Juliet C. Frankland

Fungal succession - unravelling the unpredictable

The nature and mechanisms of successions of fungi in soil and plant litter are discussed, and an autecological study of a basidiomycete used to illustrate some methods of approach.

SPATIAL AND SEASONAL VARIATIONS IN SOIL, LITTER AND GROUND VEGETATION IN SOME LAKE DISTRICT WOODLANDS

The ecologist who wishes to record the chemical and physical properties of the soil in relation to a particular problem is usually confronted with a number of queries on how and when to sample. Soil properties can vary considerably in semi-natural areas and only scanty information is available on the appropriate size, number and density of samples and time of sampling. Extrapolation from published data is difficult, since the sites are often inadequately described and sampling errors are rarely recorded, so that the design of new experiments or surveys tends to depend more on arbitrary factors and available time rather than on scientific considerations. The aim of this study was to measure at different times of the year certain properties of the ground vegetation, litter and mineral soil, in three relatively homogeneous woodlands, in order to determine the magnitude of seasonal change. A single sampling procedure was adopted, but sampling intensity was much greater than normally used, so as to assess the value of different sampling intensities for adequate description of the existing conditions. Seasonal fluctuations in the properties of soils are frequently reported, but there is considerable disagreement on the timing and magnitude of these changes (Raupach 1951; Robertson & Simpson 1954). The heterogeneity of soil is often stressed and relatively large differences in the chemical content or pH of a soil, over distances of only a few centimetres, have been demonstrated (Purvis & Davidson 1948; Ferrari & Vermeulen 1955). Piper & Prescott (1949), among others, have suggested that such variations in pH from point to point are of greater significance than the seasonal trends, but the data are inconclusive. Baker & Clapham (1939) studied annual trends in the pH of woodland soils, but spatial variations were not examined in detail. On the whole, plant and soil investigations have concentrated on agricultural soils where conditions are very different from those of natural undisturbed habitats. In this investigation, the ground vegetation, litter and mineral soil of three woodlands in the Lake District of north-west England were sampled intensively at regular intervals to record spatial and monthly fluctuations in pH, total weight, moisture content and chemical composition (Na, K, Ca, Mg, P, N, Si and ash). In each woodland, areas were chosen which appeared relatively homogeneous and yet were large enough to be representative of a forest type. The selected woodland sites were, as regards topography and vegetation, probably among the most uniform to be found in the Lake District and consisted of two stands of fairly mature oak (Quercus petraea (Mattuschka) Liebl.) on mullto moder-type humus and a plantation of larch (Larix decidua Mill.) on mor humus. It is therefore possible to compare two similar and two very different types of woodland.

Fungal communities on decaying wheat straw of different resource qualities

Abstract Stem internodes or leaves of wheat ( Triticum aestivum L.) straw were buried in litter bags in an arable soil at 10cm depth. The bags were sampled after 13, 22 and 32 weeks to determine the comparative frequency of fungal species on the two contrasting substrata and change in chemical composition of the straw. The internodes of lower resource quality with their high C-to-N ratio and high % lignin decomposed more slowly than the leaves. Occurrence of “resource-specific” fungi related to differences in resource quality at particular stages in decomposition were distinguished.

Fungal Decomposition of Bracken Petioles

Frankland (1966) described a succession of fungi on decaying petioles of bracken (Pteridium aquilinum (L.) Kuhn) in six habitats and tentatively ascribed chemical changes in the bracken to the action of certain predominant fungi. In the present investigation, some individual members of the fungal succession were grown on sterile bracken and changes in the chemical composition (carbon, nitrogen, ash, soluble carbohydrates, holocellulose, a-cellulose and lignin), dry weight and pH were followed. The aim was to evaluate the potential role of these fungi in bracken decomposition. Previous investigators of the fungal decomposition of plant material have used similar laboratory cultures of sterile litter (Lindeberg 1944, 1947; Mikola 1954; Saito 1960; Chastukhin 1962). In this investigation gamma radiation was used to sterilize the braclten instead of the more conventional methods, which involve drastic heat treatment or the inconvenience of gaseous chemicals and difficulties in moisture regulation. Major physical or chemical changes in bracken petioles after irradiation were not detected.

Nutrient and carbon dioxide release by interacting species of straw-decomposing fungi

Pairs of fungi were incubated on wheat straw in microcosms for 10 weeks. Release of Na+, K+ and NH4+-N was similar from all combinations, but Ca2+, Mg2+ and PO43--P release depended on the species. In Agrocybe gibberosa/Chaetomium globosum and Sphaerobolus stellatus/Chaetomium globosum combinations, there was evidence of interactions which suppressed the predicted rate of phosphate release, and in all the mixed species combinations there were interactions which increased the rate of fungal respiration above that of the more combative fungus in pure culture. ei]{gnR}{fnMerckx}

Resource Capture by Interacting Fungal Colonizers of Straw

Nine species of microfungi and eight basidiomycetes were assessed singly and in pairwise or three-way combination for their potential capacity for primary resource capture of agar media, sterile straw and sterile soil. When single species were ranked by extension rate, results on straw and soil agreed broadly with those from agar media, although the rates were much slower in straw. In pairwise and 3-way interactions on sterile soil, colonization proceeded as predicted from the mycelial extension rates of single species on agar, sterile soil and sterile straw, although extension of some species was significantly slower in combination than singly. There was some agreement between the outcome of pairwise interactions observed on 2% malt extract agar medium and sterile soil of four test species, and on straws in non-sterile soil of Agrocybe gibberosa . The four species could be ranked in combative order: A. gibberosa = Sphaerobolus stellatus ≫ Mucor hiemalis and Chaetomium globosum . Cord formation by basidiomycetes was more pronounced in soil than on agar media, and when in close proximity to other species.

Enzyme production by Mycena galopus mycelium in artificial media and in Picea sitchensis F1 horizon needle litter

Mycena galopus is among the most important leaf litter decomposers in UK coniferous and angiosperm woodlands, having the potential to utilise all the major constituents of plant litter. Even so, the enzyme or combination of enzymes produced by M. galopus responsible for lignin depolymerisation was previously unknown. A range of media from liquid and semi-solid cultures to more natural substrata was tested to determine whether laccase was produced by an isolate of M. galopus, M9053. Malt extract liquid medium (MEL) with 2,5-xylidine favoured laccase production as compared with the same medium containing the inducers veratryl alcohol, veratryl aldehyde, veratric acid, homoveratric acid, vanillic acid or p-anisic acid. A semi-solid medium of cereal bran in phosphate buffer and a solid medium of Picea sitchensis F1 horizon needle litter were also not as effective as MEL with 2,5-xylidine as an inducer. Compared with six other isolates of the same species grown in MEL without inducers, M9053 exhibited rates of laccase activity fairly typical for M. galopus. An isolate from a dark coloured basidiome of M. galopus, but not var. nigra, exhibited the greatest activity while var. candida showed relatively low laccase activity. Marasmius androsaceus exhibited peak laccase production several days later than M. galopus. In addition, a manganese-dependent peroxidase that was responsible for 15% (in MEL culture fluid) and 39% (in needle litter extract III) of ligninolytic activity was produced by M9053. A further peroxidase was found to be the major ligninolytic constituent in MEL extracts (53%), and had a similar contribution to total activity (29%) as laccase (32%) in needle litter fraction III. Mycena galopus produced water- and buffer-extractable mannases and xylanases when grown on needle litter.

Effects of elevated atmospheric CO2 on fungal competition and decomposition of Fraxinus excelsior litter in laboratory microcosms.

Evidence that chemical changes in litter exposed to elevated CO 2 might alter the composition and function of fungal communities in soil is presented. Some potential effects of elevated atmospheric CO 2 on the decomposition of Fraxinus excelsior leaf litter and the interactions of the colonizing fungi, growing singly or in simple associations in microcosms, were investigated. Fungal colonization was monitored by analysis of the ergosterol content of litter and specific PCR-amplified ribosomal DNA spacer products. After 2 (600 ppm). After triple-species inoculation percentage α-cellulose and, in some combinations, nitrogen content was reduced on litter from seedlings grown in elevated CO 2 .

Production of a monoclonal antibody specific to Mycena galopus mycelium

Monoclonal antibodies were raised against the mycelium of a litter-decomposing basidiomycete, Mycena galopus, for use in an autecological study of the fungus in forest litter. Two clones (3E12 and 6D8), produced using particulate and whole-cell extracts of the fungus respectively, cross-reacted with several species including other Mycena species, non-Mycena basidiomycetes, zygomycetes and anamorphs or mitosporic fungi. Of these clones, 3E12 appeared to be directed against an unidentified β-glucan and 6D8 against chitin. A third clone (6E1), using as immunogen latex collected in the field from stipes of the basidiomes, was specific to M. galopus mycelium in ELISA and immunofluorescence tests and was probably directed against an unidentified polysaccharide.

Secondary effects of SO2 pollution on leachate chemistry and decay of Scots pine and mixed angiospermous leaf litters

The secondary effects of SO2 fumigation on CO2 evolution from leaf litter of Scots pine (Pinus sylverstris L.) and mixed broad-leaved species [Quercus petraea Mattuschka (Liebl.), Fraxinus excelsior L., Betula pubescens Ehrh., Betula pendula Roth., Acer pseudoplatanus L. and Corylus avellana L.] were investigated. Respiration of Phoma exigua Desm inoculated onto both types of previously fumigated (48 nl l−1), sterile litter was higher than controls (< 10 nl l−1). Much higher rates of CO2 evolution were measured from control litters than from fumigated litters after 2 weeks; the differences decreased but continued until the end of the 12-wk incubation period. Sulphate concentrations in the leachate solution from fumigated litters remained significantly higher until the end of the experiment. In addition, the pH of the leachate solution was lowered by SO2 fumigation. At the start of the experiment, the NH4+ concentration from pre-fumigated and control litters was similar, but release from the control litter was slightly greater than from pre-fumigated litter, according with measurements of CO2 evolution from the litters. The experiments indicated that environmentally-realistic concentrations of SO2 over a long period could affect leachate chemistry and this might affect the decomposition rate of leaf litters. The Scots pine litter was more affected than mixed angiospermous litter.