摘要:

Excretion of N by fungal grazers is not the dominant process by which N is released in nutrient cycling: it accounts for one eighth or less of total net N mineralization. Fungivores comprise between 21 and 76% of the fauna biomass. Other fauna, as well as fungi and bacteria, all participate in the mineralization process. Microcosm studies have shown fungal grazing can promote release of N, but immobilization by concomitant microbe production can occur in tandem with that release. Studies using field applications of biocides have had inconsistent outcomes. Fungivores contribute to nutrient cycling by the combined action of comminution, mixing, and dispersal of inoculum, which promote microbial activity. Passage through the Collembola gut has been estimated to have the capacity to bring about a 42-fold increase in nitrate concentration from food to faeces, which on an ecosystem scale could conceivably translate into a doubling of levels of nitrate. Recent laboratory work has shown that fungivores may prefer the thinner mycorrhizal hyphae that occur some distance away from the more coarse mycorrhizal hyphae in the rhizoplane. Where this occurs, grazing can be expected to have only a small impact on the effectiveness of mycorrhizal fungi for the promotion of plant nutrient absorption in the field.Key words: fungivores, fauna, soil, litter, mineralization, mycorrhizal effectiveness.

ISSN:0008-4026    

DOI:10.1139/b95-399

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Dead wood litter input to mature forest ecosystems represents 30–40% of the total biomass, containing about 1–4 and 0.1–0.8 kg/(ha∙year), of N and P, respectively. However, since wood decomposes relatively slowly, it represents a much larger proportion of the standing crop of plant litter on the forest floor, forming a large reservoir of mineral nutrients, which are unavailable for primary producers until they are released by decomposer organisms, primarily basidiomycetes and to a lesser extent ascomycetes. Readily available nutrients are utilized rapidly leaving other nutrients locked up in the recalcitrant lignocellulose complex. As decomposition proceeds the relative concentration of N and P in wood increases (i.e., carbon/nutrient ratio decreases), as C is lost as CO2, but these nutrients are rapidly sequestered in mycelial biomass. Formerly it was thought that nutrients were released when the carbon/nutrient ratio of the wood approximated that of mycelium. However, fungi are inherently greedy using excess nutrients for production of reproductive structures and foraging mycelium. The latter, which is often aggregated to form rhizomorphs or cords, grows out of wood in search of new resources, often forming extensive long-lived networks that exhibit remarkable patterns of reallocation of fungal biomass and nutrients. Within these systems, nutrients are conserved and are often relocated for many metres and may aid in establishment of mycelia in new resources. Nutrients are probably largely released when mycelia are grazed upon by invertebrates, nonbiotically damaged, interact with other fungi and bacteria, or die.Key words: ecology, lignocellulose, basidiomycetes, rhizomorph, translocatio

ISSN:0008-4026    

DOI:10.1139/b95-400

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Fungal colonization of sandstone and granite from Antarctica was studied. Granite from a church, sandstones from a monument and a courthouse in Germany, glazed bricks from a German cathedral, and some other stone types were also examined. All samples contained fungi and heterotrophic bacteria, often also cyanobacteria or algae. For cell counting and enrichment of microorganisms the samples were crushed aseptically, suspended in NaCl–Tween-80, plated on oligotrophic media, and incubated at 16–25 °C dark or in dim light. Total biomass was determined as phospholipid-bound phosphate (PLP). Rock samples were also viewed by electron microscopy. Typical viable fungal cell numbers (CFU∙g−1dry weight) were the following: sandstone 1.6 × 104, granite 6.2 × 105, and glazed bricks 1.2 × 105. Total biomass ranged from 41 (sandstone) to 137 (glaze) nmol PLP∙g−1dry weight; antarctic sandstone had 88 nmol PLP∙g−1. Fungal genera identified were the following:Alternaria,Aspergillus,Aureobasidium,Candida,Cladosporium,Paecilomyces,Phoma,Penicillium, andSporobolomyces. Scanning electron microscopy revealed fungal bridging of open spaces with their hyphae or close contact between fungal hyphae and coccal cells believed to be algae. In some cases fungi were found to produce secondary minerals or their hyphae were covered with partially etched mineral layers. Exopolymer formation was common among the endolithic microorganisms. Mites were found to feed on epiliths. In pure culture, fungi from sandstone produced in 24 h cultures organic acids (citrate, glutamate, pyruvate, malate, succinate, lactate, formate, fumarate, and oxalate). Many of these acids could also be extracted from rock samples. Fungal growth on glucose and mineral powder resulted in up to 60% cation extraction from the mineral. Some fungi were antibiotically active against bacteria or yeasts but also stimulated other bacterial isolates. In summary, epi- and endo-lithic communities contained fungi that probably contribute substantially to the deterioration of many stones and monuments.Key words: rock weathering, biomass, acid excretion, cation extra

ISSN:0008-4026    

DOI:10.1139/b95-401

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Understanding variation in tropical forest fungal populations and communities is important for assessing fungal biodiversity, as well as for understanding the regulatory roles fungi play in tropical forests. In wet tropical forests, the canopy is typically occupied by certain wood decomposers, endophytes, epiphylls, and pathogens. Aphyllophoraceous canopy fungi are a subset of species found in the understory. Marasmioid agarics in the understory often form extensive networks of rhizomorphs that trap litter; these and other aerial species are rare on the forest floor. Decomposers are stratified within the forest floor, with some species colonizing only fresh litter, others preferring decomposed litter, and others restricted to soil organic matter. Specificity to particular host substrates is frequent among tropical forest litter decomposers and contributes to spatial heterogeneity in fungal communities over the landscape. Litter basidiomycete and microfungal communities in patches of 1 m2or less do not significantly resemble communities in similar patches located at distances greater than 100 m. Disturbances induce changes in the environment and the abundance of different substrates, resulting in changes in fungal communities through time, and variation over the landscape. Severe disturbances, as well as the slight daily variations in rainfall, profoundly affect populations of fungal decomposers and their influence on plant nutrient availability.Key words: fungi, tropical forests, diversity, stratification, spatial variation, temporal variation.

ISSN:0008-4026    

DOI:10.1139/b95-402

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Past and recent research on the distribution of the vegetative mycelium and basidiomes ofMycena galopusin aPicea sitchensisplantation is reviewed as an example of a litter-decomposing member of the Basidiomycotina, occupying a spatially continuous resource that is replenished throughout the year. Using a variety of methods, the mycelia were found to be concentrated in the F1horizon and the basidiomes produced nonrandomly in aggregations or arcs around the trees. Evidence was obtained of rapid dikaryotisation of homokaryons and of the ability to outbreed with a strain fromQuercuswoodland. The dikaryotic mycelia (genets) were up to 2.5 m in diameter, perennial or renewable mycelium occupying longstanding positions. A hierarchy of causal factors, including a competing saprotroph, a mycophagous collembolan, and variations in soil properties around tree boles, is discussed. Examination of relationships between NH4+-N content, moisture, or pH of the litter and distance from a tree or relative positions of basidiomes showed that there was significantly (P < 0.01) more NH4+-N at the arc position than the average for positions either side and a tendency for pH to reach maximum values in this region. The arc system with mycelium at its centre is contrasted with typical free and tethered fairy rings.Key words: Basidiomycotina, saprotrophs,Picea, tree litter, competition, fairy rings.

ISSN:0008-4026    

DOI:10.1139/b95-403

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

At the ecosystem level, all fungal activity in arid and semiarid systems is water regulated. However, as the observation scale is changed to allow for finer resolution of moisture effects, one finds that fungal community development in deserts may be influenced by either the temporal patterning of moisture pulses, or biotic factors that extend the benefits of moisture windows. When selected biocides were applied to the root region of a desert bunchgrass,Erioneuron pulchellum, to reduce microarthropod and nematode densities, fungal species numbers associated with the root surface were not altered. The temporal pattern in species numbers apparently reflect large scale seasonal responses of the fungi, microfauna, and plants to yearly differences in the occurrences of moisture windows. For wood on the soil surface, moisture windows of short duration coupled with high temperatures restrict fungal species composition in this habitat resulting in a lack of turnover in the dominant fungal species on surface wood. However, when wood was placed in the more amenable environment of a woodrat midden, patterns of fungal community development differed significantly from that observed for wood on the soil surface. These studies indicate that our understanding of the roles of fungi in the functioning of desert ecosystems is biased because the scale at which we usually make observations is too large to account for abiotic and biotic influences on fungal activity and community development. Moreover, we have to realize that the occurrence of favorable habitats for fungi in arid systems varies considerably in space and time. One consequence of the high spatial and temporal heterogeneity in favorable habitats is that functional diversity among fungi may be greater than would be predicted based solely on abiotic considerations.Key words: deserts, environmental heterogeneity, functional diversity, scale, wood.

ISSN:0008-4026    

DOI:10.1139/b95-404

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Despite advances in mycorrhizal identification, the goal of elucidating the structure and development of mycorrhizal communities remains elusive. Fruit body production can be sporadic, morphological typing of mycorrhizae is subject to variation with environmental conditions or host, and cultural studies are labor intensive and miss fungi that cannot be isolated. Molecular techniques for identification of fungal symbionts can supplement these techniques and offer an approach that is rapid, is independent of environmental variation, and can be applied directly to large numbers of samples. Molecular approaches to mycorrhizal community analysis attempt to distinguish taxonomic groups so they can be monitored and their interactions studied. Initial characterization of community structure involves enzymatic amplification of DNA directly from mycorrhizal roots using fungus-specific primers, followed by restriction endonuclease digestion to produce taxon-specific restriction fragment patterns. Comparison of these patterns with those obtained from fungal fruit bodies or reference cultures facilitates identification of fungal symbionts. Phylogenetic relationships of fungi that cannot be matched to reference isolates can be inferred by sequencing enzymatically amplified DNA. Future directions that will result from molecular approaches include development of sampling strategies, resolution of species complexes, field observations of host specificity, elucidation of the dynamics of replacement processes (succession), and determination of the role of dispersal in community development. As additional techniques are developed for population analysis, resolution of questions related to genetic structure, variation, and gene flow will become feasible.Key words: molecular ecology, fungal community structure, PCR.

ISSN:0008-4026    

DOI:10.1139/b95-405

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A new tripartite relationship among animals, fungi, and plants, based on formation of ectomycorrhiza and on removal of animal wastes, is described. In forest habitats where animal wastes such as urine or faeces or dead bodies, mainly of mammals, have been deposited, a particular group of fungi form reproductive structures successionally after the apparent decomposition of the wastes. This natural event can be simulated by application to the soil of urea, aqueous ammonia, or nitrogen compounds that release ammonia on decomposition. Both field observations and simulation experiments show that, when these events take place in forests of ectomycorrhizal trees, ectomycorrhizal fungi fruit during the late phase in the succession. Ectomycorrhizas are in fact observed in the soils colonized by these fungi. Among these fungi,Hebelomaspp.,Laccariaspp., and a few others colonize commonly in various waste sites, whileHebeloma radicosumcolonizes specifically in moles’ deserted middens (latrines) near their nests. The animals involved here as waste depositors or cadavers seem not to feed on the fungi and the plants but may depend on them for cleaning their own habitats, since mycorrhizas should readily remove products derived from wastes. The tripartite relationship described may be viewed as a cleaning symbiosis.Key words: animal waste, ammonia, postputrefaction fungi,Hebeloma, ectomycorrhiza, cleaning symbiosis.

ISSN:0008-4026    

DOI:10.1139/b95-406

出版商:NRC Research Press    

年代:1995

数据来源: NRC