Fig. 4.

Heatmap representing the top covarying microbial taxa and metabolites in the rhizosphere of switchgrass grown with five soil nutrient and water treatments. Top associations between metabolites (columns) and ASVs (row) include i) DESeq2-determined differentially abundant ASVs (n = 37) with more than three significant positive or negative correlations (Spearman’s rank correlation, r > 0.7, P < 0.05) with metabolites; and ii) metabolites (n = 25) with more than one significant positive or negative correlation (Spearman’s rank correlation, r > 0.7, P < 0.05) with ASVs. Hierarchical clustering shows two clusters of metabolite-ASV correlations. Cluster #1 (blue lines) represents metabolites and ASVs that were more abundant in the rhizosphere when nitrogen was added (+N, +NP treatments) and Cluster #2 (brown lines) includes metabolites and ASVs that were more abundant in nitrogen-poor marginal soil (controls). Purple colors in the heatmap represent positive Spearman correlations, white represents no correlation, and green colors represent negative correlations between metabolites and ASVs.