Competition among native and invasive Phragmites australis populations: An experimental test of the effects of invasion status, genome size, and ploidy level

Among the traits whose relevance for plant invasions has recently been suggested are genome size (the amount of nuclear DNA) and ploidy level. So far, research on the role of genome size in invasiveness has been mostly based on indirect evidence by comparing species with different genome sizes, but how karyological traits influence competition at the intraspecific level remains unknown. We addressed these questions in a common‐garden experiment evaluating the outcome of direct intraspecific competition among 20 populations of Phragmites australis, represented by clones collected in North America and Europe, and differing in their status (native and invasive), genome size (small and large), and ploidy levels (tetraploid, hexaploid, or octoploid). Each clone was planted in competition with one of the others in all possible combinations with three replicates in 45‐L pots. Upon harvest, the identity of 21 shoots sampled per pot was revealed by flow cytometry and DNA analysis. Differences in performance were examined using relative proportions of shoots of each clone, ratios of their aboveground biomass, and relative yield total (RYT). The performance of the clones in competition primarily depended on the clone status (native vs. invasive). Measured in terms of shoot number or aboveground biomass, the strongest signal observed was that North American native clones always lost in competition to the other two groups. In addition, North American native clones were suppressed by European natives to a similar degree as by North American invasives. North American invasive clones had the largest average shoot biomass, but only by a limited, nonsignificant difference due to genome size. There was no effect of ploidy on competition. Since the North American invaders of European origin are able to outcompete the native North American clones, we suggest that their high competitiveness acts as an important driver in the early stages of their invasion

Directional trends in species composition over time can lead to a widespread overemphasis of year‐to‐year asynchrony

Questions: Compensatory dynamics are described as one of the main mechanisms that increase community stability, e.g., where decreases of some species on a year‐to‐year basis are offset by an increase in others. Deviations from perfect synchrony between species (asynchrony) have therefore been advocated as an important mechanism underlying biodiversity effects on stability. However, it is unclear to what extent existing measures of synchrony actually capture the signal of year‐to‐year species fluctuations in the presence of long‐term directional trends in both species abundance and composition (species directional trends hereafter). Such directional trends may lead to a misinterpretation of indices commonly used to reflect year‐to‐year synchrony. Methods: An approach based on three‐term local quadrat variance (T3) which assesses population variability in a three‐year moving window, was used to overcome species directional trend effects. This “detrending” approach was applied to common indices of synchrony across a worldwide collection of 77 temporal plant community datasets comprising almost 7,800 individual plots sampled for at least six years. Plots included were either maintained under constant “control” conditions over time or were subjected to different management or disturbance treatments. Results: Accounting for directional trends increased the detection of year‐to‐year synchronous patterns in all synchrony indices considered. Specifically, synchrony values increased significantly in ~40% of the datasets with the T3 detrending approach while in ~10% synchrony decreased. For the 38 studies with both control and manipulated conditions, the increase in synchrony values was stronger for longer time series, particularly following experimental manipulation. Conclusions: Species’ long‐term directional trends can affect synchrony and stability measures potentially masking the ecological mechanism causing year‐to‐year fluctuations. As such, previous studies on community stability might have overemphasised the role of compensatory dynamics in real‐world ecosystems, and particularly in manipulative conditions, when not considering the possible overriding effects of long‐term directional trends

LOTVS: a global collection of permanent vegetation plots

Analysing temporal patterns in plant communities is extremely important to quantify the extent and the consequences of ecological changes, especially considering the current biodiversity crisis. Long-term data collected through the regular sampling of permanent plots represent the most accurate resource to study ecological succession, analyse the stability of a community over time and understand the mechanisms driving vegetation change. We hereby present the LOng-Term Vegetation Sampling (LOTVS) initiative, a global collection of vegetation time-series derived from the regular monitoring of plant species in permanent plots. With 79 data sets from five continents and 7,789 vegetation time-series monitored for at least 6 years and mostly on an annual basis, LOTVS possibly represents the largest collection of temporally fine-grained vegetation time-series derived from permanent plots and made accessible to the research community. As such, it has an outstanding potential to support innovative research in the fields of vegetation science, plant ecology and temporal ecology

Seed-bank dynamics of native and invasive Impatiens species during a five-year field experiment under various environmental conditions

Volume: 50Start Page: 75-9

Shift in the effects of invasive soil legacy on subsequent native and invasive trees driven by nitrogen deposition

Invasive plants can interact with soil microbes to enhance their own performance. Such interactive effects may persist and later affect plant performance and their population dynamics. Such ‘invasive soil legacy’ is the specific plant–soil feedback that can affect future invasions, while it is not clear how nitrogen deposition and interspecific competition influence invasive soil legacy. Thus, we collected field soil and conducted a greenhouse experiment to investigate the effects of soil legacy of the invasive tree Rhus typhina on the performance, functional traits and soil microbial communities of R. typhina and the native tree Ailanthus altissima under three nitrogen levels with and without interspecific competition. The experiment revealed that the outcomes of invasive soil legacies were context-specific and depended on local soil nutrient levels and species competition. Specifically, nitrogen addition changed the negative conspecific soil legacy on subsequent R. typhina to a positive effect, while it became negative in A. altissima. The invasive soil legacy promoted the transpirational rate of R. typhina and A. altissima in monoculture, but inhibited it in a mixture under nitrogen deposition. Nitrogen deposition reduced bacteria and fungi biomass of A. altissima in monocultures and mixtures. In contrast, nitrogen deposition decreased bacterial and fungal biomass of R. typhina in monocultures, but enhanced them in mixtures. Therefore, changes in plant growth, transpiration rate and soil microbial biomass might contribute to the different responses of invasive and native plants to invasive soil legacies. Nitrogen deposition and interspecific competition promote the viability of invasive plants from plant–soil feedback and indicate that ranges of subsequent plants might further expand through below-ground process under nitrogen deposition in the future

Shift in the effects of invasive soil legacy on subsequent native and invasive trees driven by nitrogen deposition

Invasive plants can interact with soil microbes to enhance their own performance. Such interactive effects may persist and later affect plant performance and their population dynamics. Such ‘invasive soil legacy’ is the specific plant–soil feedback that can affect future invasions, while it is not clear how nitrogen deposition and interspecific competition influence invasive soil legacy. Thus, we collected field soil and conducted a greenhouse experiment to investigate the effects of soil legacy of the invasive tree Rhus typhina on the performance, functional traits and soil microbial communities of R. typhina and the native tree Ailanthus altissima under three nitrogen levels with and without interspecific competition. The experiment revealed that the outcomes of invasive soil legacies were context-specific and depended on local soil nutrient levels and species competition. Specifically, nitrogen addition changed the negative conspecific soil legacy on subsequent R. typhina to a positive effect, while it became negative in A. altissima. The invasive soil legacy promoted the transpirational rate of R. typhina and A. altissima in monoculture, but inhibited it in a mixture under nitrogen deposition. Nitrogen deposition reduced bacteria and fungi biomass of A. altissima in monocultures and mixtures. In contrast, nitrogen deposition decreased bacterial and fungal biomass of R. typhina in monocultures, but enhanced them in mixtures. Therefore, changes in plant growth, transpiration rate and soil microbial biomass might contribute to the different responses of invasive and native plants to invasive soil legacies. Nitrogen deposition and interspecific competition promote the viability of invasive plants from plant–soil feedback and indicate that ranges of subsequent plants might further expand through below-ground process under nitrogen deposition in the future

Characterisation of IncA/C-2 plasmids carrying an In416-like integron with the bla(VIM-19) gene from Klebsiella pneumoniae ST383 of Greek origin

The complete nucleotide sequences of three multidrug resistance (MDR) IncA/C-like plasmids from Enterobacteriaceae isolates carrying the VIM-type carbapenemase-encoding integrons In4863 (bla(VIM-19)-aacA7-dfrA1-Delta aadA1-smr2) or In4873 (bla(VIM-1)-aacA7-dfrA1-Delta aadA1-smr2) were determined, which are the first In416-like elements identified in Greece. Plasmids pKP-Gr642 and pKP-Gr8143 were from Klebsiella pneumoniae ST383 isolates, whereas plasmid pEcl-Gr4873 was from an Enterobacter cloacae ST88 isolate. Sequencing showed that pKP-Gr642 (162 787 bp) and pKP-Gr8143 (154 395 bp) consisted of the type 1 IncA/C-2 conserved backbone, the blaCMY-2-like gene-containing region, and the ARI-B (with the sul2 gene) and ARI-A (with a class 1 integron) resistance islands, like the plasmid pUMNK88-161 from the USA. The third plasmid, pEcl-Gr4873 (153 958 bp), exhibited extensive similarity with the type 2 IncA/C-2 plasmid pR55 from France. pEcl-Gr4873 carried only one resistance island of a hybrid transposon structure inserted in a different location to ARI-A in type 1 A/C-2 plasmids. In all three plasmids, the In416-like integrons In4863 or In4873 were identified within non-identical class II transposon structures. All three In416-like-carrying regions presented significant similarities with the MDR region of the IncA/C-2 plasmid pCC416 from Italy, carrying the prototype In416 integron (bla(VIM-4)-aacA7-dfrA1-Delta aadA1-smr2). These findings provided the basis for speculations regarding the evolution of IncA/C-2 plasmids with In416-like integrons, and confirmed the rapid evolution of some IncA/C-2 plasmid lineages. Considering the broad host range of IncA/C-2 molecules, it seems that pKP-Gr642, pKP-Gr8143 and pEcl-Gr4873 plasmids might support the diffusion of In416-like integrons among Enterobacteriaceae. (C) 2015 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved

Functional trait trade-offs define plant population stability across different biomes.

Ecological theory posits that temporal stability patterns in plant populations are associated with differences in species ecological strategies. However, empirical evidence is lacking about which traits, or trade-offs, underlie species stability, especially across different biomes. We compiled a worldwide collection of long-term permanent vegetation records (greater than 7000 plots from 78 datasets) from a large range of habitats which we combined with existing trait databases. We tested whether the observed inter-annual variability in species abundance (coefficient of variation) was related to multiple individual traits. We found that populations with greater leaf dry matter content and seed mass were more stable over time. Despite the variability explained by these traits being low, their effect was consistent across different datasets. Other traits played a significant, albeit weaker, role in species stability, and the inclusion of multi-variate axes or phylogeny did not substantially modify nor improve predictions. These results provide empirical evidence and highlight the relevance of specific ecological trade-offs, i.e. in different resource-use and dispersal strategies, for plant populations stability across multiple biomes. Further research is, however, necessary to integrate and evaluate the role of other specific traits, often not available in databases, and intraspecific trait variability in modulating species stability

Functional traits trade-offs define plant population stability scross different biomes

Ecological theory posits that temporal stability patterns in plant populations are associated with differences in species’ ecological strategies. However, empirical evidence is lacking about which traits, or trade-offs, underlie species stability, especially across different biomes. We compiled a worldwide collection of long-term permanent vegetation records (greater than 7000 plots from 78 datasets) from a large range of habitats which we combined with existing trait databases. We tested whether the observed inter-annual variability in species abundance (coefficient of variation) was related to multiple individual traits. We found that populations with greater leaf dry matter content and seed mass were more stable over time. Despite the variability explained by these traits being low, their effect was consistent across different datasets. Other traits played a significant, albeit weaker, role in species stability, and the inclusion of multi-variate axes or phylogeny did not substantially modify nor improve predictions. These results provide empirical evidence and highlight the relevance of specific ecological trade-offs, i.e. in different resource-use and dispersal strategies, for plant populations stability across multiple biomes. Further research is, however, necessary to integrate and evaluate the role of other specific traits, often not available in databases, and intraspecific trait variability in modulating species stability