A rice pot experiment was conducted to investigate the effect of phosphorus addition on the abundance of autotrophic CO2-fixation microorganisms using phosphorus-limited paddy soil from the Changsha Observation and Research Station for the Agricultural Environment. Rice seedlings were transplanted in the paddy soil with or without phosphorus addition, corresponding to P-treated-pot (P) or control pot (CK), respectively. Rhizosphere soils were collected from the P and CK treatments during the tillering and shooting stages. The physical and chemical soil properties were measured and the abundance of autotrophic CO2-fixation microorganisms was quantified with a real-time PCR technique based on four functional genes (cbbL, cbbM, accA, and aclB) involved in three CO2-fixation pathways (CBB cycle, rTCA cycle, and 3-hydroxypropionate/4-hydroxybutyrate cycle). The results show that phosphorus addition improves the concentrations of DOC and Olsen-P and the pH value, whereas negative effects on the MBC and NH4+-N concentrations are revealed during the tillering stage. The effect of phosphorus addition on the NO3--N concentration in the tillering and shooting stages differs. Phosphorus addition significantly increases the abundances of the cbbL, cbbM, accA, and aclB genes, which are 156%, 99%, 110%, and 193% higher than those of the CK treatment in the tillering stage. However, this positive effect is not notable for the cbbL, accA, and aclB genes during the shooting stage. Redundancy analysis (RDA) shows that Olsen-P is the environmental factor that most significantly affects the abundance of autotrophic CO2-fixation microorganisms.
Keywords: autotrophic CO2-fixation microorganism; gene abundance; phosphorus; phosphorus-limited paddy soil; rhizosphere soil.