Differences in life history strategies of bacteria between paddy and upland soils and implications for carbon sequestration

Previous studies on the life strategies of soil bacteria in response to organic matter (OM) inputs have largely focused on unsaturated upland soils rather than flooded soils. Through meta -analysis and soil incubation experiments, we found that, unlike in upland soils, Actinobacteria and Proteobacteria in paddy soils exhibited oligotrophic traits. This divergence arises from both differential responses of shared taxa to moisture conditions and compositional turnover toward taxa with distinct physiological and ecological traits. The life history strategies of some bacterial phyla could shift with soil moisture and the C:N ratio of added OM. Importantly, the content of bacterial necromass carbon in soil mineral-associated organic carbon (MABNC) was associated with the prevalence of copiotrophs. Therefore, bacteria that contribute to organic carbon sequestration in upland soils may not play the same role in paddy soils. The increase in MABNC in OM-amended soils after four weeks of incubation was mainly associated with Firmicutes in flooded paddy soils, whereas it was associated with Actinobacteria and Proteobacteria in unsaturated upland soils. These findings improve the application of the copiotroph-oligotroph framework and advance our understanding of bacteria-mediated carbon sequestration in flooded soils.