Fig. 4: Classification of bacterial nutrient response based on averages at different taxonomic levels.

Outlined points represent the isotopic enrichment (¹³C and ¹⁸O) of bacterial lineages at specified taxonomic levels over a 7-day incubation, based on the mean excess atom fraction (EAF) of their constituent taxa (shown by small points with lines to their representative group). Colors represent approximations of ecological life history strategies generated from bivariate Gaussian finite mixture models and specifying two components. Panels show classification of bacterial taxa based on isotopic composition of: A Classes, B Orders, C Families, and D Genera. Black lines represent the first axes generated from principal components analyses of ¹⁸O and ¹³C EAF values in each treatment, expressing a composite measure of bacterial growth. Lines perpendicular to the principal component represent average growth of representative lineages while smaller lines parallel to the principal component represent the differences between growth of representative lineages and individual amplicon sequence variants. Soil treatments (C and CN) represent a carbon amendment (1000 μg glucose per g dry soil) and a carbon and nitrogen amendment (glucose + 100 μg-N [NH₄]₂SO₄ per g dry soil) respectively. For direct comparison with ¹³C, EAF values of ¹⁸O were divided by 0.6 (µ) to account for multiple oxygen sources utilized during bacterial growth.