Ecological aspects of mycorrhizal symbiosis: with special emphasis on the functional diversity of interactions involving the extraradical mycelium

Different symbiotic mycorrhizal associations between plantsand fungi occur, almost ubiquitously, in a wide range of terrestrialecosystems. Historically, these have mainly been consideredwithin the rather narrow perspective of their effects on theuptake of dissolved mineral nutrients by individual plants.More recent research has placed emphasis on a wider, multifunctionalperspective, including the effects of mycorrhizal symbiosison plant and microbial communities, and on ecosystem processes.This includes mobilization of N and P from organic polymers,release of nutrients from mineral particles or rock surfacesvia weathering, effects on carbon cycling, interactions withmyco-heterotrophic plants, mediation of plant responses to stressfactors such as drought, soil acidification, toxic metals, andplant pathogens, as well as a range of possible interactionswith groups of other soil micro-organisms. Mycorrhizal fungiconnect their plant hosts to the heterogeneously distributednutrients required for their growth, enabling the flow of energy-richcompounds required for nutrient mobilization whilst simultaneouslyproviding conduits for the translocation of mobilized productsback to their hosts. In addition to increasing the nutrientabsorptive surface area of their host plant root systems, theextraradical mycelium of mycorrhizal fungi provides a directpathway for translocation of photosynthetically derived carbonto microsites in the soil and a large surface area for interactionwith other micro-organisms. The detailed functioning and regulationof these mycorrhizosphere processes is still poorly understoodbut recent progress is reviewed and potential benefits of improvedunderstanding of mycorrhizosphere interactions are discussed. Key words: Arbuscular mycorrhiza, biotic interactions, carbon flow, ectomycorrhiza, ericoid mycorrhiza, mycelium, nutrient uptake, symbiosis, weathering Received 22 January 2008; Revised 7 February 2008 Accepted 7 February 2008     

The Multifunctional Role of Ectomycorrhizal Associations in Forest Ecosystem Processes

Belowground biological interactions that occur among plant roots, microorganisms and animals are dynamic and substantially influence ecosystem processes. Among these interactions, the ectomycorrhizal (ECM) symbiosis is remarkable but unfortunately these associations have mainly been considered within the rather narrow perspective of their effects on the uptake of dissolved mineral nutrients by individual plants. More recent research has placed emphasis on a wider, multifunctional perspective, including the effects of ectomycorrhizal symbiosis on plant and microbial communities, and on ecosystem processes. This includes mobilization of N and P from organic polymers, release of nutrients from mineral particles or rock surfaces via weathering, effects on carbon cycling, interactions with mycoheterotrophic plants, mediation of plant responses to stress factors such as drought, soil acidification, toxic metals, and plant pathogens, rehabilitation and regeneration of degraded forest ecosystems, as well as a range of possible interactions with groups of other soil microorganisms. Ectomycorrhizas are almost invariably characterized by a Hartig net composed of highly branched hyphae which entirely surround the outer root cortical cells. The Hartig net is the place of massive bidirectional exchanges of nutrients between the host and the fungus. Through these branched hyphae ectomycorrhizal fungi connect their plant hosts to the heterogeneously distributed nutrients required for their growth, enabling the flow of energy-rich compounds required for nutrient mobilization whilst simultaneously providing conduits for the translocation of mobilized products back to their hosts. In addition to increasing the nutrient absorptive surface area of their host plant root systems, the extraradical mycelium of ectomycorrhizal fungi provides a direct pathway for translocation of photosynthetically derived carbon from their hosts to microsites in the soil and a large surface area for interaction with other soil micro-organisms. The detailed functioning and regulation of these mycorrhizosphere processes is still poorly understood and needs detailed molecular approach to study these mycorrhizosphere processes but recent progress in ectomycorrhizal associations is reviewed and potential benefits of improved understanding of mycorrhizosphere interactions are discussed.     

Warmer winters increase the rhizosphere carbon flow to mycorrhizal fungi more than to other microorganisms in a temperate grassland

A decisive set of steps in the terrestrial carbon (C) cycle is the fixation of atmospheric C by plants and the subsequent C‐transfer to rhizosphere microorganisms. With climate change winters are expected to become milder in temperate ecosystems. Although the rate and pathways of rhizosphere C input to soil could be impacted by milder winters, the responses remain unknown. To address this knowledge‐gap, a winter‐warming experiment was established in a seminatural temperate grassland to follow the C flow from atmosphere, via the plants, to different groups of soil microorganisms. In situ ¹³CO₂ pulse labelling was used to track C into signature fatty acids of microorganisms. The winter warming did not result in any changes in biomass of any of the groups of microorganisms. However, the C flow from plants to arbuscular mycorrhizal (AM) fungi, increased substantially by winter warming. Saprotrophic fungi also received large amounts of plant‐derived C—indicating a higher importance for the turnover of rhizosphere C than biomass estimates would suggest—still, this C flow was unaffected by winter warming. AM fungi was the only microbial group positively affected by winter warming—the group with the closest connection to plants. Winter warming resulted in higher plant productivity earlier in the season, and this aboveground change likely induced plant nutrient limitation in warmed plots, thus stimulating the plant dependence on, and C allocation to, belowground nutrient acquisition. The preferential C allocation to AM fungi was at the expense of C flow to other microbial groups, which were unaffected by warming. Our findings imply that warmer winters may shift rhizosphere C‐fluxes to become more AM fungal‐dominated. Surprisingly, the stimulated rhizosphere C flow was matched by increased microbial turnover, leading to no accumulation of soil microbial biomass.     

丛枝菌根菌诱导植物抗病的内在机制

应用菌根真菌诱导植物抗病性是近年化学生态学和病害生物防治研究的热点．研究表明,丛枝菌根真菌(AMF)对土传病原物具有一定拮抗或抑制作用,能提高植物对土传病害的抗／耐病性．在菌根根际,各种菌群不断产生相互作用,AMF在其中起着抑制病原菌、促进有益菌生长的作用,可与其他桔抗菌结合,用做生防菌．AMF提高植物抗病性的机制还有这样几种假设：(1)植物营养得到改善;(2)竞争作用;(3)根系形态结构改变;(4)根际微生物区系变化;(5)诱导抗性及诱导系统抗性,即AMF侵染植物根系后,诱导植物体内酚酸类代谢产物增加,使植物产生局部或系统防御反应．深人研究AMF提高植物抗病性的机制,有助于正确理解菌根的抗病作用,使其能尽快地成为植物病害生物防治中的一种新方法,在生态农业中发挥作用。     

The role of mycorrhizae and plant growth promoting rhizobacteria (PGPR) in improving crop productivity under stressful environments

Both biotic and abiotic stresses are major constrains to agricultural production. Under stress conditions, plant growth is affected by a number of factors such as hormonal and nutritional imbalance, ion toxicity, physiological disorders, susceptibility to diseases, etc. Plant growth under stress conditions may be enhanced by the application of microbial inoculation including plant growth promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes can promote plant growth by regulating nutritional and hormonal balance, producing plant growth regulators, solubilizing nutrients and inducing resistance against plant pathogens. In addition to their interactions with plants, these microbes also show synergistic as well as antagonistic interactions with other microbes in the soil environment. These interactions may be vital for sustainable agriculture because they mainly depend on biological processes rather than on agrochemicals to maintain plant growth and development as well as proper soil health under stress conditions. A number of research articles can be deciphered from the literature, which shows the role of rhizobacteria and mycorrhizae alone and/or in combination in enhancing plant growth under stress conditions. However, in contrast, a few review papers are available which discuss the synergistic interactions between rhizobacteria and mycorrhizae for enhancing plant growth under normal (non-stress) or stressful environments. Biological interactions between PGPR and mycorrhizal fungi are believed to cause a cumulative effect on all rhizosphere components, and these interactions are also affected by environmental factors such as soil type, nutrition, moisture and temperature. The present review comprehensively discusses recent developments on the effectiveness of PGPR and mycorrhizal fungi for enhancing plant growth under stressful environments. The key mechanisms involved in plant stress tolerance and the effectiveness of microbial inoculation for enhancing plant growth under stress conditions have been discussed at length in this review. Growth promotion by single and dual inoculation of PGPR and mycorrhizal fungi under stress conditions have also been discussed and reviewed comprehensively.     

Manganese reduction in the rhizosphere of mycorrhizal and nonmycorrhizal maize

The influence of rhizosphere microorganisms and vesicular-arbuscular (VA) mycorrhiza on manganese (Mn) uptake in maize (Zea mays L. cv. Tau) plants was studied in pot experiments under controlled environmental conditions. The plants were grown for 7 weeks in sterilized calcareous soil in pots having separate compartments for growth of roots and of VA mycorrhizal fungal hyphae. The soil was left either uninoculated (control) or prior to planting was inoculated with rhizosphere microorganisms only (MO-VA) or with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol and Gerd.) Gerdemann and Trappe] (MO+VA). Mycorrhiza treatment did not affect shoot dry weight, but root dry weight was slightly inhibited in the MO+VA and MO-VA treatments compared with the uninoculated control. Concentrations of Mn in shoots decreased in the order MO-VA > MO+VA > control. In the rhizosphere soil, the total microbial population was higher in mycorrhizal (MO+VA) than nonmycorrhizal (MO-VA) treatments, but the proportion of Mn-reducing microbial populations was fivefold higher in the nonmycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The most important microbial group taking part in the reduction of Mn was fluorescent Pseudomonas. Mycorrhizal treatment decreased not only the number of Mn reducers but also the release of Mn-solubilizing root exudates, which were collected by percolation from maize plants cultivated in plastic tubes filled with gravel quartz sand. Compared with mycorrhizal plants, the root exudates of nonmycorrhizal plants had two fold higher capacity for reduction of Mn. Therefore, changes in both rhizosphere microbial population and root exudation are probably responsible for the lower acquisition of Mn in mycorrhizal plants.     

丛枝菌根网络的生态学功能研究进展

丛枝菌根(AM)真菌是陆地生态系统中重要的土壤微生物之一.其在土壤生态系统中延伸出的根外菌丝,可以通过菌丝融合的方式形成丛枝菌根网络(AMN).AMN在土壤生态系统中发挥着重要功能：一方面,AMN可以改变土壤的理化性质,其根外菌丝分泌物可以影响土壤微生物生存的微环境,进而改变土壤微生物的群落组成;另一方面,AM真菌的根外菌丝可以吸收土壤养分,并通过AMN将吸收的营养物质在宿主植物间进行分配,调节植物物种之间的竞争关系.为了全面阐述AMN在生态系统中的功能,本文围绕最新的AMN研究成果,探究AM真菌根外菌丝在土壤中相互融合的机制、AMN影响土壤微生物的数量和组成、调节植物群落的生态学机理,以及AMN调节地下资源、植物种内和种间竞争、影响植物群落的多样性和丰富度等生态系统功能.阐述在全球变化过程中AMN与大气氮沉降、CO₂浓度升高以及温度升高的相关性,探究其在维持生态系统稳定性中的作用,并对本领域未来的发展方向和应用前景进行展望.     

Carbon allocation mediated by arbuscular mycorrhizal fungi alters the soil microbial community under various phosphorus levels

Studies have shown that arbuscular mycorrhizal fungi (AMF) can shape the rhizosphere microbial community of the host plant, but the underlying mechanisms are unclear. Here, we tested the hypotheses that AMF may affect the rhizosphere microbial community by mediating carbon (C) allocation of the host plant, and that this mediation may be modulated by the soil phosphorus (P) level. Using a split-root system, we conducted a microcosm experiment with three main effects (soil P level: 5 or 25 mg kg⁻¹; AMF: with or without inoculation; and spatial niche (i.e., rhizosphere, hyphosphere, and mycorrhizosphere). Host plant growth benefited from AMF under low soil-P conditions. ¹³CO₂ isotope labeling showed that AMF increased C allocation to the colonized root and AMF mycelia under low-P conditions, which promoted AMF growth. ¹³C-DNA-SIP and 16S rRNA sequencing further indicated that the enhanced C allocation from the host altered the soil microbial community. Our results suggest that AMF enhances the C allocation of the host plant below ground, which can shape microbial community composition. These AMF effects were greater with a low than with a high level of soil P.     

AM真菌在植物病虫害生物防治中的作用机制

丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与大约80%的陆生高等植物形成共生体。由土传病原物侵染引起的土传病害被植物病理学界认定为最难防治的病害之一。研究表明,AM真菌能够拮抗由真菌、线虫、细菌等病原体引起的土传性植物病害,诱导宿主植物增强对病虫害的耐/抗病性。当前,利用AM真菌开展病虫害的生物防治已经引起生态学家和植物病理学家的广泛关注。基于此,围绕AM真菌在植物病虫害生物防治中的最新研究进展,从AM真菌改变植物根系形态结构、调节次生代谢产物的合成、改善植物根际微环境、与病原微生物直接竞争入侵位点和营养分配、诱导植株体内抗病防御体系的形成等角度,探究AM真菌在植物病虫害防治中的作用机理,以期为利用AM真菌开展植物病虫害的生物防治提供理论依据,并对本领域未来的发展方向和应用前景进行展望。     

丛枝菌根化翅果油树幼苗根际土壤微环境

以我国二级濒危保护植物翅果油(Elaeagnus mollis)为供试植物, 通过温室盆栽试验, 研究接种丛枝菌根真菌对翅果油树幼苗根际土壤微生态环境的影响。试验设计分4个组: 摩西球囊霉(Glomus mosseae)单独接种组(GM)、脆无梗囊霉(Acaulospora delicata)单独接种组(AD)、混合接种组(GM + AD)、不接种的对照组(CK)。测定了菌根侵染率、生物量、根际微生物数量、土壤pH值、土壤酶活性及其对N、P营养的影响等指标。结果显示: 菌根真菌对3个接种组均有侵染, 其中, GM + AD的侵染率最大(90.5%), 生态学效应最好; 与对照组相比, 接种组的生物量均明显提高(p < 0.05), 其中GM + AD组生物量显著增加, 是CK组的2.2倍; AM菌根对根部微生物种群数量产生一定的影响, 主要是使根面上的细菌、放线菌、固氮菌的数量显著增加(p < 0.05); AM菌根使根际pH值降低, 与菌根侵染率呈显著负相关关系(p < 0.05); 接种组根际土壤磷酸酶、脲酶、蛋白酶的活性增加, 根际土壤的磷酸酶、蛋白酶的活性增加量与菌根侵染率呈极显著相关关系(p < 0.01); 接种组的根际土壤中, 可直接被植物吸收利用的N、P元素出现富集现象, 与菌根侵染率呈显著相关关系(p < 0.05)。研究表明: 丛枝菌根的形成改善了翅果油树幼苗的微生态环境, 提高了根际土壤肥力。     

林木共生菌系统及其作用机制——以杨树为例

杨树（Populus）是重要造林树种,也是研究林木基础生物学性状的模式材料。不仅如此,杨树可与多种细菌（内生细菌、内生固氮菌和根际促生菌）和真菌（外生菌根真菌、丛枝菌根真菌和内生真菌）类群建立共生关系,为揭示树木和微生物之间的互惠共生机制提供了理想模型。这些共生菌能积极调控林木生长发育、营养吸收和生理生态过程。目前在杨树-双色蜡蘑（Laccaria bicolor）形成的外生菌根发育、提高杨树耐盐、耐重金属的生理与分子机制、叶片内生真菌群落结构与病害发生、菌根辅助细菌和菌丝内共生细菌-真菌-杨树形成的三重跨界共生等方面取得多项突破。近年来,一批模式草本植物微生物组（microbiome）计划相继实施,对共生菌群落结构和功能的认识有了革命性的进步。以美洲黑杨、毛果杨和胶杨为代表的林木微生物组研究也已启动,表明宿主基因型和环境因子可显著影响共生菌群落结构与物种组成;在根际（rhizosphere）和内生（endosphere）环境存在结构和功能迥异的菌群。另一方面,以根系为诱饵,通过宿主表型来推测菌群功能的反向"钓鱼"策略将推动林木根际微生物工程研究,为揭示杨树-微生物群落的相互关系、菌群进化搭建了研究模型。总之,深入认识多元微生物对林木表型和生理代谢的表观遗传学调控机制将为今后创制新型菌剂并用于高效育苗和抗性育种提供新的思路,具有重要的科学意义和应用价值。     

Controls for rhizosphere microorganisms to study effects of vesicular-arbuscular mycorrhizae on Artemisia tridentata

Seven treatments were set up to test the effects of vesicular-arbuscular (VA) mycorrhizal fungi and other rhizosphere microorganisms on the growth of Artemisia tridentata ssp. tridentata. Soil sievings had no significant effect on root or shoot mass. Spores and surface-sterile spores were a poor inoculum source, but roots and fresh soil caused 45–75% mycorrhizal infection. Whereas root-inoculated plants still had low growth responses by the end of the experiment, fresh soil inoculum caused the greatest response, and partial fresh inoculum caused a lesser response. These results suggest that fresh soil is an appropriate inoculum for this plant-fungal-soil system, and that the major effect on plant growth of the fresh soil inoculum is from the mycorrhizal fungi and not from the other microorganisms, because the sievings had no effect on plant growth. In addition, soil dilution plating of saprophytic fungi showed 85% species similarity between sterile and fresh soil inoculum by the end of the experiment. Since the effects of non-VA microorganisms are complex and varied, we suggest that researchers work out the type of mycorrhizal controls that best suit their system.     

Fate of polycyclic aromatic hydrocarbons (PAH) in the rhizosphere and mycorrhizosphere of ryegrass

Polycyclic aromatic hydrocarbons (PAH) can be degraded in the rhizosphere but may also interact with vegetation by accumulation in plant tissues or adsorption on root surface. Previous studies have shown that arbuscular mycorrhizal (AM) fungi contribute to the establishment and maintenance of plants in a PAH contaminated soil. We investigated the fate of PAH in the rhizosphere and mycorrhizosphere including biodegradation, uptake and adsorption. Experiments were conducted with ryegrass inoculated or not with Glomus mosseae P2 (BEG 69) and cultivated in pots filled with soil spiked with 5 g kg⁻¹ of anthracene or with 1 g kg⁻¹ of a mixture of 8 PAH in a growth chamber. PAH were extracted from root surfaces, root and shoot tissue and rhizosphere soil and were analysed by GC-MS. In both experiments, 0.006 – 0.11‰ of the initial extractable PAH concentration were adsorbed to roots, 0.003 – 0.16‰ were found in root tissue, 0.001‰ in shoot tissue and 36 – 66% were dissipated, suggesting that the major part of PAH dissipation in rhizosphere soil was due to biodegradation or biotransformation. With mycorrhizal plants, anthracene and PAH were less adsorbed to roots and shoot tissue concentrations were lower than with non mycorrhizal plants, which could contribute to explain the beneficial effect of AM fungi on plant survival in PAH contaminated soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of heavy metal pollution on mycorrhizal colonization and function: physiological, ecological and applied aspects

 High concentrations of heavy metals in soil have an adverse effect on micro-organisms and microbial processes. Among soil microorganisms, mycorrhizal fungi are the only ones providing a direct link between soil and roots, and can therefore be of great importance in heavy metal availability and toxicity to plants. This review discusses various aspects of the interactions between heavy metals and mycorrhizal fungi, including the effects of heavy metals on the occurrence of mycorrhizal fungi, heavy metal tolerance in these micro-organisms, and their effect on metal uptake and transfer to plants. Mechanisms involved in metal tolerance, uptake and accumulation by mycorrhizal hyphae and by endo- or ectomycorrhizae are covered. The possible use of mycorrhizal fungi as bioremediation agents in polluted soils or as bioindicators of pollution is also discussed. Accepted: 23 June 1997     

Is —— the rhizosphere a source of applicable multi-beneficial microorganisms for plant enhancement?

The plant faces different pedological and climatic challenges that influence its growth and enhancement. While, plant-microbes interactions throught the rhizosphere offer several privileges to this hotspot in the service of plant, by attracting multi-beneficial mutualistic and symbiotic microorganisms as plant growth-promoting bacteria (PGPB), archaea, mycorrhizal fungi, endophytic fungi, and others…). Currently, numerous investigations showed the beneficial effects of these microbes on growth and plant health. Indeed, rhizospheric microorganisms offer to host plants the essential assimilable nutrients, stimulate the growth and development of host plants, and induce antibiotics production. They also attributed to host plants numerous phenotypes involved in the increase the resistance to abiotic and biotic stresses. The investigations and the studies on the rhizosphere can offer a way to find a biological and sustainable solution to confront these environmental problems. Therefore, the interactions between microbes and plants may lead to interesting biotechnological applications on plant improvement and the adaptation in different climates to obtain a biological sustainable agricultures without the use of chemical fertilizers.     

Arbuscular mycorrhizas and biological control of soil-borne plant pathogens – an overview of the mechanisms involved

 Biological control of plant pathogens is currently accepted as a key practice in sustainable agriculture because it is based on the management of a natural resource, i.e. certain rhizosphere organisms, common components of ecosystems, known to develop antagonistic activities against harmful organisms (bacteria, fungi, nematodes etc.). Arbuscular mycorrhizal (AM) associations have been shown to reduce damage caused by soil-borne plant pathogens. Although few AM isolates have been tested in this regard, some appear to be more effective than others. Furthermore, the degree of protection varies with the pathogen involved and can be modified by soil and other environmental conditions. This prophylactic ability of AM fungi could be exploited in cooperation with other rhizospheric microbial angatonists to improve plant growth and health. Despite past achievements on the application of AM in plant protection, further research is needed for a better understanding of both the ecophysiological parameters contributing to effectiveness and of the mechanisms involved. Although the improvement of plant nutrition, compensation for pathogen damage, and competition for photosynthates or colonization/infection sites have been claimed to play a protective role in the AM symbiosis, information is scarce, fragmentary or even controversial, particularly concerning other mechanisms. Such mechanisms include (a) anatomical or morphological AM-induced changes in the root system, (b) microbial changes in rhizosphere populations of AM plants, and (c) local elicitation of plant defence mechanisms by AM fungi. Although compounds typically involved in plant defence reactions are elicited by AM only in low amounts, they could act locally or transiently by making the root more prone to react against pathogens. Current research based on molecular, immunological and histochemical techniques is providing new insights into these mechanisms. Accepted: 29 October 1996     

Effects of Pinus sylvestris root growth and mycorrhizosphere development on bacterial carbon source utilization and hydrocarbon oxidation in forest and petroleum-contaminated soils

The hypothesis that Pinus sylvestris L. root and mycorrhizosphere development positively influences bacterial community-linked carbon source utilization, and drives a concomitant reduction in mineral oil levels in a petroleum hydrocarbon- (PHC-) contaminated soil was confirmed in a forest ecosystem-based phytoremediation simulation. Seedlings were grown for 9 months in large petri dish microcosms containing either forest humus or humus amended with cores of PHC-contaminated soil. Except for increased root biomass in the humus/PHC treatment, there were no other significant treatment-related differences in plant growth and needle C and N status. Total cell and culturable bacterial (CFU) densities significantly increased in both rhizospheres and mycorrhizospheres that actively developed in the humus and PHC-contaminated soil. Mycorrhizospheres (mycorrhizas and extramatrical mycelium) supported the highest numbers of bacteria. Multivariate analyses of bacterial community carbon source utilization profiles (Biolog GN microplate) from different rhizosphere, mycorrhizosphere, and bulk soil compartments, involving principal component and correspondence analysis, highlighted three main niche-related groupings. The respective clusters identified contained bacterial communities from (i) unplanted bulk soils, (ii) planted bulk PHC and rhizospheres in PHC-contaminated soils, and (iii) planted bulk humus and rhizosphere/mycorrhizosphere-influenced humus, and mycorrhizosphere-influenced PHC contaminated soil. Correspondence analysis allowed further identification of amino acid preferences and increased carboxylic/organic acid preferences in rhizosphere and mycorrhizosphere compartments. Decreased levels of mineral oil (non-polar hydrocarbons) were detected in the PHC-contaminated soil colonized by pine roots and mycorrhizal fungi. These data further support our view that mycorrhizosphere development and function plays a central role in controlling associated bacterial communities and their degradative activities in lignin-rich forest humus and PHC-contaminated soils.     

Two Invasive Plants Alter Soil Microbial Community Composition in Serpentine Grasslands

Plant invasions pose a serious threat to native ecosystem structure and function. However, little is known about the potential role that rhizosphere soil microbial communities play in facilitating or resisting the spread of invasive species into native plant communities. The objective of this study was to compare the microbial communities of invasive and native plant rhizospheres in serpentine soils. We compared rhizosphere microbial communities, of two invasive species, Centaurea solstitialis (yellow starthistle) and Aegilops triuncialis (barb goatgrass), with those of five native species that may be competitively affected by these invasive species in the field (Lotus wrangelianus, Hemizonia congesta, Holocarpha virgata, Plantago erecta, and Lasthenia californica). Phospholipid fatty acid analysis (PLFA) was used to compare the rhizosphere microbial communities of invasive and native plants. Correspondence analyses (CA) of PLFA data indicated that despite yearly variation, both starthistle and goatgrass appear to change microbial communities in areas they invade, and that invaded and native microbial communities significantly differ. Additionally, rhizosphere microbial communities in newly invaded areas are more similar to the original native soil communities than are microbial communities in areas that have been invaded for several years. Compared to native plant rhizospheres, starthistle and goatgrass rhizospheres have higher levels of PLFA biomarkers for sulfate reducing bacteria, and goatgrass rhizospheres have higher fatty acid diversity and higher levels of biomarkers for sulfur-oxidizing bacteria, and arbuscular mycorrhizal fungi. Changes in soil microbial community composition induced by plant invasion may affect native plant fitness and/or ecosystem function.