Objective  To investigate the effects of continuous cropping of Andrographis paniculata on soil bacterial diversity and community structure.

Method  Sequencing analysis of samples from continuous cropping group (rhizosphere soil of A. paniculata continuous cropping for five years) and control group (uncultivated natural soil with the same texture as the soil around A. paniculata continuous cropping for five years) were performed using 16S rRNA gene high-throughput sequencing technology. The differences in richness, diversity and community structure of soil bacteria from two groups were analyzed.

Result  The analysis results of α diversity index showed that the bacterial richness indices (Chao1 index and Observed species index) in the soil of continuous cropping group were significantly lower than those of the control group (P<0.05), and the diversity indices (Shannon index and Simpson index) in the soil of continuous cropping group were lower than those of the control group, but the differences were not significant. Principal coordinates analysis and molecular variance analysis of community structure between groups showed that continuous cropping ofA. paniculata significantly changed soil bacterial community structure (P<0.05). A total of 2769 operational taxonomic units were detected from the soil samples of two groups, belonging to 47 phyla and 885 genera. Continuous cropping ofA. paniculata obviously changed the structure distribution of soil bacteria at the phylum and genus level. At the phylum classification level, 11 bacterial phyla including Acidobacteria, Proteobacteria, Bacteroidetes, Patescibacteria and etc. were the main bacterial communities in two groups. Compared with the control group, the relative abundance of Proteobacteria and Acidobacteria in the continuous cropping group increased by 21.97% and 46.33% respectively (P<0.05), while the relative abundance of Patescibacteria reduced by 68.99% (P<0.05). At the genus classification level, the relative abundance of 10 dominant bacterial genera changed significantly (P<0.05). Among them, compared with the control group, the relative abundance of the beneficial bacteriaFlavobacterium and Haliangiumin in the soil of continuous cropping group reduced by 78.40% and 54.55% respectively, while the relative abundance of the plant pathogenic bacterium Burkholderia-Caballeronia-Paraburkholderia in the soil of continuous cropping group increased by 804.17%.

Conclusion  After five years of A. paniculata continuous cultivation, the level of soil bacterial richness and diversity decreased. At the same time, the relative abundance of beneficial bacteria significantly reduced, while the relative abundance of pathogenic bacteria significantly increased, causing a change in the bacterial community structure. The above-mentioned changes broke the original soil microecological balance, which may be one of the important reasons for A. paniculata continuous cropping obstacles.