Vesicular-arbuscular Mycorrhizal Infection Research Articles

The role of mycorrhizas in the regeneration of some Malaysian forest trees

An investigation was made into the availability of mycorrhizal inoculum and the response of tree seedlings to mycorrhizal infection in West Malaysian forests. Spores of vesicular arbuscular (VA) mycorrhizal fungi in the soil were reduced by 25% after selective logging and by 75% after heavy logging, VA infection in the roots of plants persisting on, or colonizing, a heavily logged site was reduced by up to 75% . The most probable number (MPN) of VA propagules in sieved soil was up to ten times greater than spore density, but was also greatly reduced by heavy logging. This resulted in reduced infectivity of soil from the heavily logged site, as demonstrated by reduced VA infection of bioassay plants. The infectivity of soil declined following sun drying, but sun-dried soil devoid of vegetation retained some infectivity even after 12 months storage. Overall the data suggest that root and hyphal fragments are more important than spores as inoculum in disturbed forest, and that in undisturbed forest living roots and hyphae are likely to be important sources of infection. In a pot experiment, shoot growth of two test species, Albizia falcataria (L.) Becker and Parkia speciosa Hassk. responded more to VA mycorrhizal infection than to P fertilization over the range 0-6 g triple superphosphate per 8 kg of soil. The response to inoculation with a cocktail of ‘introduced’ VA fungi propagated in pot cultures was greater than the response to inoculation with ‘indigenous’ fungi propagated in pot cultures from roots and soil collected in undisturbed forests. Another test species, Intsia palembanica Miq., also responded better to mycorrhizal infection than to P fertilization, and better to VA mycorrhizal infection than to ectomycorrhizal infection. Intsia palembanica seedlings growing around mature dipterocarps quickly became ectomycorrhizal, suggesting that at least some ectomycorrhizal fungi infect both dipterocarps and Intsia. Shorea leprosula Miq. seedlings growing naturally in the forest had ectomycorrhizas 20 days after germination, i.e. before they had true leaves, and within 7 months supported up to 11 different ectomycorrhizal fungi. However, seedlings isolated from contact with the roots of mature Shorea trees remained uninfected in the held for up to 6 months. This shows the importance of contact with living ectomycorrhizal roots for early infection of dipterocarp seedlings, a point which should be recognized in logging operations and forest regeneration programmes.

The effect of growth substrate and fertilizer on the growth and vesicular-arbuscular mycorrhizal infection of three hosts

The effect of growth substrate in combination with two compound fertilizers or bone meal on the vesicular-arbuscular mycorrhizal (VAM) infection and growth of micropropagated strawberry (Fragaria x ananassa Duch.) and arctic bramble (Rubus arcticus L.), as well as maize (Zea mays L.) was studied in pot experiments. With all test plants, sand fertilized with bone meal was superior to the richer peat-based substrates in initiating rapid VA mycorrhizal infection and sporulation of the VAM fungi used. A fertilizing regime yielding plants of a sufficient size, which at the same time are mycorrhizal, is suggested.

Seasonality of VAM infection in three populations of Agrostis capillaris (Gramineae) on soil with or without heavy metal enrichment

Three populations of the perennial grass Agrostis capillaris, growing on limestone derived clay with and without natural enrichment of the heavy metals cadmium, lead, and zinc, and on a sandy soil polluted by a metal smelter have been investigated with regard to the percentage and seasonality of infection with vesicular-arbuscular mycorrhizal (VAM) fungi and its impact on mineral nutrition. In all populations VAM infection was lowest during winter, and highest during late summer and autumn. The population at the metal smelter site was less infected by VAM fungi than both other populations. The concentration of mineral nutrients for the three populations was clearly related to the soil concentration, but hardly modified by the degree of VAM infection.

Vesicular-arbuscular mycorrhiza in semi-arid pastures of south-west Queensland and their effect on growth responses to phosphorus fertilizers by grasses

Field and controlled environment studies were undertaken to determine the seasonal variation in vesicular-arbuscular mycorrhizal (VAM) propagules under different types of vegetation in the mulga (Acacia aneura) shrublands of south-western Queensland and how inoculation with VAM affects the growth and response to phosphorus fertilizers of several grasses common to this region. A most probable number (MPN) technique was used to estimate the number of viable VAM propagules under mulga shrubland and native pasture. There was a pronounced rise in MPN at a native pasture site from June to November, peaking at 1 propagule/g soil, before declining between November and May to non detectable concentrations. In the mulga shrubland site, MPN remained very low (less than 0.2 propagules/g soil) throughout the study. Pasture species in the field were screened for VAM infection in both winter and summer. Only three of the 14 species sampled were infected with VAM in winter (June) after a long drought. In contrast, 10 of the 14 species sampled in December possessed VAM-infected roots. A pot experiment was conducted to examine the influence of VAM inoculation on growth and the response to phosphate fertilizer of several important pasture grasses in pastures derived from mulga shrublands. The treatments comprised a factorial combination of inoculation or non-inoculation with VAM, four grass species (Aristida armata, Cenchms ciliaris cv. USA, Digitaria ammophilla, and Thyridolepis mitchelliana), and four rates of P fertilizer designed to range over very deficient to non-limiting for each species. All species except D. ammophilla produced growth responses to VAM inoculation. Though C. ciliaris and T. mitchelliana responded to VAM inoculation only in soil unamended with P fertilizer, A. amata showed growth responses across all P rates examined, suggesting some factor other than P was limiting this species. The growth response of the grasses to VAM inoculation was poorly correlated with the percentage of root infected with VAM. D. ammophilla had the highest levels of root infection (32%) despite producing no growth response to VAM. In contrast, T. mitchelliana had less than 2% of the root infected with VAM. All species had thin fibrous roots with long (0.35-0.47 mm), frequent root hairs. The differential growth responses to VAM inoculation of A. armata compared with the other grasses may provide a management strategy to control Aristida ingress into pastures established from mulga shrublands.

The effect of long-term applications of phosphorus fertilizer on populations of vesicular-arbuscular mycorrhizal fungi in pastures

We assessed whether 6-year-old applications of phosphorus (P) fertilizer to a previously unfertilized field site resulted in the selection of populations of vesicular-arbuscular (VA) mycorrhizal fungi that were more 'tolerant' of added P than the original VA mycorrhizal population at the site. In 1977, four rates of P (0, 49, 97 and 200 kg P/ha) were applied to a field site at Mt Barker, Western Australia. In 1983, either no P or a rate of P sufficient for maximum plant growth (352 kg P/ha) was applied to each of these plots and the formation of spores and colonization of roots by VA mycorrhizal fungi were examined in the following 3 years. Residual P from fertilizers applied in 1977 increased both the percentage of root length colonized and the length of root colonized by VA mycorrhizal fungi in 1983, 1984 and 1985. Colonization by 'medium hyphae' Glomus spp., Acaulospora laevis Gerd. and Trappe and fine endophyte increased in response to the 1977 applications of P. By contrast, colonization by Scutellospora calospora (Nicol. and Gerd.) Walker and Sanders decreased with the 1977 applications of P. Application of an adequate rate of P to the field plots in 1983 generally decreased the development of VA mycorrhizal infection in plots, to a greater extent where larger rates of P had previously been applied in 1977. We attributed this effect to higher initial levels of mycorrhizal colonization in the plots which received larger rates of P in 1977. The 1977 applications of P are unlikely to have resulted in the selection of strains of VA mycorrhizal fungi that are less tolerant of added P than the strains present in the unfertilized plots. There was a common relationship between VA mycorrhizal colonization and the residual value of the P applications which provided indirect evidence that there was no change in the P-tolerance of the indigenous VA mycorrhizal population in response to P applied in 1977. Interpretation of the effects of the 1977 and 1983 applications of P on VA mycorrhizal colonization was compounded by the effects these applications of P had on the botanical composition of the pasture and also on the inoculum potential in each plot. Spores of A. laevis and S. calospora were recovered from each field plot. The number of spores of A. laevis increased in response to P applied in 1977 and generally decreased in response to P applied in 1983. These effects could be directly related to the effects the 1977 and 1983 applications of P had on the length of root colonized by A. laevis in the preceding growing season.

Phosphorus efficiency of three cereals as related to indigenous mycorrhizal infection

The influence of indigenous vesicular-arbuscular mycorrhizal infection on the assessment of phosphorus (P) efficiency in wheat ( Triticum aestivum L. cv. Spear), barley (Hordeum vulgare L. cv. Galleon) and rye (Secale cereale L. cv. S.A. Commercial) was studied. P efficiency was defined in terms of uptake (mg P pot-1) or utilization (g dw mg-1 P). Experiments were set up with two soils which had low concentrations of plant available P and had been used in a previous study of P efficiency in cereals. Numbers of spores and infective propagules were significantly different in the two soils. In the soil with low propagule density, the extent of mycorrhizal infection of barley, wheat and rye increased with time. Twenty days after transplanting 3-day old seedlings, there was no difference in the percentage of root length infected (2.0%), but at 40 days, wheat (22.4%) and barley (19.3%) had significantly greater percentage of infected root than had rye (10.7%). At 30 days, wheat had a significantly higher percentage of root length infected than barley. In the soil with high propagule density, infection occurred more rapidly, so that the percentage of root length of wheat and barley infected was not significantly different at the three times of harvest. However, infection of rye significantly increased with time and was higher (31.8%) than that of barley (19.8%) at the final harvest. Mycorrhizal infection was positively correlated with efficiency of P uptake in barley, but not in wheat or rye. However, efficiency in utilization of P by barley and wheat was negatively correlated with infection. The colonization of cereals by the indigenous mycorrhizal fungi decreased with the addition of P to the soils. The results of these studies indicate the potential importance of mycorrhizal infection in assessment of P efficiency in cereals.

Response of two species ofcassiaandGliricidia sepiumto vesicular‐arbuscular mycorrhizal infection

Abstract A pot experiment was conducted to evaluate the response to vesicular‐arbuscular mycorrhizal (VAM) infection of two species of Cassia and Gliricidia sepium in an oxisol with two levels of soil P. At P level optimum for VAM activity, comparable levels of VAM infection were observed on the roots of the test species. However, the species reacted differently to VAM infection. Hence, VAM inoculation significantly stimulated dry matter accumulation in C. spectabilis and G. sepium, but had no positive influence on this variable in C. reticulata. These differences were not explainable in terms of tissue P status, because P uptake was significantly enhanced by inoculation in all the species tested. At the higher soil P level, roots of all species were colonized by the inoculum, but colonization level in C. reticulata and G. sepium was reduced. Nevertheless, only C. spectabilis benefitted from the presence VAM endophytes at this level of soil P. The results underline the significance of ascertaining the myc...

Distribution of vesicular-arbuscular mycorrhizal fungi in coal, lignite, and calcite mine spoils of India

We assessed vesicular-arbuscular mycorrhizal (VAM) fungi in coal, lignite, and calcite mine spoils. The level of VAM fungal infection and the population of VAM species in plants on the coal-waste sites were similar to those in plants on the calcite mine spoil. The plants on the coal-waste sites and their associated VAM fungi included Tephrosia purpurea (L.) Pers. with Glomus heterosporum and Sclerocystis microcarpus and Euphorbia hirta L. with G. botryoides and G. ambisporum. The recently revegetated lignite mine spoil supported Eragrostis sp. with G. globiferum, while the oldest revegetated lignite mine spoil supported Cocos nucifera L. with Scutellospora aurigloba and G. aggregatum, and Albizia lebbeck (L.) Benth. with Scutellospora dipapillosa and G. tenue. In the calcite mine spoil, roots of Mukia maderaspatana (L.) M. Romer with Sclerocystis sinuosa, G. dimorphicum, G. heterosporum and G. ambisporum and Datura metal L. with G. pustulatum and G. pulvinatum were found. The level of VAM infection and the population of VAM species in the oldest revegetated site (lignite mine spoil) were comparable with those in the coal-waste and calcite mine-spoil sites.

Categories of vesicular-arbuscular mycorrhizal dependency of host species

Brassica nigra and selected species of Leucaena and Sesbania were used as indicator hosts in a greenhouse experiment designed to establish distinct categories of mycorrhizal dependence. The plants were grown in an oxisol with different concentrations of established soil solution P in the presence or absence of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus aggregatum. The extent to which the plant species depended on the fungus for dry matter production diminished with increased concentrations of soil solution P, but the magnitude of this decrease varied from species to species. Five distinct mycorrhizal categories are proposed based on the differences observed, ranging from non-dependent to very highly dependent. The critical soil solution P concentrations that were useful for separating host species into distinct VAM-dependency groups were 0.02 and 0.2 mg/l. Species differing in their mycorrhizal dependency differed with respect to the soil solution P concentration required for the expression of maximum VAM effectiveness, the degree to which increasing concentrations of P depressed VAM infection and the pattern of immobile nutrient accumulation.

Effects of nitrate and ammonium nitrogen on vesicular-arbuscular mycorrhizal infection in letttuce (Lactuca sativa) grown in sand with nutrient solutions

Effects of nitrate and ammonium nitrogen on vesicular-arbuscular mycorrhizal infection in letttuce (Lactuca sativa) grown in sand with nutrient solutions

Influence of nitrogen on accumulation of isosojagol (a newly detected coumestan in soybean) and associated isoflavonoids in roots and nodules of mycorrhizal and non‐mycorrhizal soybean

summaryA newly detected coumestan was found to accumulate in roots of soybean (Glycine max. L., var. Amsoy 71), after infection by a vesicular arbuscular (VA) mycorrhizal fungus (Glomus intraradices, Schenck & Smith) and very strongly in nodules after nitrogen application. This coumestan was identified as a 3,9 dihydroxy 10 (γ,γ‐dimethylallyl) coumestan called isosojagol. Three other associated isoflavonoids were analysed: glyceollin I, coumestrol and daidzein. Nitrogen application decreased the concentration of these three compounds in roots, particularly in non‐mycorrhizal soybeans, whilst their concentration in nodules was not significantly affected. VA mycorrhizal infection decreased the accumulation of all the compounds analysed in nodules, although the fungus was never observed inside the nodule, but increased their accumulation in roots.

Quantification of Active Vesicular-Arbuscular Mycorrhizal Infection Using Image Analysis and Other Techniques

Methods for the objective measurement of vesicular-arbuscular mycorrhizal infection in the roots of four species of host plant are described. The methods are based on vital staining of transverse sections of fresh roots, followed by evaluation of occurrence and/or numbers of living arbuscules and hyphae per section. The most useful method involved freeze-sectioning roots embedded in gelatin containing glycerol and DMSO, followed by staining the sections with nitroblue tetrazolium overnight to reveal succinate dehydrogenese activity. Two systems of computer-aided image analysis were evaluated for measurement of the number, perimeter and cross-sectional areas of intercellular hyphae and arbuscules. This approach, which is clearly objective, is an advance on previous methods which were based on ranking sections or segments of root with respect to the intensity of development of arbuscules. The data were used to calculate the area of interface between plant and fungus in infected roots. Results are presented showing that the contribution of arbuscules to the total infection and area of interface declines markedly as plants and infections age. Differences in infection in different host/fungus combinations are also described.

VAM populations in relation to grass invasion associated with forest decline

Spruce stands in Northern Bohemia forests, damaged to various degrees by industrial pollution, have shown establishment of grass cover following tree defoliation. Populations of vesicular-arbuscular mycorrhizal (VAM) fungi were studied under this grass cover in four permanent plots with spruce under different levels of pollution stress. Soil and root samples were collected in April and June within each plot as follows: (1) sites without grass, (2) sites with initial stages of grass invasion, and (3) sites with fully developed grass cover. In all plots, the highest number of propagules were recovered from samples taken from sites having full grass cover. Mycorrhizal infection of grass was highest in the plot with the severest pollution damage and lowest in the least damaged plot. The development of grass cover and VAM infection of grass increased with tree defoliation caused by air pollution.

Effects of belowground grazing by collembola on growth, mycorrhizal infection, and P uptake of Geranium robertianum

We hypothesized that the grazing of vesicular-arbuscular mycorrhizal (VAM) hyphae by soil animals could be responsible for the lack of a direct relationship between mycorrhizal infection intensity and nutrient uptake under field conditions. To test this hypothesis, we determined the effect of a range of densities of the collembola, Folsomia candida, on growth, VAM infection, and P uptake in Geranium robertianum, a common forest herb, under greenhouse conditions. Total and aboveground growth were greater at low collembola density than either at higher collembola density or without collembola. These differences were greater when the plants were grown in a high organic content soil mix than when grown in sand. Root mass was not affected by collembola density. In the soil mix, root length decreased with increasing collembola density, but not in the sand. The percent of root length infected with VAM was lower at any collembola density than when collembola were absent. Total infected root length decreased linearly with increasing collembola density. Few significant differences in P uptake or tissue concentration were found. Thus, plant growth (but not P uptake) may be stimulated at low collembola density and inhibited at high. We discuss mechanisms which may be responsible for this non-linear response, and the implications of the pattern of response to studies of plant competition, nutrient turnover, and revegetation.

Seasonal Fluctuations of Soil Microfungi in Correlation with Some Soil Enzyme Activities and Va Mycorrhizae Associated with Certain Plants of a Typical Calcixeroll Soil in Greece

Seasonal variation ofthe soil mycoflora in a typical calcixeroll soil of northern Greece under macchia vegetation was studied. Microscopic examination ofthe soil, dilution plates, soil plates and soil washings were used. Microscopic examination of soil showed that fungi were present both as spores and mycelium. The dilution plate and soil plate method favored isolation of heavily sporulating fungi. A soil washing method favored the isolation of different fungi. Eleven fungal species appeared to be codominant: Aspergillus flavus, A. niger, Cladosporium cladosporioides, Gliocladium virens, Mucor hiemalis, Penicillium canescens, P. chrysogenum, P. citrinum, P. frequentans, P. fuscum and Trichoderma pseudokoningii. Highly organic layers supported the greatest number of fungal species and the numbers decreased with soil depth: Chaetomium globosum and Sordariafimicola occurred only in the A horizon. Alternaria alternata, Aspergillus candidus, Cladosporium cladosporioides, Penicillium simplicissimum, P. sclerotiorum, Rhizopus stolonifer and Trichothecium roseum appeared only in the A and B horizons. Twentyseven fungal species and the sterile mycelia were found in the A, B and C horizons. There were qualitative and quantitative differences in species composition between seasons. The viable microfungal population was positively correlated with some soil enzymes and microbial biomass C. Vesicular-arbuscular mycorrhizal infection examined for 25 plant species was low, with some exceptions. Only 18 plant species were mycorrhizal. Glomus macrocarpum and G fasciculatum were identified as forming VA mycorrhizae.

Seasonal Fluctuations of Soil Microfungi in Correlation with Some Soil Enzyme Activities and va Mycorrhizae Associated with Certain Plants of a Typical Calcixeroll Soil in Greece

Seasonal variation ofthe soil mycoflora in a typical calcixeroll soil of northern Greece under macchia vegetation was studied. Microscopic examination ofthe soil, dilution plates, soil plates and soil washings were used. Microscopic examination of soil showed that fungi were present both as spores and mycelium. The dilution plate and soil plate method favored isolation of heavily sporulating fungi. A soil washing method favored the isolation of different fungi. Eleven fungal species appeared to be codominant: Aspergillus flavus, A. niger, Cladosporium cladosporioides, Gliocladium virens, Mucor hiemalis, Penicillium canescens, P. chrysogenum, P. citrinum, P. frequentans, P. fuscum and Trichoderma pseudokoningii. Highly organic layers supported the greatest number of fungal species and the numbers decreased with soil depth: Chaetomium globosum and Sordariafimicola occurred only in the A horizon. Alternaria alternata, Aspergillus candidus, Cladosporium cladosporioides, Penicillium simplicissimum, P. sclerotiorum, Rhizopus stolonifer and Trichothecium roseum appeared only in the A and B horizons. Twentyseven fungal species and the sterile mycelia were found in the A, B and C horizons. There were qualitative and quantitative differences in species composition between seasons. The viable microfungal population was positively correlated with some soil enzymes and microbial biomass C. Vesicular-arbuscular mycorrhizal infection examined for 25 plant species was low, with some exceptions. Only 18 plant species were mycorrhizal. Glomus macrocarpum and G fasciculatum were identified as forming VA mycorrhizae.

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants : II. Eight wild accessions and two cultivars ofLycopersicon esculentum Mill.

An experiment was conducted to determine whether wild accessions and cultivars ofLycopersicon esculentum Mill. differed in inherent morphological, physiological or phenological traits and whether such differences would result in variation in response to vesicular-arbuscular mycorrhizal infection. While distinctions between wild accessions and cultivars were apparent (the cultivars generally had higher phosphorus use efficiencies and shorter lifespans than the wild accessions) and the cultivars were, as a group, more responsive to mycorrhizal infection than the wild accessions, there was significant variation among wild accessions and among cultivars in response to infection. Regardless of cultivation status, non-mycorrhizal plant root density was significantly negatively correlated with response to infection. Phosphorus use efficiency was generally not significantly correlated with response to infection. Mycorrhizal infection decreased phosphorus use efficiency in all accessions, but had variable effects on root density, depending upon accession and time. Finally, the vegetative response was not necessarily of the same magnitude as the reproductive response.

Effects of sulphur dioxide fumigation on Phleum pratense and vesicular‐arbuscular mycorrhizal fungi

Two experiments were conducted using controlled environment SO2 fumigation chambers which allowed only the shoots of Phleum pratense to be fumigated. Experiment 1 examined the effect of SO2 fumigation on the ability of vesicular-arbuscular (VA) mycorrhizal fungi to infect roots. Experiment 2 examined the effect of SO2 fumigation on the proliferation of VA mycorrhizas in the roots. There was a significant decrease in the amount of infection in the roots of plants exposed to SO2 . Low concentrations (0.05-0.07 μ 1-1 ) of SO2 affected the ability of VA mycorrhizal fungi to colonize and, also, to proliferate within roots. In both experiments, root colonization was the overriding factor affecting the number of tillers, leaf area, and shoot and root dry weights of infected plants. Increased VA mycorrhizal infection resulted in reductions in the plant growth parameters.

Soluble carbohydrates in roots of leek (Allium porrum) plants in relation to phosphorus supply and VA mycorrhizas

Leek plants (Allium porrum L.) inoculated with Glomus mosseae were raised on sterilized soil/sand medium amended with Ca(H2PO4)2.H2O to test the hypothesis that high concentration of soil P inhibits formation of vesicular-arbuscular (VA) mycorrhizas by reducing concentration of soluble carbohydrate in the root. When P supply was increased, from either P addition or VA mycorrhizal infection, there was initially also an increase in concentration of soluble carbohydrate in the root. At the concentration of soil P at which infection was reduced, concentration of soluble carbohydrate was at its maximum. Therefore the above hypothesis is discounted. An increased delay in infection establishment and a greater number of abortive entry points would suggest that high concentration of soil P reduces VA mycorrhizal infection by changing the anatomy of the root to make it resistant to fungal penetration.

Association of Glomus with palmarosa and its influence on growth and biomass production

Palmarosa (Cymbopogon marlinii var. motia), the source of palmarosa oil, was found to be associated with a vesicular-arbuscular mycorrhizal (VAM) fungus. The endophyte appears to be an undescribed Glomus species. Glasshouse trials showed that the mycorrhizal association enhanced growth and biomass production of palmarosa significantly. A significant increase in phosphorus uptake was observed in mycorrhizal compared to non-mycorrhizal plants and there was a similar trend in potassium uptake. The results indicated that VAM infection could enhance the productivity of essential oil-bearing grasses.