Ectomycorrhizal fungal diversity interacts with soil nutrients to predict plant growth despite weak plant-soil feedbacks

Abstract

Plant-soil feedbacks are the result of multiple abiotic and biotic mechanisms. However, few studies have addressed how feedbacks vary based on abiotic context or attempted to identify microbiota responsible for feedbacks. We investigated whether plant-soil feedbacks of an ectomycorrhizal tree (Quercus macrocarpa) varied based on soil nutrient status and whether fungal community composition and diversity could explain feedback patterns. We inoculated Q. macrocarpa seedlings with field-sampled soils taken from five soil origins – including heterospecific and conspecific trees and an old field – which were profiled using fungal DNA metabarcoding. There was a positive home vs. away plant-soil feedback, though feedbacks with individual hosts were not significant regardless of fertilization. Still, hosts harbored distinctive fungal communities that were predictive of plant growth. There was a growth promotive effect of ectomycorrhizal OTU diversity that was weakened with fertilization, suggesting context-dependent relationships between plant growth and a guild of fungal mutualists. Our results demonstrate that the host-specific accumulation of functionally important soil microbes is not always sufficient to drive species level plant-soil feedbacks. Our data provide support for a role of ECM fungal diversity in mediating plant growth responses, though it is unclear whether this effect was direct or indirect.