Fungal functional guilds, especially plant pathogens, mycorrhizal fungi, and saprotrophs are critical to ecosystem functioning and the maintenance of species diversity in terrestrial ecosystems. The importance of pathogens has gained considerable empirical support in regulating species abundance in tropical and subtropical forests by inducing negative density dependence. In addition, plant species may become locally dominant because they can take up both organic and inorganic nitrogen in soil by forming root symbioses with ectomycorrhizal fungi. However, a comprehensive study of how theses fungal guilds are related to their host abundance and how they are interacted in a framework of network is still lacking. Here, we collected 529 root tip samples from 45 plant species which cover a wide range of relative abundance (ranging from 0.1% to 10%) and phylogenetic relatedness in a subtropical forest dynamic plot in southern China. The fungal communities in root tips were assessed by massive parallel pyrosequencing and the taxa were assigned to two major guilds including plant pathogens (latency stage) and ectomycorrhizal fungi.
We found that the abundance of latent pathogens is significantly negatively correlated with their host abundance, indicating that rare plant species are under higher risk of disease than abundant species. Thus, latent pathogens may regulate species abundance by inducing a trade-off between plant defense and resource uptake ability. Consistent with this expectation, analyses of ectomycorrhizal fungi showed that their richness and abundance are significantly higher in abundant species than that in rare species. Moreover, the network structures of plant–ectomycorrhizal fungi symbioses showed that abundant plant species and rare species exhibited different levels of interaction specialization and nestedness, which illustrated an architecturally diverse ecological network in our system. Collectively, our work highlights the profound importance of belowground fungal functional guilds in regulating the diversity and composition of aboveground plant communities.