Semester

Fall

Date of Graduation

1998

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Applied and Environmental Biology

Committee Chair

Joseph B. Morton.

Abstract

Knowledge of taxonomic and functional diversity of arbuscular mycorrhizal fungi (Glomales, Zygomycetes) is important in understanding the biology and ecology of such a widespread mycorrhizal symbiosis. More definitive criteria for grouping and ranking taxa were established by reinterpreting morphological characters in selected species of Glomus (Glomaceae) and Acaulospora and Entrophospora (Acaulosporaceae) based on spore ontogenesis. Members of both families shared some patterns, such as discrete stages of spore growth and differentiation in three phases, resulting in the formation of three possible character complexes: a spore wall, flexible inner walls, and a pregermination structure. Families differed in presence or absence of one or more of these complexes. Genera diverged in subcellular organization of these complexes, and species diverged solely with changes in structure and phenotypic differences in the spore wall. With improved criteria for species delimitation, studies then were conducted to assess taxonomic structure in fungal communities. This process required methods to induce or stimulate sporulation by cryptic fungal species, such as successive propagation cycles of trap pot cultures. Trap cultures varied widely in their efficiency to detect non-sporulating species (15--100%), possibly because of differences in the environment, especially temperature, between the native habitat and greenhouse conditions. Glomus species dominated all baited communities, both in number and amount of sporulation. Infectivity of total fungal propagules was predicted by spore numbers, but infectivity was not correlated with species richness. Inocula of single isolates from three fungal communities were established from trap cultures to examine the proportion of effective and non-effective fungi present in each community. Effectiveness assays using soybean and red clover as hosts revealed that at least one fungal isolate from each community was effective in increasing plant growth and phosphorus foliar content. Fungal isolates that were highly effective or non-effective produced similar responses in both hosts, suggesting that effectiveness has a heritable component. A mix of all members of each fungal community performed as well or better than the most effective isolate in each community. These results suggest that management of indigenous fungal communities may be a preferred strategy to introduction of commercial inocula in natural or managed ecosystems.

Download

Share

COinS