Biogeography and shape of fungal fairy rings in the Apennine mountains, Italy

Aim: Fungal ‘fairy rings’ (FRs) are regular bands of vegetation caused by a centrifugal expansion of fungal mycelia. It is well established that FR fungi affect both soil chemistry and microbiome, but nothing is known about the distribution of these patterns at the regional scale. Here, we assess the abundance and occurrences of different FR shapes i.e. rings, arcs and rotors, and explore their association with geomorphology and climate. Location: The Apennine Mountains, 300-km latitudinal gradient along the Italian Peninsula. Taxon: Basidiomycetous fungi. Methods: High-resolution freely available images were gathered to study FR shapes and distribution in the Apennine region of Italy. First, 12 mountains with different elevations and geomorphology were studied to assess the colonial density and relative distribution of FR type. FR distribution and shape and size of additional 616 FRs were studied in 61 study sites and relationship with selected climatic and topographic variables were assessed using different modelling approaches. Results: Overall, 1163 FR structures were found across the study area. Arcs were the most common shape followed by rings. Rotors were rare, accounting for less than 2% of all observations. Fungal colony density varied largely both among and within sites, averaging 6.7 arcs, 2.2 rings and only 0.1 rotors per ha. On average, arcs (18.8 m) were similar in size compared to rotors (18.4 m) whilst rings were smaller (11.7 m). Arcs presented a higher frequency of occurrence on steeper slopes whilst rings were mostly found on flat and moderate slopes. FRs occurred within the altitudinal range between 546 m and 2148 m a.s.l., corresponding to temperatures between 3.4 and 12.7°C and rainfall between 1100 and 1300 mm per year. Main Conclusions: FRs are common elements of the Apennine grassland landscape where they may contribute to the maintenance of plant and microbial diversity. Better systematic identification of the fungal species involved in the formation of FRs is required. Further research that combines long-term field manipulative experiments and modelling work would help to explain the formation of rings, arcs and rotors during the ontogenetic development of fungal fronts.