Environmental determinants of the arbuscular mycorrhizal fungal infectivity of Swiss agricultural soils

Arbuscular mycorrhizal fungi are ubiquitous inhabitants of soils, and they are involved in cycling elements such as phosphorus and carbon between soils and plants. However, the environmental factors determining their activity and community structure in different soils are still not fully understood. Here, a bioassay is presented to assess the infectivity of indigenous mycorrhizal communities in twenty soils sampled in the Swiss agricultural belt north of the Alps. This bioassay indicated clear negative relationships between the mycorrhizal colonization of bioassay plant roots and the phosphorus and nitrogen concentrations in plant biomass. Further, comparison of the bioassay results with a range of physico-chemical, biological, and geographic parameters of the soils confirmed a negative relationship between the soil phosphorus status and the mycorrhizal colonization of the plants. Other parameters, such as land use, base saturation, pH, and soil texture, had little explanatory value for patterns in the growth, nutrition, and mycorrhizal colonization of the bioassay plants. The results of this study were compared with those of a previous one that used the same methods, and that examined the influence of soil pollution on mycorrhizal infectivity. It appears that the results of a mycorrhizal infectivity assay could serve as a comprehensive and rather universal indicator of soil quality.