Mycorrhizal and plant pathogenic fungi are two of the most important fungal taxa in maintaining plant diversity. Previous studies have shown phylogenetic distance among hosts strongly affect the community of mutualists and antagonists. However, the relative importance of host phylogenies driving the diversity and community composition of these two functionally different fungal taxa is little known, which hiders understanding processes structuring these ecologically critical associations and their host preference in the wild. Host-specific soil pathogens with limited dispersal potential could cause conspecific negative density dependent (NDD), thereby facilitating plant species coexistence. Contrarily, mycorrhizal fungi have empirically been shown to have specialized effects on plant which could neutralize NDD caused by pathogens. We tested host preference of these two fungal taxa by comparing their community structures along a host phylogenetic gradient. High-throughput sequencing was used to identify the fungi in 561 fine roots samples collected from a subtropical forest in south China which were then assigned to different functional categories. Generalized linear models and variation partitioning were applied to quantify variation in fungal α- and β-diversity, respectively, with predictors including host phylogeny, edaphic and topographic factors, and spatial variables.
In fungal α-diversity, host phylogenies explained 30.8% of the variation in mycorrhizal fungal species richness and 15.8% of the variation of fungal plant pathogens. Spatial autocorrelation also played an important role which predicted 7.3% and 8.4% of variations of mycorrhiza and pathogens, respectively. These results suggest that mycorrhizal fungi might have longer co-evolution history with host plants than pathogens but they both are limited in dispersal. We also found the interaction term of host phylogeny and spatial variables explained 5.8% of pathogen variation but nearly 0% of mycorrhizal fungi. This may suggest that the hosts of pathogens are more spatially structured than the hosts of mycorrhizal fungi. As for β-diversity, host phylogenies explained a comparable amount of variation in community composition of mycorrhizal fungi (18.1%) and pathogenic fungi (21.7%), suggesting these two fungal taxa have similar host preference. This study highlights the roles of host phylogeny, environmental variables and spatial autocorrelation in structuring the mycorrhizal and pathogenic fungal communities and shows these two ecologically different fungal taxa have different host preferences.