Fig. 2.

The Shannon diversity index (A) and Chao 1 (B) indicated no differences in species diversity between placebo (PL) and nitrate (BR) conditions. Non-metric multidimensional scaling (NMDS) revealed that the overall salivary microbiome composition differed between PL and BR (C). Significant differences in physiological and cognitive traits between PL and BR included increases in plasma nitrate ([NO₃⁻]) and nitrite ([NO₂⁻]) concentration (D, E); decrease in plasma [NO₂⁻]/[NO₃⁻] ratio (F); and decreases in systolic blood pressure (SBP) (G), pulmonary O₂ uptake relative to walking speed (H), and number of errors in the RVP test of sustained attention (I). In panels D-I blue symbols and lines indicate mean ± SD and red dashed lines show individual responses. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)