Effects of tree sapling diversity and nutrient addition on herb-layer invasibility in communities of subtropical species

Exotic species are assumed to alter ecosystem functioning. However, little is known of the relationships within vertically structured plant communities such as forests, where tree saplings interact with herbaceous species, especially in the early phases of succession. This relationship was tested in a common garden experiment which assessed the impacts on tree saplings and herbaceous species following nutrient addition and the introduction of exotic herb species. The experiment was established in South- East China using four broad-leaved tree species (Elaeocarpus decipiens, Schima superba, Castanea henryi and Quercus serrata) to study the relationships between tree sapling diversity, herb-layer productivity and invasibility. Tree saplings were planted in monoculture and in mixtures of two and four species. A full factorial design was applied, within which species composition was crossed with nutrient and exotic seed-addition treatments. The seed-addition treatment included mixtures of seeds from eight exotic herb species, and herb community attributes were assessed after a four month growing season. Results indicate that certain tree species negatively affect native as well as exotic herbs;however, the high productivity of native herbs had a stronger negative impact on exotic species than tree saplings. Nutrient addition increased the productivity of exotic herbs but had no effect on native herbs. Remarkably, exotic species introduction had a negative feedback effect on the growth of tree saplings, which highlights the potential of exotic herbs to diminish tree recruitment. Although tree saplings reduced invasive effects on the herb-layer during the earliest phase of forest succession, nutrient addition had a more profound and opposite effect on these invaders.

Maternal effects, malaria infections and the badge size of the house sparrow

Background: The evolution of sexual signals is not only determined by immediate sexual selection but also by selection arising from the environment and the interaction with developmental effects.In this study we aimed to investigate how the badge size of male house sparrows(Passer domesticus) is correlated to avian malaria infections as well as to prenatal testosterone exposure,measured as the 2D:4D digit ratio.The rationale behind this study is that the immunosuppressive effect of maternal testosterone deposition combined with the fitness cost imposed by parasites may cause important trade-offs to the development of secondary sexual signals.Methods: Assuming that vector abundance is a key variable associated with infection risk by avian malaria,we caught adult male sparrows from eight different populations in the Camargue,France,four of which were located in a vector-controlled area,and the other four in an untreated area.For each bird we measured its badge size,digit ratio and took blood to determine its infections status.We used PCR to identify the malaria parasite species and strain that caused the infection.Results: Contrary to our expectation,prevalence of disease did not differ across the vector-treatment regions,with around 80 % of birds being infected in both areas,and those infections were caused largely by a single strain,Plasmodium relictum SGS1.Although infected birds had a badge size not significantly different from uninfected males,there was a condition-dependent association between badge size,infection status and maternal testosterone deposition.Conclusions: This study illustrates that the complexity of temporal and ecological dimensions makes the relationships between disease,testosterone-related traits and secondary sexual signals that have been previously reported less general than thought.

Coping with drought?Effects of extended drought conditions on soil invertebrate prey and diet selection by a fossorial amphisbaenian reptile

Arid climates are characterized by a summer drought period to which animals seem adapted.However,in some years,the drought can extend for unusually longer periods.Examining the effects of these current extreme weather events on biodiversity can help to understand the effects of climate change,as models predict an increase in drought severity.Here,we examined the effects of“unusual”extended drought on soil invertebrate prey availability and on diet composition(based on fecal contents)and diet selection of a fossorial amphisbaenian,the checkerboard worm lizard Trogonophis wiegmanni.Weather data show interannual variations in summer drought duration.The abundance and diversity of soil invertebrates in spring were high,and similar to those found in a“normal”early autumn,after some rain had ended with the summer drought.In contrast,in years with“unusual”extended drought,abundance,and diversity of soil invertebrates in early autumn were very low.Also,there were seasonal changes in amphisbaenians’diet;in autumn with drought,prey diversity,and niche breadth decreased with respect to spring and autumns after some rain had fallen.Amphisbaenians did not eat prey at random in any season,but made some changes in prey selection that may result from drought-related restrictions in prey availability.Finally,in spite that amphisbaenians showed some feeding flexibility,their body condition was lower in autumn than in spring,and much lower in autumn with drought.If extended drought became the norm in the future,amphisbaenians might suffer important negative effects for their health state.

Leaf area increases with species richness in young experimental stands of subtropical trees

Aims Most biodiversity-ecosystem functioning research has been carried out in grassland ecosystems,and little is known about whether forest ecosystems,in particular outside the temperate zone,respond similarly.Here,we tested whether productivity,assessed as leaf area index(LAI),increases with species richness in young experimental stands of subtropical trees,whether this response is similar for early-season leaf area(which is dominated by evergreens)and seasonal leaf area increase(which is dominated by deciduous species),and whether responses saturate at high species richness.Methods We used a planted tree biodiversity experiment in south-east China to test our hypotheses.LAI was determined three times by digital hemispheric photography in 144 plots that had been planted with 400 trees each,forming communities with 1,2,4,8 or 16 tree species.Important Findings LAI increased significantly with tree species richness in the fifth year of stand establishment.Similar,but weaker,statistically non-significant trends were observed 1 year before.We did not observe leaf area overyielding and the presence of particularly productive and unproductive species explained large amounts of variation in leaf area,suggesting that selection-type effects contributed substantially to the biodiversity effects we found in this early phase of stand establishment.Effects sizes were moderate to large and comparable in magnitude to the ones reported for grassland ecosystems.Subtropical(and tropical)forests harbor substantial parts of global net primary production and are critical for the Earth’s carbon and hydrological cycle,and our results suggest that tree diversity critically supports these ecosystem services.

Seasonal characteristics and determinants of tree growth in a Chinese subtropical forest

Aims To quantify the seasonal differences in effects of leaf habit,species identity,initial diameter,neighborhood interaction and stand environment on tree absolute diameter growth rates in a subtropical forest in China.Methods We used man-made dendrometer bands to record radial increments of all trees with diameter at breast height(DBH)≥5 cm and height≥3 m within 25 comparative study plots(30×30 m for each)of the‘Biodiversity-Ecosystem Functioning Experiment China’(BEF-China)in the Gutianshan National Nature Reserve,Zhejiang Province,China.We measured stem circumferences twice a year from 2011 to 2014 to calculate absolute diameter growth rate of a warm and wet season(WWS,April to September)and a dry and cold season(DCS,October to the next March)for each individual tree:annual growth(GR_(year)),growth during the WWS(GR_(WWS))and growth during the DCS(GR_(DCS)).We firstly tested the differences in growth rates between different seasons using paired t-tests with Bonferroni correction.Then we applied linear mixed models to explore the effects of leaf habit,species identity,initial diameter,neighborhood interaction(indicated by richness,density and total basal area of all neighboring trees within a radius of 5 m around target trees),stand age and topography(elevation,slope and aspect)on tree growth rates of the two different seasons in three deciduous and 14 evergreen species.Important Findings GR_(year),GR_(WWS)and GR_(DCS)varied between 0.04-0.50 cm year^(−1)(mean=0.21),0.03-0.46 cm season^(−1)(mean=0.18)and 0.01-0.05 cm season^(−1)(mean=0.03)across the 17 species,respectively.GR_(WWS)was significantly higher than GR_(DCS)for all species.Growth rates of faster growing species tended to have larger absolute differences between the WWS and DCS.Tree growth rates of both seasons and of the year(GR_(year),GR_(WWS)and GR_(DCS))varied significantly among leaf habit and species,and increased allometrically with initial diameter,decreased with stand age,but were not significantly related to topography and neighborhood richness or density.GR_(WWS)decreased with neighborhood total basal area,while GR_(DCS)did not.In conclusion,species might the temporally complementary,contributing to plot growth at different times of the year.

On the combined effect of soil fertility and topography on tree growth in subtropical forest ecosystems—a study from SE China

Aims The aim of our research was to understand small-scale effects of topography and soil fertility on tree growth in a forest biodiversity and ecosystem functioning(BEF)experiment in subtropical SE China.Methods Geomorphometric terrain analyses were carried out at a spatial resolution of 5×5 m.Soil samples of different depth increments and data on tree height were collected from a total of 566 plots(667 m2 each).The soils were analyzed for carbon(soil organic carbon[SOC]),nitrogen,acidity,cation exchange capacity(CEC),exchangeable cations and base saturation as soil fertility attributes.All plots were classified into geomorphological units.Analyses of variance and linear regressions were applied to all terrain,soil fertility and tree growth attributes.Important Findings In general,young and shallow soils and relatively small differences in stable soil properties suggest that soil erosion has truncated the soils to a large extent over the whole area of the experiment.This explains the concurrently increasing CEC and SOC stocks downslope,in hollows and in valleys.However,colluvial,carbon-rich sediments are missing widely due to the convexity of the footslopes caused by uplift and removal of eroded sediments by adjacent waterways.The results showed that soil fertility is mainly influenced by topography.Monte-Carlo flow accumulation(MCCA),curvature,slope and aspect significantly affected soil fertility.Furthermore,soil fertility was affected by the different geomorphological positions on the experimental sites with ridge and spur positions showing lower exchangeable base cation contents,especially potassium(K),due to leaching.This geomorphological effect of soil fertility is most pronounced in the topsoil and decreases when considering the subsoil down to 50 cm depth.Few soil fertility attributes affect tree height after 1-2 years of growth,among which C stocks proved to be most important while pH_(KCl)and CEC only played minor roles.Nevertheless,soil acidity and a high proportion of Al on the exchange complex affected tree height even after only 1-2 years growth.Hence,our study showed that forest nutrition is coupled to a recycling of litter nutrients,and does not only depend on subsequent supply of nutrients from the mineral soil.Besides soil fertility,topography affected tree height.We found that especially MCCA as indicator of water availability affected tree growth at small-scale,as well as aspect.Overall,our synthesis on the interrelation between fertility,topography and tree growth in a subtropical forest ecosystem in SE China showed that topographic heterogeneity lead to ecological gradients across geomorphological positions.In this respect,small-scale soil-plant interactions in a young forest can serve as a driver for the future development of vegetation and biodiversity control on soil fertility.In addition,it shows that terrain attributes should be accounted for in ecological research.

Effect of clear-cutting silviculture on soil respiration in a subtropical forest of China

Aims Clear-cutting is a common forest management practice,especially in subtropical China.However,the potential ecological consequences of clear-cutting remain unclear.In particular,the effect of clear-cutting on soil processes,such as the carbon cycle,has not been quantified in subtropical forests.Here,we investigated the response of soil respiration(Rs)to clear-cutting during a 12-month period in a subtropical forest in eastern China.Methods We randomly selected four clear-cut(CC)plots and four corresponding undisturbed forest(UF)plots.Measurements of Rs were made at monthly time points and were combined with continuous climatic measurements in both CC and UF.Daily Rs was estimated by interpolating data with an exponential model dependent on soil temperature.Daily Rs was cumulated to annual Rs estimates.Important Findings In the first year after clear-cutting,annual estimates of Rs in CC(508±23g C m^(−2) yr^(−1))showed no significant difference to UF plots(480±12g C m^(−2) yr^(−1)).During the summer,soil temperatures were usually higher,whereas the soil volumetric water content was lower in CC than in UF plots.The long-term effects of clear-cutting on Rs are not significant,although there might be effects during the first several months after clear-cutting.Compared with previous work,this pattern was more pronounced in our subtropical forest than in the temperate and boreal forests that have been studied by others.With aboveground residuals off-site after clear-cutting,our results indicate that the stimulation of increasing root debris,as well as environmental changes,will not lead to a significant increase in Rs.In addition,long-term Rs will not show a significant decrease from the termination of root respiration,and this observation might be because of the influence of fast-growing vegetation after clear-cutting in situ.

Metamicrobiomics in herbivore beetles of the genus Cryptocephalus （Chrysomelidae）： toward the understanding of ecological determinants in insect symbiosis

The Cryptocephalus marginellus （Coleoptera： Chrysomelidae） complex is composed by six species that are supposed to have originated by events of allo- or parapatric speciation. In the present study we investigated the altemative hypotheses that the bacterial communities associated with six populations of this species complex are shaped by environmental factors, or reflect the proposed pattern of speciation. The microbiota associated with the six populations, from five species of the complex, have been characterized through 16S rRNA pyrotag sequencing. Based on a 97% sequence similarity threshold, data were clustered into 381 OTUs, which were analyzed using a variety of diversity indices. The microbiota of C. acquitanus and C. marginellus （Calanques） were the most diverse （over 100 OTUs）, while that from C. zoiai yielded less bacterial diversity （45 OTUs）. Taxonomic assignment revealed Proteobacteria, Tenericutes and Firmicutes as the dominant components of these beetles＇ microbiota. The most abtmdant genera were Ralstonia, Sphingomonas, Rickettsia, and Pseudomonas. Different strains of Rickettsia were detected in C. eridani and C. renatae. The analysis of β-diversity revealed high OTU turnover among the populations of C. marginellus complex, with only few shared species. Hierarchical clustering taking into account relative abundances of OTUs does not match the phylogeny of the beetles, therefore we hypothesize that factors other than phylogenetic constraints play a role in shaping the insects＇ microbiota. Environmental factors that could potentially affect the composition of bacterial communities were tested by fitting them on the results of a multi-dimensional scaling analysis. No significant correlations were observed towards the geographic distances or the host plants, while the composition of the microbiota appeared associated with altitude. The metabolic profiles of the microbiotas associated with each population were inferred from bacterial taxonomy, and interestingly, the obtained clustering pattern was consistent with the host phylogeny.

Impact of tree diversity and environmental conditions on the survival of shrub species in a forest biodiversity experiment in subtropical China

Aims Although shrubs are an important component of forests,their role has not yet been considered in forest biodiversity experiments.In the biodiversity-ecosystem functioning(BEF)experiment with subtropical tree species in south-east China(BEF-China),we factorially combined tree with shrub species-diversity treatments.Here,we tested the hypotheses that shrub survival differs between the 10 planted shrub species,with lower survival rates of late-than early-successional species and is affected by environmental conditions,such as topography and top soil characteristics,as well as by biotic factors,represented by tree,shrub and herb layer characteristics.Methods We analyzed the survival of 42000 shrub individuals in 105 plots varying in tree and shrub species richness of the BEF-China project four years after planting.Shrub survival was analyzed with generalized linear mixed effects models at the level of individuals and with variance partitioning at the plot level.Random intercept and random slope models of different explanatory variables were compared with respect to the Bayesian Information Criterion(BIC).Important Findings Survival rates differed largely between the 10 shrub species,ranging from 26%to 91%for Ardisia crenata and Distylium buxifolium,respectively.Irrespective of species identity,single abiotic factors explained up to 5%of species survival,with a negative effect of altitude and slope inclination and a positive effect of the topsoil carbon to nitrogen ratio,which pointed to drought as the major cause of shrub mortality.In contrast,neither tree nor shrub richness affected shrub survival at this early stage of the experiment.Among the biotic predictors,only herb layer species richness and cover of the dominant fern species(Dicranopteris pedata)affected shrub survival.Overall,our models that included all variables could explain about 65%in shrub survival,with environmental variables being most influential,followed by shrub species identity,while tree species diversity(species richness and identity)and herb layer characteristics contributed much less.Thus,in this early stage of the experiment the biotic interactions among shrubs and between shrubs and trees have not yet overruled the impact of abiotic environmental factors.

Expression of juvenile hormone acid O-methyltransferase and juvenile hormone synthesis in Blattella germanica

Juvenile hormone （JH）, a sesquiterpenoid synthetized by the insect corpora allata （CA）, plays critical roles in metamorphosis and reproduction. Penultimate or last step of JH synthesis is catalyzed by juvenile hormone acid O-methyltransferase （JHAMT）. Here we report the cloning and expression analysis of the JHAMT orthologue in the cockroach, Blattella germanica （L.） （BgJHAMT）. BgJHAMT is mainly expressed in CA, with only expression traces in ovary. Three different isoforms, differing in the 3＇-UTR sequence, were identified. Isoform A shows between 35 and 65 times higher expression than B and C in CA from penultimate nymphal instar and adult females. RNAi-triggered knock down of BgJHAMT produces a dramatic reduction of JH synthesis, concomitant with a decrease of fat body viteUogenin expression and basal follicle length. BgJHAMT mRNA levels in CA of females along the gonadotrophic cycle parallel, with a slight advancement, JH synthesis profile. BgJHAMT mRNA levels were reduced in starved females and in females in which we reduced nutritional signaling by knocking down insulin receptor and target of rapamycin （TOR）. Results show that conditions that modify JH synthesis in adult B. germanica females show parallel changes of BgJHAMT mRNA levels and that the JH-specifie branch of the JH synthesis pathway is regulated in the same way as the mevalonate branch. Furthermore, we demonstrate that nutrition and its signaling through the insulin receptor and TOR pathways are essential for activating BgJHAMT expression, which suggests that this enzyme can be a checkpoint for the regulation of JH production in relation to nutritional status.

Detection of fungal infection in Lolium perenne by Fourier transform infrared spectroscopy

Aims the goal of the study was to apply Fourier transform infrared(FtIr)spectroscopy followed by chemometrical data treatment for the dif-ferentiation of fungi-infected perennial ryegrass(Lolium perenne)from uninfected grass.Methods FtIr was used to rapidly discriminate between leaves of peren-nial ryegrass(L.perenne)infected by a fungal endophyte(Epichloë;asexual forms:Neotyphodium)and uninfected leaves.besides drying and grinding of the sampled leaves,no other preparation steps were needed.FtIr measurements were performed in the attenuated total reflection(at)mode.aliquots of powdered leaf samples were placed on a Znse crystal and the spectra were collected,followed by chemometrical analysis(multidimensional factor analysis,hier-archical cluster analysis).Important Findingsat-FtIr allowed a rapid detection of fungal infections in the plant material and proved to be a fast and reliable tool for the differentiation of plant biomass without the need of time-consuming sample preparation.

Dual role of FGF in proliferation and endoreplication of Drosophila tracheal adult progenitor cells

Adult progenitor cells activation is a key event in the formation of adult organs.In Drosophilat formation of abdominal adult trachea depends on the specific activation of tracheal adult progenitors(tracheoblasts)at the Tr4 and Tr5 spiracular branches.Proliferation of these tracheoblasts generates a pool of tracheal cells that migrate toward the posterior part of the trachea by the activation of the branchless/fibroblast growth factor(Bnl/FGF)signaling to form the abdominal adult trachea.Here,we show that,in addition to migration,Bnl/FGF signaling,mediated by the transcription factor Pointed,is also required for tracheoblast proliferation.This tracheoblast activation relies on the expression of the FGF ligand bnl in their nearby branches.Finally,we show that,in the absence of the transcription factor Cut(Ct),Bnl/FGF signaling induces endoreplication of tracheoblasts partially by promoting fizzy-related expression.Altogether,our results suggest a dual role of Bnl/FGF signaling in tracheoblasts,inducing both proliferation and endoreplication,depending on the presence or absence of the transcription factor Ct,respectively.

Genomic and mitochondrial evidence of ancient isolations and extreme introgression in the four-lined snake

Comparing mitochondrial and genomic phylogenies is an essential tool for investigating speciation processes,because each genome carries different inheritance properties and evolutionary characteristics.Furthermore,mitonuclear discordance may arise from ecological adaptation,historic isolation,population size changes,and sex-biased dispersal.Closely related taxa are expected to experience gene flow;however,this may not be true for insular populations or populations isolated in refugia.The four-lined snake Elaphe quatuorlineata has a fragmented distribution,separating populations of the Italian and Balkan Peninsulas,whereas several insular Aegean populations of significantly smaller body size(Cyclades island group and Skyros Island,Greece)are currently considered distinct subspecies.We constructed the species-tree phylogeny of this species utilizing genome-wide single nucleotide polymorphisms and a gene-tree based on complete cytochrome b sequences,aiming to detect convergence and discrepancies between biparentally and maternally inherited genomes.Population structuring,phylogenetic patterns and migration events among geographically defined lineages supported our hypothesis of isolation in multiple sub-refugia.Where biogeographical barriers did not restrict subsequent dispersal,extensive genetic exchange occurred between mainland Balkan populations.This process has led to the mitochondrial sweep of an ancestral mitolineage that survived only in peripheral(East Greece)and insular populations(North Cyclades and Skyros).The Central Cyclades represent an ancient lineage for both molecular markers that emerged almost 3.3 Mya.Considering their distinct morphology,insular E.quatuorlineata populations should be the future focus of an extensive sampling,especially since the mitonuclear discordance observed in this species could be related to ecological adaptations,such as the island-dwarfism phenomenon.

Photocatalytic and electrochemical degradation of methylene blue by titanium dioxide

A photoanode structure for dye-sensitized solar cells has been applied into the photocatalytic/electrochemical cooperative degradation of methylene blue solutions.The low eutectic point of titanium dioxide(TiO2)with a fluorine-doped tin dioxide(FTO)conductive layer results in a high reactivity of TiO2for the photocatalytic process as well as a good electron transfer for the electrochemical process.The porous TiO2layer maintains a large surface area for the degradations.Through the combinational process,the degradation velocity was improved by*36%,compared to a pure photocatalytic process.

Current hypotheses for the evolution of sex and recombination

The evolution of sex is one of the most important and controversial problems in evolutionary biology.Although sex is almost universal in higher animals and plants,its inherent costs have made its maintenance difficult to ex­plain.The most famous of these is the twofold cost of males,which can greatly reduce the fecundity of a sexual population,compared to a population of asexual females.Over the past century,multiple hypotheses,along with experimental evidence to support these,have been put forward to explain widespread costly sex.In this review,we outline some of the most prominent theories,along with the experimental and observational evidence sup­porting these.Historically,there have been 4 classes of theories:the ability of sex to fix multiple novel advanta­geous mutants(Fisher-Muller hypothesis);sex as a mechanism to stop the build-up of deleterious mutations in finite populations(Muller’s ratchet);recombination creating novel genotypes that can resist infection by para­sites(Red Queen hypothesis);and the ability of sex to purge bad genomes if deleterious mutations act synergis­tically(mutational deterministic hypothesis).Current theoretical and experimental evidence seems to favor the hypothesis that sex breaks down selection interference between new mutants,or it acts as a mechanism to shuf­fle genotypes in order to repel parasitic invasion.However,there is still a need to collect more data from natural populations and experimental studies,which can be used to test different hypotheses.

Does a giant tortoise taxon substitute enhance seed germination of exotic fleshy-fruited plants?

Aims The use of exotic species as taxon substitutes to restore lost ecological interactions is currently hotly debated.Aldabrachelys gigantea giant tortoises have recently been introduced to three islands in the Mascarene archipelago(Ile aux Aigrettes,Round Island and Rodrigues)to resurrect herbivory and seed dispersal functions once performed by extinct giant tortoises.However,potential unintended impacts by frugivore substitutes on native ecosystems,e.g.whether they will facilitate the germination of exotic plant species,are largely unknown.We investigated whether A.gigantea introduced to Rodrigues in 2006 could enhance the germination percentage of four widespread fleshy-fruited exotic species on the island.Using germination trials to forecast unintended impacts that could arise from the introduction of a frugivorous taxon substitute enables conservation managers to limit potential adverse negative interactions before they occur.Methods In germination trials that ran over 4 months,we investigated the effects of ingestion(gut passage and deposition in faeces)by subadult and adult A.gigantea on the germination percentage of four exotic fleshy-fruited plant species introduced to Rodrigues.We fed fruits of these plant species to sub-adult and adult A.gigantea to test how variation in age and size of the frugivore would affect seed germination.Feeding of distinctly coloured plastic pellets together with the fruits allowed us to test for individual tortoise effects on seed germination.Important Findings Ingestion by A.gigantea increased the percentage of seeds germinating of Mimusops coriacea and Lantana camara,but not percentage of germination of Veitchia merrillii or Wikstroemia indica.Seeds were more likely to germinate following ingestion by sub-adult rather than adult tortoises,which may be a consequence of the shorter gut passage time observed for sub-adults.Our results demonstrate that introduced frugivorous taxon substitutes could facilitate germination of exotic and invasive plants and highlight the need for conservation managers to weigh the risk of taxon substitutes potentially facilitating the germination and recruitment of exotic fleshy-fruited plants against the benefit of restoring lost seed dispersal functions of threatened indigenous plants.Our findings also highlight the importance of considering age and size variation in frugivores,in particular in long-lived taxa such as giant tortoises,when studying ingestion effects on the germination performance of plants.

Effects of soil warming history on the performances of congeneric temperate and boreal herbaceous plant species and their associations with soil biota

Aims Climate warming raises the probability of range expansions of warm-adapted temperate species into areas currently dominated by cold-adapted boreal species.Warming-induced plant range expansions could partly depend on how warming modifies relationships with soil biota that promote plant growth,such as by mineralizing nutri-ents.Here,we grew two pairs of congeneric herbaceous plants spe-cies together in soil with a 5-year warming history(ambient,+1.7℃,+3.4℃)and related their performances to plant-beneficial soil biota.Methods Each plant pair belonged to either the mid-latitude temperate climate or the higher latitude southern boreal climate.Warmed soils were extracted from a chamberless heating experiment at two field sites in the temperate-boreal ecotone of North America.To isolate poten-tial effects of different soil warming histories,air temperature for the greenhouse experiment was identical across soils.We hypothesized that soil with a 5-year warming history in the field would enhance the performance of temperate plant species more than boreal plant species and expected improved plant performances to have positive associations with plant growth-promoting soil biota(microbial-feeding nematodes and arbuscular mycorrhizal fungi).Important Findings Our main hypothesis was partly confirmed as only one temperate spe-cies performed better in soil with warming history than in soil with his-tory of ambient temperature.Further,this effect was restricted to the site with higher soil water content in the growing season of the sampling year(prior to soil collection).One of the boreal species performed con-sistently worse in previously warmed soil,whereas the other species showed neutral responses to soil warming history.We found a positive correlation between the density of microbial-feeding nematodes and the performance of one of the temperate species in previously wetter soils,but this correlation was negative at the site with previously drier soil.We found no significant correlations between the performance of the other temperate species as well as the two boreal species and any of the studied soil biota.Our results indicate that soil warming can modify the relation between certain plant species and microbial-feeding nematodes in given soil edaphic conditions,which might be important for plant performance in the temperate-boreal ecotone.

Maintenance of Species Differences in Closely Related Tetraploid Parasitic Euphrasia (Orobanchaceae) on an Isolated Island

Polyploidy is pervasive in angiosperm evolution and plays important roles in adaptation and speciation.However,polyploid groups are understudied due to complex sequence homology,challenging genome assembly,and taxonomic complexity.Here,we study adaptive divergence in taxonomically complex eyebrights(Euphrasia),where recent divergence,phenotypic plasticity,and hybridization blur species boundaries.We focus on three closely related tetraploid species with contrasting ecological preferences that are sympatric on Fair Isle,a small isolated island in the British Isles.Using a common garden experiment,we show a genetic component to the morphological differences present between these species.Using wholegenome sequencing and a novel k-mer approach we call“Tetmer”,we demonstrate that the species are of allopolyploid origin,with a sub-genome divergence of approximately 5%.Using2 million SNPs,we show sub-genome homology across species,with a very low sequence divergence characteristic of recent speciation.This genetic variation is broadly structured by species,with clear divergence of Fair Isle heathland Euphrasia micrantha,while grassland Euphrasia arctica and coastal Euphrasia foulaensis are more closely related.Overall,we show that tetraploid Euphrasia is a system of allopolyploids of postglacial species divergence,where adaptation to novel environments may be conferred by old variants rearranged into new genetic lineages.

Convergent patterns in multitrophic biodiversity effects on yield across ecosystems

In ecosystems managed for food or fiber production,there is often no space for biodiversity.For example,intensive cereal monocultures are usually managed towards optimized yields using herbicides,fungicides and insecticides.In such systems,biodiversity is essentially unwanted,except maybe when it improves soil health or carbon fixation.Consequently,it has been difficult to convincingly show if and where biodiversity is economically important in intensive production systems.