Presence Of Arbuscular Mycorrhiza Research Articles

Old-growth Acer macrophyllum trees host a unique suite of arbuscular mycorrhizal fungi and other root-associated fungal taxa in their canopy soil environment

ABSTRACT Canopy soils occur on tree branches throughout the temperate rainforests of the Pacific Northwest Coast and are recognized as a defining characteristic of these ecosystems. Certain tree species extend adventitious roots into these canopy soil environments. Yet, research on adventitious root-associated fungi remains limited. Our study used microscopy to compare fungal colonization intensity between canopy and forest floor roots of old-growth bigleaf maple (Acer macrophyllum) trees. Subsequently, two high-throughput sequencing platforms were used to explore the spatial and seasonal variation of root-associated fungi between the two soil environments over one year. We found that canopy and forest floor roots had similar colonization intensity and were associating with a diversity of arbuscular mycorrhizal fungi and other potential symbionts, many of which were resolved to species level. Soil environment and seasonality affected root-associated fungal community composition, and several fungal species were indicative of the canopy soil environment. In Washington State’s (USA) temperate old-growth rainforests, these canopy soil environments host a unique suite of root-associated fungi. The presence of arbuscular mycorrhizae provides further evidence that adventitious roots form fungal associations to exploit canopy soils for resources, and there may be novel relationships forming with other fungi. These soils may be providing a redundancy compartment (i.e., “nutrient reserve”), imparting a resiliency to disturbances for certain old-growth trees.

Arbuscular mycorrhizae reduce the response of important plant functional traits to drought and salinity. A meta-analysis study.

We aimed at exploring the plant functional traits whose responses to drought or salinity are altered by the presence of arbuscular mycorrhiza (AM). We performed a meta-analysis across 114 articles spanning 110 plant species or cultivars. We quantified the size effect of AM symbiosis on the stress response of several functional traits, using linear mixed model analysis (LMM). Correlation analysis between functional traits and total biomass responses to stresses were also performed through LMM. The literature search and further selection yielded seven functional traits, extracted from 114 laboratory studies, including 888 observations and 110 plant species/cultivars. Evidence for significant effects of predictor variables (type of stress, AM symbiosis and/or their interaction) on functional trait response were found for leaf area ratio (LAR), root mass fraction (RMF) and root-shoot (R:S) ratio. Our results provided evidence to accept the hypothesis that AM fungal inoculation may reduce the stress response of these plant functional traits by decreasing its magnitude. We also found a weak correlation between stress responses of these traits and total biomass variation. Although our literature search and data collection were intensive and our results robust, the scope of our conclusions is limited by the agronomical bias of plant species targeted by the meta-analysis. Further knowledge on non-cultivable plant species and better understanding of the mechanisms ruling resources allocation in plants would allow more generalised conclusions.

Effect of Low-Input Organic and Conventional Farming Systems on Maize Rhizosphere in Two Portuguese Open-Pollinated Varieties (OPV), "Pigarro" (Improved Landrace) and "SinPre" (a Composite Cross Population).

Maize is one of the most important crops worldwide and is the number one arable crop in Portugal. A transition from the conventional farming system to organic agriculture requires optimization of cultivars and management, the interaction of plant–soil rhizosphere microbiota being pivotal. The objectives of this study were to unravel the effect of population genotype and farming system on microbial communities in the rhizosphere of maize. Rhizosphere soil samples of two open-pollinated maize populations (“SinPre” and “Pigarro”) cultivated under conventional and organic farming systems were taken during flowering and analyzed by next-generation sequencing (NGS). Phenological data were collected from the replicated field trial. A total of 266 fungi and 317 bacteria genera were identified in “SinPre” and “Pigarro” populations, of which 186 (69.9%) and 277 (87.4%) were shared among them. The microbiota of “Pigarro” showed a significant higher (P < 0.05) average abundance than the microbiota of “SinPre.” The farming system had a statistically significant impact (P < 0.05) on the soil rhizosphere microbiota, and several fungal and bacterial taxa were found to be farming system-specific. The rhizosphere microbiota diversity in the organic farming system was higher than that in the conventional system for both varieties. The presence of arbuscular mycorrhizae (Glomeromycota) was mainly detected in the microbiota of the “SinPre” population under the organic farming systems and very rare under conventional systems. A detailed metagenome function prediction was performed. At the fungal level, pathotroph–saprotroph and pathotroph–symbiotroph lifestyles were modified by the farming system. For bacterial microbiota, the main functions altered by the farming system were membrane transport, transcription, translation, cell motility, and signal transduction. This study allowed identifying groups of microorganisms known for their role as plant growth-promoting rhizobacteria (PGPR) and with the capacity to improve crop tolerance for stress conditions, allowing to minimize the use of synthetic fertilizers and pesticides. Arbuscular mycorrhizae (phyla Glomeromycota) were among the most important functional groups in the fungal microbiota and Achromobacter, Burkholderia, Erwinia, Lysinibacillus, Paenibacillus, Pseudomonas, and Stenotrophomonas in the bacterial microbiota. In this perspective, the potential role of these microorganisms will be explored in future research.

Assessing the synergistic relationship of mycorrhiza and bacteria for the degradation of spent engine oil in maize grown soil

BackgroundPollution by waste hydrocarbons on soil and water bodies is an endemic problem in African countries, particularly in Nigeria. This has caused untold hardship and increase in poverty level of the people, due to the pollution of water and land; which had direct impacts on the livelihood of people. Several species of bacteria that can degrade hydrocarbon had been isolated from the root of plants. The aim of this work was to determine the ability of rhizosphere bacteria to degrade spent engine oil (SPO) in the presence of arbuscular mycorrhiza fungus.ResultsThe total aerobic count in the eight treatments ranged between 3.0 × 106 and 1.18 × 108 CFU/g. No significant difference was observed in the total aerobic count among the treatments except when compared with the control experiment (M−C−). Isolated bacteria from the polluted soil samples were identified by 16S rRNA sequencing as Bacillus cereus, Pseudomonas aeruginosa, Bacillus amyloliquefaciens, Lysinibacillus fusiformis, Bacillus enecimensis, and Paraclostridium benzoelyticum. Four of the bacteria were able to utilize spent engine oil effectively to different degrees. However, Lysinibacillus fusiformis biodegraded spent engine oil by 40%, Paraclostridium benzoelyticum by 30% and Bacillus enecimensis by 20% after 28 days of incubation. The infrared analysis result revealed that Lysinibacillus fusiformis (P6) reduced the strong and band of alcohol by 44%, carboxylic acid group by 22% and carbonyl group by 27%, respectively. This study revealed that spent engine oil at a minimum value of 50 mg/kg with arbuscular mycorrhiza fungus in the soil samples resulted in better growth for maize plant and higher total aerobic count.ConclusionsIt can thus be concluded that arbuscular mycorrhiza fungus positively impacts the ability of rhizosphere bacteria in the degradation of spent engine oil and the growth of maize plant on contaminated soil.

Nano-Zinc Oxide and Arbuscular mycorrhiza Effects on Physiological and Biochemical Aspects of Wheat Cultivars under Saline Conditions.

Saline soils are restrictive factors to agriculture in arid and semi-arid regions, plant growth and productivity. Thus, it was important to consider how, nano-zinc oxide or bulk zinc oxide alleviates the oxidative salt stress in the presence of Arbuscular mycorrhiza (AM) fungi by two wheat cultivars (Sids 13 and Sakha 94). A field experiment was carried out during two winter successive seasons to study the beneficial role of nano-zinc oxide or bulk zinc oxide with different concentrations (5 and 10 mg L-1) in enhancing growth, some biochemical and physiological of two wheat cultivars under saline soil. Soaking both wheat cultivars with nano-zinc oxide or bulk zinc oxide in the presence of AM improved growth parameters. All treatments increased significantly photosynthetic pigments, IAA, phenols contents, organic antioxidant enzyme activities and significant decrease in lipid peroxidation. some changes are observed in protein patterns, so several proteins were disappear, but others were selectively improved and synthesis of the new groups of protein was formed, some of these responses were observed through the effect of nano-zinc oxide or bulk zinc oxide and AM. Nano-ZnO (10 mg L-1) in the presence of AM was the most effective treatments on both cultivars. Results showed superiority of Sakha 94 cultivar in most growth parameters and biochemical aspects than Sids 13 cultivar.

Short Communication: Presence of arbuscular mycorrhiza in maize plantation land cultivated with traditional and improved land management

Ishaq L. 2018. Short Communication: Presence of arbuscular mycorrhiza in maize plantation land cultivated with traditional and improved land management.Trop Drylands 2: 20-24. Arbuscular mycorrhizas (AM) are one of key fungtional soil biota that can greatly contribute to crop productiviy and agricultural sustainability. Their presences could be influenced by soil condition such as land management, and the sporulation of the fungal forming mycorrhiza could be affected by season ie. rainy and dry season. Previously, it was found that the abundance of AM fungi was higher under maize cropping with traditional land management (no tillage, no input of agrochemicals) than that under maize copping system with more modern land management (tillage, agrochemical input), when the soils were sampled at rainy season. As the presence of AM fungi could be influenced by climate factor ie. rain/season, the present study was carried out to examine the abundance and diversity of AM fungi in maize plantation land cultivated with traditional and improved land management in the dry season. At each land management system, three locations of study were purposively selected, and at each location within the cropping system, three soil samples were collected. A total of 9 soil samples representing each land management system were evaluated. The variables observed included AM fungal spore density (expressed as the number of AM fungal spores per 100 g of soil) and biodiversity of AM fungi (expressed as relative abundance of AM fungal spore). It was found that the density of AM fungal spore under maize cropping system with traditional land management was 203.55 per 100g, whereas only 84.91 spores per 100 g soil were found under maize cropping system with improved land management, supporting the previous finding. Despite only six AM fungal spores morphotypes were observed under maize plantation land of both traditional and improved land management, the abundance of the morphotype was different between the two land management systems. The study needs to be extended at a broader location and time to get more representative information on the impact of land management on the abundance of AM fungi in tropical agriculture.

Physiological responses of two grapevine cultivars to combined drought and high temperature stresses in the presence of arbuscular mycorrhiza

Physiological responses of two grapevine cultivars to combined drought and high temperature stresses in the presence of arbuscular mycorrhiza

Arbuscular mycorrhizal fungi and dark septate fungi in plants associated with aquatic environments

ABSTRACT Th ere have been several reports of symbionts in the roots of plants that live in aquatic environments. Arbuscular mycorrhizal fungi (AMF) are the most common microsymbionts and possibly recolonized the aquatic environment together with plants; however, their functions and the extent of their benefi ts are unclear. Furthermore, the presence of other groups of fungi, such as dark septate fungi (DSF), with functions supposedly analogous to those of mycorrhizal fungi, has also been reported. Th e present work provides a compilation of data regarding the presence of arbuscular mycorrhizae in plants from, or under the infl uence of, aquatic environments, and co-colonization by AMF and DSF. Forty species of non-vascular plants, ferns, fern allies, and gymnosperms from 15 families, and 659 species of angiosperms from 87 families were investigated. From the fi rst group (non-fl owering plants) 57 % of the species showed arbuscular mycorrhizal structures in their tissues or roots, whereas among the second group (fl owering plants) 71 % had such structures. Among the mycorrhizal angiosperms, 52 % showed arbuscules in their roots. DSF were found in 1 % of non-fl owering plants and 5 % of angiosperms. All of these are discussed in this review.

Arbuscular mycorrhizal impacts on competitive interactions between Acacia etbaica and Boswellia papyrifera seedlings under drought stress

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses. In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies. We compared the extent of interspecific competition with that of intraspecific competition. Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza (AM) and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A. etbaica and the slowly growing species B. papyrifera. A factorial experimental design was used. The factors were AM, two water levels and five species combinations Important Findings Seedlings of both species benefitted from AM when grown alone, and the positive growth response to pulsed water availability in B. papyrifera seedlings was in contrast with the negative growth response for A. etbaica seedlings. AM also affected the competitive performance of both species. B. papyrifera was not affected by intraspecific competition, whereas A. etbaica was negatively affected compared to the seedlings grown alone. This effect was stronger in the presence of AM. In interspecific competition, A. etbaica outcompeted B. papyrifera. Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition, and the aggressivity index of A. etbaica remained unchanged. The extent to which AM influences plant competition in a drought-stressed environment may depend on belowground functional traits of the species. AM and pulsed water availability could modify the balance between intraspecific and interspecific competition. By affecting the balance between intraspecific and interspecific competition, both factors could impact the establishment and survival of seedlings.

Influence of different doses of phosphorus in the presence of arbuscular mycorrhiza and Rhizobium on the growth and yield of mungbean

Influence of different doses of phosphorus in the presence of arbuscular mycorrhiza and Rhizobium on the growth and yield of mungbean

Weathering of biotite in the presence of arbuscular mycorrhizae in selected agricultural crops

The mutual association of roots and fungus, mycorrhizae, benefits the general ecosystem by producing soil clays from primary phyllosilicates. In laboratory experiments, X-ray diffraction analyses of clay materials showed that the fungus Glomus when inoculated onto barley and canola produced various types of less K-containing phyllosilicates (e.g., illites, smectites and hydroxy-interlayered vermiculites) from biotite and left some biotite (the K-rich mineral) intact. Non-inoculated plants left no intact biotite. Both non-inoculated and inoculated alfalfa produced only some illites from biotite. We propose that mycorrhizae inoculated samples exhibit selective K-extraction from some biotite particles to benefit plant growth and at the same time leaving unaltered biotite for future extractions. However, results from molecular DNA analysis (i.e., PCR) of fungal population, X-ray absorption near edge spectroscopic analysis of the oxidation of Fe2+ to Fe3+ and K-uptake by plants seems to indicate that the K-extraction process from biotite is by no means simple. The transformation of biotite and K (and Mg)-uptake depend on the plant–fungus symbiotic system, and the formation of clay minerals will then be a function of plant type and symbiotic relations in the soils.

Arbuscular mycorrhiza maintains nodule function during external NH 4 + supply in Phaseolus vulgaris (L.)

The synergistic benefits of the dual inoculation of legumes with nodule bacteria and arbuscular mycorrhizae (AM) are well established, but the effect of an external NH(4)(+) supply on this tripartite relationship is less clear. This effect of NH(4)(+) supply was investigated with regards to the growth and function of the legume host and both symbionts. Nodulated Phaseolus vulgaris seedlings with and without AM, were grown in a sand medium with either 0 N, 1 mM or 3 mM NH(4)(+). Plants were harvested at 30 days after emergence and measurements were taken for biomass, N(2) fixation, photosynthesis, asparagine concentration, construction costs and N nutrition. The addition of NH(4)(+) led to a decline in the percentage AM colonization and nodule dry weights, although AM colonization was affected to a lesser extent. NH(4)(+) supply also resulted in a decrease in the reliance on biological nitrogen fixation (BNF); however, the AM roots maintained higher levels of NH(4)(+) uptake than their non-AM counterparts. Furthermore, the non-AM plants had a higher production of asparagine than the AM plants. The inhibitory effects of NH(4)(+) on nodule function can be reduced by the presence of AM at moderate levels of NH(4)(+) (1 mM), via improving nodule growth or relieving the asparagine-induced inhibition of BNF.

Mycorrhizal and Endophytic Fungal Colonization in Arrhenatherum elatius L. Roots According to the Soil Contamination in Heavy Metals

The aim of this work was to jointly study non-mycorrhizal (dark septate fungi) and mycorrhizal (arbuscular mycorrhizae) colonization along a large range of heavy metal pollution in soil in order to determine the effective contribution of each type of endophytes in relation to heavy metal uptake and tolerance. Hence, eight sites were chosen in the mining area of northern France with respect both to a large range of heavy metal contamination (Cd, Pb, Zn) and monospecific colonization by Arrhenatherum elatius. Root colonization with both arbuscular mycorrhizae (AM) and dark septate fungi (DSF) as well as spore density in rhizospheric soil were estimated in relation to soil characteristics. Mycorrhizal infestation (hyphae, arbuscules and vesicles) was adversely affected by soil pollution almost to exclusion. The intensity of colonization with DSF was very low in presence of AM in non-contaminated soils but higher in polluted soils. The effect of the fungal colonization on the heavy metal tolerance of Arrhenatherum elatius is discussed.

Phosphate as a limiting resource: introduction

Phosphorus (P) is commonly a limiting nutrient for both terrestrial and aquatic productivity, with the consequence that it is considered important in determining the biodiversity and biomass of natural ecosystems. P-limitation of terrestrial plants is not a recent development. Karandashov and Bucher (2005) argued that the evolutionary transition of plants from the aquatic to terrestrial habitats was contingent on the presence of arbuscular mycorrhiza, which facilitated P acquisition. As a consequence of persistent P-limitations, terrestrial plants have evolved a wide range of P acquisition strategies, including mechanisms that increase the range of chemical forms that can be accessed, the range of concentrations that can be taken up and the effective absorbing area of the roots (Lambers et al. 2008). Likewise, plants have a range of strategies for conserving P that enable them to persist in P-deficient habitats, including sclerophyllous leaves and serotinous cones. In order to ensure successful recruitment in P-limited environments they also produce P-rich seeds (e.g. Groom and Lamont 2010, this volume). P is also often a limiting nutrient in agriculture (e.g. Sanchez 2010), deficiency being redressed through applications of P-fertilisers (globally ca. 20×10 kg P annum; Smit et al. 2009). Alarmingly, the finite global stocks of P (2,400×10 kg P) are likely to be depleted within 125 years (Smit et al. 2009; Vaccari 2009). Anthropogenic modification of the global P cycle by fertiliser use as well as waste streams and detergent use have effectively doubled global P cycling since the mid-19th century (Filippelli 2002). A consequence is that many natural ecosystems are threatened by super-abundance of a formerly limiting resource, with resulting biodiversity losses (e.g. Tilman et al. 2001). This is likely to be especially true in systems where P was formerly most-limiting, such as in Mediterranean terrestrial ecosystems (Sala et al. 2000), oligotrophic lakes (Schindler et al. 2008) and nutrient-impoverished oceans (Rabalais et al. 2008). Apart from the direct biodiversity consequences of P-eutrophication, release from P-limitation combined with increased atmospheric CO2 concentration and N deposition may exacerbate the loss of biodiversity.

COMBINED EFFECT OF FOLIAR AND MYCORRHIZAL ENDOPHYTES ON AN INSECT HERBIVORE

Many foliar endophytic fungi deter herbivores from feeding on their host plants, but a previous study has suggested that their deterrent effect may be reduced in the presence of arbuscular mycorrhizae. In our study, factorial experiments determined the effects of infection of perennial ryegrass, Lolium perenne, by the foliar endophyte Neotyphodium lolii [present (+E) or absent (−E)] and the mycorrhizal fungus Glomus mosseae [present (+M) or absent (−M)] on larvae of the noctuid moth Phlogophora meticulosa. When host plants received adequate phosphorus (P), mycorrhizae and the foliar endophyte decreased the survivorship of larvae between their second and fifth instar in an additive manner. Sixth-instar larvae feeding on −M−E plants attained greater mass than those feeding on plants with one or both symbionts. There was an M × E interaction with the total amount of grass consumed per larva. The foliar endophyte increased relative consumption rate and reduced efficiency of conversion of ingested food of larvae, while the mycorrhizal fungus had no effect on insect nutritional indices. Larvae preferred −E over +E leaf blades regardless of mycorrhizal infection status. They showed no preference with respect to plant mycorrhizal status. When foraging among mixed stands of intact plants, larvae inflicted more damage on −E than on +E plants. Mycorrhizae reduced feeding damage, but only in −E plants and to a lesser extent than the foliar endophyte. The relative difference between +E and −E plants, in terms of grazing damage, was decreased but not eliminated by mycorrhizae. When P was limiting to plant growth, mycorrhizae still decreased the survivorship of larvae between their second and fifth instar, independently of the foliar endophyte. They accelerated larval development slightly. The foliar endophyte increased the survivorship of fifth-instar larvae, independently of mycorrhizae. We concluded that both foliar endophytes and mycorrhizae affected larval growth and survivorship. Some effects were additive, while others were nonadditive and depended to some extent on host P nutrition. Our findings suggest that the beneficial effect of the foliar endophyte on the host plant, in terms of insect resistance, was reduced but not eliminated by mycorrhizae.

Response of free-living soil protozoa and microorganisms to elevated atmospheric CO 2 and presence of mycorrhiza

Possible interactions between mycorrhiza, atmospheric CO 2, free-living soil microorganisms and protozoa were investigated in pot experimental systems. Pea plants ( Pisum sativum L. cv. Solara) were grown under ambient (360 μl l −1) or elevated (700 μl l −1) atmospheric CO 2 concentration with or without the presence of the arbuscular mycorrhizal (AM) fungus Glomus caledonium. It was hypothesised that (1) the populations of free-living soil protozoa would increase as a response to elevated CO 2, (2) the effect of elevated CO 2 on protozoa would be moderated by the presence of mycorrhiza and (3) the presence of arbuscular mycorrhiza would affect soil protozoan numbers regardless of atmospheric CO 2. After 3 weeks growth there was no difference in bacterial numbers (direct counts) in soil, but the number of free-living bacterial-feeding protozoa was significantly higher under elevated CO 2 and was significantly reduced in the mycorrhizal treatments. These effects on protozoa disappeared after 5 and 9 weeks. Neither mycorrhiza nor CO 2 concentration had any substantial effect on the microbial community structure as evaluated by phospholipid fatty acid analysis. The increased protozoan populations under elevated CO 2 suggest increased bacterial production, whereas the lower populations in response to presence of mycorrhiza suggest a depressing effect on bacterial production by AM colonisation.

Effect of arbuscular mycorrhizae on soil microbial populations and associated plant performance of the salt marsh grass Spartina patens

The effect of arbuscular mycorrhizae (AM) on soil microbial populations and on growth performance of the high salt marsh plant Spartina patens was investigated in a AM suppression study on field-collected soil cores with S. patens. The application of benomyl resulted in a significant reduction of AM colonization on roots of S. patens, but did not completely suppress AM. Non-treated cores had significantly greater colonization (26 ± 6%) than either benomyl- (12 ± 7%) or benomyl-phosphorus-treated (7 ± 3%) cores at a depth of 2.5 cm. Colonization differences between cores declined with depth (5.0 and 7.5 cm), however, so that at 7.5 cm there was no difference between treatments. This decline was attributed to a reduction in oxygen availability with depth as evidenced by decreasing redox potential. Basic environmental conditions generally resembled those found at the field site. There were no environmental differences between treatments at the depths examined. Cell numbers and specific biomass of DAPI-stained organisms as well as members of the Domain Bacteria were significantly higher when AM colonization was suppressed, while those of the Domains Eucarya and Archaea were not significantly influenced. The increase in both microbial and bacterial population size and biomass in the presence of lower levels of AM colonization is most likely due to increases in carbon exudation to soil and rhizosphere populations that accompany AM suppression. PCR-RFLP analysis of nifH amplicons in bulk soil and rhizosphere at varying depths through the soil cores showed differences in banding patterns between rhizosphere and soil material in the presence of AM. The lack of such strong differences in the benomyl-treated cores suggests that AM colonization more strongly affects the nitrogen-fixing population than do physicochemical conditions (e.g. redox potential) alone. Plant growth performance assessed by analyzing root and leaf biomass, as well as excitation transfer efficiency of open photosynthesis system II (PS II) reaction centers (Fv/Fm) was not significantly influenced by AM. Significant differences were found between treatments for C/N ratios and nitrogen content in leaf tissue, indicating that suppression of AM increased plant nitrogen acquisition.

Rhizosphere effects on microbial community structure and dissipation and toxicity of polycyclic aromatic hydrocarbons (PAHs) in spiked soil.

Phytoremediation of soils polluted with polycyclic aromatic hydrocarbons (PAHs) has so far neglected the possible role of the ubiquitous symbiotic associations between plant roots and fungi known as arbuscular mycorrhizas. A time course laboratory experiment with clover and ryegrass grown on spiked [500 + 500 + 50 mg kg-1 of anthracene, chrysene and dibenz(a,h)anthracene] soil demonstrated for the first time that dissipation of condensed PAHs may be enhanced in the presence of arbuscular mycorrhiza [66 and 42% reductions in chrysene and dibenz(a,h)anthracene, respectively, versus 56 and 20% reductions in nonmycorrhizal controls]. Addition of a surfactant accelerated initial PAH dissipation but did not attain final PAH concentrations below those obtained with nonmycorrhizal plants. Toxicity tests (earthworm survival and bioluminescence inhibition in Vibrio fischeri) indicated that mycorrhiza reduced the toxicity of PAHs and/or their metabolites and counteracted a temporally enhanced toxicity mediated by surfactant addition. Phospholipid fatty acid profiles demonstrated that the imposed treatments altered the microbial community structure and indicated that the mycorrhiza-associated microflora was responsible for the observed reductions in PAH concentrations in the presence of mycorrhiza.

Effect of phosphate and the arbuscular mycorrhizal fungus Glomus intraradices on disease severity of root rot of peas ( Pisum sativum ) caused by Aphanomyces euteiches

The effects of inorganic phosphate levels and the presence of arbuscular mycorrhiza on disease severity of Aphanomyces euteiches in pea roots were studied. Disease severity on roots and epicotyl as well as the oospore number within infected root tissue were correlated with the phosphorus (P) level in the growth medium. The arbuscular mycorrhizal fungus Glomus intraradices increased P uptake and the P concentration in the plant but reduced disease development in peas. Polyacrylamide gel electrophoresis followed by densitometry of glucose-6-phosphate dehydrogenase specific to A.euteiches was used to measure the activity of the pathogen in roots. The enzyme activity increased with disease severity and disease incidence, except in plants supplemented with P at the highest level, where a peak in activity was seen 12 days after inoculation with the pathogen, followed by a decrease in activity. The epicotyl of mycorrhizal plants showed a reduction in disease severity although this part of the plants was not mycorrhizal. Thus, an induced systemic factor may be responsible for increased resistance in mycorrhizal plants.

Physical, Chemical and Biological Characterisation of a Steelworks Waste Site at Port Kembla, NSW, Australia

Large spoils of metal-rich filtercake from the Port Kembla BHP steelworks were characterised by certain physical, chemical and biological parameters. The vegetation was assessed for potential metal hyperaccumulators and the presence of arbuscular mycorrhizae in the rhizospheres. Fresh filtercake ( 4 yr). Among the naturally colonising plants, Ricinus communis and Sonchus oleraceus are regarded the most suitable options for zinc and cadmium removal, respectively. Arbuscular mycorrhizal infection (particularly with Glomus and Gigaspora strains) should be promoted for optimum soil reclamation.