Dose Effect of Pig Manure Addition on Cbbl-Harboring Bacterial Community in a Paddy Soil

CO2 fixation by autotrophic microbes has a significant effect on C cycle in agricultural filed. Organic fertilization is an eco-friendly strategy for environmental protection and agricultural sustainability via ameliorating soil microbial community. However, the information of the dose effect of organic fertilizer on soil CO2 fixing microbes has been less documented. In this study, the cbbL gene, a key gene in the Calvin-Benson-Bassham cycle, was used to characterize the CO2-fixing microbes under the gradient rates of pig manure (PM) addition (0, 1400, 2800, 5600, 11,200, 22,400, and 44,800 kg ha(-1)) in a 5-year field experiment with a double-rice cropping system in the red soil region of China. The results showed that Proteobacteria and Actinobacteria accounted for similar to 99.4 % of total cbbL-harboring bacteria in average. High PM doses (22,400 and 44,800 kg ha(-1)), rather than Low PM doses (11,200 kg ha(-1) and less), would significantly change the cbbL-harboring bacterial community attributes. Specifically, high PM doses decreased the alpha-diversity of cbbL-harboring bacterial community and the relative abundances of some lineages belonging to Proteobacteria and Actinobacteria, such as Bradyrhizobium Methylibium, and Variovorax, but increased the proportions of some stress-tolerant taxa (i.e. Hydrogenophaga and Methyloferula). Redundancy analysis (RDA) and partial least squares path modeling (PLS-PM) showed that pH, AP, and metals (Cu and Zn) negatively influenced the cbbL-harboring bacterial diversity and components through PM addition. Collectively, our study demonstrated that high PM addition would potentially threaten the soil cbbL-harboring microbes, and a rational application of manure-derived organic fertilizer should be addressed in agriculture for maintaining soil bio-diversity in future.