Spatial distribution of arbuscular mycorrhizal fungal spores in a hot spot field site.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous soil microorganisms establishing mu-tualistic symbioses with most land plants and playing key roles in plant nutrition and health. Their spatial distribution patterns have been investigated at global and regional scales, while little is known of their community composition at smaller scales. In this work, a small field previously identified as a large repository of AMF diversity, was investigated in order to determine spatial variation in AMF spore communities. Spore number and identity were assessed in soil collected from 12 sampling points across the experimental field (9x134 m). Spores were identified to species level and their distribu-tion was correlated with soil structure and characteristics. A total of 47 species belonging to 14 genera were detected. Mantel test showed that AMF community composition was significantly correlated with soil characteristics. AMF and soil variables were autocorrelated within a distance of 10 m, suggesting the occur-rence of a small scale spatial heterogeneity. Most taxa displayed aggregated distribution, as revealed by the variance to mean ratio. Soil characteristics differentially affected dis-tribution patterns of individual taxa within the field, both at the family and species level. Differential responses of individual AMF taxa to edaphic factors play a role in shaping the distribution and heterogeneity of AMF communities, consistently with the small scale spatial patterns of soil physical and chemical properties. Studies on the spatial patterns of whole AMF communities and individual taxa are fun-damental for improving our knowledge on the ecological drivers of native AMF distribu-tion at the local scale.