Microplastics in the Rhizosphere: Consequences on Root Exudation and Microbial Communities

Introduction: Important agricultural crops can establish symbiotic relationships with microbial communities in the soil, forming mutually beneficial exchanges of nutrients. These root-soil-microbial interactions rely on naturally occurring soil properties which can be altered by microplastics. Plastic particles from biosolids added to soil as a nutrient source are potentially ecotoxic and may interfere with normal root functioning. The effects of biosolid microplastics on root-soil-microbial interactions is investigated on agricultural crops grown in soils amended with artificial microplastics that reflect reported biosolids microplastic properties. Methods: Agricultural crops (soybean, wheat, and alfalfa) were grown in soil amended with artificially created microplastics that reflect reported biosolid microplastic properties. Harvested rhizosphere soil samples were adjusted to 30% water holding capacity and incubated at 25C for MicroRESP analysis, or frozen to preserve root exudates. Root exudate samples were collected by centrifuge extraction method. Incubated soil for MicroRESP was added to deepwell plates, additionally 15 carbon substrates were added, and indicator plates stacked overtop with a seal for standard incubation. After incubation the change in the indicator plates at 572nm was recorded using Biotek Epoch 2 plate reader. Results: Preliminary analysis of the exudates revealed the ratio of sugars in exudates was 2.9:1.7:1 sucrose, glucose, fructose. Organic acids are still under analysis. Preliminary analysis of the MicroRESP samples has demonstrated a strong microbial respiration response to all added carbon substrates, with respiration rates up to 3x those of the control soil. Conclusion: Given the stage of the data analysis, no conclusions can be drawn at this time