Evaluating Community Level Consequences of Intraspecific Variation in an Arbuscular Mycorrhizal Fungus

There is substantial genetic, trait and functional variation variation among arbuscular mycorrhizal fungi (AMF) species. Whether this variability has community level consequences, for plant and AMF communities is not well understood, which is concerning given the wide use of AMF as biofertilizers. This study investigates whether conspecific AMF affect resident AMF and plant communities. 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 that AMF isolate identity (1) affected plant communities through changes to relative host biomass, (2) differentially affected turnover of resident AMF taxa, (3) affected the abundance of introduced isolate in host roots, and (4) differentially affected host performance and fitness. 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.