Physical disturbance introduced during soil management practices (such as tillage) may disintegrate the soil structure, causing pronounced changes in the soil microbial community involved in biogeochemical processes, such as carbon sequestration. Changes in bacterial community composition have been repeatedly observed alongside factors affecting the stability of soil structure, including tillage, drying and rewetting, and "sieved" and "ground" soil treatments, partially due to the breakdown of aggregates resulting in the creation or loss of ecological niches for microbes. Autotrophic bacteria are a prospective contributor to mitigate the CO₂ concentration in the atmosphere; however, their responses to changes to ecological niches caused by physical disruption are not well understood.

To address this, the research group from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) used the soils were sieved to experimentally generate disturbed soils, and intact core soils without disturbance were collected as the corresponding undisturbed soils. Using a continuous labelling technique with ¹⁴CO₂, and the incorporation of microbial assimilated ¹⁴C with depth were determined by 14C in soil organic carbon pools (¹⁴C-SOC, ¹⁴C-MBC and ¹⁴C-DOC⁴) at the end of 110 days incubation. They also used real-time PCR to identify how the abundance of CO₂ fixation bacteria changes in response to the physical disturbance.

The researchers found that soil disturbance altered the abundance of cbbL-carrying autotrophic bacteria, and this shift in autotrophic bacterial abundance was accompanied by significant changes in CO₂ fixation, resulting in significant enhancement of soil organic carbon concentration. The increase in CO₂ fixation capacity is attributed to the improvement of specific CO₂ fixation in disturbed soils, probably due to changes in air permeability, water, and nutrient infiltration following soil disturbance. Moreover, the response of autotrophic bacteria and their CO₂ fixation capacity to disturbance depended on soil type, and the influence was not restricted to surface soil (0-1cm). The relative higher CO₂ fixation capacity detected in disturbed soils in this study showed that physical disturbance of the soil can benefit regulation of atmospheric CO₂ concentration and increase soil carbon sequestration, and can be applied as an optimal land management strategy.

Therefore, researchers can get conclusion that the effect of soil disturbance on ¹⁴C was not restricted to the surface soil (0-1cm), but the treatment showed an effect along the soil profile, indicating that the alterations in soil structure following physical disturbance can affect the microbial CO₂ fixation process in subsoil (1-5 cm and 5-17 cm). External disturbance, such as sieving, can improve the conditions by increasing the infiltration of nutrients and the diffusion rate of ¹⁴CO₂ to greater depth, thus stimulating growth of autotrophic bacteria in deep soil. In addition, changes in soil respiration as a result of soil disturbance may increase the ¹⁴CO₂ emission from the decomposition of recent assimilates, which increases the microbial CO₂ fixation capacity in deep disturbed soils. Moreover, the changes in soil structure caused by soil disturbance can also affect the transport of microbial-assimilated new carbon from the surface soil to the subsoil, which is reported to be an important source of new carbon recovered in deep soil.

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; 41503081).

This study entitled "Effect of simulated tillage on microbial autotrophic CO₂ fixation in paddy and upland soils"has been online in Scientific Reports (doi: 10.1038/srep19784). The full-text can be download at http://www.nature.com/articles/srep19784.

Contact: GE Tida

E-mail: gtd@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences