Examination of fungal life strategies assists the understanding of the patterns of occurrence of an organism (or rather species) in nature. Fungi prevalent in disturbed situations tend to have many R-selected characteristics, although these are often combined with C-selected and S-selected characteristics depending upon the biotic and abiotic conditions to which their life strategies are best adapted. Many fungi probably exhibit different life strategies at different times during their life-cycle.

The likely consequences of disturbance of the mycorrhizal mycelial network in soil are considered, emphasis being placed on the impact of small-scale events upon infection in vesicular-arbuscular and ectomycorrhizal systems. The importance of the intact network is stressed and the effects of its disruption upon infection processes and upon the nutrition of natural plant communities and of crops is analysed. It is considered that the most serious effect of disturbance will be to reduce the inoculum potential of the fungi and hence to decrease the vigour of infections that occur. The impact of these effects is likely to be felt most seriously at the stage of seedling establishment, and the interactions between disturbance events, mycorrhizal infection and plant successional processes are discussed.

Soil Collembola may be partially responsible for observed reductions in effectiveness of vesicular-arbuscular mycorrhizal (VAM) associations in the field, compared with sterile soil experiments. Feeding damage to hyphae in soil is envisaged as a mechanism by which translocation of phosphorous from beyond root depletion zones to the plants is reduced. Previous work has demonstrated such effects in pots and in a cultivated field plot, and direct observation of feeding has been made. This paper briefly reviews this evidence and presents an experiment in which insecticide reduced the density of Collembola in a seminatural grassland soil, and increased phosphorus inflow into roots of Holcus lanatus. In addition, survey data are reported which show that hyphal grazing is ecologically feasible, as Collembola and infected roots are spatially associated with one another in the soil profile. It is suggested that hyphal grazing by these arthropods has important consequences for VAM function in natural vegetation systems.

Findings from the first two years of a long-term study of conifer log decomposition are presented. Log decomposition is regulated by the physical and chemical states, and development of decomposer foodwebs. The functional group with the greatest initial effect on the log is the channelisers, represented in our study by ambrosia and bark beetles. They not only create multitudes of channels into the logs but vector the initial decomposer community. Ambrosia beetles exclude certain elements of the decomposer community from channels until they vacate the log, at the end of their reproductive phase. The foodweb during the early stages of decomposition includes nitrogen-fixing and other bacteria, fungi, protozoa, nematodes, and arthropods. Seasonal fluctuations of temperature and moisture are hypothesised to work in tandem to modulate the activities of the decomposer community.

Coprophilous fungi form an easily recognised ecological group adapted to severe disturbance. They survive as spores on herbage and are ingested, chewed, subjected to digestion, exposed to competition within the gut, egested and then suffer further competition and environmental variation. Studying the ecology of fungi on rabbit dung has several advantages, both for research and teaching. These include ready availability, ease of replication, simple techniques for varying the environment and levels of competition, and the possibility of adding spores to sterilised food. This is illustrated by studies on three aspects of the ecology of coprophilous fungi.

The ability of Ascobolus crenulatus Karsten, Chaetomium bostrychodes Zopf and Sordaria macrospora Auersw. to produce biomass within, fruit upon, and degrade rabbit faeces was followed using semi-natural faecal resource units (copromes) (Wood & Cooke 1984, 1987). On these criteria the performance of the fungi was in the order C. bostrychodes > S. macrospora > A. crenulatus. Species mixtures produced only slightly higher degradation rates than those effected by single species. This implied competition for available nutrients which was also indicated by depressed fruiting of all species in species mixtures when compared with fruiting levels of each species grown individually. For single species the time of onset and subsequent fruiting level were determined by the time at which sufficient resources could be allocated to reproduction rather than simply to hyphal extension rates.

The agarics fruiting in natural and anthropogenic disturbed habitats are considered. The early colonists of such environments are species either able to utilise ephemeral resources or able to move nutrients quickly from one source to another. A suite of micro-characters uniting the species concerned is given. Attention is drawn to those agarics recorded from burns in various parts of the world, and from arctic-alpine areas. The concept of a geomorphological escalator is explored.

The volcanic island of Surtsey in the Westmann Islands, Iceland, was formed by a series of submarine eruptions from 1963 to 1967. It is a natural area, giving scientists the opportunity to study the biological succession without interference from man. In 1972, the occurrence of micro-fungi in soil samples gathered at different locations on the island was assessed by counting and identifying the fungal colonies growing out on different agar media, containing various amounts of soil extract.

Although current models of the roles of VA mycorrhizas in succession describe the fungal effects on the plant, they ignore the immigration patterns of the fungi. It is suggested here that the vectors of spore immigration (animals and wind) determine the pattern of re-invasion with respect to the patches of vegetation establishing on a disturbed site. The environment dictates the dominant vector. If invasion is facilitated by animals (locomotion), such as at Mount St Helens, they inoculate patches of plants, not individuals, and the patches change faster than immigration rates. Thus, the island biogeography equilibrium model is not applicable to describe VA mycorrhizal fungal establishment. If invasion is by wind (mass flow), such as in a cold desert system, inoculum is rapidly distributed across a site and VA mycorrhizal fungal richness and density rapidly equilibrates with its resource, a single shrub. By applying these models, a priori prediction of establishment following catastrophic disturbance might be possible, as opposed to mere description.

The development of fungal assemblages on root-surfaces of Agropyron trachycaulum growing in control, peat, fertiliser, or sewage-amended oil sand tailings was followed over a four-year period. Although the number of fungal species isolated from the root-surfaces differed significantly among the amendments, species numbers did not change significantly within treatments over the four years. The species composition of the assemblages, however, changed considerably from year to year. Species abundance distributions for fungal assemblages from the control, peat, and fertiliser amended spoil were best described by logarithmic functions. Distributions from the sewage-treated spoil were best fitted by exponential functions. Although species composition changed over time, the forms of the species abundance distributions were not altered. The observed structure and dynamic nature of fungal assemblages on root-surfaces may not be a consequence of disturbance, but may be a typical feature of such assemblages. High nutrient addition to mine spoils can result in altered species abundance patterns, and may lead to a decrease in community stability.

The impact of severe soil disturbance on soil fungal community composition and function and how this relates to the resultant decomposition/mineralisation process is very poorly understood. Consequently, research was conducted to determine: (a) to what degree fungal community structure and potential function are altered in a sub-alpine coal mine spoil (Luscar, Alberta), and (b) how do alterations in the fungal community affect patterns of fungal colonisation and decomposition of plant residues deposited on recently mined soil.

The evolutionary significance of natural fire disturbance regimes in the development of post-fire fungal and herb communities is examined. Before a fire the soil microflora exhibits a general fungistasis, microbial competition is great, nutrients are limiting, and carbonicolous ascomycetes are in a dormant phase. Also in mature chaparral shrub communities the soil microflora is implicated in soil toxicity that prevents seeds of some species from germinating in the interval between burns. Fire results in the deposition of ash and charred wood, a release of nutrients, the elimination of competitors (e.g. shrub cover, soil microflora), an increase in soil alkalinity, the removal of soil toxicity/fungistasis, and cues the germination of constitutively dormant ascospores and seeds. The cue for germination of the chaparral fire annuals appears to be components of the hemicellulose fraction, produced during the charring of wood, but this fraction has not been tested for its ability to cue ascospore germination. Germination in the absence of fire would be “suicidal” because neither the carbonicolous ascomycetes nor the post-fire annuals are able to compete successfully in these pre-burn habitats. The frequency of burning and the uneven heating of the soil surface creates patchiness with a corresponding increase in the species richness of the post-burn community.

While the effects of acid rain on soil biology and chemistry have been widely reported, relatively few studies have appeared on the effects of air pollutants on fungi. Air pollutants are, however, likely to cause both toxic (destructive) and enrichment disturbance effects on fungal populations. Such responses are best seen at sites located close to point source emissions, such as coking works and metal processing and sour gas plants, where pollutant concentrations will be locally high. Toxic disturbance by, for example, heavy metals will generally reduce fungal biomass and species composition leading to the impairment of important processes such as litter decomposition. Enrichment disturbance effects of air pollutants on fungal communities are less easily recognised, but occur when a pollutant, e.g. a phenol, acts as a nutrient, thereby leading to an increase in the total, or more unusually a specific part of, the fungal community. This paper reviews the literature on point source emission effects on fungi, with particular emphasis being given to the pitfalls encountered in such studies.

Many freshwater streams are predominantly heterotrophic, the energy source for all trophic levels of the biota being derived from allochthonous plant litter that is degraded by saprotrophic micro-organisms. Leaves falling into streams have most of their soluble constituents leached out within twenty-four hours of submersion. Few of the resident terrestrial saprotrophs survive in the aquatic environment and the leaves are rapidly colonised by freshwater fungi, particularly aquatic hyphomycetes (Chamier & Dixon 1982a; Chamier et al. 1984). These fungi produce all the enzymes required to degrade the structural polysaccharides of leaf cell walls and those of resident terrestrial fungi. Some species can degrade lignified tissue (Chamier & Dixon 1982b; Chamier 1985). Little is known of the enzymic capabilities of freshwater bacteria.

Laboratory soil samples are disturbed soils which resemble the arable condition so common in the external world. They have many advantages for study of colonisation of buried substrates and activity may be monitored continuously by the use of a newly-developed automatic electrolytic respirometer. A condensed account of experiments is given in which colonisation of hair in soil samples is followed by measurement of overall metabolism and by direct microscopy.

The microbial populations on cereal straw at harvest are characteristic of the phylloplane. Incorporation of straw into soil represents an enrichment disturbance and results in a rapid stimulation of soil microbial activity. The dominant fungal colonists of the straw in soil were found to vary with soil water potential over a twenty-eight week period of incorporation. The dominant fungal genera were Penicillium and Mucor, followed by Gliocladium, Fusarium and Trichoderma. Basidiomycetes were only isolated from straw in a wet (−0.1 MPa) soil. Prior inoculation of straw with Gliocladium roseum (Link) Banier resulted in changes in the dominance of these fungi, particularly in a dry soil. In vitro data on spore germination, germ tube extension and growth of these soil fungi on agar media were not correlated with those on unsterile straw leaf sheaths or sterile straw segments.

The composition of the mycoflora growing on wheat straw decomposing in three arable soil types and following two methods of incorporation was monitored throughout one cropping season. Fusarium species, Trichoderma species and Chaetomium globosum were the most frequently isolated cellulose-decomposers during the autumn and early spring on all treatments. Around some straws the brown colour of lignin was replaced by a dark red coloration: if this was cleared subsequently, it was considered to indicate the presence of lignin-decomposing species. Colonies of a Typhula sp., a lignin-decomposing basidiomycete, developed from some of the straws surrounded by cleared zones. In late spring more lignin-decomposing basidiomycetes were isolated, none of which had previously been described on, nor isolated from, wheat straw decomposing in the field. These basidiomycetes, characterised by slower extension rates than Typhula, were more frequent on straw ploughed-in at two sites. Typhula was more numerous where the straw had been incorporated by tined implements. The composition of the cellulolytic fungal community differed between treatments. Inoculation of straw with pure and mixed cultures of Fusarium culmorum, Trichoderma viride, Chaetomium globosum and the lignin-decomposing basidiomycetes had varied effects on the decay rate.

The size and activity of the fungal component of the straw-decomposing soil microbial biomass was investigated for three sites in eastern Scotland. The fungi were found (by means of selective substrate-amended respiration, FDA-active hyphal lengths, and cellulolytic plate count) increasingly to dominate the soil microbial biomass with repeated enrichment disturbance from straw incorporation. Development of a biomass with a greater fungal component was also associated with an increased biomass C:N ratio response to straw inputs and more rapid decomposition of 14C-labelled straw, suggesting that continued straw incorporation can cause a “substrate-adapted” microbial biomass to develop which is able to decompose straw increasingly rapidly.

Some roofs that are thatched with combed wheat reed develop patches of more rapid decay within an otherwise uniform matrix of less rapid decay. Changes in the length and weight of reed from patches and matrix were estimated for one roof by comparison with samples of unused, undecayed reed. The fungal communities associated with patches and matrix were analysed using a particle plating method and the distribution of patches between and within roofs was analysed for departures from randomness. Reed from a patch was shorter than from the surrounding matrix due to more rapid loss of length. Weight loss was greatest at the thatch surface but only extended into the thatch for 8.5 cm in both cases. It is therefore probable that the decomposer communities of patches and matrix respond similarly to an environmental variable, probably water potential, that varies with depth. Fungal community analysis indicated that distinct functional units, or associations, of four and two taxa were present in the matrix and patches respectively. An analysis of patch distribution on a sample of roofs indicated that certain roofs are predisposed to develop patches. However, on individual roofs patches are distributed randomly. Predisposition may be due to relatively high levels of endogenous nitrogen in the thatching reed.