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Microplastic fibers affect dynamics and intensity of CO 2 and N 2 O fluxes from soil differently
Summary
Researchers conducted controlled experiments adding microplastic fibers to soil and measuring effects on carbon dioxide and nitrous oxide gas fluxes. The study found that microplastic fibers altered greenhouse gas emissions from soil differently for CO2 versus N2O, suggesting microplastics can disrupt soil biogeochemical cycling.
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 CO 2 and N 2 O 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 ). 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 CO 2 and N 2 O 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 CO 2 were increased by microplastic presence, whereas N 2 O 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 O 2 supply: this will have stimulated CO 2 production, since mineralization benefits from better aeration. Increased O 2 would at the same time have inhibited denitrification, a process contributing to N 2 O 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.