Mycorrhizal fungi and pathogens influenced the
diversity-productivity relationship
The SEM that included richness of plant pathogens and ECM (Fig. 1C,
Table S4) explained 35% of the variability in tree productivity and
provided a better fit than the null model (Fisher’s C = 13.933, P =
0.008 on 4 df; Fig. 1D). Tree species richness (std. coef. = -0.18, P =
0.007) and functional identity (std. coef. = -0.32, P < 0.001)
were negatively associated with pathogen richness but pathogen richness
was not related to productivity (P = 0.767). Tree species richness had a
positive effect on ECM richness (std. coef. = 0.25, P = 0.013), and ECM
richness was negatively related to productivity (std. coef. = -0.19, P =
0.007). Pathogen and ECM richness had a negative, interactive effect on
productivity (std. coef. = -0.14, P = 0.027). Therefore, pathogen and
ECM richness mediated both positive and negative indirect effects of
tree species richness on productivity.