John Dighton

Litter quality influences on decomposition, ectomycorrhizal community structure and mycorrhizal root surface acid phosphatase activity

The influence of litter quality on root growth, ectomycorrhizal communities and decay processes was investigated through a litter bag experiment. Litter bags containing either pine needles, oak leaves or oak+pine mix were placed within the O horizon of a lowland pitch pine (Pinus rigida) forest in the New Jersey Pinelands. Upon retrieval, ingrown pine roots were removed and quantified for total length and percent ectomycorrhizal colonization by morphotype. Phosphatase activity was determined for dominant morphotypes. In addition, litter decay rates and N and P litter content were measured. Mixed litter (oak+pine) had highest total pine root ingrowth. Dominant ectomycorrhizal morphotypes differed in response to litter type. A tuberculate form dominated (35%) in pine litters while distinctly different nontuberculate morphotypes dominated in oak and mixed litters. High phosphatase activity of morphotypes was correlated with high phosphorus immobilization during oak leaf decay. Results indicate that a mix of forest litters (oak and pine) optimizes retention of scarce nutrients such as nitrogen and phosphorus. The diverse chemical environment of these different litter types induces different ectomycorrhizal community development which show functional differences in the way phosphorus is likely to be cycled. The influence of litter type on diversity and function of ectomycorhizae is an important step in identifying linkages between biodiversity of this group and ecosystem functions.

Fungi in Ecosystem Processes

Preface Introduction Fungi and Primary Productivity: Making Nutrients Available Fungi and Primary Productivity: Plant Growth and Carbon Fixation Fungi, Secondary Productivity, and Other Fungal-Faunal Interactions Fungi and Population and Community Regulation Fungal Interactions with Humans Synopsis and Outlook to the Future Index

Beyond the biomass : compositional and functional analysis of soil microbial communities

Characterization of soil microbial communities tracking specific components of the biomass interactions between components of the biomass relating community structure to function.

Fatty acids of fungi and nematodes: possible biomarkers in the soil food chain?

Abstract The fatty acid composition of 16 different soil fungi (ascomycetes, basidiomycetes, mitosporic fungi) and a fungal-feeding nematode Aphelenchoides sp. reared on seven fungal species was investigated. Additionally, fatty acid profiles of Aphelenchoides sp. and A. saprophilus grown on the same fungal food source,Agrocybe gibberosa, were compared. Thirteen predominant fatty acids were detected in the fungi. Most of them occurred in each of the 16 species, but relative quantities of individual fatty acids differed, in particular those of unsaturated ones. Most fungal species could be differentiated from each other on this basis. Our study revealed convergence, but also, differences, in the fatty acid composition of systematically related fungi, i.e. a taxonomic or phylogenetic relationship was not necessarily accompanied by similarity in fatty acid profiles. Nematodes comprised a wider fatty acid spectrum than fungi, with 17 predominant fatty acids, and a higher amount of long-chain, polyunsaturated acids than their fungal diet. Fungal host tissue may have supplied palmitic, oleic and linoleic acid present, whereas most of the long-chain unsaturated fatty acids were synthesized by the nematodes. Unsaturated fatty acids mainly belonged to the ω6 and 9 family, indicating a carboxyl-directed desaturation as a major metabolic pathway. The fungal host significantly affected the fatty acid profile of the nematodes. However, we could not assign individual fatty acids as biomarkers reflecting the dietary source, likely due to the considerable convergence within tested fungal species. Of the basidiomycetes analyzed Laccaria laccata, was distinctly separated from the others and this difference could also be detected in the nematodes showing the influence of food type. We conclude that the lipid composition of nematodes is controlled by both the nematode and its diet and that monitoring fatty acid patterns of soil animals may therefore provide a way to detect trophic interactions in belowground food webs.

Changes in occurrence of basidiomycete fruit bodies during forest stand development: with specific reference to mycorrhizal species

The occurrence of fruit bodies of mycorrhizal fungi under differently aged plantations of lodgepole pine and Sitka spruce on deep peat was examined. Broadly similar patterns of occurrence in relation to stand development were found in both species, but with some shift in the dominance of Lactarius rufus to older stands in Sitka spruce compared to lodgepole pine. The fruit-body successions indicated were Laccaria/Paxillus -Lactarius-Cortinarius/ Inocybe-Russula for lodgepole pine and Laccaria/Paxillus -Inocybe-Cortinarius-Lactarius for Sitka spruce. Changes in the saprotrophic agaric flora were also noted. Nolanea cetrata, Clitocybe sp. and Collybia spp. were present in greater abundance in the lodgepole pine stands, whereas a restricted flora of Marasmius androsaceus and Mycena spp. occurred under Sitka spruce. The patterns of association with tree species, together with seasonality of occurrence, are discussed in relation to resource quality of the litter and possible climatic and edaphic site characteristics.

The effect of organic-matter management on the productivity of Eucalyptus globulus stands in Spain and Portugal: tree growth and harvest residue decomposition in relation to site and treatment

Sustainable management of forest resources, including nutrient retention and protection of the soil structure, is required to ensure long-term soil fertility and productivity of later rotations. Potential depletion of soil nutrients is particularly likely in production systems based on fast-growing trees, such as eucalypts. We have studied production of second rotation Eucalyptus globulus stands at two sites in northern Spain and two in central Portugal, after replanting or coppicing, under four treatments, in which plant residues from the first crop were utilised. The residues were either removed from the sites (Treatment R), spread over the soil surface (Treatments S, uniform spreading, and W, in which the woody debris was confined to rows between the trees) or incorporated into the soil by harrowing to 15-cm depth (Treatment I). We measured tree height and girth at intervals over three growing seasons, and root biomass at the Portuguese sites. Decomposition of three residue components: leaves-plus-bark, twigs and branches, was measured in litter bags placed in the position corresponding to the placement of the organic residues. By the end of the experiment, tree height was significantly greater in Treatment I than in Treatment R at both Spanish sites, if planted as seedlings, with intermediate growth in S and W. In Portugal, tree height was smaller in R, though not significantly. DBH showed similar trends, although treatment differences were not significant. Coppiced trees grew faster than seedling trees, but a significant treatment effect on the growth was only observed at the inland Portuguese site, where it was better in Treatment I by the end of the experiment. The residues decomposed significantly faster in I than S or W at the Portuguese sites, but not in Spain. Leaves-plus-bark decomposed faster than twigs, and twigs faster than branches. The results are discussed in relation to recommended management options. # 1999 Elsevier Science B.V. All rights reserved.

Uptake and accumulation of 137Cs by upland grassland soil fungi: a potential pool of Cs immobilization

Reports of high concentrations of fallout radiocaesium in basidiomycete fruit bodies after the Chernobyl nuclear reactor accident and speculation that fungi could be long-term 137Cs accumulators led us to ask if fungi could be long-term 137Cs accumulators. We used six common upland grassland species to try to estimate their importance in the immobilization of 137Cs. Uptake of Cs by these species ranged from 44 to 235 nmol Cs g−1d.w. h−1. Efflux studies indicate that more than 40% of the Cs taken up is bound within the hyphae. We estimate that the fungal component of the soil could immobilize the total radiocaesium fallout received in upland grasslands following the Chernobyl accident.

Inhibition of growth, and effects on nutrient uptake of arctic graminoids by leaf extracts : allelopathy or resource competition between plants and microbes ?

Previous research has shown that plant extracts, e.g. from boreal dwarf shrubs and trees, can cause reduced growth of neighbouring plants: an effect known as allelopathy. To examine whether arctic and subarctic plants could also be affected by leaching of phytochemicals, we added extracts from the commonly occurring arctic dwarf shrubs Cassiope tetragona and Empetrum hermaphroditum, and from mountain birch, Betula pubescens ssp. tortuosa to three graminoid species, Carex bigelowii, Festuca vivipara and Luzula arcuata, grown in previously sterilized or non-sterilized arctic soils. The graminoids in non-sterilized soil grew more slowly than those in sterilized soil. Excised roots of the plants in non-sterilized soil had higher uptake rate of labelled P than those in sterilized soil, demonstrating larger nutrient deficiency. The difference in growth rate was probably caused by higher nutrient availability for plants in soils in which the microbial biomass was killed after soil sterilization. The dwarf shrub extracts contained low amounts of inorganic N and P and medium high amounts of carbohydrates. Betula extracts contained somewhat higher levels of N and much higher levels of P and carbohydrates. Addition of leaf extracts to the strongly nutrient limited graminoids in non-sterilized soil tended to reduce growth, whereas in the less nutrient limited sterilized soil it caused strong growth decline. Furthermore, the N and P uptake by excised roots of plants grown in both types of soil was high if extracts from the dwarf shrubs (with low P and N concentrations) had been added, whereas the P uptake declined but the N uptake increased after addition of the P-rich Betula extract. In contrast to the adverse extract effects on plants, soil microbial respiration and soil fungal biomass (ergosterol) was generally stimulated, most strongly after addition of the Betula extract. Although we cannot exclude the possibility that the reduced plant growth and the concomitant stimulation of microbial activity were caused by phytochemicals, we believe that this was more likely due to labile carbon in the extracts which stimulated microbial biomass and activity. As a result microbial uptake increased, thereby depleting the plant available pool of N and P, or, for the P-rich Betula extract, depleting soil inorganic N alone, to the extent of reducing plant growth. This chain of events is supported by the negative correlation between plant growth and sugar content in the three added extracts, and the positive correlation between microbial activity, fungal biomass production and sugar content, and are known reactions when labile carbon is added to nutrient deficient soils.

Fate of some fungal spores associated with wheat straw decomposition on passage through the guts of Lumbricus terrestris and Aporrectodea longa.

The effect of passage through the earthworm gut on the viability of spores of saprotrophic fungi was found to vary depending on fungal and earthworm species. Of 5 fungal species fed to Lumbricus terrestris L., the spores of two (Fusarium lateritium Nees, and Agrocybe temulenta (Fries)) failed to germinate after gut passage, while germination of Trichoderma sp. and Mucor hiemalis Wehmer was significantly reduced. A similar fate was recorded for F. lateritium and M. hiemalis spores on passage through the gut of Aporrectodea longa (Ude), however in the case of Chaetomium globosum Kunze there was a significant increase in spore germination after transit through A. longa. The germination of spores of M. hiemalis increased after abrasion by soil particles in a peristaltic pump simulating the mechanical action of the earthworm gut. In contrast germination of this species was significantly reduced when spores were exposed to intestinal fluids from L. terrestris.

Fungi and ionizing radiation from radionuclides

Radionuclides in the environment are one of the major concerns to human health and ecotoxicology. The explosion at the Chernobyl nuclear power plant renewed interest in the role played by fungi in mediating radionuclide movement in ecosystems. As a result of these studies, our knowledge of the importance of fungi, especially in their mycorrhizal habit, in long-term accumulation of radionuclides, transfer up the food chain and regulation of accumulation by their host plants was increased. Micro-fungi have been found to be highly resilient to exposure to ionizing radiation, with fungi having been isolated from within and around the Chernobyl plant. Radioresistance of some fungal species has been linked to the presence of melanin, which has been shown to have emerging properties of acting as an energy transporter for metabolism and has been implicated in enhancing hyphal growth and directed growth of sensitized hyphae towards sources of radiation. Using this recently acquired knowledge, we may be in a better position to suggest the use of fungi in bioremediation of radioactively contaminated sites and cleanup of industrial effluent.