Endophyte symbiosis with tall fescue how strong are the

Review

Endophyte symbiosis with tall fescue:how strong are the impacts on communities and ecosystems?

Jennifer A.RUDGERS a ,*,Keith CLAY b

a Dept.of Ecology and Evolutionary Biology,Rice University,Houston TX 77005USA b

Dept.of Biology,Indiana University,Bloomington IN 47405USA

Keywords:Competition Herbivory

Lolium arundinaceum MAXQ endophyte

Neotyphodium coenophialum Predators Soil

Trophc interactions

a b s t r a c t

We have investigated community and ecosystem consequences of endophyte symbiosis with tall fescue over the past 13y.Lolium arundinaceum is the most abundant plant in the eastern USA,and most is infected by the wild-type KY-31endophyte Neotyphodium coeno-phialum .We established two large experimental grasslands (in 1994and in 2000)with en-dophyte-infected

or

endophyte-free

seed

sown

on

recently

plowed

herbaceous

vegetation.Other plant species established by seed or vegetative fragments.No other treat-ments were applied and plots were subject to natural biotic and abiotic variation.A third experiment examined ecological in?uences on endophyte infection dynamics starting from an intermediate infection frequency.Finally,we synthesized recent literature inves-tigating the impacts of the tall fescue endophyte on the abundance of associated arthropod species.We found wide-ranging consequences of the endophyte from signi?cant effects on soil feedback and decomposition rates,to plant-plant competition,diversity,productivity,invasibility and succession,to plant-herbivore interactions and energy ?ow through the food web.Further,we found that herbivore pressure caused rapid increases in infection frequency.Our results suggest that endophyte symbiosis in tall fescue can have a trans-forming effect on ecological systems.

a2007The British Mycological Society.Published by Elsevier Ltd.All rights reserved.

1.Introduction

Of all the systemic endophytes known in grass hosts,Neoty-phodium coenophialum in tall fescue grass has received the most attention,in part due to the dominance of tall fescue in ecological systems worldwide.A great deal of work by many researchers has been conducted to unravel the evolu-tionary and genetic history of the tall fescue-endophyte asso-ciation (Tsai et al.1994;Craven et al.2001a,b;Clay &Schardl 2002;Moon et al.2004),to understand the effect of endophyte infection on the host plant (De Battista et al.1990;Rice et al.

1990;West 1994;Malinowski &Belesky 2000;Newman et al.2003),and to elucidate the underlying alkaloid biochemistry and impacts on animal consumers (Clay &Cheplick 1989;Hill et al.1991;Agee &Hill 1994;Bush et al.1997;Panaccione et al.2001;Popay &Bonos 2005).Recent efforts have used the tools of molecular biology to create engineered endophyte strains with blocked pathways for alkaloid production (Panac-cione et al.2001;Young et al.2005).In parallel,natural endo-phyte variants with different alkaloid production pro?les have been incorporated into commercial germplasm (Bouton et al.2002;Timper et al.2005).Much research effort has also

*Corresponding author.

E-mail address:jrudgers@https://www.sodocs.net/doc/377002905.html, (J.A.

Rudgers).

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /f b r

f u n

g a l b i o l o g y r e v i e w s 21(2007)107–124

1749-4613/$–see front matter a2007The British Mycological Society.Published by Elsevier Ltd.All rights reserved.doi:10.1016/j.fbr.2007.05.002

been devoted to similar questions with perennial ryegrass (Lolium perenne),meadow fescue(L.pratense)and annual rye-grass(L.multi?orum),as well as other grasses of economic im-portance(Wilson et al.1991;White et al.1992;Bazely et al.1997; Cheplick&Cho2003;Cheplick2004a,b).New information about endophytes continues to accumulate,showing that en-dophyte alkaloids may enter the environment in unsuspected ways(Franzluebbers&Hill2005;Koulman et al.2007),and revealing that seed-transmitted,alkaloid-producing clavicipi-taceous endophytes may also occur outside of monocotyle-donous plants(Kucht et al.2004).

Independent of the dominant grasses of managed forage and turfgrass systems worldwide,there has been much effort to quantify the diversity and frequency of endophyte-infected grasses in natural systems(Clay&Leuchtmann 1989;Leuchtmann1992;Miles et al.1998;Saikkonen et al. 2000;Moon et al.2002;Zabalgogeazcoa et al.2003;Faeth et al.2006;Wei et al.2006).However,relative to agronomic systems,many fewer studies in natural systems have exam-ined experimentally how endophyte-infection affects plant performance and interspeci?c interactions(Pan&Clay 2002,2003;Faeth&Sullivan2003;Faeth et al.2004:Tintjer &Rudgers2006).While these grasses have been of little ap-plied interest because endophyte-infection is often not verti-cally-transmitted through seeds,they represent a major component of the diversity of endophytes,of grasses,and of grass/endophyte interactions.With the growing interest in perennial grasses for biofuel production(Tilman et al. 2006),the improved biomass production conferred by endo-phytes in grasses may be of interest across a wider range of host taxa,regardless of the potential for disruption of grass sexual reproduction by stroma production.

Despite the diversity of past research and work in other systems,tall fescue remains the primary focus of research and the model system for grass-endophyte research.Argu-ably,most grass endophyte interactions worldwide are be-tween tall fescue and Neotyphodium coenophialum.Tall fescue covers a signi?cant area of the eastern USA,and is increas-ingly prevalent in South America,Australia,New Zealand, China and Africa.In the lower Midwest region of the USA, most tall fescue occurs on poor soils and is either unmanaged or lightly managed by occasional mowing.Much of this tall fescue was originally planted in the1950’s and1960’s,and has persisted in situ or spread locally from original plantings. Most of it is infected by the endophyte found in the tall fescue variety KY-31.Local collections in Indiana revealed no genetic diversity and the ubiquitous distribution of this single endo-phyte genotype(Leuchtmann&Clay1990).

Over the past13y we have investigated the community and ecosystem consequences of endophyte symbiosis with tall fescue(Lolium arundinaceum)in a series of long-term and large-scale?eld experiments in the lower Midwest,USA.The results of our studies do not bear directly on highly managed agricultural or turf systems,on tall fescue in other regions,or on other endophyte-infected grass species.However,they are relevant to the primary tall fescue zone in the lower Midwest and upper Southeast of the USA(Ball et al.1993).In total,our research indicates that the endophyte of tall fescue is a key-stone species with signi?cant direct and indirect effects on community composition,trophic interactions and ecosystem processes.The integrated and cumulative effect of endophyte symbiosis in tall fescue was far greater than individual taxon-focused studies would suggest.Our experimental results were highly consistent across plant communities that were geo-graphically proximal but that differed in species composition, land use history,soil type and topography,suggesting that the effects of the endophyte symbiosis are robust and predictable. Moreover,they provide a baseline against which other studies and species can be compared.

Here,we provide an overview of the major results of our studies investigating the effects of endophyte infection of tall fescue on interspeci?c interactions,community composi-tion and diversity,and ecosystem processes,such as primary productivity and decomposition.Our null hypothesis is that endophyte infection has no effect on community and ecosys-tem properties.In addition,we compare our results to those of other relevant studies through a synthesis of recent literature on the consequences of the tall fescue endophyte for arthro-pod communities.We use this synthesis to highlight new di-rections for future research.

2.Methods

Field experiment:documenting endophyte effects

on the community

We established two large experimental grasslands(one in 1994and one in2000)where endophyte-infected(Et)or free (Eà)seed(KY-31)was sown on recently plowed herbaceous vegetation.Plot sizes were either20m?20m(N?8,upland site,1994)or30m?30m(N?16,lowland site,2000).Details of these sites and local conditions are described in Clay& Holah(1999)and in Rudgers et al.(2007).Many other plant species established from the seed bank,dispersal or vegeta-tive fragments.Both sites were also colonized by a diverse assemblage of invertebrate and vertebrate animals.Voles (Microtus spp.)were the dominant vertebrate grazer at both sites.

A series of measurements were typically taken twice per year,early in the growing season and then again late in the growing season.Vegetation was sampled by harvesting repli-cated quadrats(0.5m?0.5m)randomly distributed across the plots.All above-ground vegetation was collected,sorted by species or into functional groups(tall fescue,other grasses, forbs and litter),and then dried and weighed.These data pro-vided information on plant diversity,dominance,productivity and successional patterns(Clay&Holah1999;Matthews& Clay2001;Rudgers et al.2004).In addition,all woody plants were comprehensively censused on an approximately annual basis,identi?ed to species and measured for size(Rudgers et al.2007).Voles were sampled by live-trapping and by radio collars(Fortier et al.2000,2001;Rudgers et al.2007).Herbivo-rous arthropods were sampled by repeated sweep netting and pitfall trapping(Rudgers,unpublished).Spiders were sampled by exhaustive searching though litter in con?ned subplots,and by quantifying individual webs(Finkes et al. 2006).Alteration of soil properties following growth of Etvs. Eàtall fescue was quanti?ed by taking soil cores from quad-rats immediately following vegetation harvests,and then

108J.A.Rudgers,K.Clay

growing three test species in individual soil cores from de?ned locations(Matthews&Clay2001).

Field experiment:understanding ecological factors

affecting endophyte frequency

Separate from these experiments where plots were either sown with100%endophyte-infected or uninfected seed,an independent experiment was designed to examine the fac-tors that might cause infection frequency to increase or de-crease in mixed populations of tall fescue.A total of sixty 5m?5m plots were established in the same general area as the2000experiment described above(Clay et al.2005). All plots were sown with a50:50mixture of Etand Eàseed. Half of the plots were fenced to prevent entry by vertebrate herbivores and half of the plots were sprayed with a general contact insecticide(Malathion)to reduce insect herbivory. The two treatments were alternated with unfenced and un-sprayed controls in a2?2design.We occasionally put live traps into fenced plots to remove renegade voles.The fre-quency of infection in the fescue population was sampled twice per year for?ve years using the tissue-print immuno-blot procedure(Gwinn et al.1991;Hiatt et al.1999,2001;Hill et al.2002).Blots were kindly developed in Chris Schardl’s lab at the University of Kentucky.Vegetation was sampled at the end of the study when four0.5m?0.5m quadrats were harvested per plot and separated into four components: tall fescue,other grasses,forbs or litter.

Literature synthesis:how tall fescue-Neotyphodium symbiosis may affect terrestrial food webs

We also synthesized research conducted during the past10y on how the endophyte in tall fescue may affect associated arthropods.We included only those studies that explicitly manipulated the presence(or type)of endophyte in tall fes-cue and examined effects on other species.We focused ex-clusively on experimental studies because,while naturally occurring infected and uninfected plants may show differ-ences,effects of the endophyte cannot be separated from characteristics of the plant that may in?uence the probabil-ity or history of endophyte infection.In addition,we concen-trated on studies of wild animals rather than domesticated species.We also included endophyte-mediated in?uences on?tness related variables and the performance of animals rather than on behaviors or preferences because these ef-fects will likely have more direct effects on species distribu-tions and abundances.For each study(Appendix1),we determined the magnitude of the effect of the endophyte treatment,quanti?ed here as the log response ratio L?ln (mean endophyte-free/mean endophyte)(Hedges et al.1999)to al-low for scale-independent,cross-study comparisons of the strength of the endophyte’s in?uence.

3.Results and discussion

Plant diversity and productivity

Twice-yearly sampling of vegetation in the upland plots estab-lished in1994revealed that endophyte infection of tall fescue led to the competitive dominance of the host and suppression of other plant species(Clay&Holah1999).Endophyte-free(Eà) plots has less tall fescue,greater biomass of other perennial grasses and more forbs compared to endophyte-infected (Et)plots(Fig1).Of special note was the nearly complete loss of forbs from Etplots after four years(Clay&Holah 1999).There was no effect of endophyte infection on total pro-ductivity,but a strong effect on the proportional contribution of different groups to total plant biomass.In parallel,plant species richness steadily declined in plots with the endophyte. The design of the study allowed us to attribute changes in re-sponse variables to either endophyte infection or random en-vironmental variation among plots.For both species richness and composition of biomass,there was no effect of endophyte infection during the?rst two years of the study and all of the variation occurred between plots within a treatment.How-ever,after four years endophyte infection explained nearly 50%of the variation in response variables while plot explained very little.Thus,endophyte presence ultimately overwhelmed environmental variation in explaining plant composition.

We hypothesize that the primary mechanism driving changes in vegetation between Etand Eàplots was differen-tial herbivory,primarily by voles(see additional evidence below).We suggest that voles consumed tall fescue in the Eàplots,alleviating grazing pressure on other plant species (grasses,forbs,tree seedlings).In contrast,in Etplots voles avoided Etfescue,preferentially consuming other plants spe-cies including tree seedlings(Rudgers et al.2007).Thus,de-clines in plant diversity were mediated indirectly

through

Endophyte symbiosis with tall fescue109

altered feeding behavior in the dominant vertebrate consumer.

Strong effects of the endophyte on plant diversity are likely to be scale-dependent.At the scale of our experiments(and the scale at which tall fescue is normally planted),we expect voles to have little choice about the presence of Etfescue,be-cause territory sizes are smaller than plot or?eld sizes(Fortier et al.2001).If experiments were conducted on a smaller,less realistic scale,voles may be able to concentrate feeding in Eàpatch types and community-level responses may be less pronounced.

Finally,while voles appear to be a key driver in this sys-tem,other mechanisms may also contribute to the altered plant community.Allelopathy(Orr et al.2005),alteration of decomposition rates and soil communities(Matthews& Clay2001;Lemons et al.2005),direct competition(Clay et al.1993),and differential insect herbivory mediated by the endophyte’s presence(Breen1994)may play minor roles, and the relative importance of these mechanisms in altering the plant community remains to be determined.A few other studies have compared vegetation in contrasting areas with Etor Eàfescue but they have been uncontrolled,non-experimental or lacking in knowledge about starting condi-tions.There is a need for more?eld experiments of the types described here across a greater diversity of environmental conditions.

Plant succession

In both the upland and lowland experimental tall fescue grasslands,the presence of the endophyte suppressed the natural transition from grassland communities to forests (Rudgers et al.2007).The endophyte reduced tree abundance by60-80%across the two experimental sites.Endophyte symbiosis caused declines in the abundance and/or growth of silver maple,red osier dogwood,and white ash,but had no signi?cant in?uence on the growth or abundance of white mulberry,which was only present at the upland site(1994 planting).Importantly,consumption of tree seedlings by voles(Microtus spp.)was65%higher in plots with the endo-phyte at one(lowland)site where these data were collected (Fig2).Vole predation on woody species appears to be more severe in Etplots because the dominant plant(Ettall fescue)was unpalatable to voles,and as a result,voles

fed more heavily on other species.Finally,the endophyte in tall fescue had the overall effect of stabilizing plant com-munity composition by signi?cantly reducing temporal?uc-tuations in the presence of both woody and herbaceous plant species.Despite its negligible contribution to commu-nity biomass,the endophyte poses an important constraint on the natural transition from grasslands to forests in the Midwest.

Diversity–ecosystem functioning relationships

A large number of studies in community ecology during the past decade have investigated the impacts of biodiversity on ecosystem functioning(Hooper&Vitousek1997;Tilman 1999).We examined how endophyte infection of tall fescue modi?es the relationship between diversity and both produc-tivity and https://www.sodocs.net/doc/377002905.html,ing a graphical model,we predicted that endophyte infection would weaken the predicted corre-lation between species diversity and ecosystem properties. We tested this model using?eld data from the100%Etand100%Eà?eld plots at the upland site,which supported a diverse array of other plant species(Rudgers et al.2004).We also constructed a greenhouse experiment that experimen-tally varied the diversity of native prairie perennials in pots (Rudgers et al.2005).Once prairie communities established, we added Etor Eàtall fescue as an invader.In both?eld and greenhouse studies,we found that endophyte infection in the invader weakened the negative relationship between plant species diversity and the establishment of the invader (Fig3).These results demonstrate that the presence of

an

110J.A.Rudgers,K.Clay

endophyte in a dominant grass can modify biodiversity-eco-system functioning relationships.

Soil and plant-soil feedbacks

Most prior research has focused on the above-ground environ-ment of tall fescue and how the endophyte affects plant per-formance and interspeci?c interactions.Although the endophyte does not occur in roots,there may be indirect ef-fects on below-ground properties and processes (Pedersen et al.1988;Chu-chou et al.1992;Grewal et al.1995;Malinowski et al.1998;Franzluebbers &Hill 2005).Here,to determine if the growth of E tvs.E àfescue affects subsequent plant growth in the same soil,soil cores were removed from E tor E àexperi-mental plots following vegetation sampling,and then planted with E tor E àtall fescue,Plantago lanceolata or Trifolium repens .The growth of those species was analyzed in relation to the past endophyte status of the plot and the composition of

the harvested above-ground vegetation.We found that the en-dophyte status of the plot from which cores were obtained had no direct effect on plant performance (Matthews &Clay 2001).However,experimental plant responses suggest that,by inducing changes in plant community composition,E tfes-cue may indirectly affect soil properties.In particular,tall fes-cue biomass was lower when grown in soil previously dominated by E tfescue compared to soil previously domi-nated by Kentucky bluegrass and quackgrass (Fig 4).This pat-tern indicates negative feedback (accumulation of detrimental organisms)on the growth of E tfescue and represents a poten-tial long-term constraint on E tfescue’s ecological dominance.Interestingly,the feedback was endophyte speci?c:no effect was seen on E àfescue or in soil previously dominated by E àfescue.

Anotherimportantsoilprocessisdecompositionoflitterand other organic matter.In the lowland ?eld experiment,we used reciprocal transplants of E tand E àlitter into E tor E àplots (Lemons et al.2005).After 10m in the ?eld,decomposition of the litter was signi?cantly slower for E tfescue litter than for E àlitter(Fig5).Decompositionalsodependedonacomplexinter-action between the litter source (collected from E tor E àplots),the decomposition microenvironment (E tor E àplots),and the presence of mesoinvertebrates (manipulated by the mesh size of litter bags).When mesoinvertebrates were excluded using ?ne mesh and litter was placed in a microenvironment with the endophyte,the difference between E tand E àlitter was strongest.

Several prior studies have further examined the how en-dophyte infection affects soil properties and processes.For example,Omacini et al.(2004)found that litter decomposi-tion in microcosms using Lolium multi?orum was affected by

0246

810

12

Initial species diversity (Shannon-Weiner H)

0.0

0.5 1.0 1.5 2.0

0246810

12

N u m b e r o f L o l i u m a r u n d i n a c e u m i n d i v i d u a l s

Fig.3–The number of surviving Lolium arundinaceum individuals by initial plant species diversity (A)without the endophyte,Neotyphodium coenophialum (E-)(regression:Number [L 1.353initial diversity D 5.37,r [L 0.36,P [0.0018,n [72)and (B)with the endophyte (E D )(regression:Number [L 0.313initial diversity D 5.37,r [L 0.08,P [0.53,n [72).Reprinted with permission from Rudgers et al.(2005)

.

Endophyte symbiosis with tall fescue 111

endophyte status.Similarly,Franzluebbers and colleagues have demonstrated signi?cant changes in carbon and nitrogen pools as well as alkaloid levels in soils beneath E tversus E àtall fescue (Franzluebbers et al.1999;Franzluebbers &Hill 2005;Franzluebbers &Stuedemann 2005;Franzluebbers 2006).Other studies have documented changes in mycorrhizal and nematode communities with endophyte infection (West et al.1988;Kimmons et al.1990;Chu-chou et al.1992;Omacini et al.2006).All of these alterations could feed back to alter the performance of both tall fescue and neighboring plant species (Orr et al.2005).At this stage,it re-mains unclear to what degree changes in soil properties and communities in?uence aboveground shifts in community composition.This area is ripe for further investigation.

Factors affecting infection dynamics in mixed populations

Our prior ?eld experiments were conducted in plots with near 100%E tor E àtall fescue.This design makes it easy to detect effects of the endophyte,and re?ects the common all or nothing endophyte status of many populations of tall fescue (Clay 1997).However,many populations of endo-phyte-hosting grass species have intermediate levels of infec-tion (Latch et al.1987;Shelby &Dalrymple 1987;Saikkonen et al.2000;Spyreas et al.2001).The question arises whether intermediate infection frequencies are stable or change in a directional way towards complete infection or loss of infec-tion.In the latter case,what ecological factors may drive in-fection frequency changes?We established replicated plots with tall fescue at initial 50%infection frequency and manip-ulated herbivore pressure by a combination of fencing and/or insecticide application with controls.Infection frequency

rapidly increased from 50%to 80%over a ?ve-year period in unfenced,unsprayed plots subject to the greatest herbi-vore pressure (Fig 6,Clay et al.2005).In contrast,the smallest increase in infection frequency occurred in plots protected from both vertebrate and insect herbivory.These results revealed that herbivores select for highly infected tall fescue,at least under our experimental conditions,and strongly support the defensive mutualism hypothesis (Clay 1988).However,endophyte-infection frequency increased under all treatments indicating that other factors may also favor infected fescue (Fig 6).Alternatively,our treatments were not 100%effective and the uncontrolled herbivory may be re-sponsible for the overall increase in infection frequency.In any case,these results emphasize that the tall fescue/endo-phyte relationship is highly mutualistic under normal circum-stances in its introduced range (but see Cheplick et al.1989).

Several other studies have tracked changes in infection fre-quency over time,but have generally not applied experimen-tal treatments (Thompson et al.1989;Shelby &Dalrymple 1993).In one notable case with perennial ryegrass (Francis &Baird 1989),Argentine stem weevil herbivory drove a rapid loss of uninfected ryegrass seedlings from populations.

To

Months since sowing

C h a n g e i n p r o p o r t i o n o f t i l l e r s i n f e c t e d

-0.2

-0.10.00.10.20.30.4Fig.6–The change in endophyte frequency among treat-ments.The change in frequency was determined by sub-tracting the initial proportion of tillers infected in that plot from the proportion of tillers infected on each date.The change in proportion is bounded by 0.5and 0.5(0%and 100%infected,respectively).Over time,infection increased in all plots (time,F 8,47[29.6,P <_0.0001).Treatments di-verged over time (fence 3insecticide 3time interaction,F 8,47[2.8,P <0.01).No main effects or two-way interac-tions were signi?cant (fence,F 1,54[3.1,P <0.08;fence 3time,F 8,47[1.4,P <0.2;insecticide,F 1,54[1.9,P <0.2;insecticide 3time,F 8,47_[0.8,P <0.6;fence 3insecticide,F 1,54[0.43,P <0.5).Symbols show means ±_SE and are slightly offset to show error bars clearly.P values indicate a signi?cant difference between the dual herbivore-exclusion treatment (fenced plus insecticide)and the control (unfenced plus water)for each date.Reprinted with permission from Clay et al.(2005).

112J.A.Rudgers,K.Clay

our knowledge,in all studies where infection frequency was monitored over time,endophyte infection frequency either in-creased or remained the same but never decreased in the same population.However,there have been relatively few studies of this type,and more are needed from a variety of species.In particular,could there be frequency dependence such that the relative?tness advantage of Etfescue depends on the overall infection level in the population?Given that an-imals may be able to detoxify alkaloids up to a certain point, endophyte infection may provide no defense if its frequency is low,or the host is rare.

Literature synthesis:how endophyte symbiosis may affect terrestrial food webs

Aboveground herbivores and seed predators

The Neotyphodium endophyte in tall fescue can strongly re-duce the abundances of individual herbivores.Insects ad-versely affected by endophytes are taxonomically diverse, including generalist as well as grass specialist species in the Lepidoptera,Orthoptera,Hemiptera,Diptera,and Coleop-tera(reviewed by Latch1993;Breen1994;Clay1996;Rudgers et al.2005),see also species list in Clement et al.1994).In our survey of the recent literature(Appendix1),the strength of the endophyte effect differed among types of feeding guilds, with the strongest effects on leaf chewers and more moder-ate effects on sap(xylem and phloem)feeders.In addition, effect sizes were stronger for species characterized as grass specialists than for species known to consume a broader diet(generalists),perhaps resulting from the ability of gener-alists to dilute the toxic effects of fungal alkaloids with a more diverse diet.We found very weak effect sizes for the endophyte’s in?uence on vertebrate seed predators(no recent invertebrate studies have been conducted),especially relative to endophyte effects on vertebrate leaf chewers(rab-bits,mice,voles,etc.)(Appendix1).However,surprisingly few total species have been investigated in detail given the wide range of organisms that co-occur with tall fescue,and most studies,not unexpectedly,have focused on important forage and turf pests.

Belowground herbivores and detritivores

Despite the localization of Neotyphodium coenophialum in aboveground tissues,root-feeding insects and detritivores can be inhibited by endophyte infection.For example,Elmi et al.(2000)found complete mortality of the root knot nema-tode(Meloidogyne marylandi)in pots of endophyte-infected, but not in uninfected tall fescue.Similarly,survival of Japa-nese beetle(Popilla japonica)larvae belowground was reduced in pots of highly infected tall fescue compared to pots contain-ing lower infection levels(Oliver et al.1990),although across ?eld and lab studies,results for endophyte effects on Japanese beetles have been equivocal.Our review of current literature shows much smaller effect sizes for the endophyte on root feeders than any other herbivorous group excepting verte-brate seed predators.Weak effects on root feeders are not unexpected,given that the endophyte is localized in above-ground plant tissues.

In addition to changes in belowground herbivores,we (and others)have found plot-level changes in the detritivore assemblage.However,overall endophyte-mediated effects on detritivores were small(85%smaller effect sizes)relative to effects on invertebrate herbivores.Previous plot level studies show declines in some detritivores,including Chlor-opid?ies,oribatid mites,the collembolan species Lepidocyrtus cinereus,and in the reproductive output of earthworms(Ber-nard et al.1997;Humphries et al.2001).However,a few spe-cies appear to be unaffected or even enhanced by endophytes(e.g.earthworm abundance,Sminthurid collem-bola(Davidson&Potter1995;Bernard et al.1997),Hypogas-truridae(Lemons et al.2005)).In our work,the total abundance of one keystone detritivore group,the Collem-bola,did not signi?cantly differ between endophyte treat-ments(Etvs.Eà),but the composition of collembolan families signi?cantly diverged(Lemons et al.2005),with Hypogastruridae abundance greater in Etplots and Isotomi-dae abundance higher in Eàplots.These results are consis-tent with other studies that demonstrate Hypogastruridae tolerate toxic environments(e.g.,waste dumps and heavy metal sites)and Isotomidae are especially sensitive to envi-ronmental toxins(Fountain&Hopkin2005).A broader exam-ination of the decomposer food web is needed,and the mechanisms underlying shifts in detritivores due to the en-dophyte remain unresolved.

Predators and parasitoids

Endophytes,particularly through their effects on insect herbi-vores,can indirectly modify the abundance or composition of higher trophic levels.Indirect effects may occur through en-dophyte-mediated reductions in the quality or abundance of prey or through changes in prey behavior.Moving up through the food web,the effects of endophytes may remain similarly strong,accumulate,or attenuate.Most studies to date support attenuation of endophyte effects on arthropod predators and parasitoids,with an effect size of the endophyte that is90% smaller for predators and parasitoids relative to invertebrate herbivores.In comparison,multitrophic level effects seem stronger in related grass-endophyte systems(e.g.,perennial ryegrass-Argentine stem weevil–parasitoid,Bultman et al. 1996,1997),and Italian ryegrass-aphid-parasitoid interac-tions,(Omacini et al.2001).However,surprisingly less atten-tion has been given to multitrophic level interactions in the tall fescue system,given its ecological dominance,particu-larly in the USA.

The majority of studies testing for higher trophic level im-pacts of grass-endophyte interactions have examined parasit-oids.Parasitoids typically have more specialized diets than predators of herbivores,and may be more sensitive to the presence of microbes in plants.For example,Omacini et al. (2001)found that infected Lolium multi?orum(Italian ryegrass) reduced the rate of parasitism of aphids by several parasitoid species.

Endophyte effects on generalist predators range from endophyte-mediated enhancement of predation to endo-phyte-mediated suppression.For example,entomopatho-genic nematodes acted synergistically with the endophyte to reduce Japanese beetle(Popillia japonica)survival more

Endophyte symbiosis with tall fescue113

than either factor alone (Grewal et al.1995).In this case,fungal alkaloids appear responsible by reducing beetle con-sumption and mass and enhancing susceptibility to preda-tion (Grewal et al.1995).More recent work with Japanese beetles suggested a neutral effect of the endophyte on sus-ceptibility to nematodes (Koppenhofer et al.2003);thus,addi-tional research is needed even for this well-studied species.Surveys of generalist arthropod predators in ?eld plots sug-gest the ants,spiders (Aranae),and two beetle groups (Staph-ylinidae and Carabidae)may be insensitive to the presence of the endophyte (Bernard et al.1997;Koppenhofer et al.2003),at least when grouped at this broad taxonomic level.How-ever,our work suggests that more attention to changes in composition within large taxonomic groups,such as order or family,is likely to reveal stronger endophyte effects.For example,while we found no effects of endophyte presence

on the total abundance of spiders,there were signi?cant reductions in the abundance of two important families:the crab spiders (Thomisidae)and sheet web-weaving spiders (Linyphiidae)due to the presence of the endophyte (Finkes et al.2006,Fig 7).At this stage,we can only speculate on mechanisms driving these effects,although prey capture rates were signi?cantly lower for one common orb-weaving spider (Araneidae)in E tversus E àtall fescue plots.

Arthropod community structure

Many studies have examined the effects of endophytes on in-dividual herbivores,but few investigations have considered entire arthropod communities.In agronomic,as well as nat-uralized tall fescue ecosystems,identi?cation of these broader community level impacts are important to improv-ing pest control and conserving biodiversity.We predict,based on studies with individual herbivores,that the endo-phyte in tall fescue will reduce the overall abundance and species diversity of invertebrate herbivores.Reductions may occur directly through the deterrent action of fungal alka-loids and/or indirectly through reductions in plant diversity (bottom-up effect)or in the diversity of higher trophic levels (top-down effect).Most likely,for complex natural food webs,the endophyte will alter community structure through a mul-titude of direct and indirect pathways.To our knowledge,only three prior studies have experimentally tested for an effect of Neotyphodium coenophialum on the arthropod com-munity as a whole;none surveyed comprehensively across taxa .Murphy et al.(1993)found fewer total turfgrass pests in plots of E ttall fescue relative to E àplots.In a second study,endophyte symbiosis reduced two aphid species,two leafhoppers,a ?ea beetle,and Staphylinid beetles,but had minimal effects on mites,predaceous arthropods,earth-worms,Japanese beetles and three other aphid species (Davidson &Potter 1995).Dissertation work by Willver (sum-marized in Bernard et al.1997)found no effects of the endo-phyte on diplurans or Carabid beetles,but identi?ed declines in some other detritivores (Appendix 1).Unfortunately,most of these studies focused on the abundance responses of particular taxonomic groups and did not characterize other changes in community structure,such as species richness,taxonomic diversity,evenness,or composition.In one exception,(Muegge et al.1991)found signi?cant declines in the species richness of two insect families (Cica-dellidae and Cercopidae)in ?eld plots with the endophyte (Appendix 1).

Capturing these more detailed changes in community structure has been a goal of current research by our groups,because of our interest,more broadly,in understanding how mutualisms in?uence the dynamics of communities.In gen-eral,results show that experimental elimination of the endo-phyte in tall fescue enhances the diversity of several guilds of arthropods,including herbivores,spiders and other predators,and increases the total abundance of insect herbivores (Rudg-ers &Clay 2005and unpublished data).These patterns indi-cate that ?ner-scale investigations of non-herbivore species are likely to reveal stronger effects of the endophyte than thus far reported.

0.00.1

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0.5

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Fig 7–Effect of manipulation of the presence of Neotypho-dium coenophialum in Lolium arundinaceum on the density of spiders in the families (a)Crab spiders (Thomisidae)and (b)Sheet web spiders (Linyphiidae)surveyed in 30m 330m ?eld plots in Bloomington,Indiana.Data points represent the mean abundance of spiders,and the bars show ±1SE.For the endophyte,treatments are represented as

endophyte-infected (E D [solid circles)or endophyte-free (E-[open triangles),n [8plots per treatment.Reprinted with permission from Finkes et al.(2006).

114J.A.Rudgers,K.Clay

A role for endophyte genotype?

Endophyte genotypes differ in compatibility with grass geno-types(Leuchtmann&Clay1989a;Christensen et al.1997),pro-duction of alkaloids(Siegel et al.1990;Hill et al.1991; Wilkinson et al.2000;Leuchtmann et al.2000;Rasmussen et al.2007),resistance to herbivores(Leuchtmann et al.2000; Timper et al.2001,2005;Tintjer&Rudgers2006),production of stromata(Leuchtmann&Clay1989b),mycelial mass(Hiatt &Hill1997),and effects on the phenotypic plasticity of grasses (Cheplick1998).Endophyte genotypes that differ in the types and amounts of alkaloids they produce can have dramatically different effects on herbivores,particularly insects versus mammals.For example,endophyte genotypes have been in-troduced for forage grasses that lack the production of ergot alkaloids and consequently lack toxicity to livestock(Bouton et al.2002).Similarly,the fungal alkaloid peramine affected one species of aphid,but combinations of both peramine and loline alkaloids were required for deterrence of other aphid species(Siegel et al.1990;see also Hunt&Newman 2005).

In ongoing work,we are exploring the relative importance of plant versus endophyte genotype in affecting the diversity and abundance of other community members.Results thus far suggest that endophyte genotype does signi?cantly alter plant and insect communities,but that these effects depend on the genetic background of tall fescue.Predicting how en-dophyte genotype alters community structure may ultimately depend on testing unique combinations of both host plant and microbe genotypes.Genetic modi?cation of endophytes to eliminate the production of the mammalian toxin,ergova-line,has been accomplished(Panaccione et al.2001),and directly incorporating genes from endophytic fungi into plant genomes has been proposed(Dahlman et al.1991).To evalu-ate the environmental impacts of these advances,we will need to understand how variation among grass/endophyte genotypes affects ecological interactions within and between consumers.Because most infected tall fescue in the eastern USA hosts a single endophyte genotype found in KY-31,and because it may be highly resistant to invasion by other spe-cies or genotypes,research on genetic variation in the endo-phyte may be of greater academic than practical signi?cance except in highly managed agronomic and/or turf situations.

4.Conclusions

Our conclusions are based experimental plots where fescue seed was sown on recently plowed soil that was rapidly colo-nized by diverse plant and animal species.No treatments,if any,were applied following seeding so long-term community and ecosystem responses are integrating the cumulative ef-fects of many varying biotic and abiotic factors.Results from multiple experiments are highly consistent and repeatable, suggesting that we are measuring general,rather than idio-syncratic,effects of endophyte infection on communities and ecosystems.

Several general conclusions arise from this work.One is that community-level effects are much stronger than one would predict from studies on individual species.Second, more generally,our results indicate an important role for mutualism in structuring communities and suggest that mu-tualisms may be critical for understanding the community and ecosystem-level consequences of non-native species such as tall fescue.Third,mechanisms of community change derive from a complex mixture of direct and indirect effects (e.g.,through herbivores)of the endophyte.While we have identi?ed vole herbivory as a key indirect mechanism,the relative importance of other factors(soil feedback,allelopa-thy,insect herbivory,direct competition,etc.)in mediating community-level responses is unclear and represents an im-portant area for further study.Finally,it would be very useful to study community-level effects of endophyte symbiosis in other systems to improve generalizations and predictions, e.g.in tall fescue in different ecological settings(including where it is native),in L.perenne in Europe,USA and New Zea-land,and in other dominant native and non-native grasses worldwide.

Acknowledgements

Most of this research was supported by NSF grant DBI-0200485 to Jennifer Rudgers and NSF grant DEB-9727116to Keith Clay. Many thanks to the many post-docs,graduate students and undergraduate students who contributed to this research. This paper was is based on a contribution to the‘‘Proceedings of the6th International Symposium on Fungal Endophytes of Grasses’’held in Christchurch,New Zealand,sponsored by the New Zealand Grassland Association and edited by A.J. Popay and E.R.Thom.

Appendix1

Summary of recent studies on the effects of the tall fescue endophyte on wild animals.We included all studies pub-lished since1996identi?ed by the search terms‘‘tall fescue’’and‘‘endophy*’’and‘‘herbivor*’’(and replacing both tall fes-cue and endophyt*with species names)on Web of Science (with one notable exception(Muegge et al.1991)because it ex-amined a species richness response).We also included rele-vant data available in recent book chapters.We only included studies that experimentally manipulated endophyte presence in tall fescue and that recorded at least one?tness-related response variable to estimate animal performance. Where multiple variables were measured,an effect size was determined for each.Effect size is the log response ratio?ln (mean Eà/mean Et).Direction of the effect is for Etrelative to Eà(i.e.,lower means the response variable was lower in Etrelative to Eà).Neutral effects(assigned an effect size of zero)were those reported as non-signi?cant following statis-tical analysis.Some treatment means had to be estimated from data presented in?gures,and those are indicated in the table.

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124J.A.Rudgers,K.Clay

with复合结构专项练习96126

with复合结构专项练习（二） 一请选择最佳答案 1）With nothing_______to burn，the fire became weak and finally died out. A.leaving B.left C.leave D.to leave 2）The girl sat there quite silent and still with her eyes_______on the wall. A.fixing B.fixed C.to be fixing D.to be fixed 3）I live in the house with its door_________to the south.（这里with结构作定语） A.facing B.faces C.faced D.being faced 4）They pretended to be working hard all night with their lights____. A.burn B.burnt C.burning D.to burn 二：用with复合结构完成下列句子 1）_____________（有很多工作要做），I couldn't go to see the doctor. 2）She sat__________（低着头）。 3）The day was bright_____.（微风吹拂） 4）_________________________，（心存梦想）he went to Hollywood. 三把下列句子中的划线部分改写成with复合结构。 1）Because our lessons were over，we went to play football. _____________________________. 2）The children came running towards us and held some flowers in their hands. _____________________________. 3）My mother is ill，so I won't be able to go on holiday. _____________________________. 4）An exam will be held tomorrow，so I couldn't go to the cinema tonight. _____________________________.

With的用法全解

With的用法全解 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、 with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词 +动词不定式； 5. with或without-名词/代词 +分词。 下面分别举例： 1、 She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语）

2、 With the meal over ， we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。） The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.（with+名词+不定式，作伴随状语）He could not finish it without me to help him.（without+代词 +不定式，作条件状语） 5、She fell asleep with the light burning.（with+名词+现在分词，作伴随状语） Without anything left in the with结构是许多英 语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 二、with结构的用法 with是介词，其意义颇多，一时难掌握。为帮助大家理清头绪，以教材中的句子为例，进行分类，并配以简单的解释。在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。 1.带着，牵着…… (表动作特征)。如： Run with the kite like this.

精神分裂症的病因及发病机理

精神分裂症的病因及发病机理 精神分裂症病因：尚未明，近百年来的研究结果也仅发现一些可能的致病因素。（一）生物学因素1．遗传遗传因素是精神分裂症最可能的一种素质因素。国内家系调查资料表明：精神分裂症患者亲属中的患病率比一般居民高6.2倍，血缘关系愈近，患病率也愈高。双生子研究表明：遗传信息几乎相同的单卵双生子的同病率远较遗传信息不完全相同 的双卵双生子为高，综合近年来11项研究资料：单卵双生子同病率（56.7%），是双卵双生子同病率（12.7%）的4.5倍，是一般人口患难与共病率的35-60倍。说明遗传因素在本病发生中具有重要作用，寄养子研究也证明遗传因素是本症发病的主要因素，而环境因素的重要性较小。以往的研究证明疾病并不按类型进行遗传，目前认为多基因遗传方式的可能性最大，也有人认为是常染色体单基因遗传或多源性遗传。Shields发现病情愈轻，病因愈复杂，愈属多源性遗传。高发家系的前瞻性研究与分子遗传的研究相结合，可能阐明一些问题。国内有报道用人类原癌基因Ha-ras-1为探针，对精神病患者基因组进行限止性片段长度多态性的分析，结果提示11号染色体上可能存在着精神分裂症与双相情感性精神病有关的DNA序列。2．性格特征：约40%患者的病前性格具有孤僻、冷淡、敏感、多疑、富于幻想等特征，即内向

型性格。3．其它：精神分裂症发病与年龄有一定关系，多发生于青壮年，约1/2患者于20～30岁发病。发病年龄与临床类型有关，偏执型发病较晚，有资料提示偏执型平均发病年龄为35岁，其它型为23岁。80年代国内12地区调查资料：女性总患病率（7.07%。）与时点患病率（5.91%。）明显高于男性（4.33%。与3.68%。）。Kretschmer在描述性格与精神分裂症关系时指出：61%患者为瘦长型和运动家型，12.8%为肥胖型，11.3%发育不良型。在躯体疾病或分娩之后发生精神分裂症是很常见的现象，可能是心理性生理性应激的非特异性影响。部分患者在脑外伤后或感染性疾病后发病；有报告在精神分裂症患者的脑脊液中发现病毒性物质；月经期内病情加重等躯体因素都可能是诱发因素，但在精神分裂症发病机理中的价值有待进一步证实。（二）心理社会因素1．环境因素①家庭中父母的性格，言行、举止和教育方式（如放纵、溺爱、过严）等都会影响子女的心身健康或导致个性偏离常态。②家庭成员间的关系及其精神交流的紊乱。③生活不安定、居住拥挤、职业不固定、人际关系不良、噪音干扰、环境污染等均对发病有一定作用。农村精神分裂症发病率明显低于城市。2．心理因素一般认为生活事件可发诱发精神分裂症。诸如失学、失恋、学习紧张、家庭纠纷、夫妻不和、意处事故等均对发病有一定影响，但这些事件的性质均无特殊性。因此，心理因素也仅属诱发因

with用法归纳

with用法归纳 （1）“用……”表示使用工具，手段等。例如： ①We can walk with our legs and feet. 我们用腿脚行走。 ②He writes with a pencil. 他用铅笔写。 （2）“和……在一起”，表示伴随。例如： ①Can you go to a movie with me? 你能和我一起去看电影'>电影吗？ ②He often goes to the library with Jenny. 他常和詹妮一起去图书馆。 （3）“与……”。例如： I’d like to have a talk with you. 我很想和你说句话。 （4）“关于，对于”，表示一种关系或适应范围。例如： What’s wrong with your watch? 你的手表怎么了？ （5）“带有，具有”。例如： ①He’s a tall kid with short hair. 他是个长着一头短发的高个子小孩。 ②They have no money with them. 他们没带钱。 （6）“在……方面”。例如： Kate helps me with my English. 凯特帮我学英语。 （7）“随着，与……同时”。例如： With these words, he left the room. 说完这些话，他离开了房间。 [解题过程] with结构也称为with复合结构。是由with+复合宾语组成。常在句中做状语，表示谓语动作发生的伴随情况、时间、原因、方式等。其构成有下列几种情形： 1.with+名词(或代词)+现在分词 此时，现在分词和前面的名词或代词是逻辑上的主谓关系。 例如:1)With prices going up so fast, we can't afford luxuries. 由于物价上涨很快，我们买不起高档商品。（原因状语） 2)With the crowds cheering, they drove to the palace. 在人群的欢呼声中，他们驱车来到皇宫。（伴随情况） 2.with+名词(或代词)+过去分词 此时，过去分词和前面的名词或代词是逻辑上的动宾关系。

独立主格with用法小全

独立主格篇 独立主格，首先它是一个“格”，而不是一个“句子”。在英语中任何一个句子都要有主谓结构，而在这个结构中，没有真正的主语和谓语动词，但又在逻辑上构成主谓或主表关系。独立主格结构主要用于描绘性文字中，其作用相当于一个状语从句，常用来表示时间、原因、条件、行为方式或伴随情况等。除名词/代词+名词、形容词、副词、非谓语动词及介词短语外，另有with或without短语可做独立主格，其中with可省略而without不可以。*注：独立主格结构一般放在句首，表示原因时还可放在句末；表伴随状况或补充说明时，相当于一个并列句，通常放于句末。 一、独立主格结构： 1. 名词/代词+形容词 He sat in the front row, his mouth half open. Close to the bank I saw deep pools, the water blue like the sky. 靠近岸时，我看见几汪深池塘，池水碧似蓝天。 2. 名词/代词+现在分词 Winter coming, it gets colder and colder. The rain having stopped, he went out for a walk.

The question having been settled, we wound up the meeting. 也可以The question settled, we wound up the meeting. 但含义稍有差异。前者强调了动作的先后。 We redoubled our efforts, each man working like two. 我们加倍努力，一个人干两个人的活。 3. 名词/代词+过去分词 The job finished, we went home. More time given, we should have done the job much better. *当表人体部位的词做逻辑主语时，不及物动词用现在分词，及物动词用过去分词。 He lay there, his teeth set, his hands clenched, his eyes looking straight up. 他躺在那儿，牙关紧闭，双拳紧握，两眼直视上方。 4. 名词/代词+不定式 We shall assemble at ten forty-five, the procession to start moving at precisely eleven. We divided the work, he to clean the windows and I to sweep the floor.

精神分裂症的发病原因是什么

精神分裂症的发病原因是什么 精神分裂症是一种精神病，对于我们的影响是很大的，如果不幸患上就要及时做好治疗，不然后果会很严重，无法进行正常的工作和生活，是一件很尴尬的事情。因此为了避免患上这样的疾病，我们就要做好预防，今天我们就请广州协佳的专家张可斌来介绍一下精神分裂症的发病原因。 精神分裂症是严重影响人们身体健康的一种疾病，这种疾病会让我们整体看起来不正常，会出现胡言乱语的情况，甚至还会出现幻想幻听，可见精神分裂症这种病的危害程度。 (1)精神刺激：人的心理与社会因素密切相关，个人与社会环境不相适应，就产生了精神刺激，精神刺激导致大脑功能紊乱，出现精神障碍。不管是令人愉快的良性刺激，还是使人痛苦的恶性刺激，超过一定的限度都会对人的心理造成影响。 (2)遗传因素：精神病中如精神分裂症、情感性精神障碍，家族中精神病的患病率明显高于一般普通人群，而且血缘关系愈近，发病机会愈高。此外，精神发育迟滞、癫痫性精神障碍的遗传性在发病因素中也占相当的比重。这也是精神病的病因之一。 (3)自身：在同样的环境中，承受同样的精神刺激，那些心理素质差、对精神刺激耐受力低的人易发病。通常情况下，性格内向、心胸狭窄、过分自尊的人，不与人交往、孤僻懒散的人受挫折后容易出现精神异常。 (4)躯体因素：感染、中毒、颅脑外伤、肿瘤、内分泌、代谢及营养障碍等均可导致精神障碍，。但应注意，精神障碍伴有的躯体因素，并不完全与精神症状直接相关，有些是由躯体因素直接引起的，有些则是以躯体因素只作为一种诱因而存在。 孕期感染。如果在怀孕期间，孕妇感染了某种病毒，病毒也传染给了胎儿的话，那么，胎儿出生长大后患上精神分裂症的可能性是极其的大。所以怀孕中的女性朋友要注意卫生，尽量不要接触病毒源。 上述就是关于精神分裂症的发病原因，想必大家都已经知道了吧。患上精神分裂症之后，大家也不必过于伤心，现在我国的医疗水平是足以让大家快速恢复过来的，所以说一定要保持良好的情绪。

with复合宾语的用法(20201118215048)

with+复合宾语的用法 一、with的复合结构的构成 二、所谓"with的复合结构”即是"with+复合宾语”也即"with +宾语+宾语补足语” 的结构。其中的宾语一般由名词充当（有时也可由代词充当）；而宾语补足语则是根据 具体的需要由形容词，副词、介词短语，分词短语（包括现在分词和过去分词）及不定式短语充当。下面结合例句就这一结构加以具体的说明。 三、1、with +宾语+形容词作宾补 四、①He slept well with all the windows open.（82 年高考题） 上面句子中形容词open作with的宾词all the windows的补足语， ②It' s impolite to talk with your mouth full of food. 形容词短语full of food 作宾补。Don't sleep with the window ope n in win ter 2、with+宾语+副词作宾补 with Joh n away, we have got more room. He was lying in bed with all his clothes on. ③Her baby is used to sleeping with the light on.句中的on 是副词，作宾语the light 的补足语。 ④The boy can t play with his father in.句中的副词in 作宾补。 3、with+宾语+介词短语。 we sat on the grass with our backs to the wall. his wife came dow n the stairs,with her baby in her arms. They stood with their arms round each other. With tears of joy in her eyes ,she saw her daughter married. ⑤She saw a brook with red flowers and green grass on both sides. 句中介词短语on both sides 作宾语red flowersandgreen grass 的宾补， ⑥There were rows of white houses with trees in front of them.，介词短语in front of them 作宾补。 4、with+宾词+分词（短语 这一结构中作宾补用的分词有两种，一是现在分词，二是过去分词，一般来说，当分词所表 示的动作跟其前面的宾语之间存在主动关系则用现在分词，若是被动关系，则用过去分词。 ⑦In parts of Asia you must not sit with your feet pointing at another person.（高一第十课），句中用现在分词pointing at…作宾语your feet的补足语，是因它们之间存在主动关系，或者说point 这一动作是your feet发出的。 All the after noon he worked with the door locked. She sat with her head bent. She did not an swer, with her eyes still fixed on the wall. The day was bright,with a fresh breeze（微风）blowing. I won't be able to go on holiday with my mother being ill. With win ter coming on ,it is time to buy warm clothes. He soon fell asleep with the light still bur ning. ⑧From space the earth looks like ahuge water covered globe,with a few patches of land stuk ing out above the water而在下面句子中因with的宾语跟其宾补之间存在被动关系，故用过去分词作宾补：

with用法小结

with用法小结 一、with表拥有某物 Mary married a man with a lot of money . 马莉嫁给了一个有着很多钱的男人。 I often dream of a big house with a nice garden . 我经常梦想有一个带花园的大房子。 The old man lived with a little dog on the lonely island . 这个老人和一条小狗住在荒岛上。 二、with表用某种工具或手段 I cut the apple with a sharp knife . 我用一把锋利的刀削平果。 Tom drew the picture with a pencil . 汤母用铅笔画画。 三、with表人与人之间的协同关系 make friends with sb talk with sb quarrel with sb struggle with sb fight with sb play with sb work with sb cooperate with sb I have been friends with Tom for ten years since we worked with each other, and I have never quarreled with him . 自从我们一起工作以来，我和汤姆已经是十年的朋友了，我们从没有吵过架。 四、with 表原因或理由 John was in bed with high fever . 约翰因发烧卧床。 He jumped up with joy . 他因高兴跳起来。 Father is often excited with wine . 父亲常因白酒变的兴奋。 五、with 表“带来”，或“带有,具有”，在…身上，在…身边之意

精神分裂症的病因是什么

精神分裂症的病因是什么 精神分裂症是一种精神方面的疾病，青壮年发生的概率高，一般 在16～40岁间，没有正常器官的疾病出现，为一种功能性精神病。 精神分裂症大部分的患者是由于在日常的生活和工作当中受到的压力 过大，而患者没有一个良好的疏导的方式所导致。患者在出现该情况 不仅影响本人的正常社会生活，且对家庭和社会也造成很严重的影响。 精神分裂症常见的致病因素： 1、环境因素：工作环境比如经济水平低低收入人群、无职业的人群中，精神分裂症的患病率明显高于经济水平高的职业人群的患病率。还有实际的生活环境生活中的不如意不开心也会诱发该病。 2、心理因素：生活工作中的不开心不满意，导致情绪上的失控，心里长期受到压抑没有办法和没有正确的途径去发泄，如恋爱失败， 婚姻破裂，学习、工作中不愉快都会成为本病的原因。 3、遗传因素：家族中长辈或者亲属中曾经有过这样的病人，后代会出现精神分裂症的机会比正常人要高。 4、精神影响：人的心里与社会要各个方面都有着不可缺少的联系，对社会环境不适应，自己无法融入到社会中去，自己与社会环境不相

适应，精神和心情就会受到一定的影响，大脑控制着人的精神世界， 有可能促发精神分裂症。 5、身体方面：细菌感染、出现中毒情况、大脑外伤、肿瘤、身体的代谢及营养不良等均可能导致使精神分裂症，身体受到外界环境的 影响受到一定程度的伤害，心里受到打击，无法承受伤害造成的痛苦，可能会出现精神的问题。 对于精神分裂症一定要配合治疗，接受全面正确的治疗，最好的 疗法就是中医疗法加心理疗法。早发现并及时治疗并且科学合理的治疗，不要相信迷信，要去正规的医院接受合理的治疗，接受正确的治 疗按照医生的要求对症下药，配合医生和家人，给病人创造一个良好 的治疗环境，对于该病的康复和痊愈会起到意想不到的效果。

(完整版)with的复合结构用法及练习

with复合结构 一. with复合结构的常见形式 1.“with+名词/代词+介词短语”。 The man was walking on the street, with a book under his arm. 那人在街上走着，腋下夹着一本书。 2. “with+名词/代词+形容词”。 With the weather so close and stuffy, ten to one it’ll rain presently. 天气这么闷热，十之八九要下雨。 3. “with+名词/代词+副词”。 The square looks more beautiful than even with all the light on. 所有的灯亮起来，广场看起来更美。 4. “with+名词/代词+名词”。 He left home, with his wife a hopeless soul. 他走了，妻子十分伤心。 5. “with+名词/代词+done”。此结构过去分词和宾语是被动关系，表示动作已经完成。 With this problem solved, neomycin 1 is now in regular production. 随着这个问题的解决，新霉素一号现在已经正式产生。 6. “with+名词/代词+-ing分词”。此结构强调名词是-ing分词的动作的发出者或某动作、状态正在进行。 He felt more uneasy with the whole class staring at him. 全班同学看着他，他感到更不自然了。 7. “with+宾语+to do”。此结构中，不定式和宾语是被动关系，表示尚未发生的动作。 So in the afternoon, with nothing to do, I went on a round of the bookshops. 由于下午无事可做，我就去书店转了转。 二. with复合结构的句法功能 1. with 复合结构，在句中表状态或说明背景情况，常做伴随、方式、原因、条件等状语。With machinery to do all the work, they will soon have got in the crops. 由于所有的工作都是由机器进行，他们将很快收完庄稼。（原因状语） The boy always sleeps with his head on the arm. 这个孩子总是头枕着胳膊睡觉。（伴随状语）The soldier had him stand with his back to his father. 士兵要他背对着他父亲站着。（方式状语）With spring coming on, trees turn green. 春天到了，树变绿了。（时间状语） 2. with 复合结构可以作定语 Anyone with its eyes in his head can see it’s exactly like a rope. 任何一个头上长着眼睛的人都能看出它完全像一条绳子。 【高考链接】 1. ___two exams to worry about, I have to work really hard this weekend.（04北京） A. With B. Besides C. As for D. Because of 【解析】A。“with+宾语+不定式”作状语，表示原因。 2. It was a pity that the great writer died, ______his works unfinished. (04福建) A. for B. with C. from D.of 【解析】B。“with+宾语+过去分词”在句中作状语，表示状态。 3._____production up by 60%, the company has had another excellent year. (NMET) A. As B.For C. With D.Through 【解析】C。“with+宾语+副词”在句中作状语，表示程度。

With复合结构的用法小结

With复合结构的用法小结 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二 部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词+动词不定式； 5. with或without-名词/代词+分词。 下面分别举例： 1、She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语） 2、With the meal over ，we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。）The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.（with+名词+不定式，作伴随状语）He could not finish it without me to help him.（without+代词+不定式，作条件状语） 5、She fell asleep with the light burning.（with+名词+现在分词，作伴随状语）Without anything left in the cupboard，shewent out to get something to eat.（without+代词+过去分词，作为原因状语） 二、with结构的用法 在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。 With结构在句中也可以作定语。例如： 1.I like eating the mooncakes with eggs. 2.From space the earth looks like a huge water-covered globe with a few patches of land sticking out above the water. 3.A little boy with two of his front teeth missing ran into the house. 三、with结构的特点 1. with结构由介词with或without+复合结构构成。复合结构中第一部分与第二部分语法上是宾语和宾语补足语关系，而在逻辑上，却具有主谓关系，也就是说，可以用第一部分作主语，第二部分作谓语，构成一个句子。例如：With him taken care of，we felt quite relieved.（欣慰）→（He was taken good care of.）She fell asleep with the light burning. →（The light was burning.）With her hair gone，there could be no use for them. →（Her hair was gone.） 2. 在with结构中，第一部分为人称代词时，则该用宾格代词。例如：He could not finish it without me to help him. 四、几点说明： 1. with结构在句子中的位置：with 结构在句中作状语，表示时间、条件、原因时一般放在

with的用法

with[wIT] prep.1.与…(在)一起，带着：Come with me. 跟我一起来吧。/ I went on holiday with my friend. 我跟我朋友一起去度假。/ Do you want to walk home with me? 你愿意和我一道走回家吗 2.(表带有或拥有)有…的，持有，随身带着：I have no money with me. 我没有带钱。/ He is a man with a hot temper. 他是一个脾气暴躁的人。/ We bought a house with a garden. 我们买了一座带花园的房子。/ China is a very large country with a long history. 中国是一个具有历史悠久的大国。3.(表方式、手段或工具)以，用：He caught the ball with his left hand. 他用左手接球。/ She wrote the letter with a pencil. 她用铅笔写那封信。4.(表材料或内容)以，用：Fill the glass with wine. 把杯子装满酒。/ The road is paved with stones. 这条路用石头铺砌。5.(表状态)在…的情况下，…地：He can read French with ease. 他能轻易地读法文。/ I finished my homework though with difficulty. 虽然有困难，我还是做完了功课。6.(表让步)尽管，虽然：With all his money, he is unhappy. 尽管他有钱，他并不快乐。/ With all his efforts, he lost the match. 虽然尽了全力，他还是输了那场比赛。7.(表条件)若是，如果：With your permission, I’ll go. 如蒙你同意我就去。8.(表原因或理由)因为，由于：He is tired with work. 他工作做累了。/ At the news we all jumped with joy. 听到这消息我们都高兴得跳了起来。9.(表时间)当…的时候，在…之后：With that remark, he left. 他说了那话就离开了。/ With daylight I hurried there to see what had happened. 天一亮我就去那儿看发生了什么事。10. (表同时或随同)与…一起，随着：The girl seemed to be growing prettier with each day. 那女孩好像长得一天比一天漂亮。11.(表伴随或附带情况)同时：I slept with the window open. 我开着窗户睡觉。/ Don’t speak with your mouth full. 不要满嘴巴食物说话。12.赞成，同意：I am with you there. 在那点上我同你意见一致。13.由…照看，交…管理，把…放在某处：I left a message for you with your secretary. 我给你留了个信儿交给你的秘书了。/ The keys are with reception. 钥匙放在接待处。14 (表连同或包含)连用，包含：The meal with wine came to ￡8 each. 那顿饭连酒每人8英镑。/ With preparation and marking a teacher works 12 hours a day. 一位老师连备课带批改作业每天工作12小时。15. (表对象或关系)对，关于，就…而言，对…来说：He is pleased with his new house. 他对他的新房子很满意。/ The teacher was very angry with him. 老师对他很生气。/ It’s the same with us students. 我们学生也是这样。16.(表对立或敌对)跟，以…为对手：The dog was fighting with the cat. 狗在同猫打架。/ He’s always arguing with his brother. 他老是跟他弟弟争论。17.(在祈使句中与副词连用)：Away with him! 带他走！/ Off with your clothes! 脱掉衣服！/ Down with your money! 交出钱来！ 【用法】1.表示方式、手段或工具等时(=以，用)，注意不要受汉语意思的影响而用错搭配，如“用英语”习惯上用in English，而不是with English。2.与某些抽象名词连用时，其作用相当于一个副词：with care=carefully 认真地/ with kindness=kindly 亲切地/ with joy=joyfully 高兴地/ with anger=angrily 生气地/ with sorrow=sorrowfully 悲伤地/ with ease=easily 容易地/ with delight=delightedly 高兴地/ with great fluency =very fluently 很流利地3.表示条件时，根据情况可与虚拟语气连用：With more money I would be able to buy it. 要是钱多一点，我就买得起了。/ With better equipment, we could have finished the job even sooner. 要是设备好些，我们完成这项工作还要快些。4.比较with 和as：两者均可表示“随着”，但前者是介词，后者是连词：He will improve as he grows older. 随着年龄的增长，他会进步的。/ People’s ideas change with the change of the times. 时代变了，人们的观念也会变化。5.介词with和to 均可表示“对”，但各自的搭配不同，注意不要受汉语意思的影响而用错，如在kind, polite, rude, good, married等形容词后通常不接介词with而接to。6.复合结构“with+宾语+宾语补足语”是一个很有用的结构，它在句中主要用作状语，表示伴随、原因、时间、条件、方式等；其中的宾语补足语可以是名词、形容词、副词、现在分词、过去分词、不定式、介词短语等：I went out with the windows open. 我外出时没有关窗户。/ He stood before his teacher with his head down. 他低着头站在老师面前。/ He was lying on the bed with all his clothes on. 他和衣躺在床上。/ He died with his daughter yet a schoolgirl. 他去世时，女儿还是个小学生。/ The old man sat there with a basket beside her. 老人坐在那儿，身边放着一个篮子。/ He fell asleep with the lamp burning. 他没熄灯就睡着了。/ He sat there with his eyes closed. 他闭目坐在那儿。/ I can’t go out with all these clothes to wash. 要洗这些衣服，我无法出去了。这类结构也常用于名词后作定语：The boy with nothing on is her son. 没穿衣服的这个男孩子是她儿子。 （摘自《英语常用词多用途词典》金盾出版社） - 1 -

精神分裂症应该怎么治疗

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