John W.G. Cairney

Ectomycorrhizal fungi : key genera in profile

1 Pisolithus.- 2 Suillus.- 3 Laccaria.- 4 Hebeloma.- 5 Rhizopogon.- 6 Tuber.- 7 Scleroderma.- 8 Amanita.- 9 Paxillus.- 10 Cantharellus.- 11 Lactarius.- 12 Cenococcum.- 13 Hysterangium.- 14 Thelephora.- 15 Resupinate Ectomycorrhizal Fungal Genera.

Do ectomycorrhizal fungi exhibit adaptive tolerance to potentially toxic metals in the environment

The effects of potentially toxic metals on ectomycorrhizal (ECM) fungi and their higher plant hosts are examined in this review. Investigations at a species and community level have revealed wide inter- and intraspecific variation in sensitivity to metals. Adaptive and constitutive mechanisms of ECM tolerance are proposed and discussed in relation to proven tolerance mechanisms in bacteria, yeasts and plants. Problems with methodology and research priorities are highlighted. These include the need for a detailed understanding of the genetic basis of tolerance in the ECM symbiosis, and for studies of ECM community dynamics in polluted sites.

Ectomycorrhizas - Extending the capabilities of rhizosphere remediation?

Abstract The potential of ectomycorrhizal (ECM) associations to facilitate clean-up of soil contaminated with persistent organic pollutants (POPs) is considered. Most ECM fungi screened for degradation of POPs (e.g. polyhalogenated biphenyls, polyaromatic hydrocarbons, chlorinated phenols, and pesticides) are able to transform these compounds. Mineralization of toluene, tetrachloroethylene and 2,4-dichlorophenol in intact ECM-association rhizospheres has also been demonstrated. We review and consider the likely mechanisms by which ECM fungi can transform pollutants, the extent to which these capabilities may be utilized practically in bioremediation, along with the potential advantages and disadvantages of using ECM associations in bioremediation.

Laccases and other polyphenol oxidases in ecto- and ericoid mycorrhizal fungi.

Abstract. Polyphenol oxidases are known to be produced by a range of ectomycorrhizal (ECM) and ericoid mycorrhizal fungi. These enzymes include laccase (EC 1.10.3.2), catechol oxidase (EC 1.10.3.1) and tyrosinase (EC 1.14.18.1), between which there exists considerable overlap in substrate affinities. In this review we consider the nature and function of these enzymes, along with the difficulties associated with assigning precise enzymatic descriptions. The evidence for production of laccase and other polyphenol oxidases by ECM and ericoid mycorrhizal fungi is critically assessed and their potential significance to the mycorrhizal symbioses discussed.

Intraspecific physiological variation : implications for understanding functional diversity in ectomycorrhizal fungi

Abstract Several thousand fungal species worlwide are thought to form ectomycorrhizas (ECM) with tree hosts and there is currently much interest in determining the functional significance of such diversity in natural and managed ecosystems. While only a few taxa have been investigated in detail, it is clear that ECM fungi display extensive intraspecific variation in a range of physiological and other life-history parameters. Thus, comparative investigations of single (or even a few) isolates of different species are unlikely to provide reliable information on functional capabilities. Extensive screening of taxonomically well-defined isolates is required. This must take into account spatial and temporal variation in gene expression in mycelia growing in axenic culture or in association with a host plant.

Basidiomycete mycelia in forest soils : dimensions, dynamics and roles in nutrient distribution

Basidiomycete mycelia are ubiquitous in forest soils where they fulfil a range of key ecological functions. Population studies, based largely on basidiome collections, indicate that mycelia of many ectomycorrhizal and saprotrophic basidiomycetes can spread vegetatively for considerable distances through soil, but the extent to which these become physically or physiologically fragmented is unclear. This review considers aspects of the distribution, dynamics and translocatory activities of individual basidiomycete mycelia in forest soil, highlighting current gaps in our understanding and possible ways to address these.

Influences of anthropogenic pollution on mycorrhizal fungal communities

Mycorrhizal fungi form complex communities in the root systems of most plant species and are thought to be important in terrestrial ecosystem sustainability. We have reviewed the literature relating to the influence of the major forms of anthropogenic pollution on the structure and dynamics of mycorrhizal fungal communities. All forms of pollution have been reported to alter the structure of below-ground communities of mycorrhizal fungi to some degree, although the extent to which such changes will be sustained in the longer term is at present not clear. The major limitation to predicting the consequences of pollution-mediated changes in mycorrhizal fungal communities to terrestrial habitats is our limited understanding of the functional significance of mycorrhizal fungal diversity. While this is identified as a priority area for future research, it is suggested that, in the absence of such data, an understanding of pollution-mediated changes in mycorrhizal mycelial systems in soil may provide useful indicators for sustainability of mycorrhizal systems.

Symbiotic solution to arsenic contamination

Higher plants that are adapted to living on polluted soils are generally symbiotic with mycorrhizal fungi growing on contaminated sites. It is not known whether these fungi benefit their host plants simply by fulfilling their normal ecological functions, or by enhancing the plants resistance to pollutants. Arsenate contamination poses a particular challenge, as this toxin can enter plants through their phosphate transporters, causing mycorrhizal fungi to enhance both phosphate and arsenate uptake in plants. We have found a plant host and its mycorrhizal symbiont that have evolved in parallel to obtain phosphate but exclude arsenate.

Investigation of the influence of prescribed burning on ITS profiles of ectomycorrhizal and other soil fungi at three Australian sclerophyll forest sites

DNA was extracted from soil collected from the upper 15 cm of the profile at three sclerophyll forest sites in New South Wales three days before, and 14 d after prescribed burning events. rDNA internal transcribed spacer (ITS) regions were amplified by PCR using fungus-specific primers, and ITS products cloned. Restriction fragment length polymorphism (RFLP) analysis was conducted on the ITS clones using the endonucleases HaeIII, Hinfl, Mbol and Alul. Cloned ITS products from the three sites were thus separated into 120 RFLP types and the ITS product for each RFLP type was sequenced. Comparison of sequences with those available in the GenBank nucleotide database allowed putative assignment of ITS clones to the following functional groups: ectomycorrhizal (ECM), arbuscular mycorrhizal (AM), ericoid mycorrhizal (ERM), decomposer basidiomycetes (DEC), other soil fungi (OSF). While abundant ECM-like clones were amplified from pre-fire soils at the North Rocks and South Maroota sites, they were largely absent in the post-fire soils at these sites, being replaced mainly by microfungi. In contrast, no decrease in ECM-like ITS clones was observed at the Ridgecrop site following fire. The data indicate that, while the abundance of extraradical ECM fungal propagules in the upper soil profile may be reduced by prescribed burning, the effect is site-specific.

The effect of temperature and inorganic phosphorus supply on growth and acid phosphatase production in arctic and temperate strains of ectomycorrhizal Hebeloma spp. in axenic culture

Acid phosphatase production by 12 Hebeloma strains was usually derepressed when inorganic phosphorus in the growth medium was limited, but appeared to be constitutive in some strains. At low temperatures (≤ 12°) arctic strains produced more extracellular and wall-bound acid phosphatase, yet grew more slowly than the temperate strains. We suggest that low growth rates in arctic strains may be a physiological response to cold whereby resources are diverted into carbohydrate accumulation for cryoprotection. At near freezing temperatures, increased extracellular phosphatase production may compensate for a loss of enzyme activity at low temperature and serve to hydrolyse organic phosphorus in frozen soil over winter.