Date of Award:

5-1-1991

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology Ecology

Committee Chair(s)

Michael F. Allen

Committee

Michael F. Allen

Committee

Anne Anderson

Committee

James Haefner

Committee

David Pyke

Abstract

The major objective of this dissertation was to describe some of the factors that may be important in the establishment of vesicular-arbuscular (VA) mycorrhizal fungi following a disturbance. The specific focus of the dissertation is primarily on the interaction of the western harvester ant and VA mycorrhizal fungi and how this interaction affects the dispersion and establishment of these mutualistic endophytes. Methods were developed to test the use of polyclonal antibodies on field and greenhouse samples. This approach proved viable and allowed me to differentiate between both the extramatrical hyphae and spores of introduced and native VA mycorrhizal fungi. I found that harvester ants incorporated three types of VA mycorrhizal inoculum within their mounds: spores, hyphae, and infected root fragments. Utilizing root observation chambers, I made detailed observations of each inoculum type and the resulting growth dynamics of mycorrhizal hyphae. I classified several types of hyphal architecture. The specialized hyphal architectures of these fungi may be linked to the unique function of each hyphal type. This high degree of specialization may help explain why ant concentrated inoculum was so effective and why these fungi are efficient in increasing nutrient and water uptake of the host plant. Excavations of two ant mounds revealed the chambered core of the mound to consist of a root mat comprised of densely packed secondary roots that had been clipped by the ants and left in place as part of the architecture of the mound. This root mat material was significantly different from surrounding undisturbed vegetation in that it contained as much as 2000 to 5000 times the VA mycorrhizal fungal spore density. Results from field and root chamber experiments were similar and demonstrated that surface-deposited inoculum was not able to expand downward through the soil profile unassisted. In contrast, the mycorrhizal inoculum concentrated several centimeters below the soil surface experimentally or by the ants produced high levels of root infection. I concluded that harvester ants are a mechanism for the concentration and enrichment of VA mycorrhizal inoculum into patches that could enhance the establishment of mycotrophic plant species after mounds are abandoned.

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