Long-term tillage regime structures bacterial assimilation of xylose and cellulose

We conducted a microcosm experiment using 13C-xylose and 13C-cellulose addition to soils from a long-term field experiment with a 42-year management history of continuous corn cropping with or without moldboard plowing. Both sets of fields are managed with biomass removal, resulting in no-till biomass harvested (NTH) and plow-till biomass harvested (PTH) treatments. Past research at this long-term experimental site has demonstrated significant tillage effects on SOC and organic nitrogen pools (Moebius-Clune et al, 2008). Xylose and cellulose were selected as substrates for this experiment because they are primary components of plant cell walls which differ in their bioavailability due primarily to differences in solubility. The bioavailability of C substrates is closely related to bacterial growth dynamics, with ruderal organisms rapidly metabolizing soluble forms of C and slower-growing competitor species being more active in mineralizing insoluble C (Barnett et al, 2021).We hypothesized that a long-term tillage regime would exert selective pressure on microbial communities due to disturbance (Grimes, 1977). Specifically, we hypothesized that disturbance would alter microbial community structure, causing changes in carbon mineralization and assimilation dynamics. Furthermore, we predicted that tillage would alter carbon assimilation by bacteria by favoring growth-adapted ruderal taxa that preferentially assimilate soluble substrates such as xylose and disfavoring competitive taxa that preferentially assimilate insoluble substates such as cellulose.