Seasonally driven microecological changes among endophytic and rhizospheric bacteria and their effects on the carbohydrate content of Codonopsis pilosula from Lintao County, Gansu Province, China

The active components of carbohydrates (including fructose and glucose) contained in Codonopsis pilosula have good immunomodulatory activity. Environmental factors, such as climatic conditions, soil fertility (including soil physicochemical properties and soil enzyme activity) and rhizosphere related microorganisms, play an important role in the accumulation of carbohydrate content in C. pilosula. However, few scholars have investigated how to enhance carbohydrate content accumulation at the cultivation level. In this study, we collected samples of plants and rhizospheric soil of C. pilosula from different seasons in one cycle under natural cultivation conditions to investigate the effects of seasonal changes in soil fertility (soil physicochemical properties and soil enzyme activity) and rhizosphere related microorganisms (endophytic and rhizospheric bacteria) on plant growth and carbohydrate accumulation. We first measured the plant indicators and the corresponding physicochemical properties and enzyme activities of the rhizospheric soil under different seasons, followed by high-throughput sequencing to determine the composition and community structure of endophytic and rhizospheric bacteria, and finally explored the key factors affecting the growth and carbohydrate accumulation of C. pilosula through bioinformatics analysis methods and the establishment of PLS-PM models. In general, rhizospheric bacteria were strongly affected by seasonal changes (path Pr < 0.05) and subsequently affected plant growth synergistically with endophytic bacteria (path Pr < 0.05). At the same time, soil physicochemical properties are jointly regulated by seasonal and rhizosphere related microorganisms and thus alter carbohydrate accumulation (path Pr < 0.05). Therefore, targeted induction of the planting environment and precise bacterial population management can provide the necessary basis for the acquisition of active ingredients within the C. pilosula.