Spatial patterns and determinants of common root-associated fungi in a subtropical forest of China

Abstract

Spatial patterns of fungal populations are affected by plant distribution, abiotic factors, fungal dispersal ability and inter-species interactions. While several studies have addressed spatial patterns of some mycorrhizal, saprotrophic and pathogenic fungi, the method based on fruit-body surveys is not efficient and unreliable to study the spatial pattern of root-associated fungal species because most fungi in plant roots do not have sporocarps and cannot be identified based only on morphological traits. Our aims are (i) to determine the spatial pattern of common root-associated fungi; (ii) to evaluate whether the abundance and spatial pattern of root-associated fungi and categories of fungi, reflect their biotic and abiotic niche constraints. About 828 soil cores were collected from a 24-ha plot in a subtropical forest and Illumina Miseq was carried out to determine fungal composition in root samples and spatial patterns of 1009 common fungal Operational Taxonomic Units (OTUs) were studied using point pattern analyses. Biotic (plant community composition) and abiotic niche constraints on the presence/abundance of a fungal OTU was assessed as the n-dimensional niche hypervolumes of biotic and abiotic characteristics. Our results showed that (i) most fungal OTUs were highly spatially aggregated at small scales (less than 30 m), but that the aggregated pattern decreased, while regular and random patterns increased, with the increasing distance; (ii) A significant positive correlation was found between fungal abundance and aggregation intensity of fungal OTUs, indicating that the dominant fungi tended to be more aggregated in natural forests; (iii) Mean abundance and spatial aggregation intensity of ectomycorrhizal and pathogenic fungi were relatively higher than those of saprotrophic fungi, indicating that host plants may play an important role in determining spatial pattern of root-associated fungi; (iv) Spatial patterns of root-associated fungi depended on fungal abundance, fungal functional group, fungal taxa, biotic and abiotic niche hypervolumes of fungal OTUs.