Item – Theses Canada

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OCLC number
32546333
Author
Klironomos, John,1967-
Title
Influences of microarthropods on the functioning of endomycorrhizal associations.
Degree
Ph. D. -- University of Waterloo, 1994
Publisher
Ottawa : National Library of Canada = Bibliothèque nationale du Canada, 1994.
Description
3 microfiches.
Notes
University Microfilms order no. UMI00489939.
Includes bibliographical references.
Abstract
Temporal and spatial relationships in a maple-forest soil among mycophagous microarthropods, total hyphal length, vesicular-arbuscular mycorrhizal (VAM) fungus spores, microfungus diversity, root biomass and some abiotic variables (temperature, water content, pH, organic matter content) were investigated. Samples were obtained from spring 1991 to winter 1992 at four soil depths. Canonical correspondence analysis was used to analyze the data. Four species of sporulating VAM fungi were identified, along with 23 species of mites and collembolans, 9 of which were common. Hyphal length, VAM fungus spores, and soil animals peaked in spring and autumn. Canonical correspondence analysis suggests that animal abundance and success in the soil are dependent on a number of environmental variables. The most important variables that influence microarthropod community structure are: (i) temperature, (ii) water content, (iii) pH, (iv) total length of fungal hyphae, and (v) diversity of melanized fungi. However, the relative importance of these variables changes with increasing soil depth. I have also shown a relationship between arthropod populations and their food supply under field conditions, a phenomenon which has rarely been documented with microarthropods. The feeding preferences of six species of arthropods for three soil fungi commonly associated with roots of Acer saccharum, (Glomus macrocarpum, Alternaria sp. and Trichoderma sp.), in Southern Ontario, were investigated under controlled laboratory conditions. Experiments were also conducted, in vitro, to determine animal feeding responses to (i) increasing hyphal biomass, (ii) the presence of root vs litter fungal substrates, and (iii) Glomus macrocarpum hyphae of different widths. Results indicate that arthropods prefer to graze in the litter region rather than in the deeper soil layers. Animals are forced to the lower regions by interspecific interactions. They also prefer to graze on hyphae of conidial fungi rather than on those of VAM fungi. When VAM-fungus hyphae are grazed, animals clearly prefer the narrower hyphae, which are those further away from the root. These data support the hypothesis that under field conditions arthropods normally cause little reduction in the efficiency of endomycorrhizal associations. That might seem obvious, since VAM fungi have existed for 400 million years, but most previous experiments apparently demonstrated the opposite effect. It is now apparent that those experiments were simplistic, involving too few organisms or too few variables. We examined how Acer saccharum seedling biomass and mycorrhizal colonization levels respond to the addition of (i) soil microarthropods, (ii) decaying litter, (iii) arthropods plus litter under microcosm conditions. The addition of fauna was associated with decreased arbuscular ($-$38%) and hyphal ($-$30%) colonization, and increased vesicular colonization (+112%), with no effect on plant biomass. The addition of decaying litter was associated with decreased arbuscular colonization ($-$51%), increased hyphal (+24%) and vesicular (+117%) colonization, and extra-radical hyphal length (+38%), and decreased shoot ($-$43%) and root ($-$23%) biomass. However, there was a strong interaction between decaying litter and soil fauna and the addition of both was associated with enhanced arbuscular colonization (+59%), vesicular colonization (+85%), and increased shoot biomass (+32%), and shoot/root biomass ratio (+25%). It is clear that a better understanding of the dynamics involved in such interactions between soil organisms can have profound implications for soil management practices in agriculture, forestry, and areas requiring revegetation.
ISBN
0315894946
9780315894945