Detection of horizontal spatial structure of soil fungal communities in natural forest

Investigating spatial patterns present in soil fungal community structure is essential to understanding the scale of the ecological impact these fungi have on the plant community, as well as how the interactions between soil fungi and the plant community vary from place to place. While previous studies have assessed the horizontal spatial structure of soil fungal communities, few studies consider how this changes vertically. We studied species composition of soil fungi from O- and A-horizons in a Castanopsis-dominated temperate forest, and compared horizontal spatial autocorrelation in species composition between two soil horizons (O- versus A- horizons). Pyrosequencing analysis yielded 67,265 sequencing reads, summed across all the 48 forest soil samples. Clustering analysis using a 95 percents sequence similarity cut-off resulted in 597 molecular operational taxonomic units (OTUs), sixty-eight percent of which were identified as fungi, represented by four phyla. Both of the O- and A-horizons hosted ectomycorrhizal genera (e.g. Russula, Cortinarius and Tomentella) and possibly saprotrophic Mortierella, but some orders of soil fungi (e.g. Helotiales and Hypocreales) appeared to occur more frequently at O- horizon than at A-horizon. Comparison of fungal species composition between the two horizons showed that A-horizon communities were more dissimilar in species composition with each other than the O-horizon communities were. Mantel test showed that the horizontal spatial structure differed between the horizons; the O-horizon communities resembled each other in composition within the range of 50 m, while the A-horizon communities lacked such horizontal autocorrelation. Different scale of patchiness suggests that the compositions of the soil fungal communities might be mixed by fungal dispersal differently across the horizons. These findings highlight that multilayer perspective of soil fungal communities might enhance our understanding about the impacts they have on spatial dynamics of the aboveground plant community in nature.