Long-term tillage regime structures bacterial carbon assimilation

Microbial growth dynamics are deterministic of the fate of carbon in soil, responsible for the transformation of new carbon inputs and their stabilization on soil surfaces. Bacterial life history strategies are predictive of C substrate assimilation and growth response. High disturbance management practices such as tillage alter microbial community structure but have a poorly described impact on life histories that are central to C metabolism. We conducted a DNA stable isotope probing experiment using soil from a long-term field experiment with a 42-year legacy of no-till or annual moldboard plowing. We predicted that divergent legacies of disturbance would result in bacterial communities with distinct life histories, altering C assimilation dynamics. We incubated soil from each tillage regime with ¹³ C-xylose and ¹³ C-cellulose, two substrates that are components of plant litter and which differ in bioavailability. We identified 730 bacterial taxa that incorporated the labeled substrates and tracked their abundance in bulk microcosm soil over a 30 day period. Carbon addition rapidly altered bacterial community structure and function, with tilled soils demonstrating lower mineralization rates of each substrate. Xylose-assimilating taxa exhibited significantly lagged growth in tilled soils relative to no-till. We also found a higher number and diversity of late (day 30) cellulose incorporators in no-till soil, suggesting that minimal disturbance resulted in a longer residence time of ¹³ C-cellulose in members of the bacterial community. We show that soil management practices shape the path of carbon through bacterial communities by altering dynamic growth responses and secondary incorporation of carbon.