Date of Award


Publication Type


Degree Name



Earth and Environmental Sciences


Microbial community;Microplastics;Rhizosphere;Root exudates


Cameron Proctor


Biosolids are semi-solid by-products from wastewater treatment plants where contaminants such as microplastics can accumulate, and transfer into the root zone causing ecotoxic effects to the rhizosphere microbial community. Furthermore, microplastics can alter soil properties which have a strong control on the size and diversity of the rhizosphere microbial community and its ability to consume root-borne carbon compounds. Using the MicroRESP system the respiration of the rhizosphere microbial community of soybeans subjected to microplastic biosolid mimics of two types (PET sheets and PPT beads) and two concentrations (2,000 vs 15,000 particles/kg dry soil) was quantified. Baseline respiration rates from extracted rhizosphere soil without amendment revealed no statistically significant differences (p< 0.05) between PET and PPT plastic types at similar concentrations, but microplastic concentration increased respiration rates ~20-34% relative to the control at 15,000 particles/kg dry soil. To investigate whether the rhizosphere microbial community adapted to a unique diet of root-borne carbon, respiration rates were measured using substrate induced respiration using 15 common root exudates. Principal component analysis was conducted to determine if unique patterns of carbon utilization occurred. The loadings in the first principal component were similar (average -0.257, standard deviation 0.016) and the broken stick method suggested only the first principal component was significant. Hence, the average of all exudates was determined and statistical significant differences were detected (ANOVA p< 0.05) with concentration, plastic type and biosolid treatments statistically significant compared to the control (Tukey HSD p< 0.05) with the only exception the PET low treatment.