Ectomycorrhizal and arbuscular mycorrhizal colonization of two species of floodplain willows

To understand the relationships between the distribution of Chosenia arbutifolia and Salix sachalinensis and their mycorrhizal colonization, changes in the quality and types of ectomycorrhizas and arbuscular mycorrhizas of the seedlings of two species were studied at five different sites with different soil conditions in the floodplain of the Satsunai River, Hokkaido. High ectomycorrhizal and low arbuscular mycorrhizal colonization were found in roots of both plants. Ectomycorrhizal colonization of S. sachalinensis in wet sandy or muddy soil conditions was at the same level as that in dry gravelly sites. In contrast, ectomycorrhizal colonization of C. arbutifolia seedlings was lower from wet sandy sites than that from dry gravelly sites. In all study sites, the same three morphological types of ectomycorrhizas were dominant.     

Occurrence of arbuscular mycorrhiza on aged Eucalyptus

Eucalyptus despite the fact that Eucalyptus seedlings do form both endomycorrhiza and ectomycorrhiza early during their developement. In the present study, all the structures of arbuscular mycorrhiza were observed within roots of four Eucalyptus species of 15, 17 and more than 50 years old at three different sites in northern Algeria. Arbuscular mycorrhiza frequency was assessed in roots of 15-years old Eucalyptus camaldulensis species, during two periods in 2 consecutive years (July and November of 1996 and 1997). Intensity of root colonization was dependent on the time of sampling and attained 42% in July 1997. Accepted: 17 September 1999     

A history of research on arbuscular mycorrhiza

This is not a review paper in the traditional sense, of which there are many. Three of the most influential reviews that summarized well some of the older literature include those by Nicolson (1967), Gerdemann (1968) and Mosse (1973). Instead, in this brief and incomplete work, we attempt to show the historical development of research on arbuscular mycorrhizas. We owe much to those who have written other historical accounts, including Rayner (1926–1927), Trappe and Berch (1985), Mosse (1985), Schenck (1985), Harley (1991) and Allen (1996), but the contents of this work naturally reflect our own ignorance, interests and biases. It was often difficult to distinguish between the historical and the contemporary, and we did not use any specific cutoff date in making this distinction. The degree to which we include contemporary literature was determined by our own assessment of its connectedness to older literature. In any case, we hope this will be of some interest to those of you who study the arbuscular mycorrhiza, and that it will serve the purpose of providing what we consider to be an important historical context for current researchers. We wish you good fortune in your research.Taken from a paper presented at the COST 8.38 meeting AM Research in Europe (Pisa, Italy): The Dawning of a New Millenium     

Plant signals and fungal perception during arbuscular mycorrhiza establishment

Arbuscular mycorrhizal (AM) fungi are obligate symbionts that need their plant hosts to complete their life cycle. In the absence of the plant, germlings arrest growth after a few days and retract most of their cytoplasm back into the multinuclear spores. The spores can germinate again during more favorable conditions. How AM fungi recognize compatible host roots and activate their symbiotic program is not yet understood. However, research in this field in the last years has shed light into this topic. We, and others, have approached some of these aspects by studying changes in fungal gene expression observed at early stages of development, before and at the plant recognition stage in an attempt to identify genes and proteins featuring as key regulators in the switch between the asymbiotic and symbiotic style of life. The molecular bases of this recognition process are now starting to be understood and point to common signaling pathways shared with other microbe-plant associations and to arbuscular mycorrhiza specific signaling pathways.     

Interspecific competition and arbuscular mycorrhiza: Importance for the coexistence of two calcareous grassland species

Two naturally coexisting grassland species—Centaurea jacea (often predominating) andFragaria vesca (subordinate) were grown together in a pot experiment of factorial design, where competition and arbuscular mycorrhiza (AM) inoculation were used as treatments. The effects of competition were one-sided, i.e. the mass ofF. vesca decreased relatively more than that ofC. jacea as a result of competition. The root and total mass ofC. jacea increased with AM inoculation whileF. vesca did not respond. The mass difference betweenC. jacea andF. vesca in a particular pot increased when plants were mycorrhizal, mostly due to the mass increase ofC. jaceae. This can be explained by the differential response of these species to AM. We did not find any indirect indication of the interplant transfer of resources. The results of this experiment show the more unbalanced competition (larger differences in biomass) resulting from AM infection of plants. *** DIRECT SUPPORT *** A02DO006 00010     

环境污染物对丛枝菌根(AM)形成及功能的影响

丛枝菌根(AM)具有植物和微生物的双重特性,在污染土壤修复中受到越来越多的重视.AM在修复污染土壤的同时,也深受污染物毒害的影响,从而降低AM在污染土壤修复中的作用.如何减少环境污染物对AM的不利影响,是AM应用中需要考虑的问题.从有机和无机污染物角度, 综述了不同污染物对AM形成及功能的影响,并分析了可能的影响机理.大量研究表明,无论是有机污染物还是无机污染物,都会对AM的结构、形成和功能产生破坏性影响,主要表现在孢子萌发、侵染率、菌丝伸长受抑制等.有机污染物可能通过影响光合产物向AM真菌的分配, 间接影响AM真菌的活性,而重金属则通过抑制AM真菌活性, 直接对其产生影响.     

Accumulation of reactive oxygen species in arbuscular mycorrhizal roots

We investigated the accumulation of reactive oxygen species (ROS) in arbuscular mycorrhizal (AM) roots from Medicago truncatula, Zea mays and Nicotiana tabacum using three independent staining techniques. Colonized root cortical cells and the symbiotic fungal partner were observed to be involved in the production of ROS. Extraradical hyphae and spores from Glomus intraradices accumulated small levels of ROS within their cell wall and produced ROS within the cytoplasm in response to stress. Within AM roots, we observed a certain correlation of arbuscular senescence and H₂O₂ accumulation after staining by diaminobenzidine (DAB) and a more general accumulation of ROS close to fungal structures when using dihydrorhodamine 123 (DHR 123) for staining. According to electron microscopical analysis of AM roots from Z. mays after staining by CeCl₃, intracellular accumulation of H₂O₂ was observed in the plant cytoplasm close to intact and collapsing fungal structures, whereas intercellular H₂O₂ was located on the surface of fungal hyphae. These characteristics of ROS accumulation in AM roots suggest similarities to ROS accumulation during the senescence of legume root nodules.     

模拟增温和丛枝菌根对门源草原毛虫幼虫生长发育的影响

采用开顶式生长室(Open top chamber, OTC)模拟增温和苯菌灵抑制丛枝菌根研究上述两种因素综合作用下门源草原毛虫幼虫的生长速率、蛹化时间和蛹重。结果表明,增温和丛枝菌根抑制及其交互作用均对门源草原毛虫幼虫生长速率产生了显著影响。相比对照组而言,增温使该指标升高了34%。丛枝菌根抑制未对上述指标产生显著影响。增温和丛枝菌根抑制的交互作用使门源草原毛虫幼虫生长速率较对照组升高了16%,而较增温组降低了13%。增温处理下雌、雄幼虫的蛹化时间分别为204、218 d,而不增温处理下分别为212、223 d。增温使得雌、雄幼虫的蛹化时间较不增温处理分别提前了2%和4%。增温和不增温处理下的雌、雄虫蛹化时间差分别为15、12 d。增温将上述时间差扩大了25%。此外,增温及其与丛枝菌根抑制的交互作用对门源草原毛虫雌虫蛹重的影响显著,而对于雄虫的蛹重来说,仅增温处理的影响显著。增温和增温丛枝菌根抑制处理,使得雌蛹重较对照组增大了22%和8%。增温使雄蛹重增大了18%。首次研究了增温和丛枝菌根对植食性昆虫的综合影响。     

Microbial ecology of the arbuscular mycorrhiza

Arbuscular mycorrhizal (AM) fungi interact with a wide variety of organisms during all stages of their life. Some of these interactions such as grazing of the external mycelium are detrimental, while others including interactions with plant growth promoting rhizobacteria (PG PR) promote mycorrhizal functioning. Following mycorrhizal colonisation the functions of the root become modified, with consequences for the rhizosphere community which is extended into the mycorrhizosphere due to the presence of the AM external mycelium. However, we still know relatively little of the ecology of AM fungi and, in particular, the mycelium network under natural conditions. This area merits attention in the future with emphasis on the fungal partner in the association rather than the plant which has been the focus in the past.     

丛枝菌根对枳实生苗抗旱性的影响研究

在自然水分干旱胁迫和胁迫解除复水条件下,研究了丛枝菌根对1年生枳实生苗生长和抗旱性的影响.结果表明,接种丛枝菌根真菌Glomusmosseae93显著增加枳实生苗的株高、茎粗和鲜重,提高了幼苗移栽成活率.在自然水分干旱胁迫和胁迫解除复水过程中,丛枝菌根提高或者极显提高了叶片可溶性糖含量、叶片和根系的可溶性蛋白质含量、超氧化物歧化酶活性、过氧化物酶活性和过氧化氢酶活性,从而提高了枳实生苗的渗透调节能力,增强了其保护系统能力,降低了细胞膜脂过氧化,使枳实生苗抗旱能力增强.表明丛枝菌根真菌增强寄主植物抗旱能力的作用机制与保护系统相关.     

丛枝菌根（AM）生物技术在现代农业体系中的生态意义

菌根是植物根系与特定的土壤真菌形成的共生体,有利于生态系统中养分循环,协助植物抵御不良环境胁迫．自然条件下,大多数植物表现一定的菌根依赖性,在植株根系发育过程中如能与适宜的菌根真菌形成良好的菌根结构,可提高产量,改善品质,其中丛枝菌根是最普遍的类型．丛枝菌根帮助植物抵御不良环境胁迫及病虫害,促进植物健康生长,可减少化学肥料、杀虫剂施用量,以减少对环境、生态不利的化学物质施用量．丛枝菌根共生体可加速根系生长,提高对移动性低的无机离子吸收,加速养分循环利用,增强植物对不良胁迫(生物与非生物)因素的耐受力,形成良好的土壤结构,提高植物群体的多样性．文章综述了丛枝菌根真菌生态特征,丛枝菌根对寄主植物的影响,丛枝菌根生物技术应用于农业体系的生态意义及其应用潜力．     

Effects of arbuscular mycorrhiza and phosphorus application on artemisinin concentration in <Emphasis Type="Italic">Artemisia annua</Emphasis> L.

Annual wormwood (Artemisia annua L.) produces an array of complex terpenoids including artemisinin, a compound of current interest in the treatment of drug-resistant malaria. However, this promising antimalarial compound remains expensive and is hardly available on the global scale. Synthesis of artemisinin has not been proved to be feasible commercially. Therefore, increase in yield of naturally occurring artemisinin is an important area of investigation. The effects of inoculation by two arbuscular mycorrhizal (AM) fungi, Glomus macrocarpum and Glomus fasciculatum, either alone or supplemented with P-fertilizer, on artemisinin concentration in A. annua were studied. The concentration of artemisinin was determined by reverse-phase high-performance liquid chromatography with UV detection. The two fungi significantly increased concentration of artemisinin in the herb. Although there was significant increase in concentration of artemisinin in nonmycorrhizal P-fertilized plants as compared to control, the extent of the increase was less compared to mycorrhizal plants grown with or without P-fertilization. This suggests that the increase in artemisinin concentration may not be entirely attributed to enhanced P-nutrition and improved growth. A strong positive linear correlation was observed between glandular trichome density on leaves and artemisinin concentration. Mycorrhizal plants possessed higher foliar glandular trichome (site for artemisinin biosynthesis and sequestration) density compared to nonmycorrhizal plants. Glandular trichome density was not influenced by P-fertilizer application. The study suggests a potential role of AM fungi in improving the concentration of artemisinin in A. annua.     

Herbivory and intraspecific competition in a stream caddisfly population

Summary Field experiments were conducted to assess the effects of different population densities of the herbivorous caddisfly Helicopsyche borealis on periphyton biomass and on its own growth rate in Big Sulphur Creek, a third-order stream in northern California, USA. Stream enclosures were used to vary grazer density from one-eighth to twice natural density (1/8X–2X) in two experiments (35 d and 60 d), which spanned the period of most rapid larval growth. Periphyton biomass and chlorophyll a were inversely related to grazer density. Grazer densities of 1/8X–1/2X moderately reduced periphyton when compared to an ungrazed control, whereas densities of 1X–2X greatly depleted periphyton. The growth rate of H. borealis larvae declined with increasing larval density. Growth rate was highest at densities of 1/8X–1/2X; larvae grew more slowly at 1X and showed no growth at 2X. Weekly supplementation of periphyton to 1/4X, 1X, and 2X densities significantly increased the final body mass of larvae at 1X and 2X (by 26% and 50%, respectively, compared to unsupplemented larvae) but did not change the body mass of larvae at 1/4X. These results suggest that periphyton is a limiting resource in Big Sulphur Creek and that H. borealis larvae compete exploitatively for that resource. Intraspecific competition may be an important, but often overlooked, feature of many herbivore populations in streams.     

Field response of wheat to arbuscular mycorrhizal fungi and drought stress

Mycorrhizal plants often have greater tolerance to drought than nonmycorrhizal plants. This study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi inoculation on growth, grain yield and mineral acquisition of two winter wheat (Triticum aestivum L.) cultivars grown in the field under well-watered and water-stressed conditions. Wheat seeds were planted in furrows after treatment with or without the AM fungi Glomus mosseae or G. etunicatum. Roots were sampled at four growth stages (leaf, tillering, heading and grain-filling) to quantify AM fungi. There was negligible AM fungi colonization during winter months following seeding (leaf sampling in February), when soil temperature was low. During the spring, AM fungi colonization increased gradually. Mycorrhizal colonization was higher in well-watered plants colonized with AM fungi isolates than water-stressed plants. Plants inoculated with G. etunicatum generally had higher colonization than plants colonized with G. mosseae under both soil moisture conditions. Biomass and grain yields were higher in mycorrhizal than nonmycorrhizal plots irrespective of soil moisture, and G. etunicatum inoculated plants generally had higher biomass and grain yields than those colonized by G. mosseae under either soil moisture condition. The mycorrhizal plants had higher shoot P and Fe concentrations than nonmycorrhizal plants at all samplings regardless of soil moisture conditions. The improved growth, yield and nutrient uptake in wheat plants reported here demonstrate the potential of mycorrhizal inoculation to reduce the effects of drought stress on wheat grown under field conditions in semiarid areas of the world.     

Influence of two legume species on hyphal production and activity of two arbuscular mycorrhizal fungi

 Two arbuscular mycorrhizal (AM) fungi (Glomus mosseae and G. intraradices) were compared for abundance of intraradical and soil-borne hyphae in association with Astragalus sinicum, a small-seeded, and Glycine max, a large-seeded legume. A. sinicum was more responsive than G. max to mycorrhizal formation, especially at early growth stages. Biomass allocation was greater in roots than shoots for mycorrhizal A. sinicum, while the opposite was true for G. max. Hyphal development in root and soil compartments was estimated by trypan blue staining and after staining for succinate dehydrogenase (SDH) or alkaline phosphatase (ALP) activity. Total fungal abundance increased steadily in roots and soil with time to a maximum 8 weeks after planting. SDH- and ALP-active AM hyphae increased in roots during plant growth but decreased in soil at later harvests. Mycorrhizal root mass in A. sinicum and G. max increased about 14-fold and 2.5-fold, respectively, but total length of soil hyphae produced per plant differed little, so that the pattern of AM soil to root abundance of the two fungi varied considerably with the host plant. Accepted: 23 July 1997     

Effect of competition on stable carbon isotope ratios of two tussock grass species

Summary Previous studies have shown that plant carbon isotope composition varies when plants experience differences in water and nutrient availability. However, none have addressed the effect of root interactions, including competition for these soil resources, on carbon isotope ratios. We studied the effect of interspecific root interactions on the productivity and carbon isotope ratios of two Great Basin tussock grass species (Agropyron desertorum and Pseudoroegneria spicata). We compared grasses grown in mixture with sagebrush (Artemisia tridentara) to grasses in similar mixtures but where root interactions with sagebrush were limited by fiberglass partitions. During both years of the study, tussocks growing in competition with sagebrush produced tissue with more negative ¹³C values than grasses experiencing limited root interaction with sagebrush. The magnitude of this difference (0.5 to 0.9%) is similar to that found in other studies when soil fertility and moisture availability were altered.     

Environmental and genetic effects on the formation of ectomycorrhizal and arbuscular mycorrhizal associations in cottonwoods

Although both environment and genetics have been shown to affect the mycorrhizal colonization of host plants, the impacts of these factors on hosts that can be dually colonized by both ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) fungi are less understood. We examined the influence of environment and host crosstype on the EM and AM colonization of cottonwoods (Populus angustifolia and natural hybrids) by comparing levels of colonization of trees growing in common gardens that differed in elevation and soil type. We also conducted a supplemental watering experiment to determine the influence of soil moisture on AM and EM colonization. Three patterns emerged. First, garden location had a significant impact on mycorrhizal colonization, such that EM colonization was 30% higher and AM colonization was 85% lower in the higher elevation garden than the lower elevation garden. Second, crosstype affected total (EM + AM) colonization, but did not affect EM or AM colonization. Similarly, a significant garden × crosstype interaction was found for total colonization, but not for EM or AM colonization. Third, experimental watering resulted in 33% higher EM colonization and 45% lower AM colonization, demonstrating that soil moisture was a major driver of the mycorrhizal differences observed between the gardens. We conclude that environment, particularly soil moisture, has a larger influence on colonization by AM versus EM fungi than host genetics, and suggest that environmental stress may be a major determinant of mycorrhizal colonization in dually colonized host plants.     

The invasive plant species Centaurea maculosa alters arbuscular mycorrhizal fungal communities in the field

While several recent studies have described changes in microbial communities associated with exotic plant invasion, how arbuscular mycorrhizal fungi (AMF) communities respond to exotic plant invasion is not well known, despite the salient role of this group in plant interactions. Here, we use molecular methods (terminal restriction fragment length polymorphism analyses based on the large subunit of the rRNA gene) to examine AMF community structure in sites dominated by the invasive mycorrhizal forb, Centaurea maculosa Lam. (spotted knapweed), and in adjacent native grassland sites. Our results indicate that significant AMF community alteration occurs following C. maculosa invasion. Moreover, a significant reduction in the number of restriction fragment sizes was found for samples collected in C. maculosa-dominated areas, suggesting reduced AMF diversity. Extraradical hyphal lengths exhibited a significant, on average 24%, reduction in C. maculosa-versus native grass-dominated sites. As both AMF community composition and abundance were altered by C.maculosa invasion, these data are strongly suggestive of potential impacts on AMF-mediated ecosystem processes. Given that the composition of AMF communities has the potential to differentially influence different plant species, our results may have important implications for site restoration after weed invasion.     

The incidence of arbuscular mycorrhiza in two submerged Isoëtes species

We investigated the occurrence of arbuscular mycorrhizal fungi in the roots of Isoëtes lacustris and I. echinospora. These submerged lycopsids are the only macrophyte species inhabiting the bottom of two acidified glacial lakes in the Czech Republic. Arbuscular mycorrhizal (AM) fungi were detected in the roots of both species but the percentage of root colonization was both low and variable. Nevertheless, planting Littorella uniflora in the sediments from Isoëtes rhizosphere revealed high levels of viable AM propagules in both lakes. While AM colonization of Isoëtes roots did not exceed 25%, the average colonization of Littorella roots amounted to more than 80%. Although colonization of quillwort roots by AM fungi is evident, the taxonomic identity and role of these AM fungi in plant growth remain unclear. In addition to AM fungi, root-colonizing dark septate endophytic fungi were observed in both Isoëtes species.