不同施肥处理对丛枝菌根真菌生态分布的影响

研究了在东北海伦实验站长期定位培肥实验地不同施肥处理下丛枝菌根（Arbuscular Mycorrhizal,AM）真菌生长发育状况（包括侵染率、菌丝量和孢子数）,同时还分析了不同施肥处理下AM真菌群落生态分布和特征.结果表明施肥处理,尤其是磷肥（NP2K）处理显著降低AM真菌侵染玉米根系,而根外菌丝长度和孢子数并无显著变化,这和施肥处理下AM真菌的种群结构发生变化有关.随着土壤肥力的增高,土壤中AM真菌种的丰度和密度都有增加的趋势,而当肥力增高到一定程度后（磷肥和钾肥继续增加到NP2K和NPK2处理后）,土壤中AM真菌种的丰度和密度都有下降的趋势;从AM真菌属在不同肥力处理下出现的频度来看,Glomus属在7个处理中出现的频度最高,在每一个肥力处理中都有分布,Acaullospora属次之,Entrohospora属则只是出现在NK处理下;而Glomus属中出现频度最高的种是Glomus mosseae,其次是Glomus caledonium;再次是Glomus diaphanium,这说明施肥处理会影响到AM真菌种属的分布,进而影响到AM真菌的群落结构和生态分布.     

Aquaporin genes GintAQPF1 and GintAQPF2 from Glomus intraradices contribute to plant drought tolerance

Arbuscular mycorrhizal (AM) symbiosis, established between AM fungi (AMF) and roots of higher plants, occurs in most terrestrial ecosystems. It has been well demonstrated that AM symbiosis can improve plant performance under various environmental stresses, including drought stress. However, the molecular basis for the direct involvement of AMF in plant drought tolerance has not yet been established. Most recently, we cloned two functional aquaporin genes, GintAQPF1 and GintAQPF2, from AM fungus Glomus intraradices. By heterologous gene expression in yeast, aquaporin localization, activities and water permeability were examined. Gene expressions during symbiosis in expose to drought stress were also analyzed. Our data strongly supported potential water transport via AMF to host plants. As a complement, here we adopted the monoxenic culture system for AMF, in which carrot roots transformed by Ri-T DNA were cultured with Glomus intraradices in two-compartment Petri dishes, to verify the aquaporin gene functions in assisting AMF survival under polyethylene glycol (PEG) treatment. Our results showed that 25% PEG significantly upregulated the expression of two aquaporin genes, which was in line with the gene functions examined in yeast. We therefore concluded that the aquaporins function similarly in AMF as in yeast subjected to osmotic stress. The study provided further evidence to the direct involvement of AMF in improving plant water relations under drought stresses.     

Relatedness among arbuscular mycorrhizal fungi drives plant growth and intraspecific fungal coexistence

Arbuscular mycorrhizal fungi (AMF) form symbioses with most plant species. They are ecologically important determinants of plant growth and diversity. Considerable genetic variation occurs in AMF populations. Thus, plants are exposed to AMF of varying relatedness to each other. Very little is known about either the effects of coexisting AMF on plant growth or which factors influence intraspecific AMF coexistence within roots. No studies have addressed whether the genetics of coexisting AMF, and more specifically their relatedness, influences plant growth and AMF coexistence. Relatedness is expected to influence coexistence between individuals, and it has been suggested that decreasing ability of symbionts to coexist can have negative effects on the growth of the host. We tested the effect of a gradient of AMF genetic relatedness on the growth of two plant species. Increasing relatedness between AMFs lead to markedly greater plant growth (27% biomass increase with closely related compared to distantly related AMF). In one plant species, closely related AMF coexisted in fairly equal proportions but decreasing relatedness lead to a very strong disequilibrium between AMF in roots, indicating much stronger competition. Given the strength of the effects with such a shallow relatedness gradient and the fact that in the field plants are exposed to a steeper gradient, we consider that AMF relatedness can have a strong role in plant growth and the ability of AMF to coexist. We conclude that AMF relatedness is a driver of plant growth and that relatedness is also a strong driver of intraspecific coexistence of these ecologically important symbionts.     

Arbuscular mycorrhizal fungi alter plant allometry and biomass-density relationships

Background and Aims

Plant biomass–density relationships during self-thinning are determined mainly by allometry. Both allometry and biomass–density relationship have been shown to vary with abiotic conditions, but the effects of biotic interactions have not been investigated. Arbuscular mycorrhizal fungi (AMF) can promote plant growth and affect plant form. Here experiments were carried out to test whether AMF affect plant allometry and the self-thinning trajectory.

Methods

Two experiments were conducted on Medicago sativa L., a leguminous species known to be highly dependent on mycorrhiza. Two mycorrhizal levels were obtained by applying benomyl (low AMF) or not (high AMF). Experiment 1 investigated the effects of AMF on plant growth in the absence of competition. Experiment 2 was a factorial design with two mycorrhizal levels and two plant densities (6000 and 17 500 seeds m⁻²). Shoot biomass, root biomass and canopy radius were measured 30, 60, 90 and 120 d after sowing. The allometric relationships among these aspects of size were estimated by standardized major axis regression on log-transformed data.

Key Results

Shoot biomass in the absence of competition was lower under low AMF treatment. In self-thinning populations, the slope of the log (mean shoot biomass) vs. log density relationship was significantly steeper for the high AMF treatment (slope = –1·480) than for the low AMF treatment (–1·133). The canopy radius–biomass allometric exponents were not significantly affected by AMF level, but the root–shoot allometric exponent was higher in the low AMF treatment. With a high level of AMF, the biomass–density exponent can be predicted from the above-ground allometric model of self-thinning, while this was not the case when AMF were reduced by fungicide.

Conclusions

AMF affected the importance of below-ground relative to above-ground interactions and changed root vs. shoot allocation. This changed allometric allocation of biomass and altered the self-thinning trajectory.     

Positive Feedback between Mycorrhizal Fungi and Plants Influences Plant Invasion Success and Resistance to Invasion

Negative or positive feedback between arbuscular mycorrhizal fungi (AMF) and host plants can contribute to plant species interactions, but how this feedback affects plant invasion or resistance to invasion is not well known. Here we tested how alterations in AMF community induced by an invasive plant species generate feedback to the invasive plant itself and affect subsequent interactions between the invasive species and its native neighbors. We first examined the effects of the invasive forb Solidago canadensis L. on AMF communities comprising five different AMF species. We then examined the effects of the altered AMF community on mutualisms formed with the native legume forb species Kummerowia striata (Thunb.) Schindl. and on the interaction between the invasive and native plants. The host preferences of the five AMF were also assessed to test whether the AMF form preferred mutualistic relations with the invasive and/or the native species. We found that S. canadensis altered AMF spore composition by increasing one AMF species (Glomus geosporum) while reducing Glomus mosseae, which is the dominant species in the field. The host preference test showed that S. canadensis had promoted the abundance of AMF species (G. geosporum) that most promoted its own growth. As a consequence, the altered AMF community enhanced the competitiveness of invasive S. canadensis at the expense of K. striata. Our results demonstrate that the invasive S. canadensis alters soil AMF community composition because of fungal-host preference. This change in the composition of the AMF community generates positive feedback to the invasive S. canadensis itself and decreases AM associations with native K. striata, thereby making the native K. striata less dominant.     

The effects of salt stress and arbuscular mycorrhiza on plant neighbour effects and self-thinning

Abiotic and biotic factors can alter the nature and strength of plant–plant interactions and therefore self-thinning (density-dependent mortality), but few studies have looked at how such factors interact. We investigated how salt stress and arbuscular mycorrhizal fungi (AMF) influence plant neighbour effects and self-thinning in experimental populations of Medicago sativa. We obtained two mycorrhizal levels by applying the fungicide benomyl (low AMF) or not (high AMF) at three salinity levels (0.05%, 0.2% and 0.5%). In experiment 1, we investigated how salinity and AMF interact to influence plant interaction intensity using a neighbour removal treatment. In experiment 2, we investigated how self-thinning dynamics vary under salinity conditions and different AMF levels at two initial plant densities (6000 and 17,500 seeds m^?2). Shoot biomass and plant density were measured 30, 60 and 90 days after sowing. Standardized major axis regression was used to estimate self-thinning parameters. In experiment 1, AMF increased competitive plant neighbour effects when there was no salinity stress, but this enhancement was not significant with increasing salinity. In experiment 2, there were effects of salinity and AMF on the self-thinning trajectory. The slope of the log (mean shoot biomass per unit area) vs. log density relationship was significantly steeper for the high AMF treatment than for the low AMF treatment without salinity, but the effect of AMF level on the self-thinning exponent was not significant under the two higher salinity levels. The effect of AMF treatments on the intercept of the self-thinning line was not significant at 0.2% salinity but was significant at 0.5% salinity, higher elevation for high AMF treatment. In self-thinning populations, AMF decreased the survival rate without salinity, but increased the survival rate at the highest salinity level. Our results support the hypothesis that salinity and AMF interact to influence plant neighbour effects and self-thinning. Under no-salinity conditions, AMF increased competition, steepened the self-thinning line and decreased survival rate, but these effects of AMF were not significant in the presence of salinity.     

Genetic variability in a population of arbuscular mycorrhizal fungi causes variation in plant growth

Different species of arbuscular mycorrhizal fungi (AMF) alter plant growth and affect plant coexistence and diversity. Effects of within-AMF species or within-population variation on plant growth have received less attention. High genetic variation exists within AMF populations. However, it is unknown whether genetic variation contributes to differences in plant growth. In our study, a population of AMF was cultivated under identical conditions for several generations prior to the experiments thus avoiding environmental maternal effects. We show that genetically different Glomus intraradices isolates from one AMF population significantly alter plant growth in an axenic system and in greenhouse experiments. Isolates increased or reduced plant growth meaning that plants potentially receive benefits or are subject to costs by forming associations with different individuals in the AMF population. This shows that genetic variability in AMF populations could affect host-plant fitness and should be considered in future research to understand these important soil organisms.     

Differential modulation of host plant delta13C and delta18O by native and nonnative arbuscular mycorrhizal fungi in a semiarid environment

Native, drought-adapted arbuscular mycorrhizal fungi (AMF) often improve host-plant performance to a greater extent than nonnative AMF in dry environments. However, little is known about the physiological basis for this differential plant response. Seedlings of Olea europaea and Rhamnus lycioides were inoculated with either a mixture of eight native Glomus species or with the nonnative Glomus claroideum before field transplanting in a semiarid area. Inoculation with native AMF produced the greatest improvement in nutrient and water status as well as in long-term growth for both Olea and Rhamnus. Foliar delta18O measurements indicated that native AMF enhanced stomatal conductance to a greater extent than nonnative AMF in Olea and Rhamnus.delta13C data showed that intrinsic water-use efficiency in Olea was differentially stimulated by native AMF compared with nonnative AMF. Our results suggest that modulation of leaf gas exchange by native, drought-adapted AMF is critical to the long-term performance of host plants in semiarid environments. delta18O can provide a time-integrated measure of the effect of mycorrhizal infection on host-plant water relations.     

蒙古韭共生真菌及其菌根形态学的研究

本文对生长于内蒙古中西部草原和荒漠地区的蒙古韭Alliummongolicum进行了菌根侵染状态的调查研究。发现蒙古韭的根系有丛枝菌根真菌侵染,其菌根类型为疆南星型(Arum-type)。不同地区采集的蒙古韭菌根侵染率不同,由8.76%至36.12%,侵染率与真菌种的丰富度及孢子密度关系不显著。从7个样点的蒙古韭根际土壤中,分离到丛枝菌根真菌26种:无梗囊霉属5种、球囊霉属18种、内养囊霉属和盾巨孢囊霉属各1种,并有1个未知属种。由此可见,球囊霉和无梗囊霉2个属的种出现频度占绝对优势。除了聚生球囊霉Glomusfasciculatum在沙坡头出现最多外,其它样点中Acaulosporasp.1、缩球囊霉G.constrictum、透光球囊霉G.diaphanum和卷曲球囊霉G.convolutum都有较高的出现频度。尽管不同样地蒙古韭根际土壤中丛枝菌根真菌种的丰富度及孢子密度有差异,但样地之间的优势种有相似性。     

接种AM真菌对玉米和油菜种间竞争及土壤无机磷组分的影响

在温室盆栽条件下,分别模拟单作、间作和尼龙网分隔种植,比较接种丛枝菌根(arbuscular mycorrhizal, AM)真菌Glomus intraradices和Glomus mosseae对菌根植物玉米和非菌根植物油菜生长和磷吸收状况的影响,并分析土壤中各无机磷组分的变化。结果发现,接种AM真菌可以促进土壤中难溶性磷(Ca₁₀-P和O-P)向有效态磷转化,并显著降低总无机磷含量 (P<0.05),显著提高菌根植物玉米的生物量和磷吸收量(P<0.05),特别是在间作体系中使玉米的磷营养竞争比率显著提高了45.0%-104.1% (P<0.05),显著降低了油菜的生物量和磷吸收量(P<0.05),从而增强了了菌根植物的竞争优势,降低了非菌根植物与菌根植物的共存能力。揭示了石灰性土壤中AM真菌对植物物种多样性的影响,有助于更加全面地理解AM真菌在农业生态系统中的作用。     

VA真菌对构树(Broussonetia papyrifera)幼苗物质代谢的影响

石灰岩地区因其干旱瘠薄的生境特征,植被难以恢复,然而仍有一些适生植物如构树生长良好,原因可能与根际微生物有关。就石灰岩适生植物构树（Broussorretia papyrifera）进行菌根真菌摩西球囊霉（Glomus mosseea）、地表球囊霉（Glomus versiforme）、透光球囊霉（Glomus diaphanum）的单独接种、混合接种和不接种处理,幼苗生长3个月后测定其生理指标,以期从代谢水平上了解植物对VA真菌的生理响应。结果表明：构树幼苗叶片可溶性糖、蛋白质,脯氨酸和叶绿素均较非接种处理有不同程度的显著提高,丙二醛含量则较对照降低。各代谢物质存在一定相关性。在物质代谢水平上,构树幼苗对不同VA真菌处理有不同的生理响应。宿主植物和VA真菌之间存在一定的相互选择。接种VA真菌提高了石灰岩适生植物构树的抗逆性。     

AM真菌在煤矿废弃物中生态适应性的初步研究

以粉煤灰、草炭、蛭石、河沙为培养基质,分别对4种不同AM真菌:Glomus mosseae,G.diaphanum,G.intraradices和G.versiforme的生态适应性进行研究。结果表明,菌根的侵染率、孢子密度和菌丝长度分别与菌根真菌种类、培养基质状况及寄主植物种类有关。4种基质的扩繁效果顺序为:河沙>粉煤灰>草炭>蛭石。G.mosseae和G.diaphanum在基质中的产孢量和菌丝长度优于G.intraradices和G.versiforme,可作为优势菌株。4种菌根真菌在粉煤灰中对寄主的侵染率均达到60%以上,粉煤灰作为菌根真菌培养基质具有更大潜力和实际应用价值。     

Phylogenetic conservatism in plant‐soil feedback and its implications for plant abundance

We examined whether plant‐soil feedback and plant‐field abundance were phylogenetically conserved. For 57 co‐occurring native and exotic plant species from an old field in Canada, we collected a data set on the effects of three soil biota treatments on plant growth: net whole‐soil feedback (combined effects of mutualists and antagonists), feedback with arbuscular mycorrhizal fungi (AMF) collected from soils of conspecific plants, and feedback with Glomus etunicatum, a dominant mycorrhizal fungus. We found phylogenetic signal in both net whole‐soil feedback and feedback with AMF of conspecifics; conservatism was especially strong among native plants but absent among exotics. The abundance of plants in the field was also conserved, a pattern underlain by shared plant responses to soil biota. We conclude that soil biota influence the abundance of close plant relatives in nature.     

Differential influence of native and introduced arbuscular mycorrhizal fungi on growth of dominant and subordinate plants

The impact of arbuscular mycorrhizal fungi (AMF) on plant ecosystems has been intensively reported. In this research, we explored the difference between native and introduced AMF in promoting the growth of dominant and subordinate plant species. In glasshouse experiments, dominants and subordinates from subtropical grasslands were colonized by native AMF or introduced AMF, Glomus versiforme. The biomass revealed that mycorrhizal dependencies (MD) on the native AMF of the dominants were much higher than those of the subordinates, while MD on the introduced AMF changed following the replacement of native AMF with introduced AMF. A close relationship between biomass promotion and increase in phosphorus uptake was observed, indicating the important role of AMF-enhanced nutrient acquisition by roots. Our results show that plant community structures are partly determined by MD on native AMF, and could be modified by introducing exogenous AMF species.     

Variable responses of old-field perennials to arbuscular mycorrhizal fungi and phosphorus source

If arbuscular mycorrhizal fungi (AMF) promote phosphorus partitioning of plant hosts, they could provide one mechanism for the maintenance of plant community diversity. We investigated whether AMF improved the ability of old field perennials to grow on a range of phosphorus sources and whether AMF facilitated differential performance of plant species on different phosphorus sources (phosphorus niche partitioning). We manipulated form of phosphorus (control versus different inorganic and organic sources) and AM fungal species (control versus four individual AMF species or an AMF community) for five old field perennials grown in a greenhouse in individual culture. Based on biomass after four months of growth, we found no evidence for phosphorus niche partitioning. Rather, we found that effects of AMF varied from parasitic to mutualistic depending on plant species, AMF species, and phosphorus source (significant Plant × Fungus × Phosphorus interaction). Our results suggest that the degree of AMF benefit to a plant host depends not only on AMF species, plant species, and soil phosphorus availability (as has also been found in other work), but can also depend on the form of soil phosphorus. Thus, the position of any AMF species along the mutualism to parasitism continuum may be a complex function of local conditions, and this has implications for understanding plant competitive balance in the field.     

Host preferences of arbuscular mycorrhizal fungi colonizing annual herbaceous plant species in semiarid mediterranean prairies

In this study, we have analyzed and compared the diversities of the arbuscular mycorrhizal fungi (AMF) colonizing the roots of five annual herbaceous species (Hieracium vulgare, Stipa capensis, Anagallis arvensis, Carduus tenuiflorus, and Avena barbata) and a perennial herbaceous species (Brachypodium retusum). Our goal was to determine the differences in the communities of the AMF among these six plant species belonging to different families, using B. retusum as a reference. The AMF small-subunit rRNA genes (SSU) were subjected to nested PCR, cloning, sequencing, and phylogenetic analysis. Thirty-six AMF phylotypes, belonging to Glomus group A, Glomus group B, Diversispora, Paraglomus, and Ambispora, were identified. Five sequence groups identified in this study clustered to known glomalean species or isolates: group Glomus G27 to Glomus intraradices, group Glomus G19 to Glomus iranicum, group Glomus G10 to Glomus mosseae, group Glomus G1 to Glomus lamellosum/etunicatum/luteum, and group Ambispora 1 to Ambispora fennica. The six plant species studied hosted different AMF communities. A certain trend of AMF specificity was observed when grouping plant species by taxonomic families, highlighting the importance of protecting and even promoting the native annual vegetation in order to maintain the biodiversity and productivity of these extreme ecosystems.     

Are there benefits of simultaneous root colonization by different arbuscular mycorrhizal fungi?

Arbuscular mycorrhizal fungal (AMF) communities were established in pots using fungal isolates from a single field in Switzerland. It was tested whether multispecies mixtures provided more phosphorus and supported greater plant growth than single AMF species. Two host plants, medic (Medicago truncatula) and leek (Allium porrum), were inoculated with three AMF species (Glomus mosseae, G. claroideum and G. intraradices), either separately or in mixtures. The composition of the AMF communities in the roots was assessed using real-time PCR to determine the copy number of large ribosomal subunit genes. Fungal communities in the roots were usually dominated by one AMF species (G. mosseae). The composition of the communities depended on both plant identity and the time of harvest. Leek colonized by a mixture of G. claroideum and G. intraradices acquired more P than with either of the two AMF separately. Direct evidence is provided for functional complementarity among species within the AMF community colonizing a single root system. Competition among the species poses a major challenge in interpreting experiments with mixed inoculations, but this is greatly facilitated by use of real-time PCR.     

Arbuscular mycorrhizal fungal phylogeny-related interactions with a non-host

Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with most vascular plants including some gymnosperm species. Although species in the gymnosperm family Pinaceae normally develop ectomycorrhizal associations, AMF hyphae and vesicles, typical of members of the Suborder Glomineae, have been reported in the roots of some Pinaceae species. However, it is not known whether AMF belonging to various species and suborders are able to colonize roots of Pinaceae species and to what extent this influences the performance of Pinaceae seedlings. We tested in each of the Glomaceae, Acaulosporaceae and Gigasporineae AMF families two species for their ability to colonize and affect the growth of Pinus strobus (eastern white pine) in the presence or absence of an AMF host plant (Trifolium pretense—red clover). Glomus intraradices was the only AMF that colonized pine roots, predominantly in the presence of clover, forming intracellular hyphae and vesicles but not arbuscules. Colonization, however, did not relate to increased pine biomass and the overall presence of AMF, regardless of colonization abilities, resulted in a biomass reduction. This effect on pine seedling biomass was explained by the AMF family to which the AMF belonged, indicating that the effects of AMF on the non-host pine may be related to phylogeny. Acaulosporaceae species reduced pine biomass the most whereas, Gigasporineae species had the smallest effect on biomass. These preliminary results suggest that AMF may affect the soil microflora differently among AMF families in previously unsuspected ways with potential consequences for non-AMF host growth.