Ectomycorrhizal Fungi Explain More Variation in Rhizosphere Nutrient Availability than Root Traits in Temperate Forests

Abstract

Plant roots, mycorrhizas and saprotrophic microbial communities interact to regulate plant nutrition and nutrient cycling. However, the role of mycorrhizal fungi in controlling rhizosphere nutrient availability remains poorly understood. Here, we sampled rhizosphere soils from seven ectomycorrhizal (EcM) tree species to investigate the influence of mycorrhizal fungi on soil nutrient availability. Our results indicate that nitrogen (N) and phosphorus (P) availability in rhizosphere soils vary depending on the ectomycorrhizal tree species. The abundance of ectomycorrhizal fungal operational taxonomic units (OTU) accounts for more variation in rhizosphere N and P availability than root traits and the saprotrophic microbial community. As the abundance of ectomycorrhizal fungal OTUs increases, rhizosphere available N content initially decreases and then increases, while available P content decreases.  Root diameter, chemical traits, and the abundance of saprotrophic microbial OTUs were strongly correlated with ectomycorrhizal fungal OTU abundance, suggesting that interactions among roots, ectomycorrhizal fungi and saprotrophic microbes regulate rhizosphere N and P availability. Our results emphasize the importance of ectomycorrhizal fungi in governing rhizosphere nutrient availability in temperate forests. Incorporating these effects into models should improve simulations of forest biogeochemical cycles and inform forest management strategies in the context of global change.

Keywords: Ectomycorrhizal fungi, Nitrogen and phosphorus availability, Rhizosphere, Root traits, microorganisms