Fig. 2: Structure and alpha diversity of total and actively growing bacterial communities based on traditional and H₂¹⁸O qSIP-filtered 16S rRNA gene profiling.

Principal coordinates analysis (PCoA) of weighted UniFrac distances between bacterial communities assessed with (a) traditional 16S rRNA gene profiles and (b) H₂¹⁸O qSIP-filtered 16S rRNA gene profiles representing the actively growing communities (i.e., ASVs that did not incorporate a significant quantity of ¹⁸O were removed prior to analysis). Moisture history and fungal inoculum explained a total of 30% of the variation in total community structure (p < 0.001; n = 6 replicates) and 86% of variation in actively growing community structure (p < 0.001; n = 6 replicates). Ellipses show treatment groupings in (a, b). Inverse Simpson’s diversity index in (c) total and (d) actively growing communities. Letters denote the results of a Tukey’s HSD test (no significant differences between total communities; p < 0.01 for comparisons between actively growing communities; n = 6 replicates). Bold lines represent median values; whiskers represent upper and lower quartiles. For all plots, uninoculated, R. irregularis-inoculated, and S. bescii-inoculated soils are represented in black, yellow, and blue, respectively. Water-replete and water-limited soils are represented in dark or light color shades, solid or dashed boxplot outlines, and circles or asterisks, respectively.