Figure 5.

Multivariate regression tree analysis of the associated relationship of (A) bacterial and (B) archaeal communities and physicochemical parameters. For both figures, 7-split trees are visualized. Statistics information is listed under individual trees, including the residual error (the reciprocal of the R² of the model), cross-validated error and standard error. Under each branch, a small bar plot is given to represent the normalized abundance of species. The corresponding residual error and sample numbers under each branch are also listed. Values under each split point indicate percentages of variance explained by the split (Complexity R²). Units for ${\text{NH}}_4^{+}$, ${\text{NO}}_2^{-}$ and ${\text{NO}}_3^{-}$ concentrations refer to Table 1.