Fig. 6.

Serotonin effects on switchgrass plant phenotype and growth of rhizosphere microorganisms. (A and B) 25-d-old switchgrass seedlings (n = 9) grown with exogenous application of 0.1 mM of serotonin (+SER) or controls (−SER). Serotonin effects on secondary root number (A) and total root length (B). Significant differences between added-serotonin and controls were assessed by ANOVA, asterisks reflect P < 0.05. (C) Optical density (OD₆₀₀) of rhizosphere bacteria cultures after 130 h of growth in 1/10 R2A medium with 0, 0.1, or 0.5 mM of serotonin. Values have been scaled to the highest OD for each isolate across the row. The highest OD of the isolate is 100% (dark purple) and the lowest OD is 0% (dark green), meaning that isolate growth has been completely inhibited. Orange cells indicate isolates related to ASVs with significant negative correlations with serotonin (−SER) and brown cells indicate isolates matched to ASVs with positive correlations (+SER). Positive and negative correlations between specific ASV (shown in parentheses) and serotonin shown inside of each cell. Asterisks indicate significantly different OD₆₀₀ between the 0.1 and 0.5 mM serotonin treatments (n = 4) and a control treatment without serotonin (0 mM, n = 4) at P < 0.05 by means of the Kruskal–Wallis test.