Microbial CO2 fixation in two agricultural soils of contrasting soil texture

Soil microbial autotrophs play an important role in mitigating atmospheric CO2 uptake and they are sensitive to soil properties. However, little is known about how soil texture impacts microbial CO2 fixation processes. Here, a... [ view full abstract ]

Soil microbial autotrophs play an important role in mitigating atmospheric CO2 uptake and they are sensitive to soil properties. However, little is known about how soil texture impacts microbial CO2 fixation processes. Here, a loam clay paddy soil and a sand clay loam paddy soil collected from the same location were incubated with continuous 14C-CO2 labeling, aiming to evaluate the effect of soil texture on microbial CO2 fixation. The CO2 fixation bacterial communities were investigated by quantitative PCR and clone libraries targeting the cbbL gene, which encodes ribulose-1,5-bisphosphate carboxylase oxygenase (RubisCO). After 110 days incubation, the incorporation of 14C-CO2 to soil organic carbon (14C-SOC) were significantly differed in two soils (P<0.05). Higher amount of 14C-SOC was observed in sand loam clay soil (1350.57 ± 62.01 mg kg-1) than loam clay (1036.53 ± 37.89 mg kg-1) at 0‒1 cm soil depth, whereas trend reversed for 14C-SOC concentration at 1‒5 cm and 5‒17 cm soil depth. 14C-SOC concentrations decreased with increasing soil depths irrespective of soil texture. The differences in incorporation rates of two soils were also reflected by specific CO2 fixation activity, which is the ratio of 14C-SOC concentrations to cbbL gene copy numbers. The compositions of bacterial autotrophs were distinct in two soils, with clones from different soils forming different clusters in the phylogenetic tree. These results indicate that soil texture has a strong impact on the activity and composition of autotrophic bacteria, and improvement of soil texture is helpful for microbial sequestration of CO2.