The impact of wildfire on vesicular-arbuscular mycorrhizal fungi and their potential to influence the re-establishment of post-fire plant communities

Wildfires are a typical event in many Australian plant communities. Vesicular-arbuscular mycorrhizal (VAM) fungi are important for plant growth in many communities, especially on infertile soils, yet few studies have examined the impact of wildfire on the infectivity of VAM fungi. This study took the opportunity offered by a wildfire to compare the infectivity and abundance of spores of VAM fungi from: (i) pre-fire and post-fire sites, and (ii) post-fire burned and unburned sites. Pre-fire samples had been taken in May 1990 and mid-December 1990 as part of another study. A wildfire of moderate intensity burned the site in late December 1990. Post-fire samples were taken from burned and unburned areas immediately after the fire and 6 months after the fire. A bioassay was used to examine the infectivity of VAM fungi. The post-fire soil produced significantly less VAM infection than the pre-fire soil. However, no difference was observed between colonization of plant roots by VAM fungi in soil taken from post-fire burned and adjacent unburned plots. Soil samples taken 6 months after the fire produced significantly more VAM than corresponding soil samples taken one year earlier. Spore numbers were quantified be wet-sieving and decanting of 100-g, air-dried soil subsamples and microscopic examination. For the most abundant spore type, spore numbers were significantly lower immediately post-fire. However, no significant difference in spore numbers was observed between post-fire burned and unburned plots. Six months after the fire, spore numbers were the same as the corresponding samples taken 1 year earlier. All plants appearing in the burned site resprouted from underground organs. All post-fire plant species recorded to have mycorrhizal associations before the fire had the same associations after the fire, except for species of Conospermum (Proteaceae), which lacked internal vesicles in cortical cells in the post-fire samples.     

Effect of liming on spore germination,germ tube growth and root colonization by vesicular-arbuscular mycorrhizal fungi

Summary The effect of soil acidity on spore germination, germ tube growth and root colonization of vesicular-arbuscular mycorrhizal (VAM) fungi was examined using a Florida Ultisol. Soil samples were treated with 0, 4, 8 and 12 meq Ca/MgCO₃/100 g soil and each lime level received 0, 240, and 720 ppm P as superphosphate. Corn (Zea mays L.) was planted in the soil treatments, inoculated with eitherGlomus mosseae orGigaspora margarita spores and grown for 31 days. Acid soil inhibits mycorrhizal formation byG. mosseae through its strong fungistatic effect against the spores. The dolomitic lime increased mycorrhizal formation by both fungal species.G. margarita is much less sensitive to acidic conditions thanG. mosseae. Al ions are a very important component of the fungistatic property against the VAM symbiosis. VAM fungus adaptation may be important for plants growing on infertile acid soils if soil inoculation with these fungi is to contribute significantly to low-input technology for tropical agricultural systems.     

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.     

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^{–  1}soil 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. Received: 16 May 1995 / Accepted: 7 February 1996     

Dynamics of vesicular-arbuscular mycorrhizae during old field succession

Summary The species composition of vesicular-arbuscular mycorrhizal (VAM) fungal communities changed during secondary succession of abandoned fields based on a field to forest chronosequence. Twenty-five VAM fungal species were identified. Seven species were clearly early successional and five species were clearly late successional. The total number of VAM fungal species did not increase with successional time, but diversity as measured by the Shannon-Wiener index tended to increase, primarily because the community became more even as a single species, Glomus aggregatum, became less dominant in the older sites. Diversity of the VAM fungal community was positively correlated with soil C and N. The density of VAM fungi, as measured by infectivity and total spore count, first increased with time since abandonment and then decreased in the late successional forest sites. Within 12 abandoned fields, VAM fungal density increased with increasing soil pH, H₂O soluble soil C, and root biomass, but was inversely related to extractable soil P and percent cover of non-host plant species. The lower abundance of VAM fungi in the forest sites compared with the field sites agrees with the findings of other workers and corresponds with a shift in the dominant vegetation from herbaceous VAM hosts to woody ectomycorrhizal hosts.     

Glomalean mycorrhizal fungi from tropical Australia

 The isolation of vesicular-arbuscular mycorrhizal (VAM) fungi from natural (savanna, rocky hill, wetland and rainforest) and disturbed (minesite) habitats in a seasonally-dry tropical region in the Northern Territory of Australia into open-pot cultures was undertaken to supplement knowledge about the diversity of these fungi. This experiment considered factors affecting the diversity of fungi obtained in trap cultures started using diluted soil from field sites and two host plants. A range of soil phosphorus and other nutrient levels from severely deficient to sufficient for maximal growth was used to determine the impact of nutrition on mycorrhizal associations of sorghum (Sorghum sp.) and clover (Trifolium subterraneum). Soil cores taken from pots at 6-week intervals provided roots and soil to assess mycorrhiza formation and sporulation without substantial damage to plants. The identification of VAM fungi to genus by observing morphological patterns within clover roots revealed substantial differences in fungus populations between soils and a moderate effect of nutrient levels on fungal diversity. Changes in the proportion of different fungi in roots over the 31 weeks of the experiment were also observed. Glomus spp. were initially the most abundant fungi within roots, but Scutellospora spp. gradually became more dominant at later harvests, while colonisation by Acaulospora spp. was limited at all times. For both clover and sorghum, sporulation was limited and was dominated by single species of Scutellospora and Acaulospora. This contrasted with the much higher diversity of spore types in the original field soils.     

Effects of Metal Phytoextraction Practices on the Indigenous Community of Arbuscular Mycorrhizal Fungi at a Metal-Contaminated Landfill

Phytoextraction involves use of plants to remove toxic metals from soil. We examined the effects of phytoextraction practices with three plant species (Silene vulgaris, Thlaspi caerulescens, and Zea mays) and a factorial variation of soil amendments (either an ammonium or nitrate source of nitrogen and the presence or absence of an elemental sulfur supplement) on arbuscular mycorrhizal (AM) fungi (Glomales, Zygomycetes) at a moderately metal-contaminated landfill located in St. Paul, Minn. Specifically, we tested whether the applied treatments affected the density of glomalean spores and AM root colonization in maize. Glomalean fungi from the landfill were grouped into two morphotypes characterized by either light-colored spores (LCS) or dark-colored spores (DCS). Dominant species of the LCS morphotype were Glomus mosseae and an unidentified Glomus sp., whereas the DCS morphotype was dominated by Glomus constrictum. The density of spores of the LCS morphotype from the phytoremediated area was lower than the density of these spores in the untreated landfill soil. Within the experimental area, spore density of the LCS morphotype in the rhizosphere of mycorrhizal maize was significantly higher than in rhizospheres of nonmycorrhizal S. vulgaris or T. caerulescens. Sulfur supplement increased vesicular root colonization in maize and exerted a negative effect on spore density in maize rhizosphere. We conclude that phytoextraction practices, e.g., the choice of plant species and soil amendments, may have a great impact on the quantity and species composition of glomalean propagules as well as on mycorrhiza functioning during long-term metal-remediation treatments.     

ROLE OF MYCORRHIZAL FUNGUS ORIGIN IN GROWTH AND NUTRIENT UPTAKE BY GERANIUM ROBERTIANUM

Prior field studies have shown that populations of forest herbs on relatively nutrient poor soils have higher vesicular-arbuscular mycorrhizal (VAM) infection intensity than plants on rich soils. However, the growth responses and ability to take up P against the soil nutrient gradient are often not linearly related to infection intensity. To determine if intraspecific differences among populations of the common VAM fungus Glomus occultum could differentially affect growth and nutrient uptake, Geranium robertianum seedlings were inoculated with Glomus occultum isolated from four forest types along a gradient of soil fertility, and grown in a greenhouse at P levels typical of the extremes of that gradient. Plants given inoculum from relatively infertile forest sites generally produced greater root, shoot, and total mass than plants given inoculum from fertile sites or uninoculated plants, especially at the low P supply rate. Total P uptake and both P and N uptake efficiency were also highest in plants given inocula from low fertility sites. These results indicate that local adaptation and intraspecific variations in the ability of VAM fungi to induce growth and nutrient uptake effects on host plants may be as important as interspecific differences among VAM fungus species.     

Topsoil storage effects on primary production and rates of vesicular-arbuscular mycorrhizal development inAgropyron trachycaulum

Summary A greenhouse study was conducted to determine the effects of stockpiling prairie grassland topsoil for 3 years on mycorrhizal development and root and shoot production of slender wheatgrass. The vesicular-arbuscular mycorrhizal (VAM) fungi involved in the symbiosis were also assessed as was the decomposition potential of the soil. During the first week of growth, VAM development in grasses grown in the stockpiled soil lagged behind that observed for grasses in the undisturbed soil. However, by 3 weeks, the mycorrhizal infection in plants in the stockpiled soil had reached levels similar to that in plants in the undisturbed soil. The dominant species of VAM fungi involved in the symbiosis at 8 weeks after planting shifted fromGlomus fasciculatum in the undisturbed soil toG. mosseae in the stockpiled soil. The delay in initial VAM infection and shift in VAM fungal species did not significantly affect plant productivity which was greatest in the stockpiled soil. The greater shoot production exhibited by grasses in the stockpiled soil was attributed to higher levels of NO₃-N in the stockpiled than undisturbed soil. The potential of the soil to decay dead slender wheatgrass roots was not altered by stockpiling.     

The Vesicular Arbuscular Mycorrhiza Associated with Three Cultivars of Rice (Oryza sativa L.)

The present study deals with the occurrence of vesicular arbuscular mycorrhizal fungi in three cultivars of rice in Barak valley. Three cultivars of rice were Pankaj, Malati and Ranjit. The results revealed the association of VAM fungi in all the cultivars of rice. The association was maximum in Pankaj cultivar followed by Malati, and Ranjit, respectively, in all the three sampling phases. All the three cultivars of rice crop showed maximum soil spore population and number of VAM fungal species at the harvesting phase (135 DAS) and minimum at the phase of maturation (90 DAS). Glomus species were found dominating followed by Acaulospora species. Glomus microcarpum, Glomus claroideum, Glomus mosseae and Acaulospora scrobiculata were found in all the three fields.     

Interactions between water-stress and different mycorrhizal inocula on plant growth and mycorrhizal development in maize and sorghum

Maize (Zea mays) and sorghum (Sorghum bicolor) were inoculated with a range of VAM fungi and grown under water-stressed and unstressed conditions. There was considerable variation amongst the inocula in their effects on plant growth. Inoculation with Glomus clarum produced the biggest plants in each host, with Glomus monosporum and Acaulospora sp. giving the least growth overall. Root infection produced by the different inocula also varied, but levels were not correlated with effects on plant growth. Water-stress reduced plant growth, with the effects not being altered by mycorrhizal infection. VAM infection levels were not affected by water-stress. Spore production from most inocula was reduced by water-stress, both in total spore numbers and in terms of spores per gram plant weight. Sporulation of G. clarum, G. epigeum and G. monosporum were affected less by stress than were the other inocula. Spore production was in general greater on sorghum than on maize, but the host effect varied amongst the inocula.     

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.     

Categories of vesicular-arbuscular mycorrhizal dependency of host species

Summary 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.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3547     

Indigenous populations of arbuscular mycorrhizal fungi and soil aggregate stability are major determinants of leek (Allium porrum L.) response to inoculation with Glomus intraradices Schenck & Smith or Glomus versiforme (Karsten) Berch

 Knowledge of physical, chemical and biological soil characteristics influencing plant response to inoculation with arbuscular mycorrhizal (AM) fungi would help to distinguish soils where inoculation could be profitable. The relationship between leek (Allium porrum L.) response to mycorrhizal inoculation with Glomus intraradices Schenck & Smith or G. versiforme (Karsten) Berch and soil texture, bulk density, particle density, porosity, pH, organic matter content, available P, K, Ca, Mg, Fe, Zn, Cu, and Mn, soil structure, soil mycorrhizal potential (SM), preceding crop mycorrhizal potential, composition of indigenous mycorrhizal fungal communities, and the abundance of spores of different species, was studied in 81 agricultural soils using Principal Component Analysis and regression analysis. The nature of the indigenous AM fungi population was an important determinant of leek response to inoculation (RTI). In soils with more than 200 μg available P g^–1, SM potential accounted for over 27% of RTI with G. intraradices and G. versiforme, RTI being high in soils with low SM potential. In low P soils, however, a positive relation between the abundance of water stable soil aggregates in the 0.5–2 mm diameter range and RTI was most important. Low soil Zn and high porosity, abundant total mycorrhizal spore as well as scarcity of spores of G. aggregatum and of the group G. etunicatum-rubiforme were also associated to high RTI. The influence of water stable aggregation of soil on RTI was modulated by soil P levels. Abundance of soil aggregates was positively related to RTI at low soil P levels, but negatively related to RTI at high P levels. Different relationships were found between soil variables and spore abundance of different AM fungi species. Some AM species appear to have as yet undefined similarities or complementarities at the biological or ecological levels. Accepted: 23 July 1997     

Effects of metal phytoextraction practices on the indigenous community of arbuscular mycorrhizal fungi at a metal-contaminated landfill

Phytoextraction involves use of plants to remove toxic metals from soil. We examined the effects of phytoextraction practices with three plant species (Silene vulgaris, Thlaspi caerulescens, and Zea mays) and a factorial variation of soil amendments (either an ammonium or nitrate source of nitrogen and the presence or absence of an elemental sulfur supplement) on arbuscular mycorrhizal (AM) fungi (Glomales, Zygomycetes) at a moderately metal-contaminated landfill located in St. Paul, Minn. Specifically, we tested whether the applied treatments affected the density of glomalean spores and AM root colonization in maize. Glomalean fungi from the landfill were grouped into two morphotypes characterized by either light-colored spores (LCS) or dark-colored spores (DCS). Dominant species of the LCS morphotype were Glomus mosseae and an unidentified Glomus sp., whereas the DCS morphotype was dominated by Glomus constrictum. The density of spores of the LCS morphotype from the phytoremediated area was lower than the density of these spores in the untreated landfill soil. Within the experimental area, spore density of the LCS morphotype in the rhizosphere of mycorrhizal maize was significantly higher than in rhizospheres of nonmycorrhizal S. vulgaris or T. caerulescens. Sulfur supplement increased vesicular root colonization in maize and exerted a negative effect on spore density in maize rhizosphere. We conclude that phytoextraction practices, e.g., the choice of plant species and soil amendments, may have a great impact on the quantity and species composition of glomalean propagules as well as on mycorrhiza functioning during long-term metal-remediation treatments.     

Effects of vesicular-arbuscular mycorrhizal inoculation at different soil P availabilities on growth and nutrient uptake of in vitro propagated coffee (Coffea arabica L.) plants

 In a pot experiment, the growth and the nutrient status of in vitro propagated coffee (Coffea arabica L.) microcuttings were investigated for 5 months following vesicular-arbuscular mycorrhizal (VAM) inoculation with either Acaulospora melleae or Glomus clarum at four soil P availabilities. Control plants remained P-deficient even at the highest soil P availability while mycorrhizal plants were P-sufficient at all soil P availabilities. Growth of control plants was only improved at the highest soil P availability. In P-deficient soil, neither of the two VAM species improved plant growth. Plant growth increased by 50% following inoculation with either A. melleae or G. clarum when P availability went from deficient to low. No further plant growth improvement was induced by either VAM species at intermediate and high soil P levels. Nevertheless, growth of plants inoculated with G. clarum was still significantly greater than that of non-mycorrhizal plants at the highest soil P availability. Root colonization by G. clarum increased with increasing soil P availability while root colonization by A. mellea decreased with soil P level increasing above low P availability. Soil P availability also affected Zn nutrition through its influence on VAM symbiosis. With increasing soil P availability, foliar Zn status increased with G. clarum or decreased with A. mellea in parallel to root colonization by VAM. This study demonstrates the beneficial effects of VAM inoculation on in vitro propagated Arabica coffee microcuttings, as shown previously for seedlings. This study also demonstrates differences in tolerance to soil P availability between VAM species, most likely resulting from their differing abilities to enhance coffee foliar P status. Accepted: 14 November 1996     

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.     

西双版纳热带雨林中丛枝菌根真菌的初步研究*

对西双版纳热带雨林中30个科的42种植物根系的丛枝菌根真菌定居情况进行了调查,并从这些植物的根际土壤中分离鉴定了分属于无梗囊霉属(Acaulospora)、球囊霉属(Glomus)和硬囊霉属(Sclerocystis)的25种丛枝菌根真菌。对热带雨林土壤中丛枝菌根真菌的孢子密度（spore density）、物种丰富度（species richness）以及已鉴定种的出现频率进行统计分析发现：热带雨林土壤中丛枝菌根真菌的孢子密度在每100g土壤116~1560个之间,平均478个;物种丰富度在2~7之间,平均为4.5;无梗囊霉属和球囊霉属真菌是热带雨林土壤中丛枝菌根真菌的优势类群。     

Arbuscular mycorrhiza of Arnica montana under field conditions—conventional and molecular studies

Two distinct populations of Arnica montana, an endangered medicinal plant, were studied under field conditions. The material was investigated using microscopic and molecular methods. The analyzed plants were always found to be mycorrhizal. Nineteen arbuscular mycorrhizal fungal DNA sequences were obtained from the roots. They were related to Glomus Group A, but most did not match any known species. Some showed a degree of similarity to fungi colonizing liverworts. Conventional analysis of spores isolated from soil samples allowed to identify different fungal taxa: Glomus macrocarpum, Glomus mosseae, Acaulospora lacunosa, and Scutellospora dipurpurescens. Their spores were also isolated from trap cultures.     

Response of citronella Java (Cymbopogon winterianus Jowitt) to VA mycorrhizal fungi and soil compaction in relation to P supply

Nutrient acquisition and growth of citronella Java (Cymbopogon winterianus Jowitt) was studied in a P-deficient sandy soil to determine the effects of mycorrhizal symbiosis and soil compaction. A pasteurized sandy loam soil was inoculated either with rhizosphere microorganisms excluding VAM fungi (non-mycorrhizal) or with the VAM fungus, Glomus intraradices Schenck and Smith (mycorrhizal) and supplied with 0, 50 or 100 mg P kg^-1 soil. The soil was compacted to a bulk density of 1.2 and 1.4 Mg m^-3 (dry soil basis). G. intraradices substantially increased root and shoot biomass, root length, nutrient (P, Zn and Cu) uptake per unit root length and nutrient concentrations in the plant, compared to inoculation with rhizosphere microorganisms when the soil was at the low bulk density and not amended with P. Little or no plant response to the VAM fungus was observed when the soil was supplied with 50 or 100 mg P kg^-1 soil and/or compacted to the highest bulk density. At higher soil compaction and P supply the VAM fungus significantly reduced root length. Non-mycorrhizal plants at higher soil compaction produced relatively thinner roots and had higher concentrations and uptake of P, Zn and Cu than at lower soil compaction, particularly under conditions of P deficiency. The quality of citronella Java oil measured in terms citronellal and d-citronellol concentration did not vary appreciably due to various soil treatments.