Influence of Two Root Media and Three Vermicompost Amendments on Bacterial Communities in a Greenhouse Container Garden Model System.

The aim of this study was to determine the impact of two root media and three vermicompost amendments on the root zone bacterial communities and harvest mass of lettuce grown in a greenhouse container garden model system. Lettuce seeds were planted in seven root media/amendment conditions. Lettuce was later harvested, and root media DNA was extracted for 16S rRNA sequencing to determine the composition of, as well as the alpha and beta diversity of, the bacterial communities. Fresh weight, dry weight, and percentage dry weight of lettuce were calculated under each treatment. Results indicate that the peat-lite growth media without any additions had the lowest rhizosphere bacterial alpha diversity compared to the other six growth media. Bacterial communities from containers with peat-lite media were significantly different than those from containers with compost-based media as measured by beta diversity. Moreover, the compost-based medium with vermicompost condition tended to result in a higher percentage dry weight lettuce than lettuce grown under the peat-lite condition. The peat-lite treatment condition had the numerically lowest dry weight (%) and bacterial diversity. Addition of vermicompost amendments had varying impacts on bacterial diversity, bacterial community composition, and harvest mass. Overall, this experiment establishes a protocol which can be applied for further understanding of the impact of root media type and vermicompost amendments on rhizosphere bacterial diversity and harvest mass.