菌根真菌对土壤呼吸以及凋落物分解的影响

土壤呼吸是植物固定的碳由陆地生态系统进入大气的主要途径之一; 凋落物分解是养分循环的重要环节。陆地植物的90%以上可同菌根真菌形成共生关系, 菌根真菌对于植物获取环境中的养分具有重要的作用。然而, 其对土壤呼吸和凋落物分解的影响却经常在生态系统对环境变化的响应研究中被忽视。本文系统地综述了国内外相关研究进展, 对菌根真菌如何影响土壤呼吸和凋落物分解这两个过程及这种影响如何受到环境变化的制约做了全面的分析, 并对以往研究中存在的问题以及未来的研究方向提出了展望。     

Effects of arbuscular mycorrhizal fungi and P-solubilizing Pseudomonas fluorescence (ATCC-17400) on morphological traits and mineral content of sesame

Sesame (Sesamum indicum L.) is an important staple crop of the family Pedaliaceae. The commercial production of sesame is still dependent on the applications of chemical fertilizers. Mycorrhiza inoculum resulted in better morphological and biochemical traits in vegetables. Thus, here the outcome of arbuscular mycorrhizal fungi (AMF) and Pseudomonas fluorescence (ATCC-17400) inoculation was studied in the pot culture experiment. Primarily, there seems to be a promising opportunity of AMF in sesame under pot and field trials because of enhanced morphological parameters, especially root weight, and disparities in nutrients and metabolites. The AMF appears to be an option to boost plant growth, mineral content, and sesame yield. The AMF treatment with Pseudomonas fluorescence strain (ATCC-17400) determined the maximum values for the morphological traits and mineral content. Overall, our study highlights mycorrhizal fungi and other microbes efficacy in achieving a successful sesame production.     

春兰菌根真菌CL-3菌株的鉴定及共生体系的构建

采用分离自野生春兰(Cymbidium goeringii)根部的真菌CL-3菌株, 进行了春兰内生菌根真菌的人工接种、再分离及其共生培养研究。通过对CL-3菌株形态学观察和ITS序列同源性分析, 发现该菌株ITS序列与Acremonium strictum的亲缘关系最为接近, 序列同源性为100%。用CL-3菌株接种春兰组培苗, 接种后2个月可从组培苗中再分离获得该菌株, 且CL-3菌株处理苗的鲜重增长率达80.5%, 经方差分析, 与对照相比有显著差异。通过石蜡切片和染色, 在已接种的组培苗的根部组织中可观察到CL-3菌株存在。表明CL-3菌株能与组培幼苗成功建立共生培养体系。     

Early responses of wild plant seedlings to arbuscular mycorrhizal fungi and pathogens

Many plants form associations with arbuscular mycorrhizal fungi (AMF) because they profit from improved phosphorus nutrition and from protection against pathogens. Whereas mycorrhiza-induced pathogen protection is well understood in agricultural plant species, it is rarely studied in wild plants. As many pathogens infest plants in the first days after germination, mycorrhiza-induced pathogen protection may be especially important in the first few weeks of plant establishment.Here, we investigated interacting effects of AMF and the seedling pathogen Pythium ultimum on the performance of six- to seven-week-old seedlings of six wild plant species of the family Asteraceae in a full factorial experiment.Plant species differed in their response to AMF, the pathogen and their interactions. AMF increased and the pathogen decreased plant biomass in one and three species, respectively. Two plant species were negatively affected by AMF in the absence, but positively or not affected in the presence of the pathogen, indicating protection by AMF. This mycorrhiza-induced pathogen protection is especially surprising as we could not detect mycorrhizal structure in the roots of any of the plants.Our results show that even seedlings without established intraradical hyphal network can profit from AMF, both in terms of growth promotion in the absence of a pathogen and pathogen protection. The function of AMF is highly species-specific, but tends to be similar for more closely related plant species, suggesting a phylogenetic component of mycorrhizal function. Further studies should test a wider range of plant species, as our study was restricted to one plant family, and investigate whether plants profit from early mycorrhizal benefits in the long term.     

Developmental processes of achlorophyllous orchid, <Emphasis Type="Italic">Epipogium roseum</Emphasis>: from seed germination to flowering under symbiotic cultivation with mycorrhizal fungus

We have achieved the symbiotic cultivation of an apparently achlorophyllous orchid, Epipogium roseum Lindl., with a mycorrhizal fungus isolated from an underground organ of this orchid. Although the seed germination rate was extremely low, subsequent growth from protocorm to flowering was induced in a medium containing volcanic soils and sawdust. Stolons elongated from each protocorm, and rhizomes were formed at certain intervals on the stolons. Some of the rhizomes developed into a coralloid form, and tubers were formed from the coralloid rhizomes. The coralloid rhizomes degenerated concurrently with maturation of the tubers. Six months after seed sowing, around 80 tubers were produced from a single protocorm. An inflorescence appeared from each of the large tubers, and the process to flowering was observed in one of these. Consequently, the developmental processes from seed to flowering in E. roseum was clearly revealed in this study.     

Essential mycorrhizal partners of the endemic Chilean orchids Chloraea collicensis and C. gavilu

Orchids are obligate mycoheterotrophic plants, relying on fungal nutrient resources to grow for their entire life or until they develop into photosynthetic seedlings. In Chile, orchids are represented by 7 genera and 63 species, 27 of which are endemic. Some Chilean species are considered endangered or rare, but many are insufficiently known. This study aims to isolate, culture, and identify fungal species found in symbiosis with the endemic Chilean orchids Chloraea collicensis Kraenzl. and Chloraea gavilu Lindl. for their potential to be used in future conservation programs. Roots of both species of orchids were collected in the field and those presenting pelotons were firstly cultured in agar-water and thereafter sub-cultured in potato dextrose agar media. Fungal colony growth was measured under the dissecting microscope. Fungal isolates from C. gavilu showed a higher growth rate than isolates from C. collicensis and could be used as inoculum for seed germination in further studies. Isolated colonies showed morphological characteristics of the form genus Rhizoctonia and presented two nuclei per cell. The ITS-nrDNA sequences confirmed their morphological identification as species of Tulasnella.     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.     

Molecular identification of the mycorrhizal fungi of the epiparasitic plant Monotropastrum humile var. glaberrimum (Ericaceae)

Achlorophyllous monotropoid plants (Monotropoideae, Ericaceae) are epiparasites that obtain all of their carbon from their host plants via connections with mycorrhizal fungi. The mycorrhizal fungi of the epiparasitic monotropoid Monotropastrum humile var. glaberrima were identified based on mitochondrial, large ribosomal DNA sequences, and were compared with those of another variety, M. humile var. humile. The fungi that inhabit M. humile var. glaberrimum belong to the Thelephoraceae, whereas that of M. humile var. humile is a member of the Russulaceae. Two explanations are possible for this phenomenon: a misunderstanding of the taxonomic position of M. humile var. glaberrimum, or a change in the fungal partner within the Monotropastrum.     

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.     

Specificity and localised distribution of mycorrhizal fungi in the soil may contribute to co-existence of orchid species

Co-occurring orchid species tend to occupy different areas and associate with different mycorrhizal fungi, suggesting that orchid mycorrhizal (OrM) fungi may be unevenly distributed within the soil and, therefore, impact the aboveground spatial distribution of orchids. To test this hypothesis, we investigated spatial variations in the community of potential OrM associates within the roots of three co-habitating orchid species (Anacamptis morio, Gymnadenia conopsea, and Orchis mascula) and the surrounding soil in an orchid-rich calcareous grassland in Southern Belgium using 454 amplicon pyrosequencing. Putative OrM fungi were broadly distributed in the soil, although variations in community composition were strongly related to the proximal host plant. The diversity and frequency of sequences corresponding to OrM fungi in the soil declined with increasing distance from orchid plants, suggesting that the clustered distribution of orchid species may to some extent be explained by the localised distribution of species-specific mycorrhizal associates.     

Response of citronella Java (Cymbopogon winterianus Jowitt) to VA mycorrhizal fungi and soil compaction in relation to P supply

Nutrient acquisition and growth of citronella Java (Cymbopogon winterianus Jowitt) was studied in a P-deficient sandy soil to determine the effects of mycorrhizal symbiosis and soil compaction. A pasteurized sandy loam soil was inoculated either with rhizosphere microorganisms excluding VAM fungi (non-mycorrhizal) or with the VAM fungus, Glomus intraradices Schenck and Smith (mycorrhizal) and supplied with 0, 50 or 100 mg P kg^-1 soil. The soil was compacted to a bulk density of 1.2 and 1.4 Mg m^-3 (dry soil basis). G. intraradices substantially increased root and shoot biomass, root length, nutrient (P, Zn and Cu) uptake per unit root length and nutrient concentrations in the plant, compared to inoculation with rhizosphere microorganisms when the soil was at the low bulk density and not amended with P. Little or no plant response to the VAM fungus was observed when the soil was supplied with 50 or 100 mg P kg^-1 soil and/or compacted to the highest bulk density. At higher soil compaction and P supply the VAM fungus significantly reduced root length. Non-mycorrhizal plants at higher soil compaction produced relatively thinner roots and had higher concentrations and uptake of P, Zn and Cu than at lower soil compaction, particularly under conditions of P deficiency. The quality of citronella Java oil measured in terms citronellal and d-citronellol concentration did not vary appreciably due to various soil treatments.     

Production of B-group vitamins by mycorrhizal fungi and actinomycetes isolated from the root zone of pine (Pinus sylvestris L.)

Summary Studies were carried out on synthesis of B-group vitamins by mycorrhizal fungi and actinomycetes (Streptomyces sp.) derived from soil, rhizosphere and mycorrhizosphere of pine.None of the fungal isolates produced biotin. The vitamin produced in largest amounts by the mycorrhizal fungi was thiamin.In general more actinomycetes isolated from the rhizosphere than from the root free soil produced B-group vitamins. This was particularly true for thiamin.The amount of vitamins produced was higher in actinomycetes than the amounts produced by the mycorrhizal fungi.This research was carried out under problem MR.II. 16 coordinated by the Institute of Dendrology, Polish Academy of Sciences.     

Response of endangered plant species to inoculation with arbuscular mycorrhizal fungi and soil bacteria

Three endangered plant species, Plantago atrata and Pulsatilla slavica, which are on the IUCN red list of plants, and Senecio umbrosus, which is extinct in the wild in Poland, were inoculated with soil microorganisms to evaluate their responsiveness to inoculation and to select the most effective microbial consortium for application in conservation projects. Individuals of these taxa were cultivated with (1) native arbuscular mycorrhizal fungi (AMF) isolated from natural habitats of the investigated species, (2) a mixture of AMF strains available in the laboratory, and (3) a combination of AMF lab strains with rhizobacteria. The plants were found to be dependent on AMF for their growth; the mycorrhizal dependency for P. atrata was 91%, S. umbrosus-95%, and P. slavica-65%. The applied inocula did not significantly differ in the stimulation of the growth of P. atrata and S. umbrosus, while in P. slavica, native AMF proved to be the less efficient. We therefore conclude that AMF application can improve the ex situ propagation of these three threatened taxa and may contribute to the success of S. umbrosus reintroduction. A multilevel analysis of chlorophyll a fluorescence transients by the JIP test permitted an in vivo evaluation of plant vitality in terms of biophysical parameters quantifying photosynthetic energy conservation, which was found to be in good agreement with the results concerning physiological parameters. Therefore, the JIP test can be used to evaluate the influence of AMF on endangered plants, with the additional advantage of being applicable in monitoring in a noninvasive way the acclimatization of reintroduced species in nature.     

Use of mycorrhizal fungi and phosphorus fertilization to improve the yield of onion (Allium cepa L.) plant

Improving the economical yield of commonly cultivated crops is one of the most pressing social and scientific issues in modern agriculture. This paper was conducted to investigate the bio-efficacy of arbuscular mycorrhizal fungi (AMF) in improving phosphorous (P) utilization and increasing the yield of onion plant grown in sandy soil under a drip irrigation system. The obtained results showed that AMF inoculation of onion and application of 120 kg P fertilizer ha⁻¹ significantly increased the fresh and dry weights, chlorophyll content of onion as well as P concentration in the root, shoot, and bulb during two growing seasons. Moreover, AMF increased the bioavailability of P in the rhizosphere and significantly enhanced the N-utilization by the inoculated plant. The economic yield of the onion plant inoculated by AMF and fertilized by different doses of P fertilizer was much higher than that obtained by the control (without AMF). These findings indicated that inoculating the onion plant in the field with AMF could be very effective in increasing the yield of the onion plant. Additionally, this study suggests AMF as a low-cost and promising candidate for the sustainable production of the onion crop using reclaimed sandy soils and a drip irrigation system.Keyword: Onion, Mycorrhizal Fungi, Economic yield, P fertilization, N utilization, ¹⁵N     

Production of auxins and gibberellin-like substances by mycorrhizal fungi,bacteria and actinomycetes isolated from soil and the mycorrhizosphere of pine (Pinus silvestris L.)

Summary Production of auxins and gibberellin-like substances by mycorrhizal fungi, bacteria and actinomycetes isolated from the mycorrhizosphere of Scots pine was studied. Chromatography and biossays were used.Most of the organisms required tryptophan for auxins production. The highest biological activity exhibited substances located at R_f 0.2–0.4.The organisms produced minute amounts of gibberellin-like substances which appeared at different R_f values. It was stated that auxins production is much more common among the root zone organisms of pine than the production of gibberellin-like substances.This research was carried out under problem MR.II.16 coordinated by the Institute of Dendrology, Polish Academy of Sciences.     

Cryptostylis species (Orchidaceae) from a broad geographic and habitat range associate with a phylogenetically narrow lineage of Tulasnellaceae fungi

While many Australian terrestrial orchids have highly specialized mycorrhizal associations, we tested the hypothesis that the geographically widespread orchid genus Cryptostylis associates with a diversity of fungal species. Using fungal isolation and molecular approaches, we investigated the mycorrhizal associations of five Australian Cryptostylis species (27 sites sampled) and included limited sampling from three Asiatic Cryptostylis species (two sites). Like related orchid genera, Tulasnellaceae formed the main fungal associations of the Cryptostylis species we sampled, although some ectomycorrhizal, ericoid and saprotrophic fungi were detected infrequently. Each species of Australian Cryptostylis associated with three to seven Tulasnella Operational Taxonomic Units (OTUs), except for C. hunteriana where only one Tulasnella OTU was detected. In total, eleven Tulasnella OTUs associated with Australian Cryptostylis. The Asiatic Cryptostylis associated with four different Tulasnella OTUs belonging to the same lineage as the Australian species. While five Tulasnella OTUs (T. australiensis, T. prima, T. warcupii, T. densa, and T. punctata) were used by multiple species of Australian Cryptostylis, the most commonly used OTU differed between orchid species. The association with different Tulasnella fungi by Cryptostylis species co-occurring at the same site suggests that in any given environmental condition, Cryptostylis species may intrinsically favour different fungal OTUs.     

Temporal dynamics of tuber formation and related processes in a crossing population of potato (Solanum tuberosum)

The chronological relationships between stolon formation, stolon tip swelling, tuber initiation, flowering, senescence, growth and resorption of tubers were studied under field conditions in a diploid population of potato with 238 genotypes, the parental clones and seven tetraploid cultivars. Timing of tuber initiation was not closely related to the timing of stolon formation, flowering and duration of the plant cycle. Tuber initiation very often preceded stolon branching. The number and size distribution of tubers were largely influenced by the degree of stolon branching, the length of the stolon swelling period and tuber resorption. The peak production of stolons and swollen stolon tips largely took place within the flowering period, although in most genotypes, some stolon tip swelling took place until the end of the plant cycle. More information on the general temporal relationships between events related to tuber formation and plant development will contribute to a better understanding of the physiological and genetic basis of the processes leading to the production of harvestable tubers.     

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.     

Effect of physical, chemical and environmental characteristics on arbuscular mycorrhizal fungi in Brachiaria decumbens (Stapf) pastures

Aim:  To evaluate the effects of soil physical and chemical factors (pH, conductivity, humidity, available phosphorus and organic matter) and environmental factors (temperature, relative air humidity, altitude and atmospheric pressure) on arbuscular mycorrhizal fungi (AMF)– Brachiaria decumbens grass relationship. Furthermore to establish patterns of microbiological responses that allow to differentiate the study sites in two relief types.
Methods and Results:  Mycorrhizal characteristics (spore density, external hyphae and root colonizations by hyphae, vesicles and arbuscules), physical and chemical factors in soil and environmental factors were measured.
Conclusions:  The effect of physical, chemical and environmental factors on microbiological variables was related to the type of relief 'valley and hilly terrain'; the AMF behaviour was affected only over narrower ranges of evaluated variables. Similarly, the colonization of B. decumbens roots by AMF hyphae, vesicles and the mycorrhizal spore density follow different patterns according to the relief type.
Significance and Impact of the Study:  The type of relief is one of the factors to be taken into consideration to evaluate the AMF inoculum and root colonization of these pastures, because of the influence of slope – as physical property of soil – on AMF.