR]

Aim A major challenge in ecology is to understand how multiple causal factors, which may interact, drive success of non-native plants in new ranges. In this study we addressed the role of introduction history, climatic suitability, native range size, species traits and their interactions in the establishment of Chinese woody species in Europe. Location China (native range), Europe (new range). Methods We tested whether establishment of 449 Chinese woody species in Europe was associated with residence time (time since earliest planting), planting frequency, climatic suitability, native range size and species traits. We also considered possible nonlinear effects and interactions among these variables. For the 38 species that have established in Europe, we further tested whether these variables and interactions explained their establishment in multiple European countries. Results Establishment of the 449 species in Europe was positively associated with residence time, planting frequency and climatic suitability. Except residence time, these factors were also positively associated with establishment of the 38 species in multiple countries. None of the traits tested had statistically significant main effects on establishment in Europe, but, for the established species, longer flowering period and having compound leaves were positively associated with establishment in multiple countries. The positive association between establishment in Europe and residence time was stronger for evergreen than for deciduous species. In addition, evergreens, unlike deciduous species, showed a positive association between establishment in Europe and fruiting duration. Moreover, establishment in multiple countries was positively associated with planting frequency for species with compound leaves but not for species with simple leaves, and the association between the establishment and fruiting duration changed from negative to moderately positive as climatic suitability increased. Main conclusions Introduction history and climatic suitability explain most of the variation in establishment, and modulate the role of species traits, such as leaf retention, leaf type and fruiting duration. [ABSTRACT FROM AUTHOR]

Disentangling direct and indirect interactions among alien and native plants is essential to understanding the success of alien plants in multispecies communities, but studies have only focused on direct pairwise interactions. Moreover, it is also essential to explore phylogenetic and functional mechanisms driving these interactions., In a greenhouse experiment, we selected nine groups of alien and native plant species from the herbaceous flora of Germany to disentangle their direct and indirect interactions. Each group had an alien (A) that is common or rare in Germany (i.e. non-native range), two natives that are phylogenetically closely related (Nclose) and distantly related (Ndist) to A respectively, and a distantly related 'target' native (T). We grew the four species of each group alone, and in two-species and three-species combinations. Specifically, we tested whether competition is greater between A and Nclose than between A and Ndist, whether presence of Nclose rather than Ndist indirectly alleviates competition of A on T, and whether these interaction patterns depend on commonness of A. Moreover, we tested how intensity of these interactions is explained by phylogenetic distance, functional traits (height, seed mass, SLA, leaf size, specific root length, leaf area ratio, root length ratio (root length/plant mass), shoot weight ratio) and traits-based functional distance., We found A had stronger competition on Nclose than on Ndist. In turn, A was more suppressed by Nclose than by Ndist, but this was only true for rare rather than common A. The presence of Ndist rather than Nclose indirectly reduced competition of A on T. The intensity of these interactions was not explained by phylogenetic or functional distance, but by some of the functional traits. Specifically, a plant experienced stronger competition when it was shorter and had smaller leaves and lower shoot weight ratio, and when its neighbours were taller, had greater SLA, leaf area ratio and shoot weight ratio, and had a lower root length ratio., Synthesis. Functional traits can help explain competitive interactions. While direct competition tended to be stronger between more closely related alien and native plants, this did not indirectly facilitate other co-occurring native plants. [ABSTRACT FROM AUTHOR]

Background and Aims Recent studies have suggested that responses to shading gradients may play an important role in establishment success of exotic plants, but hitherto few studies have tested this. Therefore, a common-garden experiment was conducted using multiple Asian woody plant species that were introduced to Europe >100 years ago in order to test whether naturalized and non-naturalized species differ in their responses to shading. Specifically, a test was carried out to determine whether naturalized exotic woody species maintained better growth under shaded conditions, and whether they expressed greater (morphological and physiological) adaptive plasticity in response to shading, relative to non-naturalized species. Methods Nineteen naturalized and 19 non-naturalized exotic woody species were grown under five light levels ranging from 100 to 7 % of ambient light. For all plants, growth performance (i.e. biomass), morphological and CO2 assimilation characteristics were measured. For the CO2 assimilation characteristics, CO2 assimilation rate was measured at 1200 μmol m–2 s–1 (i.e. saturated light intensity, A1200), 50 μmol m–2 s–1 (i.e. low light intensity, A50) and 0 μmol m–2 s–1 (A0, i.e. dark respiration). Key Results Overall, the naturalized and non-naturalized species did not differ greatly in biomass production and measured morphological and CO2 assimilation characteristics across the light gradient. However, it was found that naturalized species grew taller and reduced total leaf area more than non-naturalized species in response to shading. It was also found that naturalized species were more capable of maintaining a high CO2 assimilation rate at low light intensity (A50) when grown under shading. Conclusions The results indicate that there is no clear evidence that the naturalized species possess a superior response to shading over non-naturalized species, at least not at the early stage of their growth. However, the higher CO2 assimilation capacity of the naturalized species under low-light conditions might facilitate early growth and survival, and thereby ultimately favour their initial population establishment over the non-naturalized species. [ABSTRACT FROM PUBLISHER]

Understanding the links between causes and consequences of biodiversity is key to achieving conservation of both biodiversity and its functions, yet previous studies have mostly studied them independently. Ecologists have developed bipartite frameworks of high-level processes to understand mechanisms of species coexistence (niche and fitness differences) and biodiversity effects on ecosystem functioning (complementarity and selection effects) and stability (species stability and asynchrony). These high-level processes represent combined effects of low-level processes, which mediate either positive or negative associations between coexistence and biodiversity effects on functioning or stability. Our synthesis, based on high-level processes, provides a first step towards an integrative framework of biodiversity science. Future research needs to address low-level processes using more mechanistic approaches across broader contexts and scales. The global biodiversity crisis has stimulated decades of research on three themes: species coexistence, biodiversity–ecosystem functioning relationships (BEF), and biodiversity–ecosystem functional stability relationships (BEFS). However, studies on these themes are largely independent, creating barriers to an integrative understanding of the causes and consequences of biodiversity. Here we review recent progress towards mechanistic integration of coexistence, BEF, and BEFS. Mechanisms underlying the three themes can be linked in various ways, potentially creating either positive or negative relationships between them. That said, we generally expect positive associations between coexistence and BEF, and between BEF and BEFS. Our synthesis represents an initial step towards integrating causes and consequences of biodiversity; future developments should include more mechanistic approaches and broader ecological contexts. [ABSTRACT FROM AUTHOR]

Chilling (0–18°C) and freezing (<0°C) are two distinct types of cold stresses. Epigenetic regulation can play an important role in plant adaptation to abiotic stresses. However, it is not yet clear whether and how epigenetic modification (i.e., DNA methylation) mediates the adaptation to cold stresses in nature (e.g., in alpine regions). Especially, whether the adaptation to chilling and freezing is involved in differential epigenetic regulations in plants is largely unknown. Chorispora bungeana is an alpine subnival plant that is distributed in the freeze-thaw tundra in Asia, where chilling and freezing frequently fluctuate daily (24 h). To disentangle how C. bungeana copes with these intricate cold stresses through epigenetic modifications, plants of C. bungeana were treated at 4°C (chilling) and -4°C (freezing) over five periods of time (0–24 h). Methylation-sensitive amplified fragment-length polymorphism markers were used to investigate the variation in DNA methylation of C. bungeana in response to chilling and freezing. It was found that the alterations in DNA methylation of C. bungeana largely occurred over the period of chilling and freezing. Moreover, chilling and freezing appeared to gradually induce distinct DNA methylation variations, as the treatment went on (e.g., after 12 h). Forty-three cold-induced polymorphic fragments were randomly selected and further analyzed, and three of the cloned fragments were homologous to genes encoding alcohol dehydrogenase, UDP-glucosyltransferase and polygalacturonase-inhibiting protein. These candidate genes verified the existence of different expressive patterns between chilling and freezing. Our results showed that C. bungeana responded to cold stresses rapidly through the alterations of DNA methylation, and that chilling and freezing induced different DNA methylation changes. Therefore, we conclude that epigenetic modifications can potentially serve as a rapid and flexible mechanism for C. bungeana to adapt to the intricate cold stresses in the alpine areas. [ABSTRACT FROM AUTHOR]

Models of natural processes necessarily sacrifice some realism for the sake of tractability. Detailed, parameter‐rich models often provide accurate estimates of system behaviour but can be data‐hungry and difficult to operationalize. Moreover, complexity increases the danger of 'over‐fitting', which leads to poor performance when models are applied to novel conditions. This challenge is typically described in terms of a trade‐off between bias and variance (i.e. low accuracy vs. low precision).In studies of ecological communities, this trade‐off often leads to an argument about the level of detail needed to describe interactions among species. Here, we used data from a grassland biodiversity experiment containing nine locally abundant plant species (the Jena 'dominance experiment') to parameterize models representing six increasingly complex hypotheses about interactions. For each model, we calculated goodness‐of‐fit across different subsets of the data based on sown species richness levels, and tested how performance changed depending on whether or not the same data were used to parameterize and test the model (i.e. within vs. out‐of‐sample), and whether the range of diversity treatments being predicted fell inside or outside of the range used for parameterization.As expected, goodness‐of‐fit improved as a function of model complexity for all within‐sample tests. In contrast, the best out‐of‐sample performance generally resulted from models of intermediate complexity (i.e. with only two interaction coefficients per species—an intraspecific effect and a single pooled interspecific effect), especially for predictions that fell outside the range of diversity treatments used for parameterization. In accordance with other studies, our results also demonstrate that commonly used selection methods based on AIC of models fitted to the full dataset correspond more closely to within‐sample than out‐of‐sample performance.Synthesis. Our results demonstrate that models which include only general intra and interspecific interaction coefficients can be sufficient for estimating species‐level abundances across a wide range of contexts and may provide better out‐of‐sample performance than do more complex models. These findings serve as a reminder that simpler models may often provide a better trade‐off between bias and variance in ecological systems, particularly when applying models beyond the conditions used to parameterize them. [ABSTRACT FROM AUTHOR]