Effect of simulated tillage on microbial autotrophic CO2 fixation in paddy and upland soils

Abstract Tillage is a common agricultural practice affecting soil structure and biogeochemistry. To evaluate how tillage affects soil microbial CO 2 fixation, we incubated and continuously labelled samples from two paddy soils and two upland soils subjected to simulated conventional tillage (CT) and no-tillage (NT) treatments. Results showed that CO 2 fixation ( 14 C-SOC) in CT soils was significantly higher than in NT soils. We also observed a significant, soil type- and depth-dependent effect of tillage on the incorporation rates of labelled C to the labile carbon pool. Concentrations of labelled C in the carbon pool significantly decreased with soil depth, irrespective of tillage. Additionally, quantitative PCR assays revealed that for most soils, total bacteria and cbbL -carrying bacteria were less abundant in CT versus NT treatments and tended to decrease in abundance with increasing depth. However, specific CO 2 fixation activity was significantly higher in CT than in NT soils, suggesting that the abundance of cbbL -containing bacteria may not always reflect their functional activity. This study highlights the positive effect of tillage on soil microbial CO 2 fixation and the results can be readily applied to the development of sustainable agricultural management.