Fungal Microfeatures in Topsoils Under Fairy Rings in Pyrenean Grasslands

Soil reflects ecosystem processes and is influenced by gradual biospheric changes, which can affect its biotic components. In fairy rings, soil morphology, physicochemical properties, and biota are interconnected within a shared environmental space. In La Bertolina grasslands, while fungal and bacterial genomics have been investigated, the micromorphological soil effects of these rings have not. This study micromorphologically analyzed thin sections of three fairy rings at four zones: the ring center, the zone of peak growth in 2013 (R13), the predicted growth zone for 2019 (R19), and outside the ring. From each zone, two thin soil sections were prepared, totaling 24 samples. Fungal structures were exhaustively described according to morphological criteria following reference by multiple authors. The soil was a calcareous, loamy Regosol, and showed moderately developed crumb or laminar microstructures. Nine types of fungal structures were identified, consistent with genomic findings in the zone. Although fungal abundance did not vary across zones, mesofauna droppings were more frequent in R13 and R19, which was related to higher nutrient or water availability due to the fungal activity. Regarding the groundmass of the topsoil, neither the composition nor the microstructure of the surface horizons varied according to the moment of appearance of the ring at the sampled points.