Objective  Effects of biochar addition on the microbial community and phenolic acids in rhizosphere soil at site of continuous-cropping of tobacco at various growth stages were investigated.

  Method  The changes on the contents of 7 phenolic acids and microbial communities in the rhizosphere soil under conventional and biochar-added fertilizations were determined by HPLC and high-throughput sequencing techniques for the analysis.

  Result  Six out of the 7 phenolic acids were detected in the soil specimens at all tobacco growth stages. With the addition of biochar in the fertilizer, aside from cinnamic acid that showed no significant variation, the contents of p-hydroxybenzoic acid, vanillic acid, syringic acid, 4-coumaric acid, and ferulic acid in the soil were lower than those under the control treatment of conventional fertilization. Compared to control, the total phenolic acid in the soil fertilized with added biochar decreased at the resettling, vigorous growing, and harvesting tobacco stages by 1.86%, 11.36%, and 40.44%, respectively. Biochar improved the diversity and richness of rhizosphere microbial community as well. At the vigorous tobacco growing stage, the bacteria and fungi OTU abundance under biochar treatment were 1.23 times and 1.07 times of control, respectively. Compared with the conventional fertilization, the biochar addition increased the Shannon, ACE and Chao1 indices on bacteria by 12.43%, 23.0%, and 23.0%, respectively, during the vigorous growing stage; and, by 0.32%, 2.40%, and 1.25%, respectively, during the harvesting stage. On fungi, the Shannon, ACE and Chao1 indices were raised by 6.54%, 6.67%, and 7.43%, respectively, in the vigorous growing stage; and, by 57.93%, 8.60%, and 26.37%, respectively, in the harvesting stage.

  Conclusion  It appeared that biochar significantly improved and upgraded the tobacco-growing soil by creating a healthy micro-ecological rhizosphere. The addition also alleviated some of the detrimental effects of the allelopathic autotoxicity generated from continuous cropping.