The Bacterial Metabolite Indole Inhibits Regeneration of the Planarian Flatworm Dugesia japonica

Planarian flatworms have been used for over a century as models for regeneration. Planarians live in aquatic environments with constant exposure to microbes, but the mechanisms by which bacteria may mediate planarian regeneration are largely unknown. We characterized the microbiome of laboratory populations of the planarian Dugesia japonica and determined how individual bacteria impact D. japonica regeneration. Eight to ten taxa in the phyla Bacteroidetes and Proteobacteria consistently occur across planarian colonies housed in different research laboratories. Individual members of the D. japonica microbiome can delay regeneration including the development of eye spots and blastema formation. The microbial metabolite indole is produced in significant quantities by two bacteria that are consistently found in the D. japonica microbiome and contributes to delays in regeneration. Collectively, these results provide a baseline understanding of the bacteria associated with the planarian D. japonica and demonstrate how metabolite production by host-associated microbes can affect regeneration.

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The planarian worm Dugesia japonica is colonized by Bacteroidetes and Proteobacteria

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Many of these bacteria can be cultured and experimentally manipulated

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Some bacteria can inhibit regeneration, including eye and blastema formation

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Indole produced by planarian-associated bacteria contributes to regeneration delays

Indigo- and indirubin-producing strains of Proteus and Psychrobacter are associated with purple rind defect in a surface-ripened cheese

The rinds of surface-ripened cheeses have expected aesthetic properties, including distinct colors, that contribute to overall quality and consumer acceptance. Atypical rind pigments are frequently reported in small-scale cheese production, but the causes of these color defects are largely unknown. We provide a potential microbial explanation for a striking purple rind defect in a surface-ripened cheese. A cheese producer in the United States reported to us several batches of a raw-milk washed-rind cheese with a distinctly purple rind. We isolated a Proteus species from samples with purple rind defect, but not from samples with typical rind pigments, suggesting that this strain of Proteus could be causing the defect. When provided tryptophan, a precursor in the indigo and indirubin biosynthesis pathway, the isolated strain of Proteus secreted purple-red pigments. A Psychrobacter species isolated from both purple and normal rinds also secreted purple-red pigments. Using thin-layer chromatography and liquid chromatography-mass spectrometry, we confirmed that these bacteria produced indigo and indirubin from tryptophan just as closely related bacteria make these compounds in purple urine bag syndrome in medical settings. Experimental cheese communities with or without Proteus and Psychrobacter confirmed that these Proteobacteria cause purple pigmentation of cheese rinds. Reports of purple rinds in two other cheeses from Europe and the observation of pigment production by Proteus and Psychrobacter strains isolated from other cheese rinds suggest that purple rind defect has the potential to be widespread in surface-ripened cheeses.

Extensive horizontal gene transfer in cheese-associated bacteria

Acquisition of genes through horizontal gene transfer (HGT) allows microbes to rapidly gain new capabilities and adapt to new or changing environments. Identifying widespread HGT regions within multispecies microbiomes can pinpoint the molecular mechanisms that play key roles in microbiome assembly. We sought to identify horizontally transferred genes within a model microbiome, the cheese rind. Comparing 31 newly sequenced and 134 previously sequenced bacterial isolates from cheese rinds, we identified over 200 putative horizontally transferred genomic regions containing 4733 protein coding genes. The largest of these regions are enriched for genes involved in siderophore acquisition, and are widely distributed in cheese rinds in both Europe and the US. These results suggest that HGT is prevalent in cheese rind microbiomes, and that identification of genes that are frequently transferred in a particular environment may provide insight into the selective forces shaping microbial communities.

DOI:http://dx.doi.org/10.7554/eLife.22144.001

From the depths of the ocean to the lining of the human gut, almost every environment on Earth is home to a unique community of microorganisms referred to as a microbiome. Within these communities, unrelated microorganisms can exchange genetic information through a process known as horizontal gene transfer. For example, genes linked to antibiotic resistance are often transferred between different microorganisms, which can create increasingly drug resistant microbes and has important implications for human health.

Horizontal gene transfer has been studied for almost 100 years, but examining it directly is challenging because, almost by definition, it requires studying a community of microbes rather than one microbe in isolation. As such, researchers are looking for simple models of microbial communities that can be easily manipulated in experiments.

Bonham et al. have now turned to the outer surface of cheese, also known as cheese rind, to better understand horizontal gene transfer. As a model system, the cheese rind microbiome is relatively simple to work with because cheese rind is easy to replicate in the laboratory, and the microbes growing on cheese can be grown on their own or in combinations with other microbes. By comparing the genetic material of 165 cheese-associated bacteria to one another, Bonham et al. identified over 4,000 genes that were shared between the bacteria, including several large clusters of genes that were shared by many species.

Many of the identified genes (about 23% to be precise) appear to help the microorganisms acquire nutrients that are known to be in short supply on the surface of cheese surface, including iron. Bacteria typically use specialized molecules called siderophores to scavenge for iron and uptake systems to carry the iron-bound siderophore back into the cell. Notably, only the genes associated with the uptake systems were found in some of the shared gene clusters. This finding suggests that horizontal gene transfer has allowed some microbes to “cheat” and take up iron-bound siderophores without expending energy to produce the siderophores themselves.

Using the cheese rind microbiome as a model system, it becomes possible to explore how horizontal gene transfer works in more detail than before. A better understanding of this process can then be applied to other important microbiomes, including those where genes conferring antibiotic resistance are commonly exchanged.

DOI:http://dx.doi.org/10.7554/eLife.22144.002

Planarian regeneration in space: Persistent anatomical, behavioral, and bacteriological changes induced by space travel

Regeneration is regulated not only by chemical signals but also by physical processes, such as bioelectric gradients. How these may change in the absence of the normal gravitational and geomagnetic fields is largely unknown. Planarian flatworms were moved to the International Space Station for 5 weeks, immediately after removing their heads and tails. A control group in spring water remained on Earth. No manipulation of the planaria occurred while they were in orbit, and space‐exposed worms were returned to our laboratory for analysis. One animal out of 15 regenerated into a double‐headed phenotype—normally an extremely rare event. Remarkably, amputating this double‐headed worm again, in plain water, resulted again in the double‐headed phenotype. Moreover, even when tested 20 months after return to Earth, the space‐exposed worms displayed significant quantitative differences in behavior and microbiome composition. These observations may have implications for human and animal space travelers, but could also elucidate how microgravity and hypomagnetic environments could be used to trigger desired morphological, neurological, physiological, and bacteriomic changes for various regenerative and bioengineering applications.

Multiple Vitamin K Forms Exist in Dairy Foods

Background: The plant-based form of vitamin K (phylloquinone, vitamin K-1) has been well quantified in the US diet. Menaquinones (vitamin K-2) are another class of vitamin K compounds that differ from phylloquinone in the length and saturation of their side chain, but they have not been well characterized in foods. Objectives: The objectives of this study were to 1) quantify phylloquinone and the different forms of menaquinones [menaquinone (MK) 4-MK13] in milk, yogurt, Greek yogurt, creams, and cheeses and 2) compare the menaquinone contents of full-fat, reduced-fat, and nonfat dairy products. Methods: All dairy samples were either obtained from the USDA National Food and Nutrient Analysis Program or purchased from retail outlets. Phylloquinone and menaquinone concentrations in these dairy products were quantified by mass spectrometry technology. Results: Full-fat dairy products contained appreciable amounts of menaquinones, primarily in the forms of MK9, MK10, and MK11. We also measured modest amounts of phylloquinone, MK4, MK8, and MK12 in these products. In contrast, there was little MK5-7 or MK13 detected in the majority of dairy products. The total vitamin K contents of soft cheese, blue cheese, semi-soft cheese, and hard cheese were (means ± SEMs): 506 ± 63, 440 ± 41, 289 ± 38, and 282 ± 5.0 µg/100 g, respectively. Nonfermented cheeses, such as processed cheese, contained lower amounts of vitamin K (98 ± 11 µg/100 g). Reduced-fat or fat-free dairy products contained ∼5-22% of the vitamin K found in full-fat equivalents. For example, total vitamin K contents of full-fat milk (4% fat), 2%-fat milk, 1%-fat milk, and nonfat milk were 38.1 ± 8.6, 19.4 ± 7.7, 12.9 ± 2.0, and 7.7 ± 2.9 µg/100 g, respectively. Conclusions: To the best of our knowledge, this is the first report of menaquinone contents of US dairy products. Findings indicate that the amount of vitamin K contents in dairy products is high and proportional to the fat content of the product.

Fecal menaquinone profiles of overweight adults are associated with gut microbiota composition during a gut microbiota-targeted dietary intervention

BACKGROUND

Emerging evidence supports novel roles for vitamin K in cardiometabolic health, some of which may be unique to the bacterially synthesized vitamin K forms known as menaquinones. However, factors influencing menaquinone biosynthesis by the gut microbiota and associations with cardiometabolic health have not been examined.

OBJECTIVE

The objective of this study was to identify associations between fecal menaquinone profiles, gut microbiota composition, and biomarkers of cardiometabolic health.

DESIGN

The menaquinone profile and gut microbiota structure were periodically measured in fecal samples collected from 77 overweight Chinese adults who consumed a prescribed diet previously shown to alter gut microbiota composition and to improve cardiometabolic biomarkers.

RESULTS

Covariance among menaquinones within individual fecal samples partitioned individuals into 2 distinct groups, herein introduced as menaquinotypes of the human gut. Menaquinotypes were characterized by differences in menaquinone (MK) 5 and MK9-MK13 and differences in the relative abundance of several operational taxonomic units (OTUs) delineated at the species level, predominantly within the genera Prevotella spp. and Bacteroides spp. Fecal MK4, MK6, and MK8 decreased during the intervention (P < 0.05); and longitudinal changes in the relative abundance of >100 OTUs were associated with altered fecal content of ≥1 individual menaquinone. The strongest and most consistent relations were between Prevotella spp. and MK5 and MK11-MK13, between Bacteroides spp. and MK9 and MK10, and between Escherichia/Shigella spp. and MK8. Neither individual menaquinones nor menaquinotypes were longitudinally associated with markers of glycemia, insulin resistance, or inflammation.

CONCLUSIONS

These findings suggest that variability in fecal menaquinone content is predominantly determined by relatively few genera within the gut microbiota and that diet-mediated alterations in gut microbiota composition may provide a feasible approach for altering gut menaquinone content. This trial was registered at the Chinese Clinical Trials Registry as ChiCTR-TRC-09000353.

Fermented foods as experimentally tractable microbial ecosystems

Microbial communities of fermented foods have provided humans with tools for preservation and flavor development for thousands of years. These simple, reproducible, accessible, culturable, and easy-to-manipulate systems also provide opportunities for dissecting the mechanisms of microbial community formation. Fermented foods can be valuable models for processes in less tractable microbiota.

Cheese rind communities provide tractable systems for in situ and in vitro studies of microbial diversity

Tractable microbial communities are needed to bridge the gap between observations of patterns of microbial diversity and mechanisms that can explain these patterns. We developed cheese rinds as model microbial communities by characterizing in situ patterns of diversity and by developing an in vitro system for community reconstruction. Sequencing of 137 different rind communities across 10 countries revealed 24 widely distributed and culturable genera of bacteria and fungi as dominant community members. Reproducible community types formed independent of geographic location of production. Intensive temporal sampling demonstrated that assembly of these communities is highly reproducible. Patterns of community composition and succession observed in situ can be recapitulated in a simple in vitro system. Widespread positive and negative interactions were identified between bacterial and fungal community members. Cheese rind microbial communities represent an experimentally tractable system for defining mechanisms that influence microbial community assembly and function.

Transposable element dynamics among asymbiotic and ectomycorrhizal Amanita fungi

Transposable elements (TEs) are ubiquitous inhabitants of eukaryotic genomes and their proliferation and dispersal shape genome architectures and diversity. Nevertheless, TE dynamics are often explored for one species at a time and are rarely considered in ecological contexts. Recent work with plant pathogens suggests a link between symbiosis and TE abundance. The genomes of pathogenic fungi appear to house an increased abundance of TEs, and TEs are frequently associated with the genes involved in symbiosis. To investigate whether this pattern is general, and relevant to mutualistic plant-fungal symbioses, we sequenced the genomes of related asymbiotic (AS) and ectomycorrhizal (ECM) Amanita fungi. Using methods developed to interrogate both assembled and unassembled sequences, we characterized and quantified TEs across three AS and three ECM species, including the AS outgroup Volvariella volvacea. The ECM genomes are characterized by abundant numbers of TEs, an especially prominent feature of unassembled sequencing libraries. Increased TE activity in ECM species is also supported by phylogenetic analysis of the three most abundant TE superfamilies; phylogenies revealed many radiations within contemporary ECM species. However, the AS species Amanita thiersii also houses extensive amplifications of elements, highlighting the influence of additional evolutionary parameters on TE abundance. Our analyses provide further evidence for a link between symbiotic associations among plants and fungi, and increased TE activity, while highlighting the importance individual species’ natural histories may have in shaping genome architecture.

Diet rapidly and reproducibly alters the human gut microbiome

Long-term diet influences the structure and activity of the trillions of microorganisms residing in the human gut^1–5, but it remains unclear how rapidly and reproducibly the human gut microbiome responds to short-term macronutrient change. Here, we show that the short-term consumption of diets composed entirely of animal or plant products alters microbial community structure and overwhelms inter-individual differences in microbial gene expression. The animal-based diet increased the abundance of bile-tolerant microorganisms (Alistipes, Bilophila, and Bacteroides) and decreased the levels of Firmicutes that metabolize dietary plant polysaccharides (Roseburia, Eubacterium rectale, and Ruminococcus bromii). Microbial activity mirrored differences between herbivorous and carnivorous mammals², reflecting trade-offs between carbohydrate and protein fermentation. Foodborne microbes from both diets transiently colonized the gut, including bacteria, fungi, and even viruses. Finally, increases in the abundance and activity of Bilophila wadsworthia on the animal-based diet support a link between dietary fat, bile acids, and the outgrowth of microorganisms capable of triggering inflammatory bowel disease⁶. In concert, these results demonstrate that the gut microbiome can rapidly respond to altered diet, potentially facilitating the diversity of human dietary lifestyles.

Real-time metabolomics on living microorganisms using ambient electrospray ionization flow-probe

Microorganisms such as bacteria and fungi produce a variety of specialized metabolites that are invaluable for agriculture, biological research, and drug discovery. However, the screening of microbial metabolic output is usually a time-intensive task. Here, we utilize a liquid microjunction surface sampling probe for electrospray ionization-mass spectrometry to extract and ionize metabolite mixtures directly from living microbial colonies grown on soft nutrient agar in Petri-dishes without any sample pretreatment. To demonstrate the robustness of the method, this technique was applied to observe the metabolic output of more than 30 microorganisms, including yeast, filamentous fungi, pathogens, and marine-derived bacteria, that were collected worldwide. Diverse natural products produced from different microbes, including Streptomyces coelicolor , Bacillus subtilis , and Pseudomonas aeruginosa are further characterized.

Gender differences in binge eating and behavioral correlates among college students

PURPOSE

The purpose of this study was to investigate gender differences in binge eating and associated behavioral correlates in college students.

METHODS

A webbased survey was conducted with 2073 students (mean age 19.8 yr; range 18-23 yr). Multiple logistic regression was used to calculate odds ratios and 95% confidence intervals for the factors associated with binge eating.

RESULTS

Twenty-nine percent of students reported recent bingeing. Factors associated with binge eating included being female, having a higher body mass index, current tobacco use, and exercising to lose weight. Women were more likely to binge eat (73.8%; χ(2)=32.3; p≤0.001), report loss of control (45%; χ(2)=16.3; p≤0.001), self induced vomiting (20.7%; χ(2)=15.9; p≤0.001), and laxative use (6.7%; χ(2)=8.93; p≤0.001).

CONCLUSIONS

Results generated from this study suggest that gender-disparate behaviors are potential targets for future tailored interventions.

The irreversible loss of a decomposition pathway marks the single origin of an ectomycorrhizal symbiosis

Microbial symbioses have evolved repeatedly across the tree of life, but the genetic changes underlying transitions to symbiosis are largely unknown, especially for eukaryotic microbial symbionts. We used the genus Amanita, an iconic group of mushroom-forming fungi engaged in ectomycorrhizal symbioses with plants, to identify both the origins and potential genetic changes maintaining the stability of this mutualism. A multi-gene phylogeny reveals one origin of the symbiosis within Amanita, with a single transition from saprotrophic decomposition of dead organic matter to biotrophic dependence on host plants for carbon. Associated with this transition are the losses of two cellulase genes, each of which plays a critical role in extracellular decomposition of organic matter. However a third gene, which acts at later stages in cellulose decomposition, is retained by many, but not all, ectomycorrhizal species. Experiments confirm that symbiotic Amanita species have lost the ability to grow on complex organic matter and have therefore lost the capacity to live in forest soils without carbon supplied by a host plant. Irreversible losses of decomposition pathways are likely to play key roles in the evolutionary stability of these ubiquitous mutualisms.

Geographically structured host specificity is caused by the range expansions and host shifts of a symbiotic fungus

The inability to associate with local species may constrain the spread of mutualists arriving to new habitats, but the fates of introduced, microbial mutualists are largely unknown. The deadly poisonous ectomycorrhizal fungus Amanita phalloides (the death cap) is native to Europe and introduced to the East and West Coasts of North America. By cataloging host associations across the two continents, we record dramatic changes in specificity among the three ranges. On the East Coast, where the fungus is restricted in its distribution, it associates almost exclusively with pines, which are rarely hosts of A. phalloides in its native range. In California, where the fungus is widespread and locally abundant, it associates almost exclusively with oaks, mirroring the host associations observed in Europe. The most common host of the death cap in California is the endemic coast live oak (Quercus agrifolia), and the current distribution of A. phalloides appears constrained within the distribution of Q. agrifolia. In California, host shifts to native plants are also associated with a near doubling in the resources allocated to sexual reproduction and a prolonged fruiting period; mushrooms are twice as large as they are elsewhere and mushrooms are found throughout the year. Host and niche shifts are likely to shape the continuing range expansion of A. phalloides and other ectomycorrhizal fungi introduced across the world.

Amanita thiersii is a saprotrophic fungus expanding its range in the United States

Although most species in the genus Amanita form ectomycorrhizal associations, a few are reported to be saprotrophs living in grassland habitats. Little is known about the ecology and distribution of these free-living Amanita species. We describe the ecology of Amanita thiersii, a species commonly collected in lawns throughout the Mississippi River Basin. Stable isotopes of carbon, transcriptomic sequences and patterns of growth on complex carbon sources provide evidence for A. thiersii as a saprotrophic species. Sporocarps of A. thiersii are less depleted in (13)C compared to published data for ectomycorrhizal fungi, supporting a saprotrophic mode of carbon acquisition in the field. Orthologs of cellulase genes known to play key roles in the decomposition of cellulose in other basidiomycetes were identified in a transcriptome of A. thiersii, establishing that this species has the genetic potential to degrade cellulose. Amanita thiersii also can use artificial cellulose or sterile grass litter as a sole carbon source. DNA sequences of three nuclear gene regions and banding patterns from four inter-simple sequence repeat markers were identical across 31 populations from throughout the known range of the species, which suggests the genetic diversity of A. thiersii populations is low. Maps of A. thiersii collections made from the 1950s until present suggest this species is experiencing a range expansion. It was reported first in 1952 in Texas and now occurs in nine states north to Illinois. These data provide an ecological context for interpreting the genome of A. thiersii, currently being sequenced at the United States Department of Energy's Joint Genome Institute.

Distribution and abundance of the introduced ectomycorrhizal fungus Amanita phalloides in North America

Despite a growing awareness of the global reach of ectomycorrhizal (EM) fungal introductions, little is known about the fate of introduced EM fungi in novel ranges. Using herbarium specimens, species distribution models, and field collections of sporocarps, root tips and extramatrical mycelia, we assessed the distribution and abundance of the European species Amanita phalloides in North America. There are two distinct ranges of the fungus, one along the West Coast (California to British Columbia) and the second on the East Coast (Maryland to Maine). As predicted by a species distribution model, the West Coast range is larger. Amanita phalloides is more frequently found in native forests on the West Coast than on the East Coast. At Point Reyes Peninsula in California, A. phalloides dominates community sporocarp biomass, and is frequent as root tips. In individual soil cores at Point Reyes, root tips of A. phalloides make up 50% of total root tip biomass. Hyphae of A. phalloides are frequent, but make up only 2% of total hyphal biomass. The contrasting patterns of the distribution and abundance of A. phalloides on the East and West Coasts of North America may influence both its future spread and its impacts.

Global patterns of ectomycorrhizal introductions

Plants have often been moved across the globe with intact root systems. These roots are likely to have housed symbiotic ectomycorrhizal (EM) fungi and the movement of plants may have facilitated the introduction of EM fungi.Here, we report data compiled from a newly created database of EM fungal introductions.We estimate the magnitude of EM fungal introductions around the world and examine patterns associated with these introductions. We also use the data to develop a framework for understanding the invasion biology of EM fungi.At least 200 species of basidiomycete and ascomycete EM fungi have been moved from native ranges to novel habitats. The majority of recorded introductions are associated with Pinus or Eucalyptus plantations in the southern hemisphere. Most introduced species appear to be constrained from spreading in novel habitats and associate only with their introduced hosts. Aspects of life history, including host range, may influence the ability of EM species to establish or invade. Human-caused introductions of EM fungi are a common and global phenomenon.The mechanisms controlling EM fungi in novel habitats and potential impacts of EM fungal introductions are almost entirely unknown.

Co-morbidity and disorder-related distress and impairment in purging disorder

BACKGROUND

Recent studies suggest that purging disorder (PD) may be a common eating disorder that is associated with clinically significant levels of distress and high levels of psychiatric co-morbidity. However, no study has established evidence of disorder-related impairment or whether distress is specifically related to PD rather than to co-morbid disorders.

METHOD

Three groups of normal-weight women [non-eating disorder controls (n=38), with PD (n=24), and with bulimia nervosa (BN)-purging subtype (n=57)] completed structured clinical interviews and self-report assessments.

RESULTS

Both PD and BN were associated with significant co-morbidity and elevations on indicators of distress and impairment compared to controls. Compared to BN, PD was associated with lower rates of current and lifetime mood disorders but higher rates of current anxiety disorders. Elevated distress and impairment were maintained in PD and BN after controlling for Axis I and Axis II disorders.

CONCLUSIONS

PD is associated with elevated distress and impairment and should be considered for inclusion as a provisional disorder in nosological schemes such as the Diagnostic and Statistical Manual to facilitate much-needed research on this clinically significant syndrome.

Small-scale spatial heterogeneity of arbuscular mycorrhizal fungal abundance and community composition in a wetland plant community

Although it has become increasingly clear that arbuscular mycorrhizal fungi (AMF) play important roles in population, community, and ecosystem ecology, there is limited information on the spatial structure of the community composition of AMF in the field. We assessed small-scale spatial variation in the abundance and molecular diversity of AMF in a calcareous fen, where strong underlying environmental gradients such as depth to water table may influence AMF. Throughout an intensively sampled 2 x 2 m plot, we assessed AMF inoculum potential at a depth of 0-6 and 6-12 cm and molecular diversity of the AMF community using terminal restriction fragment length polymorphism of 18S rDNA. Inoculum potential was only significantly spatially autocorrelated at a depth of 6-12 cm and was significantly positively correlated with depth to water table at both depths. Molecular diversity of the AMF community was highly variable within the plot, ranging from 2-14 terminal restriction fragments (T-RFs) per core, but the number of T-RFs did not relate to water table or plant species richness. Plant community composition was spatially autocorrelated at small scales, but AMF community composition showed no significant spatial autocorrelation. Saturated soils of calcareous fens contain many infective AMF propagules and the abundance and diversity of AMF inoculum is patchy over small spatial scales.

Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms

The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat.

Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms

The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat.

Abrupt rise in atmospheric CO2 overestimates community response in a model plant–soil system

Attempts to understand the ecological effect of increasing atmospheric CO2 concentration, [CO2], usually involve exposing today's ecosystems to expected future [CO2] levels. However, a major assumption of these approaches has not been tested--that exposing ecosystems to a single-step increase in [CO2] will yield similar responses to those of a gradual increase over several decades. We tested this assumption on a mycorrhizal fungal community over a period of six years. [CO2] was either increased abruptly, as is typical of most [CO2] experiments, or more gradually over 21 generations. The two approaches resulted in different structural and functional community responses to increased [CO2]. Some fungi were sensitive to the carbon pulse of the abrupt [CO2] treatment. This resulted in an immediate decline in fungal species richness and a significant change in mycorrhizal functioning. The magnitude of changes in fungal diversity and functioning in response to gradually increasing [CO2] was smaller, and not significantly different to those with ambient [CO2]. Our results suggest that studies may overestimate some community responses to increasing [CO2] because biota may be sensitive to ecosystem changes that occur as a result of abrupt increases.