Responses of Salsola kali and Panicum virgatum to mycorrhizal fungi, phosphorus and soil organic matter: implications for reclamation

1. Owing to the difficulty of finding terrestrial ecosystems without mycorrhizas, their influence on plant community dynamics is not easy to discern. This study utilized unreclaimed taconite mine tailings as a mycorrhiza-free ecosystem to gain insights about the influence of arbuscular mycorrhizas and soil organic matter on the growth of Salsola kali (an early successional colonist of taconite tailings) and Panicum virgatum (a late successional grass planted during reclamation).
2. To assess relative mycorrhizal responsiveness, Panicum and Salsola were grown in taconite tailings along an experimental phosphorus gradient with and without mycorrhizal fungal inoculum isolated from reclaimed taconite tailings. At low phosphorus concentrations, mycorrhizal inoculum enhanced the growth (height and dry mass) of Panicum , but it decreased growth at the two highest phosphorous concentrations. At no phosphorus level did mycorrhizal inoculum enhance the growth of Salsola but it decreased growth at the highest phosphorus concentrations.
3. In field plots, mycorrhizal inoculum and organic soil amendment (compostedpapermill sludge) enhanced the growth of Panicum and decreased the growth of Salsola .
4. In this experiment, mycorrhizal inoculum enhanced the growth of the late successional grass but, during reclamation operations, manipulating edaphic conditions to favour mycotrophy may be more cost-effective than large-scale inoculation. The results of this study suggest that mycotrophy is favoured by increasing soil organic matter and avoiding heavy fertilization.     

丛枝菌根在煤矸石山土地复垦中的应用

煤矸石是采煤和洗煤过程中排出的固体废弃物,一方面占用了大量的土地资源,另一方面也成为固、液和气三害俱全的污染源,造成了一系列生态环境问题。以宁夏大武口洗煤厂煤矸石山复垦地为实验点,在自然状况下接种丛枝菌根真菌,研究其对煤矸石山土地复垦的生态效果。结果表明,菌根在煤矸石山土地复垦中具有较好的生态效果。接种菌根真菌13个月后能够提高植被成活率15%,促进植株生长和发育。植株生长快,植被的盖度高于对照9%,增加了生物物种的丰度。接种菌根后植株的侵染率高达90%以上,菌丝长度较对照伸长1.4倍,扩大了根系的范围,有利于维持该生态系统的稳定性。     

Suppression of fungal and nematode plant pathogens through arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi represent ubiquitous mutualists of terrestrial plants. Through the symbiosis, plant hosts, among other benefits, receive protection from pathogens. A meta-analysis was conducted on 106 articles to determine whether, following pathogen infection of AM-colonized plants, the identity of the organisms involved (pathogens, AM fungi and host plants) had implications for the extent of the AM-induced pathogen suppression. Data on fungal and nematode pathogens were analysed separately. Although we found no differences in AM effectiveness with respect to the identity of the plant pathogen, the identity of the AM isolate had a dramatic effect on the level of pathogen protection. AM efficiency differences with respect to nematode pathogens were mainly limited to the number of AM isolates present; by contrast, modification of the ability to suppress fungal pathogens could occur even through changing the identity of the Glomeraceae isolate applied. N-fixing plants received more protection from fungal pathogens than non-N-fixing dicotyledons; this was attributed to the more intense AM colonization in N-fixing plants. Results have implications for understanding mycorrhizal ecology and agronomic applications.     

中国植物丛枝菌根侵染特征研究

丛枝菌根真菌在生态系统和植物生长过程中发挥着重要作用,目前对其生理生态功能的研究备受关注,但主要集中在丛枝菌根真菌对植物促生作用方面。植物的菌根侵染特征是表征真菌与植物共生紧密程度的重要标志,也是评价植物生态适应性的关键指标,然而针对我国植物丛枝菌根发育特征及其分布特点的系统性研究尚属空白。【目的】探究我国植物丛枝菌根真菌的侵染特征,及其在不同生态系统和气候区域中的分布规律,为推动丛枝菌根研究的发展提供基础数据。【方法】利用全球植物菌根数据库“FungalRoot”和605篇中文文献的植物菌根侵染特征数据,并补充生态系统、气候区域、植物类型和植物生长年限等共47 700组数据,建立了中国植物丛枝菌根侵染信息数据库,并以此为基础进行研究。【结果】我国植物丛枝菌根真菌侵染率在0-55%占69.7%,55%-100%占30.3%,绝大多数植物丛枝菌根真菌侵染强度、菌丝丰度、泡囊丰度和丛枝丰度均分布在40.0%以下。丛枝菌根共生形态中,A型占比最大,为56.3%。农田、荒漠、草地生态系统的植物丛枝菌根真菌侵染率相近,分别为51.8%、51.6%、51.8%,而森林生态系统的侵染率较低,为40.4%。荒漠生态系统植物的丛枝菌根真菌侵染强度、菌丝丰度、泡囊丰度和丛枝丰度最高,分别达到46.0%、47.1%、37.2%和31.2%。根据气候区域,植物的侵染水平由高到低排序为暖温带(53.3%)>热带(50.0%)>中温带(45.2%)>亚热带(42.2%)。草本植物的侵染水平高于木本植物,多年生植物高于一年生植物。木本植物中,灌木的侵染率水平最高,为46.3%,其次是乔木和藤本植物,均为43.9%。草本植物在侵染强度和菌丝丰度上高于木本植物,分别为30.2%和32.5%,而木本植物在泡囊和丛枝丰度方面具有优势,分别为19.5%和23.4%。我国丛枝菌根植物中,被子植物占据绝大多数,共有110科,占比达到90.2%,蕨类、裸子、石松门植物较少。【结论】我国大部分植物丛枝菌根真菌侵染率在55%以下,侵染特征等指标分布在40.0%以下;同时,不同生态系统、气候区域、植物类型和生长年限均会对侵染特征产生不同程度的影响。     

Phosphorus uptake by a community of arbuscular mycorrhizal fungi in jarrah forest

Communities of indigenous arbusuclar mycorrhizal (AM) fungi are expected to alter phosphorus uptake and biomass productivity of plants according to characteristics of the life cycles of the fungi present and the way they interact with each other inside roots and with host plants. Differences in the relative abundance of AM fungi inside roots could influence P uptake if the fungi present differ in effectiveness at accessing P and transferring it to the plant. However, it is difficult to assess the contribution of AM fungi under field conditions. We investigated P uptake, from point sources of P placed 2, 4 and 6 cm from roots, by plants colonised by a community of AM fungi in jarrah forest soil. Roots were retained within a mesh bag to prevent them from growing towards the point source of P. The relative abundance of morphotypes of fungi inside roots and the P status of plants were assessed after 12 and 16 weeks. First, a bioassay was carried out in undisturbed forest soil cores using two host plants, a forest understorey plant Phyllanthus calycinus Labill and the annual pasture species subterranean clover (Trifolium subterraneaumL.), to assess the infectivity of the indigenous community of AM fungi. Roots of both bioassay host plants were colonised in similar proportions by morphotypes of AM fungi resembling Glomus, Acaulospora, Scutellospora and fine endophytes. In this bioassay, there were positive correlations between the proportion of root length colonised and plant biomass and P uptake for P. calycinus, but not for subterranean clover. In the experiment assessing the capacity of P. calycinus to access P placed at increasing distances from the root, shoot P content and concentration in P. calycinus were greater when P was placed 2 cm compared with 4 and 6 cm from roots. The length of hyphae in the vicinity of the point source of P decreased with increasing distance from the plant. The extent to which the individual AM fungi were involved in P uptake is not known. The Glomus morphotype was dominant at both times of sampling.     

Species of plants and associated arbuscular mycorrhizal fungi mediate mycorrhizal responses to CO2 enrichment

It has been suggested that enrichment of atmospheric CO₂ should alter mycorrhizal function by simultaneously increasing nutrient‐uptake benefits and decreasing net C costs for host plants. However, this hypothesis has not been sufficiently tested. We conducted three experiments to examine the impacts of CO₂ enrichment on the function of different combinations of plants and arbuscular mycorrhizal (AM) fungi grown under high and low soil nutrient availability. Across the three experiments, AM function was measured in 14 plant species, including forbs, C₃ and C₄ grasses, and plant species that are typically nonmycorrhizal. Five different AM fungal communities were used for inoculum, including mixtures of Glomus spp. and mixtures of Gigasporaceae (i.e. Gigaspora and Scutellospora spp.). Our results do not support the hypothesis that CO₂ enrichment should consistently increase plant growth benefits from AM fungi, but rather, we found CO₂ enrichment frequently reduced AM benefits. Furthermore, we did not find consistent evidence that enrichment of soil nutrients increases plant growth responses to CO₂ enrichment and decreases plant growth responses to AM fungi. Our results show that the strength of AM mutualisms vary significantly among fungal and plant taxa, and that CO₂ levels further mediate AM function. In general, when CO₂ enrichment interacted with AM fungal taxa to affect host plant dry weight, it increased the beneficial effects of Gigasporaceae and reduced the benefits of Glomus spp. Future studies are necessary to assess the importance of temperature, irradiance, and ambient soil fertility in this response. We conclude that the affects of CO₂ enrichment on AM function varies with plant and fungal taxa, and when making predictions about mycorrhizal function, it is unwise to generalize findings based on a narrow range of plant hosts, AM fungi, and environmental conditions.     

喀斯特植被演替过程土壤丛枝菌根真菌(AMF)多样性

喀斯特生态系统维持了丰富的微生物多样性,丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)结构和组成会随喀斯特植被演替而改变。以贵州贵阳花溪、毕节织金和关岭花江典型喀斯特区域按时空替代法采集了乔木林、灌木林和草本群落样地土壤,采用Illumina HiSeq分子测序技术,通过OTU聚类分析、物种注释及数据库比对,探索了喀斯特不同演替阶段土壤AMF物种多样性。结果表明:(1)喀斯特生境土壤获得球囊菌门Glomeromycota OTU为275个,分属于4目8科13属19种,属水平上AMF丰度表明根内根孢囊霉属Rhizophagus为优势属,花江拥有最高AMF丰富度,缩隔球囊霉Septoglomus constrictum、根内根孢囊霉Rhizophagus intraradices、Claroideoglomus sp. MIB8381和稀有内养囊霉Entrophospora infrequens均分布于各样地的不同植被演替阶段,为常见种。(2)AM真菌多样性Shannon指数与Simpson指数在不同演替阶段表现为花溪:乔木≈灌木草本(P0.05)、花江:灌木≈草本乔木(P0.05)、织金:乔木灌木草本,但差异不显著,Chao1和Abundance-based coverag estimator(ACE)指数表现为花江灌木≈草地乔木(P0.05)。(3)Spearman相关性分析表明土壤全磷与AMF ACE指数显著负相关,且与Chao1指数极显著负相关;速效磷与Shannon和Simpson指数显著负相关。(4)典范对应分析(Canonical Correlation Analysis,CCA)表明土壤全氮、速效氮、有机质、全磷和速效钾与AMF群落分布有显著相关性。结果表明喀斯特植被演替过程中土壤丛枝菌根真菌多样性随着演替进行或升高或降低,无一致变化规律,并与土壤理化性质关系密切,其中以磷的影响最大。     

AM真菌在有机农业发展中的机遇

在农田生态系统中,许多农作物均为丛枝菌根(AM)真菌的优良宿主植物,当AM真菌与这些宿主植物建立共生关系之后,AM真菌的存在有益于宿主植物的生长。然而,传统农业耕作模式中化学肥料和农药的施用、耕作制度的不断调整和非宿主植物的种植等都不利于AM真菌的建植。有机农业生态系统排除了化学肥料和农药的施用,减少了对AM真菌生长不利的因素,促进了土壤中AM真菌数量的增加和群落多样性的提高。同时,AM真菌可以通过多种方式改善土壤物理结构、提高农作物对干旱胁迫的耐受能力以及宿主植物对病虫害的抗性/耐性、抑制杂草生长、促进营养物质的吸收,进而提高植物的生长和改善产品的品质。基于此,围绕AM真菌在有机农业发展中的生态学功能展开论述,分析当前有机农业生态系统存在的问题,探讨利用AM真菌发展有机农业的可行性及其发展的机遇,以期促进AM真菌在有机农业发展中的应用。     

Molecular diversity of arbuscular mycorrhizal fungi colonising Hyacinthoides non-scripta (bluebell) in a seminatural woodland

Arbuscular mycorrhizal (AM) fungi form symbiotic associations with plant roots. Around 150 species have been described and it is becoming clear that many of these species have different functional properties. The species diversity of AM fungi actively growing in roots is therefore an important component of ecosystem diversity. However, it is difficult to identify AM fungi below the genus level from morphology in planta , as they possess few informative characters. We present here a molecular method for identifying infrageneric sequence types that estimate the taxonomic diversity of AM fungi present in actively growing roots. Bluebell roots were sampled from beneath two different canopy types, oak and sycamore, and DNA sequences were amplified from roots by the polymerase chain reaction with fungal-specific primers for part of the small subunit ribosomal RNA gene. Restriction fragment length polymorphism among 141 clones was assessed and 62 clones were sequenced. When aligned, discrete sequence groups emerged that cluster into the three families of AM fungi: Acaulosporaceae, Gigasporaceae and Glomaceae. The sequence variation is consistent with rRNA secondary structure. The same sequence types were found at both sampling times. Frequencies of Scutellospora increased in December, and Acaulospora increased in abundance in July. Sites with a sycamore canopy show a reduced abundance of Acaulospora , and those with oak showed a reduced abundance of Glomus . These distribution patterns are consistent with previous morphological studies carried out in this woodland. The molecular method provides an alternative method of estimating the distribution and abundance of AM fungi, and has the potential to provide greater resolution at the infrageneric level.     

Community structure of arbuscular mycorrhizal fungi at different soil depths in extensively and intensively managed agroecosystems

The vertical distribution of spores of arbuscular mycorrhizal fungi (AMF) was investigated in soil profiles of extensively and intensively managed agroecosystems, including two permanent grasslands, a vineyard and two continuously mono-cropped maize fields. The number of AMF spores decreased with increasing soil depth--most drastically in the grasslands and the vineyard--but there was a large diversity of AMF species even in the deepest soil layers (50-70 cm). This was particularly striking in the maize fields where the highest species numbers were found below ploughing depth. Some species sporulated mainly, or exclusively, in the deep soil layers, others mainly in the top layers. Soil samples were used to inoculate trap cultures. Up to 18 months after inoculation, there was no conspicuous difference in the species composition among the trap cultures representing different soil depths, and only a weak match to the species composition determined by analysis of field samples. Our results indicate that the AMF communities in deep soil layers are surprisingly diverse and different from the topsoil. Thus, deep soil layers should be included in studies to get a complete picture of AMF diversity.     

Communities, populations and individuals of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi in the phylum Glomeromycota are found globally in most vegetation types, where they form a mutualistic symbiosis with plant roots. Despite their wide distribution, only relatively few species are described. The taxonomy is based on morphological characters of the asexual resting spores, but molecular approaches to community ecology have revealed a considerable unknown diversity from colonized roots. Although the lack of genetic recombination is not unique in the fungal kingdom, arbuscular mycorrhizal fungi are probably ancient asexuals. The long asexual evolution of the fungi has resulted in considerable genetic diversity within morphologically recognizable species, and challenges our concepts of individuals and populations. This review critically examines the concepts of species, communities, populations and individuals of arbuscular mycorrhizal fungi.     

Effect of arbuscular mycorrhizal fungi, organic fertilizer and soil sterilization on maize growth

The effects of inoculation with arbuscular mycorrhizal (AM) fungi, organic fertilizer (F) applications, and soil sterilization on maize growth were evaluated in a pot experiment. The experiment was in a completely randomized factorial design (2 × 4 × 2) with six replicates for each treatment. There were two soil treatments (sterilized soil, SS and unsterilized soil, US), four organic fertilizer treatments (0.0, 0.5, 1.0 and 2.0 g kg^?1 soil), and two AM fungi treatments (inoculation with Glomus mosseae, +AM and uninoculated control, ?AM). Inoculated plants generally had greater AM colonization, plant height, dry weight and phosphorus (P) uptake than uninoculated controls, and these parameters were significantly increased as the organic fertilizer application increased up to 0.5 g kg^?1 but decreased or had no significant effect compared to the uninoculated plants at the highest fertilizer rate (2.0 g kg^?1). Plant growth, P uptake and AM colonization of root system were significantly higher in sterilized soil compared to the unsterilized control. Our results indicated that the inoculation of AM fungi in field soil with optimal organic fertilizer application greatly improved maize growth and nutrient uptake, and the effect was greater under sterilized soil condition.     

Reduced growth of autumn-sown wheat in a low-P soil is associated with high colonisation by arbuscular mycorrhizal fungi

Autumn-sown wheat (Triticum aestivum) was studied over two seasons in south-eastern Australia, on a low-P soil where indigenous arbuscular mycorrhizal fungi (AMF) were known to provide little nutritional benefit to crops. It was hypothesised that AMF would be parasitic under these circumstances. Shoot dry mass and water soluble carbohydrate (WSC) reserves in roots and shoots were measured for wheat grown with or without P-fertiliser, in plots where crop sequences had produced either high or low colonisation by AMF. Application of P-fertiliser greatly increased crop growth and decreased colonisation by AMF. At tillering, colonisation by AMF ranged from 24 to 66% of root length when no P was applied and from 11 to 32% when P was applied. At each P-level, high colonisation correlated with reductions of around 20% in stem and root WSC concentrations (first season) or shoot WSC content and shoot dry mass (much drier second season). Impacts on yield were not significant (first season) or largely masked by water-stress and frost (second season). While the major fungal root diseases of the region were absent, interactions between crop sequence and other unknown biotic constraints could not be discounted. The results are consistent with the parasitic impacts of colonisation by AMF being induced primarily through the winter conditions experienced by the crops until anthesis. It is concluded that wheat in south-eastern Australia may benefit from reduced colonisation by AMF, which could achieved through selected crop sequences or, perhaps, targeted wheat breeding programs.     

Effect of arbuscular mycorrhizal fungi, organic fertilizer and soil sterilization on maize growth ☆

The effects of inoculation with arbuscular mycorrhizal (AM) fungi, organic fertilizer (F) applications, and soil sterilization on maize growth were evaluated in a pot experiment. The experiment was in a completely randomized factorial design (2 × 4 × 2) with six replicates for each treatment. There were two soil treatments (sterilized soil, SS and unsterilized soil, US), four organic fertilizer treatments (0.0, 0.5, 1.0 and 2.0 g kg^-1 soil), and two AM fungi treatments (inoculation with Glomus mosseae, +AM and uninoculated control, －AM). Inoculated plants generally had greater AM colonization, plant height, dry weight and phosphorus (P) uptake than uninoculated controls, and these parameters were significantly increased as the organic fertilizer application increased up to 0.5 g kg^-1 but decreased or had no significant effect compared to the uninoculated plants at the highest fertilizer rate (2.0 g kg^-1). Plant growth, P uptake and AM colonization of root system were significantly higher in sterilized soil compared to the unsterilized control. Our results indicated that the inoculation of AM fungi in field soil with optimal organic fertilizer application greatly improved maize growth and nutrient uptake, and the effect was greater under sterilized soil condition.     

Relationship of seed source and arbuscular mycorrhizal fungi inoculum type to growth and colonization of big bluestem (Andropogon gerardii)

Big bluestem (Andropogon gerardii) is a key grass of tallgrass prairies and is commonly included in restoration projects. In many cases, it has been found to benefit significantly from arbuscular mycorrhizal (AM) fungi, however results have varied under non-sterile soil conditions. This study investigated the effects of two types of AM fungi inoculum (commercial and prairie) on growth and root colonization of big bluestem from five different seed sources grown in non-sterile soils. Seed sources were collected from five remnant prairies in the Tallgrass Prairie Peninsula located in the Midwestern United States. Growth of big bluestem and root length colonized by AM fungi was highly variable among seed source treatments. Overall, percentage of root length colonized by AM fungi was positively correlated with the total dry weight of plants, and plants that received inoculum generally grew better than those that did not receive inoculum. Inoculum treatment affected both big bluestem growth and percentage root length colonized and there was an interaction between seed source and inoculum treatment relative to colonization. Root colonization responses were not significantly different between the prairie and commercial inoculum types, although there was a significant response between plants that received additional inoculum as opposed to no additional inoculum. Seed sources from Ohio and Illinois had the highest biomasses and greatest percentage of root length colonized while plants from Wisconsin and Missouri grew poorly and had low root colonization. These results demonstrate the importance of considering both seed source and inoculum type before the incorporation of AM inoculum to prairie restoration projects.