Date of Completion

Spring 5-11-2023

Project Advisor(s)

Daniel Gage, Jonathan Klassen, Robert Bagchi

University Scholar Major

Biological Sciences


Agricultural Science | Biodiversity | Bioinformatics | Environmental Microbiology and Microbial Ecology | Genetics | Population Biology


Protists are known to increase plant growth through two main mechanisms: the microbial loop and the alteration of the root microbiome. The microbial loop is a nutrient recycling method in which protists provide inorganic nitrogen ions to the plant. Alteration of root microbiome leads to the removal of plant pathogens and shifting communities towards plant growth-promoting bacteria (PGPB). This study aimed to elicit which mechanism could produce the largest boost in shoot weight for Medicago truncatula. A series of microcosm experiments were explored in which M. truncatula was grown with variable microbiome structures to allow for mechanism differentiation. The resulting shoot weights showed no difference between treatment groups. The failure to observe the differences between mechanisms was likely due to the bacteria in the inoculum not being able to proliferate in the sandy soils in which M. truncatula was planted. As a result, the growth promotion mechanisms were not able to occur as they both require bacterial presence. Additionally, Cercomonas was observed to increase shoot weight with nitrogen fertilizer application in a protist-only growth experiment. Future directions include repeating the experiment in a more native soil conformation and conducting 15N tracing experiments with fertilizer to determine if Cercomonas enhances fertilizer uptake.