The influence of Rhizobium and arbuscular mycorrhizal fungi on nitrogen and phosphorus accumulation by Vicia faba

BACKGROUND AND AIMS: The aim of this study was to investigate the effects of the interactions between the microbial symbionts, Rhizobium and arbuscular mycorrhizal fungi (AMF) on N and P accumulation by broad bean (Vicia faba) and how increased N and P content influence biomass production, leaf area and net photosynthetic rate. METHODS: A multi-factorial experiment consisting of four different legume-microbial symbiotic associations and two nitrogen treatments was used to investigate the influence of the different microbial symbiotic associations on P accumulation, total N accumulation, biomass, leaf area and net photosynthesis in broad bean grown under low P conditions. KEY RESULTS: AMF promoted biomass production and photosynthetic rates by increasing the ratio of P to N accumulation. An increase in P was consistently associated with an increase in N accumulation and N productivity, expressed in terms of biomass and leaf area. Photosynthetic N use efficiency, irrespective of the inorganic source of N (e.g. NO3- or N2), was enhanced by increased P supply due to AMF. The presence of Rhizobium resulted in a significant decline in AMF colonization levels irrespective of N supply. Without Rhizobium, AMF colonization levels were higher in low N treatments. Presence or absence of AMF did not have a significant effect on nodule mass but high N with or without AMF led to a significant decline in nodule biomass. Plants with the Rhizobium and AMF symbiotic associations had higher photosynthetic rates per unit leaf area. CONCLUSIONS: The results indicated that the synergistic or additive interactions among the components of the tripartite symbiotic association (Rhizobium-AMF-broad bean) increased plant productivity.     

Response of strawberry to inoculation with arbuscular mycorrhizal fungi under very high soil phosphorus conditions

A field study was done to assess the potential benefit of arbuscular mycorrhizal (AM) inoculation of elite strawberry plants on plant multiplication, under typical strawberry nursery conditions and, in particular, high soil P fertility (Mehlich-3 extractible P=498 mg kg⁻¹). Commercially in vitro propagated elite plants of five cultivars (‘Chambly,’ ‘Glooscap,’ ‘Joliette,’ ‘Kent,’ and ‘Sweet Charlie’) were transplanted in noninoculated growth substrate or in substrate inoculated with Glomus intraradices or with a mixture of species (G. intraradices, Glomus mosseae, and Glomus etunicatum) at the acclimation stage and were grown for 6 weeks before transplantation in the field. We found that AM fungi can impact on plant productivity in a soil classified as excessively rich in P. Inoculated mother plants produced about 25% fewer daughter plants than the control in Chambly (P=0.03), and Glooscap produced about 50% more (P=0.008) daughter plants when inoculated with G. intraradices, while the productivity of other cultivars was not significantly decreased. Daughter plant shoot mass was not affected by treatments, but their roots had lower, higher, or similar mass, depending on the cultivar–inoculum combination. Root mass was unrelated to plant number. The average level of AM colonization of daughter plants produced by noninoculated mother plants did not exceed 2%, whereas plants produced from inoculated mothers had over 10% of their root length colonized 7 weeks after transplantation of mother plants and ∼6% after 14 weeks (harvest), suggesting that the AM fungi brought into the field by inoculated mother plants had established and spread up to the daughter plants. The host or nonhost nature of the crop species preceding strawberry plant production (barley or buckwheat) had no effect on soil mycorrhizal potential, on mother plant productivity, or on daughter plant mycorrhizal development. Thus, in soil excessively rich in P, inoculation may be the only option for management of the symbiosis.     

Synergistic interaction of Rhizobium leguminosarum bv. viciae and arbuscular mycorrhizal fungi as a plant growth promoting biofertilizers for faba bean (Vicia faba L.) in alkaline soil

Egyptian soils are generally characterized by slightly alkaline to alkaline pH values (7.5–8.7) which are mainly due to its dry environment. In arid and semi-arid regions, salts are less concentrated and sodium dominates in carbonate and bicarbonate forms, which enhance the formation of alkaline soils. Alkaline soils have fertility problems due to poor physical properties which adversely affect the growth and the yield of crops. Therefore, this study was devoted to investigating the synergistic interaction of Rhizobium and arbuscular mycorrhizal fungi for improving growth of faba bean grown in alkaline soil. A total of 20 rhizobial isolates and 4 species of arbuscular mycorrhizal fungi (AMF) were isolated. The rhizobial isolates were investigated for their ability to grow under alkaline stress. Out of 20 isolates 3 isolates were selected as tolerant isolates. These 3 rhizobial isolates were identified on the bases of the sequences of the gene encoding 16S rRNA and designated as Rhizobium sp. Egypt 16 (HM622137), Rhizobium sp. Egypt 27 (HM622138) and Rhizobium leguminosarum bv. viciae STDF-Egypt 19 (HM587713). The best alkaline tolerant was R. leguminosarum bv. viciae STDF-Egypt 19 (HM587713). The effect of R. leguminosarum bv. viciae STDF-Egypt 19 and mixture of AMF (Acaulospora laevis, Glomus geosporum, Glomus mosseae and Scutellospora armeniaca) both individually and in combination on nodulation, nitrogen fixation and growth of Vicia faba under alkalinity stress were assessed. A significant increase over control in number and mass of nodules, nitrogenase activity, leghaemoglobin content of nodule, mycorrhizal colonization, dry mass of root and shoot was recorded in dual inoculated plants than plants with individual inoculation. The enhancement of nitrogen fixation of faba bean could be attributed to AMF facilitating the mobilization of certain elements such as P, Fe, K and other minerals that involve in synthesis of nitrogenase and leghaemoglobin. Thus it is clear that the dual inoculation with Rhizobium and AMF biofertilizer is more effective for promoting growth of faba bean grown in alkaline soils than the individual treatment, reflecting the existence of synergistic relationships among the inoculants.     

Responses of soil microbial catabolic diversity to arbuscular mycorrhizal inoculation and soil disinfection

Although it is usually admitted that arbuscular mycorrhizal (AM) fungi are key components in soil bio-functioning, little is known on the response of microbial functional diversity to AM inoculation. The aims of the present study were to determine the influence of Glomus intraradices inoculum densities on plant growth and soil microflora functional diversity in autoclaved soil or non-disinfected soil. Microbial diversity of soil treatments was assessed by measuring the patterns of in situ catabolic potential of microbial communities. The soil disinfection increased sorghum growth, but lowered catabolic evenness (4.8) compared to that recorded in the non-disinfected soil (6.5). G. intraradices inoculation induced a higher plant growth in the autoclaved soil than in the non-disinfected soil. This AM effect was positively related to inoculum density. Catabolic evenness and richness were positively correlated with the number of inoculated AM propagules in the autoclaved soil, but negatively correlated in the non-disinfected soil. In addition, after soil disinfection and AM inoculation, these microbial functionality indicators had higher values than in the autoclaved or in the non-disinfected soil without AM inoculation. These results are discussed in relation to the ecological influence of AM inoculation, with selected fungal strains and their associated microflora on native soil microbial activity.     

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.     

Genetic processes in arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi (Glomeromycota) colonize roots of the majority of land plants and facilitate their mineral nutrient uptake. Consequently, AM fungi play an important role in terrestrial ecosystems and are becoming a component of sustainable land management practices. The absence of sexual reproductive structures in modern Glomeromycota combined with their long evolutionary history suggest that these fungi may represent an ancient asexual lineage of great potential interest to evolutionary biology. However, many aspects of basic AM fungal biology, including genome structure, within-individual genetic variation, and reproductive mode are poorly understood. These knowledge gaps hinder research on the mechanisms of AM fungal interactions with individual plants and plant communities, and utilization of AM fungi in agricultural practices. I present here the current state of research on the reproduction in AM fungi and indicate what new findings can be expected in the future.     

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.     

中国盐碱土壤中AM菌的生态分布

对我国盐碱土壤中丛枝菌根（Ａｒｂｕｓｃｕｌａｒ Ｍｙｃｏｒｒｈｉｚａ,ＡＭ） 菌的种属构成、生态分布状况进行了研究．结果表明,不同地区ＡＭ 菌种属构成不同,其种属组成、分布与土壤类型、碱化度和土壤有机质含量有关．盐渍化砂土、壤土和粘土中,Ｇｌｏｍｕｓ 属的真菌数量最多,Ａｃａｕｌｏｓｐｏｒａ 属次之,而Ｇｌｏｍｕｓ 属中的Ｇ．ｍｏｓｓｅａｅ 则是分布最为广泛的菌种．随土壤碱化度的增加,Ｇｌｏｍｕｓ ｍｏｓｓｅａｅ 出现频率随之相对增加．在一定范围内有机质含量越高,土壤中ＡＭ 菌种和属的种类就越多．ＡＭ 菌的种属组成因不同寄主植物而异,其中豆科植物根围中ＡＭ 菌分布的种属数量最多．     

Seasonal dynamics of arbuscular mycorrhizal fungi in differing wetland habitats

The dynamics and role of arbuscular mycorrhizal fungi (AMF) have been well described in terrestrial ecosystems; however, little is known about how the dynamics of AMF are related to the ecology of wetland ecosystems. The seasonal dynamics of arbuscular mycorrhizal (AM) colonization within different wetland habitats were examined in this study to determine the factors that influence AM associations and to further assess the ecological role of AMF in wetlands. Fen and marsh habitats of four wetlands in west central Ohio were sampled monthly from March to September. AMF were found at all four sites for each month sampled and were present in all of the dominant plant species. A significant effect of month (P<0.001) on AM colonization did occur and was attributable to maximum colonization levels in the spring and minimum levels in late summer. This trend existed in all four wetlands in both fen and marsh habitats, regardless of variation in water levels, percent soil moisture, or available phosphorus levels. Because abiotic factors had minimal influence on AM colonization variation and the level of AM colonization paralleled plant growth patterns, we conclude that the AM seasonal dynamic was in response to plant phenology. Our data suggest that AM associations in temperate fen and marsh habitats are prevalent in the spring during new root and vegetative growth, even for plants experiencing flooded conditions. Evidence of an overriding AM seasonal trend indicates that future studies should include a seasonal component to better assess the role and distribution of AMF in wetland ecosystems.     

Effects of long-term NP-fertilization on abundance and diversity of arbuscular mycorrhizal fungi under a maize cropping system

Diversity of arbuscular mycorrhizal fungi (AMF) in 27-year long-term NP-fertilization plots under a maize cropping system in Thailand was studied through spore morphological characterization. The plots received 0–0, 60–60, 120–120 and 180–180 kg N-P₂O₅ ha^–1 year^–1 as ammonium sulfate and triple superphosphate. The plots were sampled monthly for one year, the AMF spores were counted and morphotyped, and taxa were identified after morphotyping and monospecific pot culture. Spore number g^–1 soil, relative spore abundance and Shannon-Wiener indexes were calculated. Sixteen putative taxa were recorded from the field of which nine sporulated on maize roots in pot culture. The long-term fertilization caused decreases in AMF total spore numbers and variation in species diversity depended on sampling time. Effects of fertilization on spore number and also relative spore abundance varied with species and sampling time. Among the nine species sporulating under maize, only Acaulospora sp.1 showed no change (P > 0.003 after Bonferroni correction) in spore number with fertilization in the field; and was therefore classified as an AMF species insensitive to fertilization. Spores of Entrophospora schenckii, Glomus mosseae, Glomus sp.1, Glomus geosporum-like and Scutellospora fulgida, though they decreased in absolute numbers in response to fertilization, showed no change (P > 0.003 after Bonferroni correction) in relative abundance; these species were classified as AMF species slightly sensitive to fertilization. Three unidentified species of Glomus, though they decreased in absolute numbers in response to fertilization, showed decreases (P < 0.003 after Bonferroni correction) in relative abundance; these species were classified as AMF species highly sensitive to fertilization.     

Different growth response of five co-existing stoloniferous plant species to inoculation with native arbuscular mycorrhizal fungi

Five species of stoloniferous plants originating from the same field site (Galeobdolon montanum, Glechoma hederacea, Potentilla anserina, Ranunculus repens and Trifolium repens) were studied with respect to their interaction with arbuscular mycorrhizal (AM) fungi. More specifically, the question was addressed whether mycorrhizal growth response of host plant species could be related to their vegetative mobility. The roots of all the species examined were colonised with AM fungi in the field, with the percentage of colonisation varying among species from approximately 40% to 90%. In a subsequent pot experiment, plants of all the species were either left non-inoculated or were inoculated with a mixture of three native AM fungi isolated from the site of plant origin (Glomus mosseae, G. intraradices and G. microaggregatum). AM fungi increased phosphorus uptake in all the plant species; however, plant growth response to inoculation varied widely from negative to positive. In addition to the biomass response, AM inoculation led to a change in clonal growth traits such as stolon number and length or ramet number in some species. Possible causes of the observed differences in mycorrhizal growth response of various stoloniferous plants are discussed.     

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.     

Putative sites for nutrient uptake in arbuscular mycorrhizal fungi

Nutrition of the arbuscular mycorrhiza (AM) is addressed from a fungal point of view. Intraradical and extraradical structures proposed as preferential sites for nutrient acquisition in arbuscular mycorrhizal (AM) fungi are considered, and their main features compared. This comparison includes the formation and function of branched structures (either intra- or extraradical) as putative nutrient uptake sites with unique morphological and physiological features in the AM fungal colony. The morphology and functioning of these structures are further affected by intra- or extraradical environmental factors. A model is presented which portrays the intrinsic developmental and physiological duality of the AM fungus. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Increasing phosphorus removal in willow and poplar vegetation filters using arbuscular mycorrhizal fungi

Fast growing woody species are increasingly used in vegetation filters for wastewater treatment. Their efficiency in phosphorus (P) removal notably depends on plant uptake and storage in aboveground tissues. In this study, Populus NM5 (P. nigra × P. maximowiczii), Salix miyabeana (SX64) and Salix viminalis (5027) were planted in pots to evaluate the influence of colonization by arbuscular mycorrhizal fungi (AMF) Glomus intraradices on P uptake using two different P concentrations in irrigation water. Based on analysis of the foliar and woody components, our results show that the two treatments (inoculation with G. intaradices and P-irrigation) interact differently with total P content. Foliar P content is principally enhanced by the P-irrigation concentration, whereas the mycorrhizal colonization increases stem P content. In the presence of G. intraradices, both S. miyabeana and S. viminalis showed a 33% increase in stem P content. The latter finding is mainly due to an increase in biomass production, without modification of the P concentration, indicating that AMF associations affect P use efficiency. Thus, using arbuscular mycorrhizal fungi for phytoremediation strategies may increase biomass productivity and hence improve pollutant uptake.     

Response of 11 eucalyptus species to inoculation with three arbuscular mycorrhizal fungi

 Numerous publications have reported growth stimulation of Eucalyptus following ectomycorrhizal inoculation in nursery or field conditions. Although Eucalyptus species can also form arbuscular mycorrhiza, their dependency on this type of mycorrhiza is still debatable. This paper presents information on the effect of inoculation of arbuscular mycorrhizal fungi on eucalypt growth. Twenty weeks after mycorrhizal inoculation, Eucalyptus seedlings' stem dry weight could be increased up to 49% compared to non-inoculated control plants. Intensity of root colonization by a given fungus depended on the host species, but it was not related to a plant growth response. Leaf phosphorus concentration of non-inoculated Eucalyptus seedlings varied greatly between species. Increases in leaf phosphorus concentration following mycorrhizal infection were not necessarily associated with plant growth stimulation. The most mycorrhiza-dependent Eucalyptus species tended to be those having the highest leaf phosphorus concentration in the absence of a fungal symbiont. These mycorrhiza-dependent Eucalyptus species seem to have greater phosphorus requirements and consequently to rely more on the symbiotic association. Accepted: 1 September 1995     

间作作物种间相互作用对马铃薯根际土壤丛枝菌根真菌的影响

为揭示间作作物种间相互作用对土壤丛枝菌根(AM)真菌的影响,以马铃薯单作(T0)为对照,基于高通量测序平台的方法,研究了连续3年马铃薯‖玉米(T1)、马铃薯‖蚕豆(T2)下马铃薯根际土壤AM真菌群落组成、多样性与土壤环境因子间的相互关系.结果表明:共获得2893个AM真菌操作分类单元(OTUs),分属1门、3纲、4目、...     

Determination of the nitrogen source for arbuscular mycorrhizal fungi by 15N application to soil and plants

The source of nitrogen in the spores of arbuscular mycorrhizal (AM) fungi was quantified by a ¹⁵N-labeling technique. N was applied as coated urea to the soil and in solution to plant shoots. Soil-applied fertilizer had a significant effect on spore % ¹⁵N (P<0.01), with a 24–75% contribution to spore N. Fertilizer applied to either alfalfa shoots or bahia grass shoots had little effect on spore % ¹⁵N, accounting for 0–14% or 1–9% of spore N, respectively. These results indicate that AM fungi obtain spore N mostly from the soil. The small amount of spore N originating from shoot-applied N may have been obtained via root exudation. Accepted: 6 November 2000     

丛枝菌根真菌产球囊霉素研究进展

球囊霉素（Glomalin）是由丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）产生的一种含金属离子的糖蛋白,由于丛枝菌根真菌在自然和人工陆生生态系统中广泛分布,丛枝菌根真菌在生态系统中的生态学功能一直是菌根生物学研究中诱人的问题。自1996年球囊霉素被发现以来,球囊霉素在土壤生态系统中的生态学功能、生态学地位日益受到重视。本文对球囊霉素作为土壤主要有机源和超级胶的功能作了简介,综述了球囊霉素的研究现状,并对其研究前景作了展望。