Seasonality of arbuscular mycorrhizal symbiosis and dark septate endophytes in a grassland site in southwest China

Arbuscular mycorrhizal and dark septate endophytic fungal colonization in a grassland in Kunming, southwest China, was investigated monthly over one year. All plant roots surveyed were co-colonized by arbuscular mycorrhizal and dark septate endophytic fungi in this grassland. Both arbuscular mycorrhizal and dark septate endophytic fungal colonization fluctuated significantly throughout the year, and their seasonal patterns were different in each plant species. The relationships between environmental (climatic and edaphic) factors and fungal colonization were also studied. Correlation analysis demonstrated that arbuscular mycorrhizal colonization was significantly correlative with environmental factors (rainfall, sunlight hours, soil P, etc.), but dark septate endophytic fungal colonization was only correlative with relative humidity and sunlight hours.     

Red list plants: colonization by arbuscular mycorrhizal fungi and dark septate endophytes

Since information concerning the mycorrhization of endangered plants is of major importance for their potential re-establishment, we determined the mycorrhizal status of Serratula tinctoria (Asteraceae), Betonica officinalis (Lamiaceae), Drosera intermedia (Droseraceae) and Lycopodiella inundata (Lycopodiaceae), occurring at one of two wetland sites (fen meadow and peat bog), which differed in soil pH and available P levels. Root colonization by arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) was quantified. Colonization by AMF appeared to be more frequent in the fen meadow than in the peat bog, and depended on the host plant. Roots of S. tinctoria and B. officinalis were well colonized by AMF in the fen meadow (35–55% root length) and both arbuscules and vesicles were observed to occur in spring as well as in autumn. In the peat bog, L. inundata showed a low level of root colonization in spring, when vesicles were found frequently but no arbuscules. In roots of D. intermedia from the peat bog, arbuscules and vesicles were observed, but AMF colonization was lower than in L. inundata. In contrast, the amount of AMF spores extracted from soil at the peat bog site was higher than from the fen meadow soil. Spore numbers did not differ between spring and autumn in the fen meadow, but they were higher in spring than in autumn in the peat bog. Acaulospora laevis or A. colossica and Glomus etunicatum were identified amongst the AMF spores extracted from soil at the two sites. S. tinctoria and B. officinalis roots were also regularly colonized by DSE (18–40% root length), while L. inundata was only rarely colonized and D. intermedia did not seem to be colonized by DSE at all.     

Wetland dicots and monocots differ in colonization by arbuscular mycorrhizal fungi and dark septate endophytes

As an initial step towards evaluating whether mycorrhizas influence composition and diversity in calcareous fen plant communities, we surveyed root colonization by arbuscular mycorrhizal fungi (AMF) and dark septate endophytic fungi (DSE) in 67 plant species in three different fens in central New York State (USA). We found colonization by AMF and DSE in most plant species at all three sites, with the type and extent of colonization differing between monocots and dicots. On average, AMF colonization was higher in dicots (58±3%, mean±SE) than in monocots (13±4%) but DSE colonization followed the opposite trend (24±3% in monocots and 9±1% in dicots). In sedges and cattails, two monocot families that are often abundant in fens and other wetlands, AMF colonization was usually very low (<10%) in five species and completely absent in seven others. However, DSE colonization in these species was frequently observed. Responses of wetland plants to AMF and DSE are poorly understood, but in the fen communities surveyed, dicots appear to be in a better position to respond to AMF than many of these more abundant monocots (e.g., sedges and cattails). In contrast, these monocots may be more likely to respond to DSE. Future work directed towards understanding the response of these wetland plants to AMF and DSE should provide insight into the roles these fungal symbionts play in influencing diversity in fen plant communities.     

Mycorrhiza does not alter low temperature impact on <Emphasis Type="Italic">Gnaphalium norvegicum</Emphasis>

Extreme arctic-alpine vegetation has relatively low affinity to form mycorrhizal symbiosis. We asked whether the mycorrhizal growth benefit for the host plant is lower at low temperatures. We investigated the role of two root-associated fungi and temperature in growth, carbon–nitrogen relations and germination of an arctic-alpine herb. Seeds of Gnaphalium norvegicum were germinated at 8° or 15°C with or without arbuscular mycorrhizal (AM, Glomus claroideum) and dark septate endophytic (DSE, Phialocephala fortinii) inocula in a climate chamber. We found that germination percentage, shoot and root biomass, shoot N% and root AM colonization were lower at 8°C than at 15°C. P. fortinii inoculation had a positive impact on germination at both temperatures, whereas G. claroideum produced no effect. N% was lower in AM plants at both temperatures. Plant biomass and shoot N content were higher in AM plants than in control plants at 15°C, but not at 8°C. DSE inoculation tended also to have positive effects on plant biomass and N content at 15°C. At 15°C, rate of photosynthesis, photosynthetic nutrient use efficiency and specific leaf area were positively affected by G. claroideum, which suggests that G. claroideum formed a carbon sink and possibly enhanced the seedling water economy. The positive effects of P. fortinii were probably due to its saprotrophic function in the substrate because it did not colonize the roots. These results suggest that the effects of AM and DSE on plant growth are affected by temperature and that the mycorrhizal benefit for the host plant was lower at the lower temperature. Low saprotrophic activity and decreased mycorrhiza-mediated nutrient acquisition may thus constrain plant nutrient acquisition in cold environments. Decreased mycorrhizal benefit may be related to the comparatively low mycotrophy of cold environment vegetation.     

Occurrence of arbuscular mycorrhizal fungi in bromeliad species from the tropical Atlantic forest biome in Brazil

The mycorrhizal status of epiphytic, rupicolous, and terrestrial bromeliad species from the Brazilian Atlantic Rain Forest has been examined. Roots of 13 species of bromeliads were analyzed for the presence of mycorrhizal structures such as arbuscules, hyphae, and vesicles as well as other fungal structures. Rhizosphere soil was sampled to identify arbuscular mycorrhizal fungal (AMF) species associated only with terrestrial bromeliad species. Most specimens collected were epiphytic bromeliads in the genera Aechmea, Bilbergia, Nidularium, Tillandsia, and Vriesea. Differentiating structures of AMF were found in only three species of bromeliads. The pattern of mycorrhizal colonization was mainly internal, and external mycelium and arbuscules were observed only in the terrestrial Nidularium procerum. Root endophytes with dark brown septate mycelium, thin external hyphae, and Rhizoctonia-like sclerotia were also detected in some root segments. A total of ten spore morphotypes were recovered from the rhizosphere of N. procerum, with Acaulospora mellea, A. foveata, and Glomus sp. being the most common species recovered. Our study demonstrated that most of the epiphytic species are not associated with AMF. We attribute this mainly to the exposed bare root conditions found in epiphytic bromeliads.     

Climate change and Epichloë coenophiala association modify belowground fungal symbioses of tall fescue host

Human alteration of symbiont genetics among aboveground endophytic Epichloë coenophiala strains within tall fescue (Schedonorus arundinaceus) has led to widespread deployment of novel grass-endophyte combinations, yet little is known about their ecological consequences. In this study, clone pairs (endophyte-infected, endophyte-free) of two tall fescue genotypes received factorial combinations of increased temperature (+3 °C) and precipitation (+30% long-term annual mean) for 2 yr. We measured root arbuscular mycorrhizal fungi (AMF), dark septate endophyte (DSE) colonization, and soil AMF extraradical hyphae (ERH) length. We hypothesized that genetically distinct grass-E. coenophiala associations would differentially affect belowground fungi, and that these relationships would be climate-sensitive. Tall fescue genotype, endophyte presence, and climate treatment interactions affected AMF arbuscules, vesicles, and ERH. DSE decreased with E. coenophiala presence but increased with warming. Genetically distinct tall fescue-E. coenophiala associations may have divergent long-term impacts on other host-symbiont interactions, potentially impacting ecosystem function and response to climate change.     

金沙江支流普渡河、小江干热河谷的丛枝菌根

调查具有不同植物群落的金沙江支流普渡河、小江干热河谷中91种常见植物的丛枝菌根真菌的侵染率及孢子密度。普渡河样地调查了56种植物,其中54种(96%)植物能形成典型的丛枝菌根,其平均孢子密度为1423±175/100g土;小江样地35种植物中有34种(97%)植物能形成典型的丛枝菌根,其平均孢子密度为601±103/100g土。单因素方差分析表明两个样地植物的AMF总感染率差异不显著,但其根际土壤中AMF孢子密度却存在显著差异,小江样地的AMF孢子密度明显低于普渡河样地。相关性分析表明,干热河谷植物的AMF感染率与其根际土壤中的AMF孢子密度之间不存在相关性。此外,调查还发现91种植物中,有61种植物(67%)在形成AM的同时,也被黑色有隔内生菌感染。     

Epichloë endophyte affects the root colonization pattern of belowground symbionts in a wild grass

Plants host multiple symbionts that interact with each other affecting plant performance and regulating their establishment. Here, we analyzed how the association with Epichloë endophytes affects belowground colonization by Dark Septate Endophytes (DSE) and arbuscular mycorrhizal fungi (AMF) in the grass Bromus auleticus. Epichloë-symbiotic (E+) and Epichloë-non symbiotic (E−) plants were sampled from a long-term experimental plot and colonization structures were analyzed in the roots. We also examined the influence of Epichloë exudates on the in vitro growth of DSE Microdochium bolleyi isolated from roots. Epichloë symbiosis increased AMF colonization, although differences were not significant. Despite the lack of differences in total DSE colonization, in concordance with in vitro findings, a higher significant abundance of microsclerotia was observed in E+ plants. A negative correlation between total mycorrhizal and DSE was found. Our findings show a more uniform root colonization pattern in E+ plants, suggesting a root symbiosis modulating role.     

Dark septate endophytes: a review of facultative biotrophic root-colonizing fungi

Dark septate root endophytes (DSE) are conidial or sterile fungi (Deuteromycotina, Fungi Imperfecti) likely to be ascomycetous and colonizing plant roots. They have been reported for nearly 600 plant species representing about 320 genera and 100 families. DSE fungi occur from the tropics to arctic and alpine habitats and comprise a heterogeneous group that functionally and ecologically overlaps with soil fungi, saprotrophic rhizoplane-inhabiting fungi, obligately and facultatively pathogenic fungi and mycorrhizal fungi. Numerous species of undescribed sterile and anamorphic taxa may also await discovery. Although DSE are abundant in washed root and soil samples from various habitats, and are easily isolated from surface-sterilized roots of ecto-, ectendo-, endo- and non-mycorrhizal host species, their ecological functions are little understood. Studies of DSE thus far have yielded inconsistent results and only poorly illustrate the role of DSE in their natural habitats. These inconsistencies are largely due to the uncertain taxonomic affinities of the strains of DSE used. In addition, because different strains of a single anamorph taxon seem to vary greatly in function, no clear generalizations on their ecological role have been drawn. This paper reviews the current literature on DSE and the ecology and discusses the need for and direction of future research.     

Different native arbuscular mycorrhizal fungi influence the coexistence of two plant species in a highly alkaline anthropogenic sediment

Different species of arbuscular mycorrhizal fungi (AMF) can produce different amounts of extraradical mycelium (ERM) with differing architectures. They also have different efficiencies in gathering phosphate from the soil. These differences in phosphate uptake and ERM length or architecture may contribute to differential growth responses of plants and this may be an important contributor to plant species coexistence. The effects of the development of the ERM of AMF on the coexistence of two co-occurring plant species were investigated in root-free hyphal chambers in a rhizobox experimental unit. The dominant shrub (Salix atrocinerea Brot.) and herbaceous (Conyza bilbaoana J. Rémy) plant species found in a highly alkaline anthropogenic sediment were studied in symbiosis with four native AMF species (Glomus intraradices BEG163, Glomus mosseae BEG198, Glomus geosporum BEG199 and Glomus claroideum BEG210) that were the most abundant members of the AMF community found in the sediment. Different AMF species did not influence total plant productivity (sum of the biomass of C. bilbaoana and S. atrocinerea), but had a great impact on the individual biomass of each plant species. The AMF species with greater extracted ERM lengths (G. mosseae BEG198, G. claroideum BEG210 and the four mixed AMF) preferentially benefited the plant species with a high mycorrhizal dependency (C. bilbaoana), while the AMF species with the smallest ERM length (G. geosporum BEG199) benefited the plant species with a low mycorrhizal dependency (S. atrocinerea). Seed production of C. bilbaoana was only observed in plants inoculated with G. mosseae BEG198, G. claroideum BEG210 or the mixture of the four AMF. Our results show that AMF play an important role in the reproduction of C. bilbaoana coexisting with S. atrocinerea in the alkaline sediment and have the potential to stimulate or completely inhibit seed production. The community composition of native AMF and the length of the mycelium they produce spreading from roots into the surrounding soil can be determinant of the coexistence of naturally co-occurring plant species.     

Comparing symbiotic performance and physiological responses of two soybean cultivars to arbuscular mycorrhizal fungi under salt stress

The presented experiments evaluated the symbiotic performance of soybean genotypes with contrasting salt stress tolerance to arbuscular mycorrhizal fungi (AMF) inoculation. In addition, the physiological stress tolerance mechanisms in plants derived from mutualistic interactions between AMF and the host plants were evaluated. Plant growth, nodulation, nitrogenase activity and levels of endogenous growth hormones, such as indole acetic acid and indole butyric acid, of salt-tolerant and salt-sensitive soybean genotypes significantly decreased at 200 mM NaCl. The inoculation of soybean with AMF improved the symbiotic performance of both soybean genotypes by improving nodule formation, leghemoglobin content, nitrogenase activity and auxin synthesis. AMF colonization also protected soybean genotypes from salt-induced membrane damage and reduced the production of hydrogen peroxide, subsequently reducing the production of TBARS and reducing lipid peroxidation. In conclusion, the results of the present investigation indicate that AMF improve the symbiotic performance of soybean genotypes regardless of their salt stress tolerance ability by mitigating the negative effect of salt stress and stimulating endogenous level of auxins that contribute to an improved root system and nutrient acquisition under salt stress.     

Comparison of two test systems for measuring plant phosphorus uptake via arbuscular mycorrhizal fungi

 Plant phosphorus uptake via external hyphae of arbuscular mycorrhizal fungi has been measured using compartmented systems where a hyphal compartment is separated from a rooting compartment by a fine mesh. By labelling the soil within the hyphal compartment with a radioactive phosphorus (P) isotope, hyphal uptake of P into the plant can be traced. The objective of this growth chamber study was to test two hyphal compartments of different design with respect to their suitabilities for measurement of hyphal P uptake. One hyphal compartment was simply a nylon mesh bag filled with ³²P-labelled soil. The labelled soil in the other hyphal compartment was completely surrounded by an 8–10 mm layer of unlabelled soil that served as a buffer zone. Mycorrhizal and non-mycorrhizal subterranean clover plants were grown in pots with a centrally positioned hyphal compartment. Uptake of radioactive P by non-mycorrhizal control plants was 25% of that by mycorrhizal plants with the mesh bag but only 3% when including the buffer zone. Based on this good control of non-mycorrhizal P uptake from within the hyphal compartment and its greater ease of handling once produced, we judged the hyphal compartment including a buffer zone to be superior to the mesh bag. Accepted: 15 September 1998     

不同盐碱度土壤中AM菌根真菌群落结构组成及影响因子

为研究黄河三角洲盐渍土壤中植物根围AM菌根真菌多样性及影响多样性的因素,从东营孤东和孤岛油区采集碱蓬和柽柳植物的根围土壤,鉴定了4种土壤试样中丛枝菌根(Arbuscular mycorrhiza,AM)的群落组成。结果表明:球囊霉属(Glomus)是盐碱地中的优势种,同时还有许多未知真菌;考察不同盐碱度情况下菌根真菌群落结构差异,结果表明:碱蓬根围土壤中AM真菌的多样性高于柽柳,孤东根围土壤AM真菌多样性比孤岛高。相关分析表明,铵态氮含量与AM真菌多样性呈现显著负相关。     

Biolistic transformation of arbuscular mycorrhizal fungi

Gene transfer systems have proved effective for the transformation of a range of organisms for both fundamental and applied studies. Biolistic transformation is a powerful method for the gene transfer into various organisms and tissues that have proved recalcitrant to more conventional means. For fungi, the biolistic approach is particularly effective where protoplasts are difficult to obtain and/or the organisms are difficult to culture. This is particularly applicable to arbuscular mycorrhizal (AM) fungi, being as they are obligate symbionts that can only be propagated in association with intact plants or root explants. Furthermore, these fungi are aseptate and protoplasts cannot be released. Recent advancements in gene transformation systems have enabled the use of biolistic technology to introduce foreign DNA linked to molecular markers into these fungi. In this review we discuss the development of transformation strategies for AM fungi by biolistics and highlight the areas of this technology which require further development for the stable transformation of these elusive organisms.     

Mycorrhiza-plant colonization patterns on a subalpine glacier forefront as a model system of primary succession

Lyman glacier in the North Cascades Mountains of Washington has a subalpine forefront characterized by a well-developed terminal moraine, inconspicuous successional moraines, fluting, and outwash. These deposits were depleted of symbiotic fungi when first exposed but colonized by them over time after exposure. Four major groups of plant species in this system are (1) mycorrhiza-independent or facultative mycotrophic, (2) dependent on arbuscular mycorrhizae (AM) (3) dependent on ericoid mycorrhiza (ERM) or ectomycorrhizae (EM), and (4) colonized by dark-septate (DS) endophytes. We hypothesized that availability of mycorrhizal propagules was related to the success of mycorrhiza-dependent plants in colonizing new substrates in naturally evolved ecosystems. To test this hypothesis roots samples of 66 plant species were examined for mycorrhizal colonization. The plants were sampled from communities at increasing distances from the glacier terminus to compare the newest communities with successively older ones. Long established, secondary successional dry meadow communities adjacent to the glacier forefront, and nearby high alpine communities were sampled for comparison. DS were common on most plant species on the forefront. Nonmycorrhizal plants predominated in the earlier successional sites, whereas the proportion of mycorrhizal plants generally increased with age of community. AM were present, mostly at low levels, and nearly absent in two sites of the forefront. ERM were present in all species of Ericaceae sampled, and EM in all species of Pinaceae and Salicaceae. Roots of plants in the long established meadow and heath communities adjacent to the forefront and the high alpine community all had one or another of the colonization types, with DS and AM predominating.     

Effects of mowing on fungal endophytes and arbuscular mycorrhizal fungi in subalpine grasslands

In French subalpine grasslands, cessation of mowing promotes dominance of Festuca paniculata, which alters plant diversity and ecosystem functioning. One of the mechanisms underpinning such effects may be linked to simultaneous changes in the abundance of fungal symbionts such as endophytes and arbuscular mycorrhizal fungi. In field conditions, mowing reduced the abundance of the endophyte Neotyphodium sp. in leaves of F. paniculata by a factor of 6, and increased mycorrhizal densities by a factor of 15 in the soil. In greenhouse experiments, the mycorrhizal colonization of Trifolium pratense and Allium porrum increased 3- fold and 3.8- fold respectively in mown vs unmown grassland soil. Significantly reduced growth of the two host plants was also observed on soil from the unmown grassland. Such opposite effects of mowing on the two functional groups of fungal symbionts could suggest interactions between these two groups, which in turn could contribute to structuring plant communities in subalpine grasslands.     

Twenty years of research on community composition and species distribution of arbuscular mycorrhizal fungi in China: a review

The biodiversity and distribution of arbuscular mycorrhizal fungi (AMF) in different ecosystems and plant communities in China has received increasing interest over the past decades. This has led to a steady increase in the number of scientific papers published on this topic. Studies have surveyed AMF-colonizing rhizospheres of most families of angiosperms, bryophytes, pteridophytes, and gymnosperms. China has about 30,000 plant species (one eighth of the plant species worldwide). A total of 104 AMF species within nine genera, including 12 new species, have been reported in environments such as croplands, grasslands, forests, and numerous disturbed environments. In this paper, we review data published over the past 20 years on AMF community composition and species distribution, the mycorrhizal status of plants, AMF spore communities in different habitats, and germplasm collections in China. Possible future trends in the study of the biodiversity of AMF are also briefly discussed. In particular, the aim of our review is to make some of the recent work published in the Chinese literature accessible to a wider international audience.