Vesicular-arbuscular mycorrhizal fungi,particularly Glomus tenue,in Venezuelan bromeliad epiphytes

The mycorrhizal status of water-impounding tank bromeliad epiphytes from three locales differing in altitude and moisture regime within Venezuelan cloud forest was examined. Species of vesicular-arbuscular mycorrhizal (VAM) fungi found in arboreal soils were compared to VAM fungi found in terrestrial soils. Sixteen of the 19 epiphytes examined for the presence of VAM fungi had roots with infection stages; 14 of these specimens showed growth of the fine endophyte Glomus tenue. Fine endophyte was the only VAM fungus found associated with epiphytes in the driest locale studied, while coarse VAM fungi (Gigaspora and Scutellospora spp.) were found at sampling locales receiving more moisture. Root infection was usually composed of intercellular hyphae and peletons; few arbuscules were observed. However, abundant extracellular hyphae were often observed tangled about roots in arboreal soil. It is concluded that epiphytic bromeliads probably benefit, at least periodically, from VAM fungi scavenging for sporadically available nutrients in arboreal soils. Glomus tenue may be particularly important as a colonizing VAM fungus in drier sites of Venezuelan cloud forest. The species composition of VAM fungi in arboreal soils was different to that of terrestrial soils sampled directly under epiphytic bromeliad perches, suggesting that VAM fungi species associated with bromeliads are dispersed to their hosts by vagile animal vectors.     

Glomalean mycorrhizal fungi from tropical Australia

 A comparison of different methods for isolation of vesicular-arbuscular mycorrhizal (VAM) fungi into open-pot cultures was undertaken as part of a study of the diversity of these fungi. Four different isolation techniques using spores separated from soil, soil trap cultures, root samples, or transplanted seedlings grown in intact soil cores were used to obtain as many fungi as possible from each site. Isolation methods were compared using paired samples from the same locations within natural (savanna, rocky hill, wetland, rainforest) and disturbed (minesite) habitats in a seasonally dry tropical region in the Northern Territory of Australia. There were large differences in (i) the efficiency (rate of increase in mycorrhizal colonisation), (ii) the proportion of successful cultures, (iii) fungal diversity (number of fungal species in each culture) and (iv) specificity (identity of species isolated) between these four procedures. However, the less-efficient procedures generally resulted in a higher proportion of cultures of one fungus, which could be used without further isolation steps. Most species of Scutellospora, Acaulospora and Gigaspora were obtained primarily from field-collected spores, but only 50% of these culture attempts were successful. Spores from these initial cultures produced mycorrhizas much more rapidly and successfully when used to start second-generation cultures. Several species of fungi, rarely recovered as living spores from field soils, were dominant in many trap cultures started from soil or roots. Most of these fungi were Glomus species, that were first distinguished by colonisation patterns in roots and eventually identified after sporulation in second- or third-generation trap cultures. These experiments demonstrated that glomalean fungi in the habitats sampled belonged to two functional categories, based on whether or not spores were important propagules. The "non-sporulating" fungi were dominant in many trap cultures, which suggests that these fungi had higher total inoculum levels in soils than other fungi. Pot-culturing methods provided additional information on fungal diversity which complemented spore occurrence data obtained using the same soil samples and provided valuable new information about the biology of these fungi. Accepted: 26 December 1998     

Increased Sporulation of Vesicular-Arbuscular Mycorrhizal Fungi by Manipulation of Nutrient Regimens

Adjustment of pot culture nutrient solutions increased root colonization and sporulation of vesicular-arbuscular mycorrhizal (VAM) fungi. Paspalum notatum Flugge and VAM fungi were grown in a sandy soil low in N and available P. Hoagland nutrient solution without P enhanced sporulation in soil and root colonization of Acaulospora longula, Scutellospora heterogama, Gigaspora margarita, and a wide range of other VAM fungi over levels produced by a tap water control or nutrient solutions containing P. However, Glomus intraradices produced significantly more spores in plant roots in the tap water control treatment. The effect of the nutrient solutions was not due solely to N nutrition, because the addition of NH₄NO₃ decreased both colonization and sporulation by G. margarita relative to levels produced by Hoagland solution without P.     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

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.     

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.     

Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize

Low-input agricultural systems that do not rely on fertilizers may be more dependent on vesicular-arbuscular mycorrhizal [VAM] fungi than conventionally managed systems. We studied populations of spores of VAM fungi, mycorrhiza formation and nutrient utilization of maize (Zea mays L.) grown in moldboard plowed, chisel-disked or no-tilled soil under conventional and low-input agricultural systems. Maize shoots and roots were collected at four growth stages. Soils under low-input management had higher VAM fungus spore populations than soils under conventional management. Spore populations and colonization of maize roots by VAM fungi were higher in no-tilled than in moldboard plowed or chisel-disked soil. The inoculum potential of soil collected in the autumn was greater for no-till and chisel-disked soils than for moldboard plowed soils and greater for low-input than conventionally farmed soil. The effects of tillage and farming system on N uptake and utilization varied with growth stage of the maize plants. The effect of farming system on P use efficiency was significant at the vegetative stages only, with higher efficiencies in plants under low-input management. The effect of tillage was consistent through all growth stages, with higher P use efficiencies in plants under moldboard plow and chisel-disk than under no-till. Plants grown in no-tilled soils had the highest shoot P concentrations throughout the experiment. This benefit of enhanced VAM fungus colonization, particularly in the low-input system in the absence of effective weed control and with likely lower soil temperatures, did not translate into enhanced growth and yield.     

Morpho-Typing and Molecular Diversity of Arbuscular Mycorrhizal Fungi in Sub-Tropical Soils of Coimbatore Region, Tamil Nadu, India

The diversity potential of arbuscular mycorrhizal fungi (AMF) in three different tropical soils of southern part of India was assessed by traditional morpho-typing of AMF-spores and by culture-independent nested-PCR of internal transcribed spacer region of ribosomal genes. The population diversity of AMF in soil was strongly correlated with available P₂O₅ in soil. Among the three different soils, black-cotton soil had more diversified AMF species than alluvial and red sandy soils. Pooled data of morpho-typing and sequence-driven analysis revealed that Glomus, Gigaspora, Scutellospora and Acaulospora are the AMF genera present in these soils. The diversity of AMF in soil differs with the mycorrhiza colonizing the plant roots.     

Dosage-dependent shift in the spore community of arbuscular mycorrhizal fungi following application of tannery sludge

The controlled disposal of tannery sludge in agricultural soils is a viable alternative for recycling such waste; however, the impact of this practice on the arbuscular mycorrhizal fungi (AMF) communities is not well understood. We studied the effects of low-chromium tannery sludge amendment in soils on AMF spore density, species richness and diversity, and root colonization levels. Sludge was applied at four doses to an agricultural field in Rolandia, Paraná state, Brazil. The sludge was left undisturbed on the soil surface and then the area was harrowed and planted with corn. The soil was sampled at four intervals and corn roots once within a year (2007/2008). AMF spore density was low (1 to 49 spores per 50 cm³ of soil) and decreased as doses of tannery sludge increased. AMF root colonization was high (64%) and unaffected by tannery sludge. Eighteen AMF species belonging to six genera (Acaulospora, Glomus, Gigaspora, Scutellospora, Paraglomus, and Ambispora) were recorded. At the sludge doses of 9.0 and 22.6 Mg ha⁻¹, we observed a decrease in AMF species richness and diversity, and changes in their relative frequencies. Hierarchical grouping analysis showed that adding tannery waste to the soil altered AMF spore community in relation to the control, modifying the mycorrhizal status of soil and selectively favoring the sporulation of certain species.     

Dual axenic culture of sheared-root inocula of vesicular-arbuscular mycorrhizal fungi associated with tomato roots

Surface-sterilized sheared-root inocula of two vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus intraradices and G. versiforme) from pot cultures associated with excised tomato roots showed significant sporulation and the production of an extensive hyphal biomass. As many as 10²–10³ axenic mature spores were recovered in Petri dishes during 3 months incubation in the dark. Propagules of both species were able to complete their vegetative life cycle in vitro and efficiently colonize Acacia albida roots after 1 month under greenhouse conditions. The effectiveness of 0.5 cm pieces of VAM roots as starter inocula indicates the high inoculum potential of intravesicle propagules.     

Mycorrhizal Interactions in Sustainable Agriculture

Abstract

Vesicular-arbuscular mycorrhizal (VAM) fungi are an intimate link between the roots of most crop plants and soils, thereby affecting the development of host plants and host soils. The role of VAM fungi in improving plant nutrition and their interactions with other soil biota have been investigated with reference to host plant growth, but little is known about how these interactions affect soil structure. The impact of cultural practices and the particular role that VAM fungi play in improving soil structure are discussed in the context of sustainable farming.     

Arbuscular mycorrhizal fungi associated with sedges on the Tibetan plateau

The arbuscular mycorrhizal (AM) status of nine dominant sedge species and the diversity of AM fungi in Tibetan grassland were surveyed in the autumn of 2003 and 2004. Most of the sedge species and ecotypes examined were mycorrhizal, but Carex moorcroftii and Kobresia pusilla were of doubtful AM status, and Kobresia humilis was facultatively mycorrhizal. This is the first report of the mycorrhizal status of eight of the nine sedge species examined. Intraradical vesicles and aseptate hyphae were the structures most frequently observed. Appressoria, coils, and arbuscules were found in the roots of a few sedge species. A strong negative correlation was found between soil organic matter content and the extent of mycorrhizal colonization. Using trap cultures, 26 species of AM fungi belonging to six genera, Glomus, Acaulospora, Paraglomus, Archaeospora, Pacispora, and Scutellospora, were isolated from the soil samples collected. The frequency of occurrence of different taxa of AM fungi varied greatly. Glomus and Acaulospora were the dominant genera, and Acaulospora scrobiculata was the most frequent and abundant species. The species richness of AM fungi was 2.73 in the study area. Species richness and diversity index differed among the sedge species but were not correlated with soil factors such as pH, available P, or organic matter content.     

Preinoculation of lettuce and onion with VA mycorrhizal fungi reduces deleterious effects of soil salinity

The hypothesis that inoculation of transplants with vesicular-arbuscular mycorrhizal (VAM) fungi before planting into saline soils alleviates salt effects on growth and yield was tested on lettuce (Lactuca sativa L.) and onion (Allium cepa L.). A second hypothesis was that fungi isolated from saline soil are more effective in counteracting salt effects than those from nonsaline soil. VAM fungi from high- and low-salt soils were trap-cultured, their propagules quantified and adjusted to a like number, and added to a pasteurized soil mix in which seedlings were grown for 3–4 weeks. Once the seedlings were colonized by VAM fungi, they were transplanted into salinized (NaCl) soil. Preinoculated lettuce transplants grown for 11 weeks in the saline soils had greater shoot mass compared with nonVAM plants at all salt levels [2 (control), 4, 8 and 12 dS m^–1] tested. Leaves of VAM lettuce at the highest salt level were significantly greener (more chlorophyll) than those of the nonVAM lettuce. NonVAM onions were stunted due to P deficiency in the soil, but inoculation with VAM fungi alleviated P deficiency and salinity effects; VAM onions were significantly larger at all salt levels than nonVAM onions. In a separate experiment, addition of P to salinized soil reduced the salt stress effect on nonVAM onions but to a lesser extent than by VAM inoculation. VAM fungi from the saline soil were not more effective in reducing growth inhibition by salt than those from the nonsaline site. Colonization of roots and length of soil hyphae produced by the VAM fungi decreased with increasing soil salt concentration. Results indicate that preinoculation of transplants with VAM fungi can help alleviate deleterious effects of saline soils on crop yield.     

Indigenous and introduced arbuscular mycorrhizal fungi contribute to plant growth in two agricultural soils from south-western Australia

Arbuscular mycorrhizal (AM) fungi occur in all agricultural soils but it is not easy to assess the contribution they make to plant growth under field conditions. Several approaches have been used to investigate this, including the comparison of plant growth in the presence or absence of naturally occurring AM fungi following soil fumigation or application of fungicides. However, treatments such as these may change soil characteristics other than factors directly involving AM fungi and lead to difficulties in identifying the reason for changes in plant growth. In a glasshouse experiment, we assessed the contribution of indigenous AM fungi to growth of subterranean clover in undisturbed cores of soil from two agricultural field sites (a cropped agricultural field at South Carrabin and a low input pasture at Westdale). We used the approach of estimating the benefit of AM fungi by comparing the curvature coefficients ( C) of the Mitscherlich equation for subterranean clover grown in untreated field soil, in field soil into which inoculum of Glomus invermaium was added and in soil fumigated with methyl bromide. It was only possible to estimate the benefit of mycorrhizas using this approach for one soil (Westdale) because it was the only soil for which a Mitscherlich response to the application of a range of P levels was obtained. The mycorrhizal benefit ( C of mycorrhizal vs. non-mycorrhizal plants or C of inoculated vs. uninoculated plants) of the indigenous fungi corresponded with a requirement for phosphate by plants that were colonised by AM fungi already present in the soil equivalent to half that required by non-mycorrhizal plants. This benefit was independent of the plant-available P in the soil. There was no additional benefit of inoculation on plant growth other than that due to increased P uptake. Indigenous AM fungi were present in both soils and colonised a high proportion of roots in both soils. There was a higher diversity of morphotypes of mycorrhizal fungi in roots of plants grown in the Westdale soil than in the South Carrabin soil that had a history of high phosphate fertilizer use in the field. Inoculation with G. invermaium did not increase the level of colonisation of roots by mycorrhizal fungi in either soil, but it replaced approximately 20% of the root length colonised by the indigenous fungi in Westdale soil at all levels of applied P. The proportion of colonised root length replaced by G. invermaium in South Carrabin soil varied with the level of application of P to the soil; it was higher at intermediate levels of recently added soil P.     

Assessment of arbuscular mycorrhizal fungi diversity in the rhizosphere of <Emphasis Type="Italic">Viola calaminaria</Emphasis> and effect of these fungi on heavy metal uptake by clover

 The ability of arbuscular mycorrhizal (AM) fungi from a metal-tolerant plant (Viola calaminaria, violet) to colonise and reduce metal uptake by a non-tolerant plant (Trifolium subterraneum, subterranean clover) in comparison to a metal-tolerant AM fungus isolated from a non-tolerant plant was studied. AM spores from the violet rhizosphere and from violet roots were characterised by polymerase chain reaction (PCR) amplification of the SSU rDNA, and sequencing. Subterranean clover was grown in pots containing a soil supplemented with Cd and Zn salts and inoculated either with a mixture of spores extracted from the violet rhizosphere or with spores of a Cd-tolerant Glomus mosseae P2 (BEG 69), or non-inoculated. The diversity of fungi, including AM fungi, colonising clover roots was assessed and analysed using terminal-restriction fragment length polymorphism. At least four different Glomus species were found in the violet rhizosphere. After 8 weeks in a growth chamber, colonisation of clover roots with spores from the violet rhizosphere increased Cd and Zn concentrations in clover roots without significantly affecting the concentrations of metals in the shoot and plant growth. G. mosseae P2 reduced plant growth and slightly increased the Cd concentration. Only one AM fungus (Glomus b) from the violet rhizosphere colonised clover roots, but other fungi were present. AM fungi from heavy metal-contaminated soils and associated with metal-tolerant plants may be effective in accumulating heavy metals in roots in a non-toxic form. Accepted: 7 July 2000     

Stimulation of vesicular-arbuscular mycorrhiza by fungicides or rhizosphere bacteria

Stimulation of vesicular-arbuscular (VA) mycorrhizal fungi may secure the early establishment of symbiosis and benefit the host plant at an earlier stage of development. The application of Bacillus mycoides resulted in particular in the acceleration of early VA mycorrhiza formation. An increase in vigour of the symbiosis could be measured later in terms of increased sporulation of the mycorrhizal fungi after shoot removal. Natural sporulation during later mycorrhizal development was affected by combination of bacteria and just one mycorrhizal isolate. The stimulation of mycorrhizal development was shown to be non-specific with regard to host plant and the isolate of the VAM fungus. However, the effect could not be achieved in all combinations of soil types and host plants. Application of the systemic fungicides triadimefon and pyrazophos promoted VAM formation. Combinations of fungicide and bacterial treatments were not synergistic.     

Alteration of growth ofSolanum opacum andPlantago drummondii and inhibition of regrowth of hyphae of vesicular-arbuscular mycorrhizal fungi from dried root pieces by manganese

Addition of MnSO₄ or MnCl₂ to a fine sandy soil from South Australia had a negative effect on shoot growth and root elongation ofSolanum opacum in the absence of significant presence of vesicular-arbuscular mycorrhiza (VAM). VAM ameliorated the reduction of plant growth by Mn, even though mycorrhizal development was decreased. Mn inhibited infection of roots by a fine endophyte less than that by some coarse endophytes. High concentrations of available Mn inhibited growth of hyphae of VAM fungi from dried root pieces, a significant source of infection by mycorrhizal fungi in the soil used.     

INFLUENCE OF SUPPLEMENTAL INORGANIC NUTRIENTS ON GROWTH,SURVIVORSHIP, AND MYCORRHIZAL RELATIONSHIPS OF SCHIZACHYRIUM SCOPARIUM (POACEAE) GROWN IN FUMIGATED AND UNFUMIGATED SOIL

Little bluestem grass Schizachyrium scoparium ([Michx.] Nash) plants were grown under field conditions for 2 years in soils fumigated with methyl bromide and chloropicrin, or in unfumigated soil, and treated with supplemental inorganic nutrients (bases calcium and magnesium) phosphorus, nitrogen, and potassium. Most differences in measured plant responses were due to interactions between fumigation and nutrient treatments. These included biomass production, root mass per unit length (μg/cm), root lengths, flowering culm production, percent colonization, colonized root length, and spore production in rhizosphere soil. Plants generally responded to mycorrhizal fungal colonization by reducing total root length and producing thicker roots. Treatment of plants with bases appeared to profoundly affect the mycorrhizal association by reducing sporulation of vesicular-arbuscular mycorrhizal fungi and increasing colonization. When fumigated or unfumigated soils were considered separately, base-treated plants produced more biomass than other treatments. Base-treated plants grown on unfumigated soil had more flowering culms and longer colonized root lengths than all other plants. Percent colonization by mycorrhizal fungi and colonized root length were positively correlated with phosphorus/nitrogen ratios, but the ratio was not correlated with plant biomass production. This suggests that phosphorus is not a limiting nutrient in our soil and investment in a mycorrhizal association may not result in enhanced plant growth. The base-nutrient effects may indicate a need to reevaluate earlier studies of macro nutrient effects that did not take into account the role played by calcium and magnesium in assessing fungus-host plant interactions.     

Mycorrhizal infection,phosphorus uptake,and phenology in Ranunculus adoneus: implications for the functioning of mycorrhizae in alpine systems

Phosphorus levels, phenology of roots and shoots, and development of vesicular arbuscular mycorrhizal (VAM) fungi were monitored for two years in natural populations of the perennial alpine herb, Ranunculus adoneus. The purpose of this study was to understand how phosphorus uptake relates to the phenology of R. adoneus and to ascertain whether arbusculus, fungal structures used for nutrient transfer, were present when maximum phosphorus accumulation was occurring. Arbuscules were only present for a few weeks during the growing season of R. adoneus and their presence corresponded with increased phosphorus accumulation in both the roots and shoots of R. adoneus. In addition, phosphorus accumulation and peaks in mycorrhizal development occurred well after plant reproduction and most plant growth had occurred. The late season accumulation of phosphorus by mycorrhizal roots of R. adoneus is stored for use during early season growth and flowering the following spring. In this way R. adoneus can flower before soils thaw and root or mycorrhizal nutrient uptake can occur.     

Interaction of vascular plants and vesicular-arbuscular mycorrhizal fungi across a soil moisture-nutrient gradient

Summary Abundance and distribution of vascular plants and vesicular-arbuscular mycorrhizal (VAM) fungi across a soil moisture-nutrient gradient were studied at a single site. Vegetation on the site varied from a dry mesic paririe dominated by little bluestem (Schizachyrium scoparium) to emergent aquatic vegetation dominated by cattail (Typha latifolia) and water smartweed (Polygonum hydropiperoides). Plant cover, VAM spore abundance, plant species richness, and number of VAM fungi represented as spores, had significant positive correlations with each other and with percent organic matter. The plant and VAM spore variables had significant negative correlations with soil pH and available Ca, Mg, P and gravimetric soil moisture. Using stepwise multiple regression, Ca was found to be the best predictor of spore abundance. Test for association between plant species and VAM fungal spores indicated that the spores of Glomus caledonium are associated with plants from dry, nutrient poor sites and spores of gigaspora gigantea are positively associated with plants occurring on the wet, relatively nutrient rich sites. Glomus fasciculatum was the most abundant and widely distributed VAM fungus and it had more positive associations with endophyte hosts than the other VAM fungi. We found no relationship between beta niche breadth of plant species and the presence or absence of mycorrhizal infection. However, our data suggest that some plant species may vary with respect to their infection status depending upon soil moisture conditions that may fluctuate seasonally or annually to favor or hinder VAM associations.