Shifts in the relative abundance of bacteria after wine-lees-derived biochar intervention in multi metal-contaminated paddy soil.

The impact of biochar application on soil ecological functions depends on the diversity of soil conditions and of the feedstocks from which biochar is obtained. Moreover, little information is available on the effect of biochar on dynamic changes in microorganisms with the development of rice plants in multi-metal-contaminated paddy soil amended with wine-lees-derived biochar. In this paper, biochar obtained from the pyrolysis of wine lees at 600°C was used to investigate the potential role of biochar in maintaining soil ecological functions, with consideration of the alteration of the microbial population over periods of rice growth. Biochar increased the soil nutrient availability, suppressed the toxicity of heavy metals and benefited the rice growth. Enzymic activities initially increased and then decreased with increasing biochar addition as well as with the growth stage. High-throughput sequencing results indicated that biochar application shifted the soil microbial community, increased the bacterial diversity and reduced the bacterial richness. The relative abundances of Actinobacteria, Firmicutes, Proteobacteria, Planctomycetes and Cyanobacteria increased with increasing biochar addition, whereas the abundance of Gemmatimonadetes decreased at higher biochar applications. With increasing biochar application, Nitrospirae, which were lowest in the 1% biochar addition treatment, first decreased and then increased. The results from this study indicated that biochar addition increased N2 fixation and improved C cycling. Redundancy analysis (RDA) indicated that RI (potential ecological risk index), AN (available nitrogen) and AP (available phosphorus) were the most important factors for bacteria and accounted for 68.7%, 58.3% and 52.4% of the variation, respectively. Therefore, the reduction of metal toxicity and the improvement of soil fertility are important mechanisms for higher bacterial abundances.