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Abstract

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts that associate with over 70% of land plants. As such, whether an association between a plant host and AMF partner is positive or negative can influence terrestrial communities. Within an AMF species there is substantial genetic, trait and functional variation (intraspecific variation) that can induce vastly different plant growth response. Whether intraspecific AMF variability has community level consequences, however, remains unexamined. This thesis investigates whether conspecific AMF (AMF isolates from the same species) have belowground or aboveground community level consequences. To achieve this, mesocosms containing natural soils and a mixed plant community were inoculated with three conspecific isolates of the AMF species, Rhizophagus irregularis and grown for 17 weeks. AMF isolate abundance, plant growth response (aboveground biomass, total foliar phosphorous, seed production), plant community response (diversity and composition) and AMF community response (diversity and composition) were measured as indicators of community response. Patterns in association between AMF isolates and plant taxa were evaluated by comparing AMF isolate abundance between hosts and AMF isolates. The results showed (1) introduced AMF abundance changed with both host identity and AMF isolate identity (2) host response differed between AMF isolates and was uneven among host species (3) uneven host response to introduced AMF isolates affected relative host biomass, and (4) introduced AMF isolates differentially affected turnover of AMF taxa within a local AMF community. These results provide empirical support for intraspecific AMF variation having community level consequences. With increasing global demand for agricultural and forestry products containing AMF, predominantly represented by a single genetic isolate of one species, there is a pressing need to incorporate intraspecific AMF variation into ecological frameworks.