Levels of organic carbon within agricultural soils in Australia continue to decline predominantly due to intensive cultivation. Such practices place sustainable use of agricultural soils at risk. The aim of the present study was to test whether selected melanised endophytic fungi could enhance organic carbon in an experimental soil. In a compartmental pot study, 20 melanised endophytic fungi significantly increased carbon in an aggregated carbon-rich Alfisol over 14 weeks, with increases of up to 17% measured. Two of these fungi increased organic carbon within microaggregates. This study demonstrates that some melanised endophytic fungi have the potential to increase levels of organic carbon within an experimental soil. Melanin, a polyaromatic compound present within the cell walls of melanised endophytic fungi, may have contributed towards increases in organic carbon, particularly if protected within soil aggregates. Deposition of aromatic carbon within aggregates would leave this carbon less susceptible to oxidation and contribute towards long-term carbon storage in soils.

The queens of many eusocial insect species are polyandrous. The evolution of polyandry from ancestral monoandry is intriguing because polyandry undermines the kin-selected benefits of high intracolonial relatedness that are understood to have been central to the evolution of eusociality. An accumulating body of evidence suggests that polyandry evolved from monoandry in part because genetically diverse colonies better resist infection by pathogens. However, a core assumption of the “parasite–pathogen hypothesis”, that there is variation in virulence among strains of pathogens, remains largely untested in vivo. Here, we demonstrate variation in virulence among isolates of Ascosphaera apis, the causative organism of chalkbrood disease in its honey bee (Apis mellifera) host. More importantly, we show a pathogen–host genotypic interaction for resistance and pathogenicity. Our findings therefore support the parasite-parasite hypothesis as a factor in the evolution of polyandry among eusocial insects.

A clearer understanding of the mechanisms that underpin the development and stabilisation of soil structure would enable a more predictable restoration of degraded soil. A hierarchical model of soil aggregation (HM) is posited that predicts soils to be self-organising systems, mediated via interactions and feedbacks between their mineral constituents, organic matter and biotic activity, which serve to create and stabilise soil structure. To determine the contribution of these latter constituents, combinations of organic matter (compost), living plant roots (three perennial species: two woody, one grass) and a community of arbuscular mycorrhizal (AM) fungi where added to a massive mine spoil in a controlled pot experiment. It was hypothesized that the absence of any of these three components would retard the development of stable soil structure, as assessed through the development of porosity, changes in bulk density, soil water retention characteristics and water-stable aggregation following a 6 month incubation period. The concentration and content of soil organic carbon (SOC), nitrogen, cation exchange capacity and pH were also determined. All three factors, organic matter, living plant roots and AM fungi were required for the development of stable soil structure, but in complex ways. Overall, the data indicate that in the presence of adequate organic matter, plant roots are key contributors to the development of soil structure which is further stabilized by AM fungi.

Knowledge of the abundance, diversity, and plant interactions of melanised root-associated fungi remains limited. The objective of this study was to isolate a wide variety of melanised root-associated fungi within the Sydney basin (NSW, Australia) and assess growth response of Trifolium subterraneum to inoculation with individual isolates. Of 902 root-associated fungi isolated from plant roots, 118 were melanised. All but two of these fungi were re-isolated from inoculated T. subterraneum seedlings after 7 weeks in a controlled environment. Approximately 60 % of the melanised root-associated fungi did not reduce plant growth. Twenty-four isolates tended to increase plant growth and were tentatively identified as predominantly ascomycetes, and one zygomycete. Melanised root-associated fungi appeared to form complex interactions with T. subterraneum, the natures of which remain to be further explored. Melanised root-associated fungi could potentially play key ecological roles including positively influencing edaphic conditions. (c) 2012 Elsevier Ltd and The British Mycological Society. All rights reserved.

The contribution of fungi to aggregation of soil is thought to be mediated via hyphal enmeshment of particles and increased adhesion between particles. The role of saprotrophic fungi in soil aggregation remains uncertain. This study explored the role of saprotrophic Trichocomaceae in water-stable aggregation of soil. Eighty-five isolates derived from agricultural and undisturbed Australian soils were identified by morphological and molecular (ITS1–5.8S rRNA–ITS2) methods. The formation and stabilisation of soil aggregates by each isolate either through increased adhesion between particles, mediated by extracellular materials, or enmeshment during hyphal growth, and the effects of nutrition on aggregation were examined. The creation of water-stable aggregates by Trichocomaceous fungi was uncommon and largely transient, whether measured by adhesive materials alone or growth of the fungus in soil. Water-stable aggregation by adhesion was increased significantly by only one isolate. The adhesive properties of extracellular materials produced by this isolate were affected by the source of carbon. When grown in soil only six isolates increased water-stable aggregation by more than 12% after three weeks. When grown on compost (complex carbon) selected isolates were capable of forming water-stable aggregates although these aggregates were generally not persistent. Mean weight diameter peaked after three weeks and declined thereafter with increased period of fungal growth. The potential to create water-stable aggregates by adhesion or soil enmeshment was isolate specific: the potential varied within species and was unrelated to extensive hyphal growth in culture. Saprotrophic Trichocomaceae are capable of aggregate formation by physical enmeshment; however the aggregates formed are not stabilised beyond the short growth period of the fungi. Any increase in water-stable aggregation by Trichocomaceae as a group is likely to be transient.

Arbuscular mycorrhizal (AM) fungi convey well documented benefits to plant growth in domesticated species. We investigated AM in Solanum centrale, a desert shrub of central Australia and traditional food for Indigenous Australians. AM were observed in roots of S. centrale from wild and cultivated stands of different ages and management regimes. Greenhouse seedlings grown in sterilised sand were provided with no or minor additions of phosphorus, with or without AM fungi. Inoculated seedlings not fertilised with phosphorus exhibited moderate AM formation. Added phosphorus resulted in an absence of AM. Inoculation did not significantly affect dry weight, root length and plant height of seedlings fertilised with phosphorus but significantly increased the size of unfertilised seedlings. Inoculation significantly increased root phosphorus content, decreased root to shoot ratio and decreased root biomass at all phosphorus additions, despite the absence of observable AM. Thus it appears AM fungi in the root zone influenced certain plant characteristics, regardless of phosphorus nutrition. Overall, S. centrale benefited from the presence of AM through increased phosphorus uptake, but only when the seedlings were growing in soil with extremely low available phosphorus. The response was immediate in our experimental system and is likely to be important in the wild.

The distribution of Rhizophlyctis rosea was examined in soils from 22 locations including disturbed and undisturbed habitats in eastern Australia. Thalli of Rh. rosea were observed on baits from 60% of the sites (67% agricultural and 33% natural soils). Within the disturbed habitats, samples from four sites that experience different temperature ranges were assessed for frequency, abundance, number of thalli and density of colonization of the baits. Lens paper baits were placed into Petri dishes with sterile deionized water and air-dried soil and incubated for up to four days at 20, 35 or 40 degrees C, and at 20 degrees C after freezing (-15 degrees C) and heating (80 degrees C) the soil. The abundance, frequency, number of thalli and density of colonization varied among the samples analysed, with the greatest abundance, number of thalli and density for Pitt Town Bottoms and the highest frequency for Pitt Town Bottoms and Narrabri soils. All isolates grew and released zoospores after heat and freezing treatments. Freezing soil before baiting increased the number of thalli and density of colonization of baits, while heating decreased the frequency and abundance of Rh. rosea.

Seventeen fungi in the Chytridiomycota were tested for their ability to use nitrate as a sole source of nitrogen in solid medium, and various organic and inorganic sources of nitrogen in liquid media. Since fourteen of the seventeen isolates grew well on solid chytrid synthetic medium (CSM) with nitrate as the sole source of nitrogen, this medium appears to be excellent for maintaining many of these fungi in culture. Growth was observed in liquid media containing nitrate, ammonium, urea, aspartate, alanine, phenylalanine, histidine and arginine as nitrogen sources. The results did not show clear patterns of nitrogen requirements within the orders tested. However, it does appear that the nitrogen requirements among zoosporic fungi are variable. Single amino acids were poor sources of both carbon and nitrogen in all fungi tested. Furthermore, since glucose and thiamine are the only organic compounds in CSM with nitrate, these results suggest that many of these fungi are capable of growth in the soil under field conditions with very little organic matter.

Fungal entomopathogens can directly regulate populations of various insects. The entomopathogen Beauveria bassiana can also endophytically colonize various plants. Endophytic colonization by entomopathogens might be more widespread than currently realized and may provide a source of indirect interactions between fungi and insects. We tested whether some common entomopathogens could colonize six crop plants. We also assessed whether the performance of two insects, Aphis gossypii and Chortoicetes terminifera, was affected by entomopathogens in plants. The entomopathogens B. bassiana, Lecanicillium lecanii and Aspergillus parasiticus individually colonized the leaves of all six crop plants when inoculated as conidia. L. lecanii also readily colonized five different cultivars of cotton. When the entomopathogens were present in the soil in which either cotton or wheat seedlings were grown, A. parasiticus was subsequently isolated from the leaves, stem and roots of both plants and B. bassiana from the leaves, stem and root of wheat only, whereas L. lecanii failed to colonize either plant through the soil. Of the three entomopathogens tested, endophytic presence of A. parasiticus reduced growth of cotton, but none reduced growth of wheat. Feeding by A. gossypii on cotton leaves colonized by either B. bassiana or L. lecanii slowed aphid reproduction, and consumption of wheat leaves colonized by either B. bassiana or A. parasiticus slowed the growth of C. terminifera nymphs. The life cycle of at least three entomopathogens potentially includes plants. The presence of entomopathogens as endophytes can influence growth and fecundity of insect herbivores, suggesting a possible role for endophytic entomopathogens in the regulation of insect populations.

We examined the reliability of measurements from a single Burkard volumetric trap to represent the distribution of airborne concentrations of spores of Alternaria and pollen across two towns in rural Australia. Each town was sampled with three traps, sited 2.0 to 4.9 km apart, simultaneously. Substantial intra-class correlation coefficients (ICC) were observed between all three sites (ICC=0.52, 95% CI 0.30-0.71 to 0.76, 95% CI 0.61-0.87) when counts of pollen and Alternaria spores were relatively high. The correlation was poor when counts were low. Highly variable distributions of cypress pollen were found to be location dependent. We further compared two central lengthwise microscopic traverses of Burkard trap samples collected daily over one year. Correlation was strong for Alternaria spores (ICC = 0.95, 95% CI 0.94-0.96), grass pollen (ICC = 0.94, 95% CI 0.91-0.96) and total non-grass pollen (ICC = 0.91, 95% CI 0.89-0.93). We conclude that a single central traverse of a Burkard trap sample collected at one location provides an acceptable measure of the concentrations of spores of Alternaria and grass pollen across the two rural towns when counts are relatively high. The measure is less reliable when counts are low.

The arbuscular mycorrhizal fungus Glomus mosseae is commonly found in agricultural fields. The cosmopolitan species is found in Africa, Europe, America, Asia and Australia. Three hypotheses may explain this worldwide distribution: First, speciation occurred before the continents separated 120 Ma; second, the distribution is a result of human-mediated dispersal related to agriculture and finally, the morphologically defined species may encompass several local endemic species. To test these hypotheses, three genes were sequenced from 82 isolates of G. mosseae originating from six continents and the resulting sequences analysed for geographical subdivision and estimation of migration between continents. Coalescent analyses estimated divergence and age of mutations. Bayesian coalescent modelling was used to reveal important past population changes in the global population. The sequence data showed no geographical structure, with identical genotypes found on different continents. Coalescence analyses indicated a recent diversification in the species, and the data could be explained by a recent population expansion in G. mosseae. The results of this study suggest that speciation and the range expansion happened much later than continental spread and that human activity may have had a major impact on the dispersal and the population structure of the fungus.

Zoosporic fungi (often called chytrids) have been observed frequently on substrata in habitats with extremely low pH but never with extremely high pH. In the present study, growth, zoospore release and survival of some zoosporic fungi (Phyla Blastocladiomycota and Chytridiomycota) isolated from soil in Australia were examined in the laboratory to assess tolerance of extremes in pH. All 21 isolates grew rapidly in both solid and liquid PYG growth media (peptone, yeast extract, glucose) with pH values near neutrality. Most of the sixteen isolates tested could be maintained in culture on solid growth media at pH 4.7 and pH 8.9. One isolate grew down to pH 2.9, four isolates down to pH 3.3 and four isolates up to pH 11.2. In liquid PYG growth media all of the eight isolates tested grew (increased biomass) at pH 5.5 and pH 7.6, most isolates grew rapidly down to pH 4.5, some grew up to pH 11.2 but none of the isolates grew rapidly, if at all, at pH 2.9. The patterns of release of zoospores broadly reflect the patterns of growth at different pH values. Twenty one isolates survived for 7d at 20°C in liquid PYG growth media adjusted to pH 4.7, nine isolates survived down to pH 2.9, twelve up to pH 9.3, eight up to pH 11.2, and three even survived at both pH 2.9 and pH 11.2. The ecological significance of these data remains unclear. Patterns of survival, patterns of growth on solid and in liquid media and relative rates of zoospore release suggest ecotypes which prefer acidic, neutral or alkaline habitats, but these physiological properties were not highly correlated with either the pH of the soils from which these fungi were isolated nor with the taxonomic group in which they are placed. In general, many zoosporic fungi appear to be well adapted to a wider range of pH values than those found in the environments from which these fungi were isolated, and they quickly recover after brief exposure to extremes of pH.

The carbon nutrition of leaf endophytes and free-living members of the genus Chaetomium were compared to better understand the interaction between endophytes and their host, and the potential for endophytes to have complex life cycles. Broadly similar potential utilisation of several carbon sources was observed among endophytes and free-living isolates of Chaetomium. All fungi developed measurable biomass on glucose, cellobiose, carboxymethyl cellulose and xylan, and crystalline cellulose was slowly cleared from agar. Pectin was poorly utilised by these isolates. Sequence analysis of the fungi indicates that diverse taxa of Chaetomium may colonise wheat leaves, and that fungi with similar sequences are found in other habitats. Endophytic isolates of Chaetomium may complete part of their life cycle in other habitats.

Sixteen isolates in the orders Blastocladiales, Chytridiales, Rhizophydiales and Spizellomycetales were incubated for 2d in liquid PYG growth medium at 33, 37, 40, 45 and 50°C. These fungi could not resume growth when returned to 20°C if the temperature of incubation was more than a few degrees above the maximum temperature for growth on solid PYG growth medium. The maximum temperatures for survival of some chytrids are probably close to the temperatures reached periodically on the surface of moist soils in warm climates. Desiccated thalli of chytrids in the Blastocladiales and Spizellomycetales can survive much higher temperatures than chytrids in the Chytridiales and Rhizophydiales. Therefore, the maximum temperature and moisture content of the soil could significantly affect the diversity of chytrids in the ecosystem.

The survival of an isolate of Hyphochytrium catenoides collected from soil in the Blue Mountains in eastern New South Wales, Australia, was tested under extreme conditions in the laboratory. This isolate recovered growth after being subjected to drying on filter paper, to heat while desiccated, to hypersalinity, to strict anaerobic conditions, to freezing temperatures, and to a short period in solutions at pH 2.8-11.2. The capacity to survive under these conditions in the laboratory suggests adaptation to fluctuating conditions in the soil. The partial DNA sequence of the 28S ribosomal RNA gene in the isolate from New South Wales was 98% similar to that in an isolate from Arizona with a similar morphology.

Very little is known about the capacity of soil chytrids to withstand freezing in the field. Tolerance to freezing was tested in 21 chytrids isolated from cropping and undisturbed soils in temperate Australia. Samples of thalli grown on peptone–yeast–glucose (PYG) agar were incubated for seven days at −15°C. Recovery of growth after thawing and transferring to fresh medium at 20°C indicated survival. All isolates in the Blastocladiales and Spizellomycetales survived freezing in all tests. All isolates in the Chytridiales also survived freezing in some tests. None of the isolates in the Rhizophydiales survived freezing in any of the tests. However, some isolates in the Rhizophydiales recovered growth after freezing if they were grown on PYG agar supplemented with either 1% sodium chloride or 1% glycerol prior to freezing. After freezing, the morphology of the thalli of all isolates was observed under LM. In those isolates that recovered growth after transfer to fresh media, mature zoosporangia were observed in the monocentric isolates and resistant sporangia or resting spores in the polycentric isolates. Encysted zoospores in some monocentric isolates also survived freezing. In some of the experiments the freezing and thawing process caused visible structural damage to the thalli. The production of zoospores after freezing and thawing was also used as an indicator of freeze tolerance. The chytrids in this study responded differently to freezing. These data add significantly to our limited knowledge of freeze tolerance in chytrids but leave many questions unanswered.

The ability of seventy isolates (comprising 43 species) of Aspergillus and Penicillium, from soil and compost, to grow on sources of carbon and phosphate from plant remains was examined. Only two isolates from compost actively degraded crystalline cellulose, though most others grew on carboxymethyl cellulose. Most isolates produced biomass on cellobiose, and all on glucose, pectin and xylan. All fungi grew on phytic acid and most on DNA. If these data indicate utilisation of carbon and organic phosphorus in nature, then isolates of Trichocomaceae from soil have limited access to cellulose and considerably greater reliance on pectin and hemicellulose. The fungi may also gain their phosphorus from organic sources. The variation within species may indicate the existence of ecotypes.

Basidiomycete communities were profiled using terminal RFLP (TRFLP) and amplified ribosomal DNA restriction analysis (ARDRA) approaches at seven field sites under differing land use in northern-central New South Wales (NSW), Australia. TRFLP data indicated greater basidiomycete species richness at sites with natural vegetation. Sixty-seven basidiomycete ARDRA-types were detected. Various putatively ectomycorrhizal fungi were detected at all sites with native vegetation. Most ectomycorrhizal taxa had affinities to the genus Tomentella, while two Pisolithus taxa and putatively ectomycorrhizal Cantharellales taxa were also detected. Although soils under woodland or grassland communities supported a range of putatively saprotrophic taxa, only members of the Ceratobasidiales were detected in soils under agricultural land use. This study is the first investigation of fungal communities in soils of northern-central NSW, Australia.