Arbuscular mycorrhizal community composition associated with two plant species in a grassland ecosystem

Arbuscular mycorrhizal (AM) fungi are biotrophic symbionts colonizing about two-thirds of land plant species and found in all ecosystems. They are of major importance in plant nutrient supply and their diversity is suggested to be an important determinant of plant community composition. The diversity of the AM fungal community composition in the roots of two plant species (Agrostis capillaris and Trifolium repens) that co-occurred in the same grassland ecosystem was characterized using molecular techniques. We analysed the small subunit (SSU) ribosomal RNA gene amplified from a total root DNA extract using AM fungal-specific primers. A total of 2001 cloned fragments from 47 root samples obtained on four dates were analysed by restriction fragment length polymorphism, and 121 of them were sequenced. The diversity found was high: a total of 24 different phylotypes (groups of phylogenetically related sequences) colonized the roots of the two host species. Phylogenetic analyses demonstrate that 19 of these phylotypes belonged to the Glomaceae, three to the Acaulosporaceae and two to the Gigasporaceae. Our study reveals clearly that the AM fungal community colonizing T. repens differed from that colonizing A. capillaris, providing evidence for AM fungal host preference. In addition, our results reveal dynamic changes in the AM fungal community through time.     

Correlation analysis between arbuscular mycorrhizal fungal community and host plant phylogeny

 为弄清丛枝菌根(arbuscular mycorrhiza, AM)真菌群落随宿主植物演化的变异规律,通过对MaarjAM数据库进行数据挖掘, 根据每个分子虚拟种(virtual taxa, VT)包含的DNA序列不少于5条的标准, 筛选出188种菌根植物。通过分析植物与其根内AM真菌的关系发现: AM真菌的物种丰富度随着寄主植物的分化而增加; 在不同的植物系统类群中, AM真菌的物种丰富度显著不同; 在起源时间较晚的被子植物和裸子植物中, AM真菌的物种丰富度显著高于起源较早的苔类、角苔类和蕨类植物类群, 而与寄生植物共生的AM真菌物种丰富度与早期植物无显著差异; 不同寄主植物进化类群间AM真菌组成差异显著。以上结果表明: AM真菌群落随着寄主植物进化而发生变化。在进化过程中, 寄主植物倾向于选择保留共生效率较高的AM真菌。     

丛枝菌根真菌群落与植物系统发育的相关性分析

为弄清丛枝菌根(arbuscular mycorrhiza, AM)真菌群落随宿主植物演化的变异规律,通过对MaarjAM数据库进行数据挖掘, 根据每个分子虚拟种(virtual taxa, VT)包含的DNA序列不少于5条的标准, 筛选出188种菌根植物。通过分析植物与其根内AM真菌的关系发现: AM真菌的物种丰富度随着寄主植物的分化而增加; 在不同的植物系统类群中, AM真菌的物种丰富度显著不同; 在起源时间较晚的被子植物和裸子植物中, AM真菌的物种丰富度显著高于起源较早的苔类、角苔类和蕨类植物类群, 而与寄生植物共生的AM真菌物种丰富度与早期植物无显著差异; 不同寄主植物进化类群间AM真菌组成差异显著。以上结果表明: AM真菌群落随着寄主植物进化而发生变化。在进化过程中, 寄主植物倾向于选择保留共生效率较高的AM真菌。     

泰山丛枝菌根真菌群落结构特征

2007年对泰山植被根围内丛枝菌根(arbuscular mycorrhiza,AM)真菌群落组成、数量、分布及其与植物多样性的关系进行了研究。从泰山傲徕峰、黑龙潭库区等样地共分离出4属16种AM真菌:球囊霉属Glomus 9种、无梗囊霉属Acaulospora 4种、巨孢囊霉属Gigaspora 2种和盾巨孢囊霉属Scutellospora1种。其中,球囊霉属Glomus及聚球囊霉Glomus fasciculatum的孢子密度、相对多度、分布频度和重要值均最高,分别为泰山植被区根围内AM真菌优势属和优势种。各样地之间Sorenson相似系数在0.60和0.85之间。植被数量与孢子密度(r=0.80,p0.01)、植物种的丰富度与AM真菌种的丰富度(r=0.77,p0.01)以及与孢子密度(r=0.59,p0.01)均呈极显著正相关关系。研究结果表明植物多样性对于提高AM真菌多样性发挥极为重要的作用。     

Arbuscular mycorrhizal fungi differ in affecting the flowering of a host plant under two soil phosphorus conditions

Aims Studies have showed that arbuscular mycorrhizal fungi (AMF) can greatly promote the growth of host plants, but how AMF affect flowering phenology of host plants is not well known. Here, we conducted a pot experiment to test whether life cycle and flowering phenology traits of host plant Medicago truncatula Gaertn can be altered by AMF under low and high soil phosphorus (P) levels.Methods The experiment was conducted in a greenhouse at Zhejiang University in China (120°19′E, 30°26′N) and had a completely randomized design with two factors: AMF treatments and soil P levels. Six AMF species (Acaulospora scrobiculata, As; Gigaspora margarita, Gma; Funneliformis geosporum, Fg; Rhizophagus intraradices, Ri; Funneliformis mosseae, Fmo and Glomus tortuosum, Gt.) were used, and two soil P levels (24.0 and 5.7 mg kg^-1 Olsen-soluble P) were designed. The six AMF species were separately inoculated or in a mixture (Mix), and a non-AMF control (NAMF) was included. When plants began to flower, the number of flowers in each pot was recorded daily. During fruit ripening, the number of mature fruits was also recorded daily. After ~4 months, the biomass, biomass P content and AMF colonization of host plant were measured. Correlation between root colonization and first flowering time, or P content and first flowering time was analyzed.Important findings Under the low P level, first flowering time negatively correlated with root colonization and biomass P. Only host plants with AMF species As, Fg, Ri, or Mix were able to complete their life cycle within 112 days after sowing. And treatment with AMF species Fg, Gt, or As resulted in two periods of rapid flower production while other fungi treatments resulted in only one within 112 days after sowing. The cumulative number of flowers produced and biomass P content were highest with species Fg. Host biomass allocation significantly differed depending on the species of AMF. Under both soil P levels, the host plant tended to allocate more biomass to fruits in the Mix treatment than in the other treatments. These results indicated that the effects of AMF on host flowering phenology and biomass allocation differed depending on AMF species and soil P levels.     

Arbuscular mycorrhizal fungal communities in plant roots are not random assemblages

We investigated whether arbuscular mycorrhizal fungal (AMF) communities in plant roots are random subsets of the local taxon pool or whether they reflect the action of certain community assembly rules. We studied AMF small subunit rRNA gene sequence groups in the roots of plant individuals belonging to 11 temperate forest understorey species. Empirical data were compared with null models assuming random association. Distinct fungal species pools were present in young and old successional forest. In both forest types, the richness of plant-AMF associations was lower than expected by chance, indicating a degree of partner selectivity. AMF communities were generally not characteristic of individual plant species, but those associated with ecological groups of plant species - habitat generalists and forest specialists - were nonrandom subsets of the available pool of fungal taxa and differed significantly from each other. Moreover, these AMF communities were the least distinctive in spring, but developed later in the season. Comparison with a global database showed that generalist plants tend to associate with generalist AMF. Thus, the habitat range of the host and a possible interaction with season played a role in the assembly of AMF communities in individual plant root systems.     

Arbuscular mycorrhizal fungal propagules in a salt marsh

The tolerance of indigenous arbuscular mycorrhizal fungi (AMF) to stressful soil conditions and the relative contribution of spores of these fungi to plant colonization were examined in a Portuguese salt marsh. Glomus geosporum is dominant in this salt marsh. Using tetrazolium as a vital stain, a high proportion of field-collected spores were found to be metabolically active at all sampling dates. Spore germination tests showed that salt marsh spores were not affected by increasing levels of salinity, in contrast to two non-marsh spore isolates, and had a significantly higher ability to germinate under increased levels of salinity (20) than in the absence of or at low salinity (10). Germination of salt marsh spores was not affected by soil water levels above field capacity, in contrast to one of the two non-marsh spore isolates. For the evaluation of infectivity, a bioassay was established with undisturbed soil cores (containing all types of AM fungal propagules) and soil cores containing only spores as AM fungal propagules. Different types of propagules were able to initiate and to expand the root colonization of a native plant species, but spores were slower than mycelium and/or root fragments in colonizing host roots. The AM fungal adaptation shown by this study may explain the maintenance of AMF in salt marshes.     

Arbuscular mycorrhizal fungal community differs between a coexisting native shrub and introduced annual grass

Arbuscular mycorrhizal fungi (AMF) have been implicated in non-native plant invasion success and persistence. However, few studies have identified the AMF species associating directly with plant invaders, or how these associations differ from those of native plant species. Identifying changes to the AMF community due to plant invasion could yield key plant–AMF interactions necessary for the restoration of native plant communities. This research compared AMF associating with coexisting Bromus tectorum, an invasive annual grass, and Artemisia tridentata, the dominant native shrub in western North America. At three sites, soil and root samples from Bromus and Artemisia were collected. Sporulation was induced using trap cultures, and spores were identified using morphological characteristics. DNA was extracted from root and soil subsamples and amplified. Sequences obtained were aligned and analyzed to compare diversity, composition, and phylogenetic distance between hosts and sites. Richness of AMF species associated with Artemisia in cultures was higher than AMF species associated with Bromus. Gamma diversity was similar and beta diversity was higher in AMF associated with Bromus compared to Artemisia. AMF community composition differed between hosts in both cultures and roots. Two AMF species (Archaeospora trappei and Viscospora viscosum) associated more frequently with Artemisia than Bromus across multiple sites. AMF communities in Bromus roots were more phylogenetically dispersed than in Artemisia roots, indicating a greater competition for resources within the invasive grass. Bromus associated with an AMF community that differed from Artemisia in a number of ways, and these changes could restrict native plant establishment.     

Arbuscular mycorrhizal fungal communities change among three stages of primary sand dune succession but do not alter plant growth

Plant interactions with soil biota could have a significant impact on plant successional trajectory by benefiting plants in a particular successional stage over others. The influence of soil mutualists such as mycorrhizal fungi is thought to be an important feedback component, yet they have shown benefits to both early and late successional plants that could either retard or accelerate succession. Here we first determine if arbuscular mycorrhizal (AM) fungi differ among three stages of primary sand dune succession and then if they alter growth of plants from particular successional stages. We isolated AM fungal inoculum from early, intermediate or late stages of a primary dune succession and compared them using cloning and sequencing. We then grew eight plant species that dominate within each of these successional stages with each AM fungal inoculum. We measured fungal growth to assess potential AM functional differences and plant growth to determine if AM fungi positively or negatively affect plants. AM fungi isolated from early succession were more phylogenetically diverse relative to intermediate and late succession while late successional fungi consistently produced more soil hyphae and arbuscules. Despite these differences, inocula from different successional stages had similar effects on the growth of all plant species. Host plant biomass was not affected by mycorrhizal inoculation relative to un‐inoculated controls. Although mycorrhizal communities differ among primary dune successional stages and formed different fungal structures, these differences did not directly affect the growth of plants from different dune successional stages in our experiment and therefore may be less likely to directly contribute to plant succession in sand dunes.     

Arbuscular mycorrhizal fungal community composition associated with Juniperus brevifolia in native Azorean forest

The communities of glomeromycotan fungi (arbuscular mycorrhizal fungi, AMF) under native Juniperus brevifolia forest from two Azorean islands, Terceira and São Miguel, were compared, mainly by spore morphology, and when possible, by molecular analysis. Thirty-nine morphotypes were detected from 12 genera. Glomeromycotan fungal richness was similar in Terceira and São Miguel, but significantly different among the four fragments of native forest. Spore diversity and community composition differed significantly between the two islands. The less degraded island, Terceira, showed 10 exclusive morphotypes including more rare types, whereas the more disturbed forest on São Miguel showed 13 morphs, mostly of common types. Forests from Terceira were dominated by Acaulosporaceae and Glomeraceae. Whereas members of Acaulosporaceae, Glomeraceae and Ambisporaceae were most frequent and abundant in those from São Miguel. Spore abundance was greatest on Terceira, and correlated with soil chemical properties (pH), average monthly temperature and relative humidity.     

Arbuscular mycorrhizal symbiosis on serpentine soils: the effect of native fungal communities on different Knautia arvensis ecotypes

Serpentine soils represent a unique environment that imposes multiple stresses on vegetation (low Ca/Mg ratios, macronutrient deficiencies, elevated heavy metal concentrations and drought). Under these conditions, a substantial role of arbuscular mycorrhizal (AM) symbiosis can be anticipated due to its importance for plant nutrition and stress alleviation. We tested whether serpentine and non-serpentine populations of Knautia arvensis (Dipsacaceae) differ in the benefits derived from native AM fungal communities. Four serpentine and four non-serpentine populations were characterised in terms of mycorrhizal colonisation and soil characteristics. The serpentine populations showed significantly lower mycorrhizal colonisation than their non-serpentine counterparts. The mycorrhizal colonisation positively correlated with soil pH, Ca and K concentrations and Ca/Mg ratio. Seedlings from each population were then grown for 3 months in their sterilised native substrates, either uninoculated or reinoculated with native AM fungi. Two serpentine and two non-serpentine populations responded positively to mycorrhizal inoculation, while no significant change in plant growth was observed in the remaining populations. Contrary to our hypothesis, serpentine populations of K. arvensis did not show higher mycorrhizal growth dependence than non-serpentine populations when grown in their native soils and inoculated with native AM fungi.     

Land use and host neighbor identity effects on arbuscular mycorrhizal fungal community composition in focal plant rhizosphere

Arbuscular mycorrhizal fungi (AMF) provide a number of ecosystem services as important members of the soil microbial community. Increasing evidence suggests AMF diversity is at least partially controlled by the identities of plants in the host plant neighborhood. However, much of this evidence comes from greenhouse studies or work in invaded systems dominated by single plant species, and has not been tested in species-rich grasslands. We worked in 67 grasslands spread across the three German Biodiversity Exploratories that are managed primarily as pastures and meadows, and collected data on AMF colonization, AMF richness, AMF community composition, plant diversity, and land use around focal Plantago lanceolata plants. We analyzed the data collected within each Exploratory (ALB Schwäbische Alb, HAI Hainich-Dün, SCH Schorfheide-Chorin) separately, and used variance partitioning to quantify the contribution of land use, host plant neighborhood, and spatial arrangement to the effect on AMF community composition. We performed canonical correspondence analysis to quantify the effect of each factor independently by removing the variation explained by the other factors. AMF colonization declined with increasing land use intensity (LUI) along with concurrent increases in non-AMF, suggesting that the ability of AMF to provide protection from pathogens declined under high LUI. In ALB and HAI mowing frequency and percent cover of additional P. lanceolata in the host plant neighborhood were important for AMF community composition. The similar proportional contribution of land use and host neighborhood to AMF community composition in a focal plant rhizosphere suggests that the diversity of this important group of soil microbes is similarly sensitive to changes at large and small scales.     

Arbuscular mycorrhizal fungi alter plant community composition along a grazing gradient in Inner Mongolia Steppe

Arbuscular mycorrhizal fungi (AMF) have a significant influence on plant productivity and diversity in non-grazing grassland. However, the interactive effects between grazing intensity and AMF on plant community composition in natural grassland communities are not well known. We conducted a field experiment that manipulated AMF colonization and grazing intensity to study the impact of AMF suppression on plant community composition and nutrient status over 2 years (2015–2016) with contrasting rainfall levels. We found that AMF root colonization was significantly reduced by the application of the fungicide benomyl as a soil drench. Grazing intensity regulated plant community composition and aboveground biomass mainly by reducing the growth of Leymus chinensis over 2 years. AMF suppression increased the growth of Chenopodium glaucum, but it did not alter other plant species across all grazing intensities. The effects of AMF suppression on plant community composition changed along a grazing gradient considerably between years: AMF suppression increased the biomass of C. glaucum across all grazing intensities in 2015, but slightly increased it in 2016. Interactions between AMF suppression and grazing intensity altered the phosphorus concentration of Stipa grandis and Cleistogenes squarrosa in 2015 but not in 2016. AMF suppression decreased the shoot phosphorus content of L. chinensis but increased that of C. glaucum across all grazing intensities. Our results indicate that grazing intensity substantially alters aboveground community biomass and affects growth of dominant species; AMF by itself have limited effects on plant communities along a grazing gradient in typical steppe.     

Adaptation to different host plant ages facilitates insect divergence without a host shift

Host shifts and subsequent adaption to novel host plants are important drivers of speciation among phytophagous insects. However, there is considerably less evidence for host plant-mediated speciation in the absence of a host shift. Here, we investigated divergence of two sympatric sister elm leaf beetles, Pyrrhalta maculicollis and P. aenescens, which feed on different age classes of the elm Ulmus pumila L. (seedling versus adult trees). Using a field survey coupled with preference and performance trials, we show that these beetle species are highly divergent in both feeding and oviposition preference and specialize on either seedling or adult stages of their host plant. An experiment using artificial leaf discs painted with leaf surface wax extracts showed that host plant chemistry is a critical element that shapes preference. Specialization appears to be driven by adaptive divergence as there was also evidence of divergent selection; beetles had significantly higher survival and fecundity when reared on their natal host plant age class. Together, the results identify the first probable example of divergence induced by host plant age, thus extending how phytophagous insects might diversify in the absence of host shifts.     

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

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

Arbuscular mycorrhizal fungi and plant symbiosis in a saline-sodic soil

The seasonality of arbuscular mycorrhizal (AM) fungi–plant symbiosis in Lotus glaber Mill. and Stenotaphrum secundatum (Walt.) O.K. and the association with phosphorus (P) plant nutrition were studied in a saline-sodic soil at the four seasons during a year. Plant roots of both species were densely colonized by AM fungi (90 and 73%, respectively in L. glaber and S. secundatum) at high values of soil pH (9.2) and exchangeable sodium percentage (65%). The percentage of colonized root length differed between species and showed seasonality. The morphology of root colonization had a similar pattern in both species. The arbuscular colonization fraction increased at the beginning of the growing season and was positively associated with increased P concentration in both shoot and root tissue. The vesicular colonization fraction was high in summer when plants suffer from stress imposed by high temperatures and drought periods, and negatively associated with P in plant tissue. Spore and hyphal densities in soil were not associated with AM root colonization and did not show seasonality. Our results suggest that AM fungi can survive and colonize L. glaber and S. secundatum roots adapted to extreme saline-sodic soil condition. The symbiosis responds to seasonality and P uptake by the host altering the morphology of root colonization.