Fig. 1

Soil microbial community composition and ecosystem functioning with progressive simplification of the soil biome. The soil diversity gradient was established by filtering inoculum through different meshes: ≤5; ≤0.25; ≤0.05, ≤0.025, ≤0.001 mm, or adding sterilized soil inoculum. Shown are (a) the mean richness of bacterial and fungal OTUs and (b) the microbial association networks where blue circles indicate individual bacterial operational taxonomic units (OTUs), red square nodes indicate individual fungal OTUs and lines indicate interlinkage between OTUs. For visual clarity, only OTUs that were detected to be present in 75% of all replicates within each treatment level are illustrated. Networks are based on subsets of a meta-network matrix where subset matrices were generated using only OTUs present within a treatment. Connectedness within the meta-network was 2.2% (70,830 links out of 3,290,596 possible links). Larger nodes indicate the OTU was relatively more abundant within that particular treatment. c The mean of ecosystem functions related to nutrient cycling for each of the soil community treatments. Error bars in a and c are standard errors and different letters indicate significant differences (Tukey HSD) between treatments (n = 8 for each treatment level with n = 10 for the sterile treatment, except for plant nutrients where n = 8)