Correlation between fine root traits and pathogen richness depends on plant mycorrhizal types

Root uptake strategies are associated with the strength of negative plant–soil feedback (PSF) induced by soil pathogens. Given the intensified effect of pathogen richness in fine roots on the strength of negative PSF through the synergistic effects of multiple pathogens, researchers have proposed a trade-off between nutrient acquisition and pathogen defence in roots. However, empirical evidence is lacking. In addition, because the interaction between pathogens and fine roots depends on the mycorrhizal types of tree species, both fine root traits and mycorrhizal types should be incorporated to reveal covariation in pathogen richness and the strength of negative PSF. In this study, we selected 50 arbuscular mycorrhizal (AM) tree species and 7 ectomycorrhizal (ECM) tree species in a subtropical forest to investigate the relationships between fine root traits and pathogen richness in fine roots and determined whether their relationships depended on plant mycorrhizal types. Our results showed that pathogen richness was negatively correlated with fine root diameter but was positively correlated with specific root length for the AM-associated species, while for the ECM-associated species, the pathogen richness was only found to have a significant negative relationship with the relative abundance of ECM fungi. These findings highlight the difference between AM- and ECM-associated species in pathogen defence and bridge the gap between root traits and pathogen richness, which is significant for improving our understanding of the potential factors mediating the strength of PSF and thus maintaining tree species diversity.