Soil disturbance and infection of Trifolium repens roots by vesicular-arbuscular mycorrhizal fungi

Removal and storage of the surface layers of soil is known to decrease the infectivity of vesicular-arbuscular mycorrhizal (VAM) fungi. Previous studies have mostly examined the effects of profound soil disturbance on the infectivity of VAM fungi. This study examined the effects of increasing degrees of topsoil disturbance on the infectivity of VAM fungi in two sites on sandstone soils in southeastern Australia. Intact soil blocks (20×20×15 cm) were taken from each of the two sites. Increasing degrees of topsoil disturbance were achieved by cutting the blocks longitudinally into four (dist. 1), nine (dist. 2), and 25 (dist. 3) equal portions. Seeds of Trifolium repens L. were sown into the blocks and harvested 14, 21, 28, 35 and 42 days after sowing. At each sampling date, total root length, root length colonised by VAM fungi and shoot dry mass were measured. VAM colonisation had commenced by 14 days in the roots of seedlings grown in intact, dist. 1, and dist. 2 soil blocks. The initiation of VAM colonisation was delayed by up to 6 weeks for seedlings grown in the dist. 3 soil blocks. The low (i.e. dist. 1) and intermediate (i.e. dist. 2) degrees of soil disturbance did not cause a delay in the initiation of VAM, bud did significantly reduce the proportion of root length colonised by VAM fungi after 21 days. After 21 days, shoot dry mass was significantly less in the seedlings grown in the dist. 3 soil blocks though not in the low and intermediate disturbance treatments. It is concluded that the most severe experimental disturbance probably disturbed the external hyphal network and root fragments (containing hyphae and vesicles), which in turn temporarily reduced the infective potential of the fungus to zero. The observed delay in the initiation of VAM in the most disturbed blocks can, therefore, be explained by the time required for hyphae to grow from other propagules in the soil which survived the disturbance event.     

Arbuscular mycorrhizal fungi reduce cadmium accumulation in plants: evidence and uncertainty

Plant and Soil - Carbon stocks in alpine meadows on the Qinghai-Tibetan Plateau are being threatened by increases in livestock herding practices. However, the extent to which current fast-growing...     

Arbuscular mycorrhizal fungi and nitrogen uptake

Nitrogen (N) is among the most important macro-nutrients significantly affecting plant growth and yield production. Accordingly, N must be supplied adequately so that optimum amounts of yield are resulted. There are different ways of supplying N to the plant including the use of chemical and biological fertilization. The chemical properties of N make it very mobile, especially under humid conditions. Hence, N must not be overfertilized with respect to the economical and environmental points of view. N Biological fertilization includes the use of plant growth-promoting rhizobacteria (PGPR) including the N-fixing bacteria, rhizobium. There are also arbuscular mycorrhizal (AM) fungi in the soil, which are symbiotic to most terrestrial plants enhancing plant growth and yield production through increasing the uptake of water and nutrients by the host plant. Numerous experiments have indicated the important role of AM fungi in enhancing P uptake by plant. However, it is yet a matter of debate that how AM fungi may affect soil N dynamic and hence plant N uptake. Some of the most important and recent aspects regarding such effects by AM fungi are highlighted, which can be of significance to health and productivity of the ecosystem.     

Arbuscular mycorrhizal fungi reduce the differences in competitiveness between dominant and subordinate plant species

In grassland communities, plants can be classified as dominants or subordinates according to their relative abundances, but the factors controlling such distributions remain unclear. Here, we test whether the presence of the arbuscular mycorrhizal (AM) fungus Glomus intraradices affects the competitiveness of two dominant (Taraxacum officinale and Agrostis capillaris) and two subordinate species (Prunella vulgaris and Achillea millefolium). Plants were grown in pots in the presence or absence of the fungus, in monoculture and in mixtures of both species groups with two and four species. In the absence of G. intraradices, dominants were clearly more competitive than subordinates. In inoculated pots, the fungus acted towards the parasitic end of the mutualism–parasitism continuum and had an overall negative effect on the growth of the plant species. However, the negative effects of the AM fungus were more pronounced on dominant species reducing the differences in competitiveness between dominant and subordinate species. The effects of G. intraradices varied with species composition highlighting the importance of plant community to mediate the effects of AM fungi. Dominant species were negatively affected from the AM fungus in mixtures, while subordinates grew identically with and without the fungus. Therefore, our findings predict that the plant dominance hierarchy may flatten out when dominant species are more reduced than subordinate species in an unfavourable AM fungal relationship (parasitism).     

Arbuscular mycorrhizal fungi in terms of symbiosis-parasitism continuum

Arbuscular mycorrhizal fungi are forming the most wide-spread mycorrhizal relationships on Earth. Mycorrhiza contributes to phosphorous acquisition, water absorption and resistance to diseases. The fungus promotes the absorption of nutrients and water from soil, meanwhile the host plant offers photosynthetic assimilates in exchange, like carbohydrates, as energy source. The plant benefits from the contribution of symbiotic partner only when nutrients are in low concentrations in soil and the root system would not be able to absorb sufficiently the minerals. When the help of mycorrhizal fungi is not necessarily needed, the host plant is making an economy of energy, suppressing the development of fungi in the internal radicular space. In this moment, the nature of relationship turns from symbiotic to parasitic, triggering a series of defensive reactions from the plant. Also, there were several cases reported when the presence of arbuscular mycorrhizal fungi negatively influenced the host plant. For example, in adverse environmental conditions, like very high temperatures, instead of determining a higher plant biomass and flowering, the mycorrhiza reduces the growth of the host plant. We conducted a pot experiment with hydroponic culture to examine the effect of arbuscular mycorrhiza on development of French marigold as a host plant. As experimental variants, the phosphorous content in nutrient medium and temperature varied. Plants were artificially infected with arbuscular mycorrhizal fungi using a commercial inoculum containing three fungal species, as following: Glomus intraradices, Glomus etunicatum and Glomus claroideum. Colonization intensity and arbuscular richness were checked using root staining with aniline blue and estimation with the Trouvelot method. To observe the differences between plants from the experimental variants, we examined the number of side shoots, flower buds and fully developed flowers, fresh biomass and total leaf area. Results show that adverse climatic conditions, like temperature shock at the beginning of growing period modified the nature of symbiosis. In this case, the physiological parameters were reduced at colonized plants, while usual, constant growing conditions permitted the normal, efficient and beneficial development of symbiosis.     

Arbuscular mycorrhizal fungi benefit drought-stressed Salsola laricina

Plant Ecology - Due to its contribution to plant drought tolerance, arbuscular mycorrhizae (AM) may play an important role in the revegetation of degraded pastures in semi-arid and arid regions....     

Arbuscular mycorrhizal fungi affect phytophagous insect specialism

The majority of phytophagous insects eat very few plant species, yet the ecological and evolutionary forces that have driven such specialism are not entirely understood. The hypothesis that arbuscular mycorrhizal (AM) fungi can determine phytophagous insect specialism, through differential effects on insect growth, was tested using examples from the British flora. In the UK, plant families and species in the family Lamiaceae that are strongly mycorrhizal have higher proportions of specialist insects feeding on them than those that are weakly mycorrhizal. We suggest that AM fungi can affect the composition of insect assemblages on plants and are a hitherto unconsidered factor in the evolution of insect specialism.     

西藏东南部地区的丛枝菌根真菌

在西藏东南部地区不同生境中的植物根围采集了土壤样品131份,从中分离并鉴定出5属32种丛枝菌根真菌,其中无梗囊霉属Acaulospora11种,原囊霉属Archaeospora1种,球囊霉Glomus17种,和平囊霉Pacispora2种,盾巨孢囊霉Scutellospora1种。其中格但无梗囊霉Acaulosporagedanensis,黄孢球囊霉Glomusflavisporum,英弗梅球囊霉Glomusinvermaium,玻利维亚和平囊霉Pacisporaboliviana为我国四个新记录种。     

Arbuscular mycorrhizal fungi in two mangroves in South China

The symbiosis between arbuscular mycorrhizal fungi (AMF) and mangrove plant species was investigated in two mangrove swamps in south China. AMF were mostly found in the form of hyphae and were commonly associated with all the mangrove species we investigated. Six AMF species belonging to the genera Glomus or Acaulospora were identified. Multiple step-wise linear regression analyses showed that hydrological conditions and phosphorus levels in the rhizosphere were the main abiotic factors affecting the colonization of mangrove species by AMF. A greenhouse experiment was conducted to evaluate the effects of AMF inoculation on the growth and nutrient uptake of a true mangrove plant species, Sonneratia apetala B. Ham. The inoculated AMF significantly improved growth, resulting in greater plant height, diameter at ground level and plant biomass, as well as increased absorption of N, P and K. These findings suggest that AMF play important roles in mangrove ecosystems.     

Arbuscular mycorrhizal structure and fungi associated with mosses

We investigated the colonization and diversity of arbuscular mycorrhizal (AM) fungi associated with 24 moss species belonging to 16 families in China. AM fungal structures, i.e. spores, vesicles, hyphal coils (including intracellular hyphae), or intercellular nonseptate hyphae, were found in 21 moss species. AM fungal structures (vesicles, hyphal coils, and intercellular nonseptate hyphae) were present in tissues of 14 moss species, and spores and nonseptate hyphae on the surface of gametophytes occurred in 15 species. AM fungal structures were present in 11 of the 12 saxicolous moss species and in six of the ten terricolous moss species, but absent in two epixylous moss species. AM fungal structures were only observed in moss stem and leaf tissues, but not in rhizoids. A total of 15 AM fungal taxa were isolated based on trap culture with clover, using 13 moss species as inocula. Of these AM fungi, 11 belonged to Glomus, two to Acaulospora, one to Gigaspora, and one to Paraglomus. Our results suggest that AM fungal structures commonly occur in most mosses and that diverse AM fungi, particularly Glomus species, are associated with mosses.     

Influence of inoculum density of two vesicular–arbuscular mycorrhizal fungi and temperature/light intensity on Trifolium repens

The influence of three inoculum densities of Glomus caledonius and G. epigaeus and two temperature/light intensity conditions was investigated on Trifolium repens. The significance of inoculation was compared to the significance of naturally occurring vesicular–arbuscular mycorrhizal (VAM) fungi and to application of soluble phosphate fertilizer. Increasing density of inoculum and the highest temperature/light intensity condition tested increased VAM infection, whereas only small differences were found between efficiency of the two introduced VAM fungi. The presence of naturally occurring VAM fungi proved as efficient in establishing infection as the most successful inoculations. Some interactions among the investigated parameters were found for several recordings. The increase in VAM infection was followed by an increase in number of nodules; in uptake of phosphorus, nitrogen, zinc, and copper; and in growth of roots and shoots. The calculated inflow of phosphate, zinc, and copper into roots was not associated with inoculum density, VAM species or temperature/light conditions. Compared to an uninoculated control without application of phosphate, inoculation with the highest spore density increased (after 18 weeks growth) the dry weight of shoot 52 fold and 7 fold for G. caledonius , and 121 fold and 9 fold for G. epigaeus at low and high temperature/light conditions, respectively. It was also found that VAM increased weight per nodule 52% when roots with no or sparse VAM infection were compared to roots with low to maximal VAM infection and 98% when roots with low VAM infection were excluded. Application of phosphate fertilizer enhanced nodulation and growth of non–mycorrhizal plants to a level similar to that of the most heavily VAM infected plants.     

Arbuscular mycorrhizal fungi, Collembola and plant growth

Arbuscular mycorrhizal fungi are ubiquitous in field soils, as are mycophagous animals such as Collembola. It has been suggested that these animals reduce the functioning of the mycorrhiza and are thus detrimental to plant growth. However, recent choice experiments suggest that Collembola preferentially feed on nonmycorrhizal fungi in the rhizosphere. If these preferences also occur in field soils, then Collembola might indirectly benefit plants through an enhancement of mycorrhizal functioning and indirect multitrophic links to foliar-feeding insect herbivores.     

Arbuscular mycorrhizal fungi influence visitation rates of pollinating insects

Abstract.  1. Arbuscular mycorrhizal (AM) fungi can increase a number of plant traits to which pollinating insects are known to respond. These include total plant size, flower number, flower size, and amount of pollen produced.
2. It was hypothesised that these effects would lead to a different visitation rate of pollinating insects on mycorrhizal and non-mycorrhizal plants. To test this idea, three species of annual plants ( Centaurea cyanus , Tagetes erecta , and Tagetes patula ) were grown with and without AM fungi and the visits by pollinating insects were recorded over a 2-month period.
3. In all three species, mycorrhizal plants experienced a greater number of pollinator visits per flower per unit time. Diptera and Hymenoptera were the predominant insects and the latter order showed the strongest response.
4. Here, it is suggested that mycorrhizal fungi increase floral visitation rates by insects, but that the mechanism varies from one plant species to another. In C. cyanus , it appears to be due to flower number per plant, in T. patula it is individual inflorescence size, and in T. patula it is nectar standing crop per inflorescence.     

未来的一种生物肥料:丛枝菌根真菌*

丛枝菌根真菌(Arbuscular Mycorrhizal Fungi,AMF)存在于几乎所有类型的土壤中,可以与绝大多数被子植物的根共生。大多数农作物、果树、蔬菜、观赏植物和花卉等都能形成丛枝菌根。AMF能促进作物吸收利用矿质养分和水分,提高作物抗逆性和抗病性,改良土壤、提高苗木移栽成活率、促进生长、提高产量和改善品质,并且可用于改善退化生态系统的土壤肥力,维持农林业的可持续发展,将成为一种新型的生物肥料被用于农林业生产。本文讨论了影响菌根侵染率的因素、AMF的生态效应和在生态农业中的应用现状和前景。     

AM真菌增强孔雀草耐阴性的效应

于温室盆栽不同光照条件（遮光率分别为0%、24%、48%、72%、96%）下,对孔雀草Tagetes patula进行接种丛枝菌根（arbuscular mycorrhiza,AM）真菌幼套近明球囊霉Claroideoglomus etunicatum、摩西斗管囊霉Funneliformis mosseae、球状巨孢嚢霉Gigaspora margarita和不接种对照处理,测定孔雀草菌根侵染率、生长指标和生理指标,旨在评价AM真菌对孔雀草耐阴性的影响。结果表明,供试AM真菌均能侵染孔雀草根系形成典型的丛枝菌根,不同遮光处理均以接种F. mosseae的侵染效果最佳,强光及弱光均不利于AM真菌侵染,当遮光率为24%时,孔雀草生长状况最佳。与不接种对照相比,接种F. mosseae显著提高了孔雀草株高、茎粗、叶面积、根冠比、比叶重、着花数和花茎,单花花期延长,提高了根系活力、叶绿素a、叶绿素b、总叶绿素和可溶性糖含量,降低了脯氨酸含量,光补偿点下降,光饱和点升高,最大净光合速率增大。结果表明,适当遮荫有利于孔雀草生长发育,接种AM真菌能增强孔雀草对光照的适应能力,促进植株生长发育,减缓弱光造成的损伤,增强其耐阴性,且以接种F. mosseae效果最好。     

Arbuscular mycorrhizal fungi reduce growth and infect roots of the non‐host plant Arabidopsis thaliana

The arbuscular mycorrhizal (AM) symbiosis is widespread throughout the plant kingdom and important for plant nutrition and ecosystem functioning. Nonetheless, most terrestrial ecosystems also contain a considerable number of non‐mycorrhizal plants. The interaction of such non‐host plants with AM fungi (AMF) is still poorly understood. Here, in three complementary experiments, we investigated whether the non‐mycorrhizal plant Arabidopsis thaliana, the model organism for plant molecular biology and genetics, interacts with AMF. We grew A. thaliana alone or together with a mycorrhizal host species (either Trifolium pratense or Lolium multiflorum) in the presence or absence of the AMF Rhizophagus irregularis. Plants were grown in a dual‐compartment system with a hyphal mesh separating roots of A. thaliana from roots of the host species, avoiding direct root competition. The host plants in the system ensured the presence of an active AM fungal network. AM fungal networks caused growth depressions in A. thaliana of more than 50% which were not observed in the absence of host plants. Microscopy analyses revealed that R. irregularis supported by a host plant was capable of infecting A. thaliana root tissues (up to 43% of root length colonized), but no arbuscules were observed. The results reveal high susceptibility of A. thaliana to R. irregularis, suggesting that A. thaliana is a suitable model plant to study non‐host/AMF interactions and the biological basis of AM incompatibility.