Effects of microbial agents on the active constituents and rhizosphere bacterial community of Gynostemma pentaphyllum

Abstract:

[Objective] To alleviate the soil microecological imbalance caused by continuous cropping and improve the quality and yield of Gynostemma pentaphyllum, we studied the effects of Streptomyces rochei D74 and the newly developed compound microbial agent T3 on the yield, quality, and rhizosphere bacterial community composition of G. pentaphyllum, aiming to determine the suitable microbial agent for this medicinal plant in continuous cropping and rotational cropping. [Methods] The five-point sampling method was used to determine the yield of G. pentaphyllum per unit area in the field. The content of main active constituents including flavonoids, polysaccharides, and saponins was determined by UV-VIS spectrophotometry and high performance liquid chromatography. The 16S rRNA gene high-throughput sequencing was employed to reveal the rhizosphere bacterial community structure of G. pentaphyllum. [Results] In the Z-zone of rotational cropping, the dry weight, total flavonoids, and total polysaccharides of the T3 group increased by 63.44%, 12.50%, and 32.90%, respectively, compared with those in the control group, and T3 outperformed D74 in improving the yield and quality. In the P-zone of continuous cropping, the dry weight, total flavonoids, and total polysaccharides of the D74 group increased by 77.41%, 112.50%, and 23.10%, respectively, compared with those in the control group, and D74 outperformed T3. The differential microorganisms enriched in the T3 group compared with the control group were beneficial microorganisms such as Novosphingobium and Rhodanbacter, and those enriched in the D74 group were Bradyrhizobium and Nitrospira. [Conclusion] Both T3 and D74 could optimize the microbial community structure in rhizosphere soil and improve the micro-environment for plant growth by recruiting beneficial microorganisms in the soil, thus increasing the content and yield of the active constituents of G. pentaphyllum. D74 and T3 demonstrate better performance in the fields of continuous cropping and rotational cropping, respectively.

Key words:compound microbial agent;plant growth-promoting bacteria in the rhizosphere;rhizosphere microbial community;Gynostemma pentaphyllum