Bacterial growth efficiency and population dynamics during community assembly on plant litter

While microbial communities drive plant litter decomposition and soil carbon (C) cycling, we still lack a framework for explaining how they control terrestrial C fate. Life history frameworks provide insight into microbial C cycling by explaining dynamics of microbial growth, resource acquisition, and survival. We used amplicon sequencing with an internal standard (ARNIS) to quantify in situ bacterial growth and death dynamics for 78 ± 14 bacterial taxa (avg ± s.d., ASVs) in microcosms containing plant litter. Although the bacterial community exhibited logistic growth during litter colonization, the individual growth of bacterial populations varied substantially from community level dynamics. Populations that dominated early colonization exhibited fast growth but also rapid death and they grew less overall than populations that were dominant later. Populations that dominated late colonization (78 ± 1.4%) continued to grow long after the community had reached carrying capacity (stationary phase). Abundance losses due to mortality were highest during late colonization, which explains why late colonizers continued growing while the community appeared stationary. The C mineralization rate correlated with the summed abundance-weighted growth rate for growing populations (r = 0.68, p < 0.0001, Pearson), which was highest during early colonization. In contrast, the net growth efficiency of the community increased over time (rho = 0.56, p < 0.0001, Spearman) and was highest during late colonization. These findings indicate that soil bacteria exhibit diverse growth strategies during community assembly, and that the assembly process is a determinant of growth efficiency and C mineralization dynamics during litter decomposition.