BayCEER Workshop 2025

Tracing the fate of Carbon: Using ¹³C-labeled litter to disentangle microplastic effects on Soil Organic Matter decomposition

P 11 in Posters

The increasing soil contamination with microplastics (MPs) raises concerns about their impact on fundamental soil processes, particularly the decomposition of soil organic matter (SOM). While MPs can alter soil microbial communities and chemistry, directly quantifying their effect on native SOM decomposition is challenging due to methodological limitations. This study employs an innovative isotopic tracing approach to precisely partition the mineralization of MP polymers from the potential destabilization of SOM in a plant-soil system.

A soil microcosm experiment was conducted, including the factors of plant presence/absence and MP addition (four types: biodegradable PBAT, PLA, conventional PE, and PET, with a no-MP control). All treatments received a dosage of 0.5% (w/w) of 50–200 µm MPs. To precisely track SOM-derived carbon, a trace amount of ¹³C-labeled plant litter was added to each microcosm, mimicking the natural input of fresh organic matter without overwhelming the system.

The total and ¹³C-labeled CO₂ fluxes were monitored throughout the incubation. This allowed for the direct quantification of the mineralization of the MP and the priming effect, i.e., the MP-induced destabilization of SOM. Additional analyses included soil chemistry and microbial community structure via 16S DNA amplicon sequencing.

We hypothesize that biodegradable MPs will exhibit a higher mineralization rate than conventional MPs. Furthermore, we predict that certain MP types, especially biodegradable ones, will induce a stronger positive priming effect, leading to increased loss of native SOM. The presence of plants is expected to modulate these effects by altering the soil microbial community and carbon dynamics.

This experiment will provide a mechanistic understanding of how different MP types influence soil carbon cycling and novel insights into the potential risks of MP pollution for soil carbon storage and ecosystem functioning.

Keywords: Microplastics (MPs), Soil Organic Matter (SOM), Priming Effect, Carbon Cycling