Optimizing the bacterial community structure and function in rhizosphere soil of sesame continuous cropping by the appropriate nitrate ammonium ratio

Abstract

Bacterial wilt has a significant effect on sesame yield, and the appropriate nitrate ammonium ratio (NO3:NH4) can alleviate the occurrence of bacterial wilt. However, its soil micro-ecological mechanism is unclear. We investigated the influences of NO3:NH4 and bacterial wilt on the bacterial community composition and function potentiality of rhizosphere soil in the sesame continuous cropping through high-throughput sequencing. The results indicated that the incidence rate of bacterial wilt was the lowest under the condition of 5:5, and the highest sesame yield was obtained. The relative abundance of Ralstonia had no significant difference among all treatments. Different ratios only had a significant impact on Shannon index, showed a downward trend with the reduction of nitrate ratio, and the α-diversity indexes of treatment 5:5 were at the middle level, while the median value of β-diversity index was at the highest level. Meanwhile, there was 98 unique OTU under treatment 5:5 condition, most of which belonged to phylum Protecbacteria, Bacteroidetes, and Cholorflexi, and that Parafilimonas was the only genus with significant difference. The relative abundances of Acidobacteria and Verrucomicrobe from rhizosphere soil of healthy plants were significantly higher than those from diseased plants, indicating that increasing the relative abundances of these phyla were beneficial for sesame continuous cropping, especially genus Candidatus_Solibacter and Bryobacter. This fertiliser can reduce the pH value (−0.37), while the decrease of pH increased the relative abundance of beneficial bacteria. Furthermore, this ratio (5:5) could significantly improve the replication and repair, cellular process and signalling of rhizosphere soil functions, which was favourable to reduce the occurrence of bacterial wilt. The available potassium, available boron, and pH had a negative correlation with the bacterial community structure in the rhizosphere soil from the healthy plants, and the contribution of these were 13.31%, 10.27% and 7.89%, respectively. Overall, the appropriate NO3:NH4 (5:5) might improve the diversity and structure of bacterial community, and related functions in the rhizosphere soil of sesame continuous cropping, and reduced the occurrence of bacterial wilt.