Microplastic fibers affect dynamics and intensity of CO2 and N2O fluxes from soil differently

Abstract

Microplastics may affect soil ecosystem functioning in critical ways, with previously documented effects including changes in soil structure and water dynamics; this suggests that microbial populations and the processes they mediate could also be affected. Given the importance for global carbon and nitrogen cycle and greenhouse warming potential, we here experimentally examined potential effects of plastic microfiber additions on CO2 and N2O greenhouse gas fluxes. We carried out a fully factorial laboratory experiment with the factors presence of microplastic fibers (0.4% w/w) and addition of urea fertilizer (100 mg N kg− 1) using one target soil. The conditions in an intensively N-fertilized arable soil were simulated by adding biogas digestate at the beginning of the incubation to all samples. We continuously monitored CO2 and N2O emissions from soil before and after urea application using a custom-built flow-through steady-state system, and we assessed soil properties, including soil structure. Microplastics affected soil properties, notably increasing soil aggregate water-stability and pneumatic conductivity, and caused changes in the dynamics and overall level of emission of both gases, but in opposite directions: overall fluxes of CO2 were increased by microplastic presence, whereas N2O emission were decreased, a pattern that was intensified following urea addition. This divergent response is explained by effects of microplastic on soil structure, with the increased air permeability likely improving O2 supply: this will have stimulated CO2 production, since mineralization benefits from better aeration. Increased O2 would at the same time have inhibited denitrification, a process contributing to N2O emissions, thus likely explaining the decrease in the latter. Our results clearly suggest that microplastic consequences for greenhouse gas emissions should become an integral part of future impact assessments, and that to understand such responses, soil structure should be assessed.

Impacts of Plastic Pollution on Ecosystem Services, Sustainable Development Goals, and Need to Focus on Circular Economy and Policy Interventions

“…MPs also reduce N 2 O emissions during extensive nitrogen fertilization. The effects of MPs on GHGs emissions should be considered in future impact evaluations, and the soil structure should be examined to better understand such impacts [159,160]. Furthermore, chemically changing processes will not eliminate the enormous amount of emissions produced, despite the possibility that the development of renewable energy-based polymeric materials could reduce GHG emissions from production units [138].…”

Micro and nanoplastics ravaging our agroecosystem: A review of occurrence, fate, ecological impacts, detection, remediation, and prospects

“…Several studies have shown that MNPs influence greenhouse gas emissions [ 94 , 159 , 160 ]. There is a need to properly understand the processes responsible for this phenomenon.…”

Interplay of plastic pollution with algae and plants: hidden danger or a blessing?

“…Microplastics could therefore favour the substrate suitable for the proliferation of these bacteria with increased production of N 2 O and CO 2 caused by their nitrifying and carbon crystallizing activity, respectively. The consequences would also lead to changes in the pH of the water as well as the release of greenhouse gases (Rillig et al, 2021).…”