Soil microbes drive phylogenetic diversity-productivity relationships in a subtropical forest

The relationship between plant diversity and
productivity, and the mechanisms underpinning that relationship, remain poorly
resolved in species-rich forests. Here we combined extensive field observations
and experimental manipulations in a subtropical forest to test how species
richness (SR) and phylogenetic diversity (PD) interact with the putative root-associated pathogens, and how these interactions mediate diversity-productivity
relationships. We show that (1) both SR and PD were positively
correlated with biomass for both adult trees and seedlings across multiple
spatial scales, but productivity was best predicted by PD, (2) significant
positive relationships between PD and productivity were observed in non-sterile soil only, and (3) root fungal
diversity was positively correlated with plant PD and SR, while the relative abundance
of putative pathogens was negatively related to plant PD. Our findings highlight
that soil pathogenic fungi play a key role in tree diversity-productivity
relationships, and that increasing phylogenetic diversity may counteract negative
effects of plant-soil feedback.