Effect of tillage practices on soil CO2 emissions, microbial C-fixation, and C-degradation functional gene abundance in Northeast China

Tillage practices affect greenhouse gases’ exchange from soil to atmosphere and thereby change global soil carbon (C) cycle. However, there is limited understanding on how tillage practices affect CO2 production by altering C-cycling functional gene composition of the soil microbes. A long-term field tillage experiment was initiated in 2012 and consisted of no-tillage (NT) and moldboard plowing (MP) both with residue returned, and conventional tillage (CT) with residue removed. In 2020, we sampled the soil and quantified soil physicochemical properties, CO2 emissions, and the microbial C-cycling functional genes which were determined by the quantitative microbial element cycling (QMEC) method. The results showed that NT and MP significantly increased CO2 accumulative emissions compared with CT, but CO2 accumulative emissions were not markedly different between NT and MP. Both NT and MP greatly increased soil C-cycling functional genes at the depth of 0–20 cm, while MP decreased C-cycling functional genes, dissolved organic carbon (DOC), and microbial biomass carbon (MBC) concentrations, resulting in a reduction of C allocation at the soil 20–30 cm depth. Furthermore, DOC and NH4+-N concentrations were the most important environmental factors for changing microbial function potential. And the ratio of absolute abundance C degradation genes and C fixation genes were both significantly related to CO2 accumulative emissions (R2 = 0.37, P < 0.05), suggesting that NT may have great soil potential to accumulate C. These findings suggest that no-tillage will be an appropriate strategy to promote the potential of soil C cycle by altering composition and functionality of soil microbial communities.