Insights into the deriving of rhizosphere microenvironments and its effects on the growth of authentic Angelica sinensis seedlings under continuous monoculture

Abstract

Purpose: Continuous monoculture leads to deterioration of soil microenvironment, which can severely threat the quality and efficiency of Angelica sinensis (A. sinensis), especially for seedlings production. However, little attention has been paid to investigate how continuous monocropping affects the growth of A. sinensis seedling, rhizosphere microbial populations, and nutrient status. Methods: A field experiment consisting of two different planting patterns - raising A. sinensis seedlings in reclamation alpine uncultivated meadow (RW) and 1-year continuous monoculture (CC), was carried out at Min County, Gansu province, China. Result: The results showed that compared with RW, the growth rate and valid quantity of A. sinensis seedlings were significantly reduced by 195.4 % and 36.7% in CC, respectively. Continuous monocropping significantly increased the rhizosphere soil pH value during the growing season, ranging from 6.18 to 7.10, while reducing the content of SOM, total N, available P and K. Glomalin, AMF spores and the number of actinomycetes, ammonifying and azotobacter were also decreased by CC. The CC treatment significantly increased the abundance of fungi. And the diversity and richness of bacterial and fungal flora in CC were lower than RW. Furthermore, the composition and structure of flora also changed that the abundance of beneficial bacteria and decreased fungi while the abundance of pathogenic bacteria and pathogens increased in CC. Thus, CC appeared to completely upend the relationship between soil nutrient availability and microbial activity. Conclusion: The results illustrated that continuous monoculture led to changes in the flora of bacteria and fungi, decreased the abundance of beneficial bacteria, and increased the abundance of harmful pathogenic bacteria and pathogens. The function of microbial population has changed from "bacteria-dominated" to "fungi-dominant". We concluded that continuous monoculture significantly reduced the growth and the efficiency of A. sinensis seedlings, deteriorated the rhizosphere soil microenvironment by increasing pH and decreasing nutrient availability, as well as altering the function of interactions between soil nutrients and microbial populations, thereby resulting in an unsuitable microenvironment for A. sinensis seedlings growth.