Fig. 3

Correlations between chemical compound concentrations and genes involved in their cycling. Nitrogen and sulphur cycling genes whose relative abundance (TPM) are strongly correlated (r² > 0.5) with the environmental concentrations of a–c ammonia (NH₃), d–e nitrate (NO₃⁻), and f–i sulphate (SO₄²⁻). Plots coloured red represent genes involved in pathways that produce the corresponding chemical compound, either directly (b, c, e) or indirectly, via an intermediate compound (a, d, g–i). Correlation between sat gene relative abundance and SO₄^2- concentrations (f) is coloured blue to indicate the gene’s involvement in SO₄^2- substrate utilisation. Shaded regions represent the 95% confidence interval of the fitted linear model. A full list of r² and p values for all evaluated nitrogen and sulphur cycling gene correlations is presented as Supplementary Table S4