soil bacterial community after stevia cultivation in 2 years continuous cropping and 8 years continuous cropping

Stevia rebaudiana Bertoni is grown worldwide as an important, natural sweetener source plant. The yield of steviol glycosides (SVglys) extracted from stevia is greatly influenced by continuous cropping. In this study, we collected roots, rhizosphere soils and bulk soils from 2 years continuous cropping (Y2) and 8 years continuous cropping (Y8). The results demonstrated that although the content of a group of SVglys were significantly increased in stevia of longer continuous cropping, it inhibited the growth of plants and lowered the leaf dry weight; as a result, the total amount of SVglys was significantly decreased. Meanwhile, continuous stevia cropping changed the physicochemical properties of soil and the composition of soil bacterial communities. The different sampling sources of root, rhizosphere soil and bulk soil had no impact on the richness of bacterial communities, while it exhibited obvious effects on the diversity of bacterial communities. Continuous cropping had a stronger effect on bacteria community composition in rhizosphere soil than in root and bulk soil. Based on LEfSe analysis, in the rhizosphere soil of Y8, the relative abundance of some beneficial bacterial genera of Sphingomonas, Devosia, Streptomyces and Flavobacterium decreased significantly, while the relative abundance of some harmful bacterial genera of Polycyclovorans, Haliangium and Nitrospira greatly increased. Moreover, the soil pH and nutrient content, especially the soil organic matter (OM), were correlated with the relative abundance of predominant bacteria at the genus level. The findings of this study provide a theoretical basis for uncovering the mechanism of obstacles in continuous stevia cropping and provide better guidance for sustainable development of the stevia.