Is the Effect of Ectomycorrhizal Fungal Diversity on Seedling Growth of Picea Asperata Mast Related to Enzyme Changes?

A small number of studies were conducted to evaluate the effect of multiple ectomycorrhizal fungal inoculations on plant growth. However, the changes in plant growth under different ectomycorrhizal fungal community diversity and their relationship with ectomycorrhizal (ECM) root and soil enzyme activities are still largely unknown. We tested the hypothesis that the more diverse ectomycorrhizal fungal community would contribute higher potential enzyme activities, which may partially explain the role of ectomycorrhizal fungal diversity in seedlings growth. A gradient of ectomycorrhizal diversity (0, 1, 2, 4, and 8 ectomycorrhizal species) was established on Picea asperata Mast seedlings grown indoors. We then linked ectomycorrhizal diversity to plant growth by measuring ectomycorrhizal root surface and soil enzyme activities, plant growth parameters, and nutrients. The results clearly showed that the differences in soil and whole root system activities of leucine aminopeptidase (LAP) and acid phosphatase (AP) among the treatments were mainly driven by ectomycorrhizal diversity. The β-glucosidase (βG), β-glucuronidase (βLU), and AP enzyme activities of the whole root system were significantly correlated with βG, βLU, and AP enzyme activities in the soil, respectively. In terms of carbon-related metabolic pathway, ectomycorrhizal diversity affected growth rate of biomass, mainly through increased total root and soil enzyme activities (βG, βLU, peroxidase (PER), and phenol oxidase (PHE)). Regarding the nitrogen-related metabolic pathway, the increased growth rate of biomass was mainly attributed to the changes in soil and whole root system enzymes that degrade N -containing compounds (NAG and LAP), and total plant nitrogen content. Our results indicate that a more diverse ectomycorrhizal fungal community contributes to higher potential enzyme activity through functional complementarity among species, which further promotes seedling growth. Our findings thus contribute to a better mechanistic link between plant growth and ectomycorrhizal fungal diversity that could be integrated into forest ecosystems to improve our understanding of carbon (C) sequestration and soil nutrient cycling.