Vesicular-arbuscular Mycorrhizal Spores Research Articles

Root colonization by vesicular arbuscular mycorrhizal in different dosage forms and effect on C3 plants root morphology

The application of vesicular arbuscular mycorrhizal (VAM) in powder dosage form has been used for a long time. However, this dosage form has a non-uniform application dose and allows VAM spores to be lost through wind and rainwater, so innovation is needed in the VAM dosage form. A study aimed at knowing dosage forms of VAM as a biological agent that affects colonization level and C3 plant‘s root morphology was carried out at Screen House Laboratory, Faculty of Agriculture, Animal Husbandry and Fisheries, University of Muhammadiyah Parepare using a factorial design based on completely randomized design (CRD). Treatment of VAM dosage forms (factor 1) used was powder (A1), sachet (A2), and tablet (A3). While the C3 plant species (factor 2) used were Puraria japonica (B1), Vigna radiata (B2), and Amaranthus gangeticus (B3). Observations were conducted on the percentage of colonized roots and the C3 plants’ root morphology. The results showed that the combined treatment of VAM dosage forms (powder, sachet, and tablets) and C3 plant species (Puraria javanica, Vigna radiata, Amaranthus gangeticus) showed significant effects on colonized roots percentage and C3 plant root morphology. So it can be recommended that VAM dosage forms (sachet and tablet) are efficient and effective for the mobilization and field application of VAM.

Effect of rhizobium, VAM and rock phosphate inoculation on growth and productivity and isolation of VAMF spores of Pisum sativum

Rhizobium, VAM and rock phosphate inoculation has a significant utilization in Pisum sativum.The present study was conducted to study the influence of rock phosphorus fertilization, Vesicular Arbuscular Mycorrhizae (VAM) and rhizobium inoculation on growth and yield parameters of Pisum sativum. The experiment was laid out in randomized complete block design during summer season at the Department of Botany University of Peshawar Pakistan. A composite soil sample was collected for analysis of soil for physical and chemical properties. Rock phosphorus fertilization, application along with AMF and rhizobium inoculation increased the growth parameters significantly. Inoculation under Phosphors deficient soil which have pivotal role in the mycorrhization, growth and productivity. Dual inoculation, Rhizobium and AMF resulted in an increase in grain yield respectively, over no inoculation in Pisum sativum. Maximum growth was observed where AMF along with rhizobium and rock phosphate inoculation were applied. It is concluded that Pisum sativum should preferably be grown with dual inoculation of VAM along with rhizobium and rock phosphate. And vesicular arbuscular mycorrhizal spores in the rhizospheric soils of Pisum sativum at three different stages,vegetative, flowering and fruiting highest spores density recorded at fruiting stage and increased with the age of plant and also effected by the treatment highest in dual inoculation as comapared to single inoculation.

Microbe-assisted phytoremediation approach for ecological restoration of zinc mine spoil dump

Mining is one of the sectors that impacts air, water and soil pollution. The various environmental problems that are associated with mining activities are deforestation, removal of fertile topsoil, unstable slopes prone to sliding and erosion, siltation of water bodies due to wash off of mineral overburden dumps, air pollution due to discharge of dust and noise pollution. The most effective means of reducing the impact of such potential hazards is rapid revegetation. Revegetation accelerates soil formation, leading to establishment of a stable ecosystem and combats the different problems. The reclamation of mine overburden is intimately associated with the recovery of a stable microbial processes and communities resembling that of a natural soil. To revegetate such eco-vulnerable system, an eco-friendly and cost-effective 'microbe-assisted phytoremediation approach' adopted to restore the nature's pattern of stable and diverse ecosystem on zinc mine spoil dumps. The approach involves isolation and inoculation of site-specific specialised nitrogen-fixing strains of Bradyrhizobium and Azotobacter species, nutrient mobilising vesicular arbuscular mycorrhizal spores of Glomus and Gigaspora sp., selection of suitable plant species (preferable multispecies) and suitable organic amendments. The results indicate that the approach restored the productivity, fertility and stability of zinc mine spoil leading to the development of sustainable ecosystem thereby mitigating the environmental hazards and improving the environmental health of the nearby contaminated sites. Microbe-assisted phytoremediation approach stabilises the negative effects of zinc mine spoil dumps rapidly within a short span of time (2-3 years) in a cost-effective way.

Temporal changes in VAM fungi in the cocoa agroforestry systems of central Cameroon

In Cameroon, cocoa trees are mostly grown in forests and without fertilization. Our aim was to learn more about the temporal dynamics of soils in cocoa agroforests by comparing young (1-4 years old) and old (over 25 years old) cocoa agroforests. Short fallow and secondary forest were used as treeless and forest references. The numbers and diversities of soil vesicular arbuscular mycorrhizal (VAM) fungi on 60 cocoa producing farms in the Central province of Cameroon were assessed based on the classical mor- photyping of spore morphology. We also observed the soil organic matter, nitrogen and major soil nutrients. VAM spore density was significantly lower in the young cocoa agroforests (16 spores g -1 dry soil) than in the old cocoa agroforests (36 spores g -1 dry soil). Levels in the nearby secondary forest (46 spores g -1 dry soil) were not significantly different from old cocoa. The spore density was significantly highest in the short fallow (98 spores g -1 dry soil). The Shannon- Weaver index also showed significantly lower biodi- versity in young cocoa (0.39) than in old cocoa agroforests (0.48), secondary forest (0.49) and short fallow (0.47). These observations were supported by significant differences in the C:N ratio, Ca, Mg, and cation exchange capacity between young and old cocoa agroforests. We concluded that unfertilized cocoa agroforests could be sustainable, despite a decrease in some soil characteristics at a young stage, due to traditional land-conversion practices based on selective clearing and burning of secondary forest.

Temporal and spatial dynamics of vesicular-arbuscular mycorrhizal fungi under the canopy of Zygophyllum dumosum Boiss. in the Negev Desert

The temporal and spatial dynamics of vesicular–arbuscular mycorrhizal (VAM) fungi were investigated in a desert ecosystem. Soil samples under the canopy of Zygophyllum dumosum were collected monthly between November 1999 and October 2000 from 0–10 and 10–20 cm depths. VAM fungal colonization and spore density were used to compare the responses of VAM fungi to soil conditions. The mean percent colonization and spore density of VAM fungi reached maximal values in November 1999 and September 2000. Soil moisture was positively correlated with colonization of VAM structure groups. Vesicular and arbuscular colonization were positively correlated with soil organic matter and total soluble N. Spore density was also positively correlated with total soluble N. Our results suggest that spore density and the extent of vesicular and arbuscular colonization are useful indicators for evaluating changes in desert soil ecosystems.

Network Establishment of Vesicular-Arbuscular Mycorrhizal Hyphae in the Rhizospheres between Trifoliate Orange and Some Plants.

The distributions of vesicular-arbuscular mycorrhizal (VAM) hyphae in the rhizospheres of trifoliate orange (Poncirus trifoliata Raf.) and some plants grown under greenhouse conditions were explored. Furthermore, the effect of the 25% MeOH eluates of bahiagrass (Paspalum notatum Flugge.) and millet (Pennisetum glaucum L. R. Br.) roots fractionated by flash chromatography on the network establishment of VAM hyphae was examined. Special acrylic root boxes with three compartments separated by nylon screens were used for the experiment. Seedlings of trifoliate orange were transplanted into one outer compartment in all boxes, and seedlings of bahiagrass, millet, cockscomb (Celosia cristata L. cv. Parade), radish (Raphanus sativus L. cv. Natsumino), and tomato (Lycopersicon esculentum Mill. cv. Fukuju) were transplanted into the other outer compartment. A VAM fungus, Gigaspora margarita Becker and Hall, was inoculated in the center compartment. In plots with only trifoliate orange seedlings, 25% MeOH eluates of bahiagrass root extract (BRE) and millet root extract (MRE) were applied into the other outer compartment once a week. A plot with only trifoliate orange seedlings and without BRE and MRE applications was also prepared as a control. The density of hyphae, percentage of infection, and number of spores in the bahiagrass and millet compartments were higher than those in the compartments with trifoliate orange. These parameters in the cockscomb, radish and tomato compartments, however, were markedly low as compared with the trifoliate orange compartments. Although few VAM hyphae and spores were observed in the control (no plant compartment), the density of hyphae in the compartments treated with BRE and MRE increased to around 18%, and a few spores were found in these compartments. Root exudates of trifoliate orange, bahiagrass, and millet stimulated the hyphal growth of G. margarita in vitro. Particularly, the stimulation by bahiagrass and millet was significantly greater than that of the control (agar only). But the hyphal length of cockscomb, radish, and tomato treatments was shorter than that of the control. These results suggest that under field conditions, root exudates will affect the behaviour of VAM fungi in the soil. Moreover, some compounds in BRE and MRE may act as chemotropic signals for attracting VAM hyphae.

The influence of vesicular-arbuscular mycorrhizal fungi alone or in combination with Meloidogyne incognita on Hyoscyamus niger L.

Three vesicular-arbuscular mycorrhizal (VAM) fungi; Glomus aggregatum, Glomus fasciculatum and Glomus mosseae were evaluated for protecting against the reproduction and infection potential of Meloidogyne incognita on black henbane, Hyoscyamus niger. Different VAM fungi enhanced the growth and biomass of the plant. The results also indicated that treatments of plants with VAM fungi increased fresh and dry root and shoot weight and decreased M. incognita populations in both soil and roots in pot experiments. A significant reduction in M. incognita reproduction potential (Rf=4.4) was observed when G. aggregatum was used. Treatment with G. aggregatum alone yielded the highest mycorrhizal infection (88%) followed by G. aggregatum + M. incognita (75%), G. mosseae (69%), G. fasciculatum (57%), G. Mosseae + M. Incognita (53%) and G. fasciculatum + M. incognita (45%). A similar trend was also observed in the multiplication of VAM spores in soil.

Post Flood Syndrome and Vesicular-Arbuscular Mycorrhizal Fungi

In the past few years large areas of the Midwest and Great Plains have been inundated with water and plant P deficiency is often a problem after such events. Soil and plant samples were collected in 1994 in Missouri and Iowa from sites flooded and fallowed in 1993. Plants were P deficient during early vegetative growth in spite of soil tests indicating adequate P availability and typical levels of starter fertilizer. The flood and fallow problem was associated with the loss of root colonizing vesicular-arbuscular mycorrhizal (VAM) fungi that benefit the plant by increasing uptake of P. The VAM fungi are dependent upon the plant for growth and reproduction and loss of host significantly reduces VAM fungal populations in soil. The VAM fungal populations increased with the presence of a crop in the year following the flood. A greenhouse study on the effect of flooding on VAM fungi indicates the number of VAM hyphae or spores producing colonization were not affected by an extended flooding period and therefore are related to the lack of host for an extended period of time in the same manner as long fallow disorder in Australia. The research conducted indicates that the Post Flood Syndrome was associated with the loss of VAM fungi. Use of starter fertilizer was beneficial in correcting Post Flood Syndrome but broadcast fertilizer application appeared to have an insignificant effect on reducing the P deficiency. The application of 80 lb P/acre as starter fertilizer produced plants that were not P deficient.

Distribution of vesicular-arbuscular mycorrhizal fungi in the natural ecosystem

Natural occurrence of vesicular-arbuscular mycorrhizal (VAM) fungi in Haryana soils showed that VAM sporulation was more intensive in the rhizosphere of nonlegumes than of legumes. Maximum number of spores (342 spores per 50 g of soil) was observed in the rhizosphere of mustard, followed by chickpea, wheat, pearl millet and pigeonpea. Four VAM generaviz. Glomus, Gigaspora, Sclerocystis andAcaulospora, were present there. Soil pH, total soil P, available P, type of soil, soil moisture and cropping season all variables influenced the VA mycorrhizal population in the natural ecosystem. Numbers of VAM spores highly correlated with the presence of total soil P and soil pH indirectly affected the VAM population through the total soil P. The spore population was abundant in sandy soils as compared to loamy sands. Drier soils had higher number of VAM spores. In summer, the VAM population in soil was less as compared to winter season.

Nitrifiers and mycorrhizae in pristine and grazed pinyon‐juniper ecosystems

We compared soils from grazed and pristine pinyon‐juniper ecosystems for the numbers of chemoautotrophic nitrifying bacteria and determined the distribution of vesicular‐arbuscular (VA) mycorrhizae and ectomycorrhizae (EM). Additionally, we report on the presence of allelopathic substances in organic horizons. Ammonium (NH4+)‐oxidizing bacteria were in greater numbers in the interspaces between the trees, ranging from 9.60 × 104 to 2.13 × 105 bacteria‐1 soil, than under canopies, 3.5 × 104 to 4.8 × 104 bacteria‐1 soil. Grazed interspace soils had over twice the number of NH4+oxidizing bacteria than any other location. There were no differences in the numbers of nitrite‐oxidizing bacteria between either vegetative covers or sites. The rate of nitrate production did not correlate with the number of nitrifiers. However, there was a significant correlation (r2 = 0.85) between mineralization coefficients of total nitrogen and the total number of nitrifiers. Fourteen known and ten unknown monoterpenes were found in soils from under pinyon pine (Pinus edulis Engelm.) and juniper [Juniperus osteosperma (Torr.) Little] canopies. VA mycorrhizal spore numbers were significantly greater under canopies than in interspace soils at both sites, with the lowest number recorded in grazed interspace soils. No differences were found in the degree of colonization of either EM or VA mycorrhizae on pinyon pine or juniper, respectively, between each site. The differences in the spatial distribution of nitrifiers and mycorrhizae emphasize the complexities of the belowground ecosystem in these woodlands despite their apparent aboveground structural simplicity.

Influence of edaphic and climatic factors on dynamics of root colonization and spore density of vesicular-arbuscular mycorrhizal fungi in Acacia farnesiana Willd. and A. planifrons W.et.A.

A study was conducted to assess the dynamics of vesicular-arbuscular mycorrhizal (VAM) fungi associated with Acacia farnesiana and A. planifrons in moderately fertile alkaline soils. The intensity of root colonization by VAM fungi and the distribution of VAM fungal structures varied with host species over a period of time. The occurrence of vesicles with varied morphology in the mycorrhizal roots indicates infection by different VAM fungal species. This was further confirmed from the presence of spores belonging to different VAM fungal species in the rhizosphere soils. Root colonization and spore number ranged from 56% – 72% and 5 – 14 g – 1soil in A. farnesiana and from 60% – 73% and 5 – 15 g – 1 soil in A. planifrons. Per cent root colonization and VAM spore number in the rhizosphere soil were inversely related to each other in both the Acacia species. However, patterns of the occurrence of VAM fungal structures were erratic. Spores of Acaulospora foveata, Gigaspora albida, Glomus fasciculatum, G. geosporum and Sclerocystis sinuosa were isolated from the rhizosphere of A. farnesiana whereas A. scrobiculata,G. pustulatum, G. fasciculatum,G. geosporum and G. microcarpum were isolated from that of A. planifrons. The response of VAM status to fluctuating edaphic factors varied with host species. In A. farnesiana though soil nitrogen (N) was positively correlated with root colonization, soil moisture, potassium and air temperature were negatively correlated to both root colonization and spore number. Per cent root colonization and spore number in A. planifrons were negatively related to each other. Further, in A. planifrons as the soil phosphorus and N were negatively correlated with the density of VAM fungal spores, the same edaphic factors along with soil moisture negatively influenced root colonization.

Vesicular-arbuscular mycorrhizal fungi in earthworm casts and surrounding soil in relation to soil management of a semi-arid tropical Alfisol

Spores and infective propagules of vesicular-arbuscular (VA) mycorrhiza were examined in earthworm casts and field soils collected from three different soil management treatments (zero tillage with straw amendment, deep tillage without amendment (bare), and zero tillage with previous perennial cropping of Stylosanthes hamata) on an Alfisol in the semi-arid tropics (SAT) of India. The average mean of spore counts and most probable number (MPN) of infective propagules of VA mycorrhiza (VAM) were significantly ( P < 0.05) higher in earthworm casts than in field soil across the three soil management treatments. There was no significant difference in the number of VAM spores or propagules among field soils from the three different soil management treatments, but the number of VAM spores and propagules in the earthworm casts from the deep tillage bare treatment was significantly higher ( P ≤ 0.05) than in the earthworm casts from the other two treatments. In the deep tillage bare treatment, the number of spores and MPN of infective propagules were significantly ( P < 0.05) higher in earthworm casts than in field soil. Therefore, it may be concluded that earthworms can concentrate VA mycorrhizal spores and propagules in their casts.

Vesicular-arbuscular mycorrhizal spore populations in sugar maple (Acer saccharum marsh. L.) forests

The numbers and types of spores of vesicular-arbuscular mycorrhizal fungi occurring in the top 15 cm of the soil in three maple forests in Eastern Canada were investigated using traditional wet-sieving/decanting methods. In the most acid site, at St. Hippolyte, Quebec, where the soil had been amended with base cations, after 1 year there was no effect on the numbers of spores present. Vesicular-arbuscular mycorrhizal spores present at St. Hippolyte consisted of Glomus rubiforme, other Glomus spp. and Acaulospora spp. Although the sporocarpic species, G. aggregatum, G. macrocarpum and G. rubiforme occurred at St. Hippolyte, they were not found at the two less acid sites (Waterloo, Ontario and Lacolle, Quebec) . Spores of Acaulospora spp. were found at all three sites, but were most abundant at St. Hippolyte. At St. Hippolyte the total number of spores was much higher than at the other two sites; at Waterloo numbers were an order of magnitude lower than at St. Hippolyte. It is suggested that G. rubiforme and Acaulospora species may be adapted to acid conditions. Seasonal patterns of spore abundance suggested that Acaulospora spp. may sporulate during the spring, whereas G. rubiforme may sporulate during the fall.

An overwintering cover crop increases inoculum of VAM fungi in agricultural soil

AbstractWe conducted a field experiment within a low-input reduced tillage trial to determine how a cover crop affects inoculum levels of vesicular-arbuscular mycorrhizal (VAM) fungi. Plots with and without the hairy vetch cover crop were established on September 30, 1993, under moldboard plow (MP), chisel-disk (CD), and no-till (NT) treatments in low-input (LI) management, and MP in conventional (CONV) management. We conducted a 3-week colonization assay in the greenhouse with bahiagrass seedlings to assess the relative colonization potential of the soils in the fall and following spring. Hairy vetch roots were colonized by indigenous VAM fungi by 65 days after planting, with plants from NT being more colonized than plants from MP or CD plots. Spore populations were greater in the LI than in the CONV system. The beneficial effect of the cover crop on VAM spore populations in soil was manifested in the spring, with theGlomustype group more abundant in plots with cover than without it. The greenhouse bioassay showed that colonization potential of spring 1994 soil samples was higher in plots with cover than without cover for both the LI and CONV systems. Just one season of an overwintering cover crop of hairy vetch increased the inoculum of VAM fungi the following spring before the next cash crop was planted.

Biostatic effect of fumigation and pesticide drenches on an endomycorrhizal-Rhizobium-legume tripartite association under field conditions

The effects of formaldehyde fumigation and pesticide drenching with Bavistin, Cuman, Copperthom, Sulfex, Furadon, and Termix at recommended rates on vesicular-arbuscular mycorrhizal (VAM) colonisation and Rhizobium sp. nodules were assessed regularly for a period of 90 days in the legumes Cajanus cajan, Dolichos biflorus, Vigna mungo, and V. unguiculata under field conditions. The fumigant and the pesticides initially reduced VAM fungal colonisation and the number of spores in all plants. Following the initial decrease there was a slow recovery, but by 90 days after emergence, root colonisation was either parallel to or still lower than the control, and the number of spores was still well below control levels for all species except C. cajan, which had more VAM spores than the control in all treatments except fumigation and Furadon. Although the number of nodules did not differ from control levels at 30 days after emergence, differences were evident during the later stages of plant growth for all species except V. unguiculata. The effect of pesticides on VAM fungi and root nodulation varied with the associated host plant species. Plant tissue P and VAM colonisation were significantly correlated in all host plants. The pesticide treatments had no marked effect on plant growth, but accumulations of nutrients in pesticide-treated plants were lower than those in untreated plants. Growth and nutrient status of the legumes varied with VAM fungal colonisation.

Effect of fungicides on vesicular-arbuscular mycorrhizal infection and nodulation in groundnut ( Arachis hypogea L.)

The effects of field application rates of six fungicides (Bavistin, Dithane, Emisan, Fytolan, Thiram and Ziram), applied both as seed dress and soil drench, on the formation and function of vesicular-arbuscular mycorrhizal (VAM) and rhizobial nodular systems in groundnut ( Arachis hypogea L.) were investigated. Fytolan treatment produced a remarkable range of positive responses in VAM infection and spore production, rhizobial nodulation and growth and yield of the host plant. The other fungicides restricted mycorrhizal infection to different levels. The rhizosphere spore count was increased in the early growth stages of the host by fungicides, but declined in the later stages. Their effect on sporulation varied depending on VAM fungal species. Root nodulation, growth and yield of the host plant were not significantly affected by the application of fungicides, excepting the interference of Emisan in the early growth stages. The inhibitory effects of Emisan on the VAM and Rhizobium colonisation resulted in a significant decrease in the growth and yield of the host plant.

Comparisons of the influence of vesicular-arbuscular mycorrhiza on the productivity of hedgerow woody legumes and cassava at the top and the base of a hillslope in alley cropping systems

We investigated the influence of vesicular-arbuscular mycorrhizal (VAM) inoculation on growth and nutrient relationships in two alley-cropping trials, one at the top and the other at the base of a hillslope. Each trial involved three woody hedgerow legumes with cassava (Manihot esculenta Crantz) as the sole intercrop. The hedgerow trees at the base of the slope showed greater survival and higher leaf dry weights than those at the top of the slope, although these parameters were not affected by VAM inoculation, either at the top or the base of the slope. In contrast to survival, the uptake of nutrients, particularly P and N, was higher for inoculated than uninoculated hedgerow trees, both at the top and at the base of slope. Increases in stem and leaf biomass and the uptake of nutrients by the trees were strongly correlated with increases in P uptake, indicating that the improvements were attributable to VAM inoculation. Cassava tuber yields at the base of the slope, from inoculated or uninoculated plants, were significantly greater than the corresponding cassava yields at the top of the slope. These increases at the base of the slope compared to the top of the slope were not attributed to available soil nutrients but to greater VAM spore density. Higher available soil moisture may have been another factor. Increasing the VAM spore density of effective mycorrhiza through proper agronomic practices at the top of a slope may bring about comparable yields on different parts of the slope.

Occurrence and isolation of vesicular–arbuscular mycorrhizae in cropped field soils of Saskatchewan, Canada

Soil and root samples collected from fields cropped to spring wheat (Triticum aestivum L. cv. Katepwa) and lentil (Lens esculenta L. cv. Eston) at 11 sites across four soil zones of Saskatchewan were analyzed for spore numbers, level of vesicular–arbuscular mycorrhizal (VAM) colonization, and VAM species. The number of VAM spores detected in field soils ranged from 78 to 272 per 100 g soil. Vesicular–arbuscular mycorrhizae colonized wheat and lentil at all the field study sites, but levels of colonization in the two crops varied from site to site and the differences were more pronounced in wheat than in lentil. Generally, lentil both exhibited a higher percentage of VAM colonized roots and contained more arbuscules and vesicles than wheat roots. However, wheat appeared to be colonized by different types of VAM depending on the field sites. Differences in VAM colonization were not related to the moisture and temperature gradient of the four soil zones or soil properties. Seven VAM species were isolated by enriching indigenous VAM mixtures (collected from wheat field soils of six field sites) on maize. The VAM isolated most closely resembled Acaulospora denticulata, Gigaspora decipiens, Glomus clarum, Glomus etunicatum, Glomus fasciculatum, Glomus mosseae, and Glomus versiforme. The species composition of the VAM community varied at the different field sites.Key words: VAM, Acaulospora, Gigaspora, Glomus.

Occurrence and importance of mycorrhizae in aquatic trees of New South Wales, Australia

Vesicular arbuscular mycorrhizal (VAM) infection was found in KOH-cleared and lactophenolblue-stained roots of Salix babylonica, Melaleuca quinquenervia and Casuarina cunninghamiana. These are all trees growing on creeks and river banks, in stationary or slowly flowing fresh or brackish waters in swamps, creeks, drains and channels, and in seepage areas of New South Wales, Australia. Larger and older roots lacked VAM infection in the inner cortex, probably due to suberisation of cells, and the endophyte was restricted to the epidermal layers. Spores and sporocarps of the VAM fungi Glomus fasciculatus, G. mosseae, Sclerocystis rubiformis, Gigaspora margarita and an unidentified Scutellospora sp. were wet sieved and decanted from aquatic sediments and soils. The presence of similar VAM fungal spores in the aquatic sediments and terrestrial soil suggests that they probably enter the aquatic sediments through run off from the land ecosystem. All three plants formed vesicular arbuscular (VA) mycorrhizae almost exclusively in the marshy, periodically inundated soils, but the same plant species formed endo-/ ectomycorrhizae when growing in soil with higher redox potentials (E h). Salix and Melaleuca tree roots possessed both VAmycorrhizae and ectomycorrhizae. VAM roots of Casuarina were equipped with both N-fixing Frankia nodules and proteoid roots. VAM endophytes did not invade nodular cortical tissues, suggesting the presence of an exclusion mechanism which needs further study. The highest VAM infection was found in nodulated specimens. Free-floating roots growing in water close to the banks were non-mycorrhizal but were mycorrhizal in the bottom-rooting state. VAM spore number and mycorrhizal infection seem to be associated with redox-potential, i.e. lower at sites such as swamps, water or sediments with lower E h values than in terrestrial soils with higher E h values. A relationship between soil moisture gradient and VAM infection pattern became apparent from the study of a C. cunninghamiana transect on a creek embankment, i.e. typical vesicles and arbuscules were found in roots from drier soils, there was a lack of arbuscules in relatively wet soils but large lipid-filled intracellular vesicles were present, and typical vesicles and arbuscules were absent in flooded creek beds where roots were associated with coenocytic intercellular hyphae with abundant lipid droplets. The importance of VA mycorrhiza, ectomycorrhizae, N-fixing root nodules and proteoid roots at the land-water interface is discussed with reference to the use of these trees as pioneering species for stabilising river and stream banks, reducing erosion, windbreaking, and as a long-term and inexpensive means of achieving biological control of aquatic weeds by shading waterways.

The propagules of vesicular-arbuscular mycorrhizal (VAM) fungi capable of initiating VAM infection after topsoil disturbance

The removal and storage of topsoil decreases the infectivity of vesicular-arbuscular mycorrhizal (VAM) fungi. The propagules of VAM fungi include spores, root fragments containing hyphae and vesicles, and soil hyphae. The viability of each type of propagule after disturbance will determine the initiation of VAM associations with plants recolonizing the disturbed site. This study aimed to examine which of the propagules of VAM fungi are capable of initiating VAM infection after soil disturbance. Soil from an open woodland site of low soil fertility, in southeastern Australia was wetsieved through a tier of three sieves (1 mm, 250 μm and 106 μm), and the following fractions were extracted: (i) root fragments, (ii) fungal hyphae, and (iii) VAM spores. Each fraction was tested to determine its potential to initiate VAM. Hyphae of VAM fungi grew from root fragments within 14 days. The VAM spore fraction initiated VAM infection after 28 days. VAM hyphal fragments did not produce any VAM infection even after 42 days.