Rotations are widely employed agricultural managements affecting the soil carbon cycle. It can affect the turnover and composition of labile organic carbon, resulting in the shifts of soil microbial communities. However, it is not clear whether rotation affects the CO₂ fixation processes driven by autotrophic bacteria. Moreover, it is poorly understood how the abundance and community composition of autotrophic CO₂ fixation bacteria respond to different rotation patterns, such as double rice rotation, rice-wheat rotation and wheat-corn rotation, three typical rotation systems in subtropical region of China.

To address this, the research group from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) used undisturbed soils under double rice rotation (RR), rice-wheat rotation (RW) and wheat-corn rotation (WC) were continuously labelled with ¹⁴CO₂ and the incorporation of microbial assimilated ¹⁴C with depth were determined by ¹⁴C in soil organic carbon (SOC¹⁴) at the end of 110 days incubation. Based on cbbL gene analysis, the abundance, diversity and composition of autotrophic bacterial communities in different cropping systems were investigated.

The researchers found that the recovery of SOC¹⁴ contents significantly differed among the three different rotation systems, with the order of RR > RW >WC, which corresponded to the shifts in the abundance, activity and composition of cbbL-containing bacteria communities. Greater SOC¹⁴ concentrations coupled with higher RubisCO activities in surface soil (0－1cm) were observed compared to the subsurface (1－5cm) and deeper layers (5－17cm). In addition, the identified OTUs responsible for the observed community differences among samples cumulatively contributed to 50.22% of the community variations and showed diverse phylogenies in relation to rotation types. Most of the identified operational taxonomic units (OTU) were related to Nitrobacter hamburgensis, Methylibium petroleiphilum, Rhodoblastus acidophilus, Bradyrhizobium, Cupriavidus metallidurans, Rubrivivax, Burkholderia, stappia and Thiobacillus thiophilus.

Therefore, they can get conclusion that rotation types regulate the abundance, activity and composition of autotrophic bacteria, resulting in significantly alterations in the potential of the microbially-assimilated atmospheric CO₂ fixation with respect to rotation practices. Partitioning of CO₂ incorporation driven by photoautotrophy and chemolithoautotrophic processes at different depths, as well as vertical transportation of fixed ¹⁴C affected by changes in soil texture as a result of different rotation managements, leading to the vertical shifts of assimilated ¹⁴C across soil depths. Understanding of these processes will be of great importance to enhance soil C sequestration by properly manipulating agricultural managements.

This study was supported financially by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB15020401), the National Natural Science Foundation of China (41271279; 41430860).

This study entitled “Cropping systems modulate the rate and magnitude of soil microbial autotrophic CO₂ fixation in soil” has been online in Frontiers in Microbiology (doi: 10.3389/fmicb.2015.00379). The full-text can be download at http://journal.frontiersin.org/article/10.3389/fmicb.2015.00379/abstract.