Mechanisms Associated with Lower Methane Emissions from Paddy Soil by Aged Polylactic Acid Microplastics

Area of Science:

• Environmental Science
• Soil Science
• Biogeochemistry

Background:

• Microplastic (MP) contamination in paddy soils is a growing concern.
• MPs can influence methane (CH4) emissions, a potent greenhouse gas.
• Mechanisms underlying MP effects on CH4, especially aged MPs, are poorly understood.

Purpose of the Study:

• To investigate the impact of pristine and aged microplastics (polyethylene and polylactic acid) on CH4 emissions from paddy soils.
• To elucidate the mechanisms by which aged MPs influence CH4 production and oxidation.
• To quantify the role of MPs in the global carbon cycle and greenhouse gas emissions.

Main Methods:

• Microcosm experiment using paddy soil incubated with pristine and aged polyethylene (PE) and polylactic acid (PLA) MPs.
• Measurement of cumulative CH4 emissions over a 50-day incubation period.
• Analysis of microbial gene abundance related to methanogenesis and CH4 oxidation.

Main Results:

• Both pristine PE and PLA MPs inhibited CH4 emissions, with PLA being more effective.
• Aging increased the CH4 mitigation efficacy of PE but decreased that of PLA.
• Aged PE altered microbial gene abundance, reducing the methanogenesis to CH4 oxidation ratio.
• Aged PLA acted as an electron shuttle, competing for electrons and inhibiting methanogenesis.

Conclusions:

• Microplastic aging significantly influences CH4 emissions from paddy soils.
• Understanding these mechanisms is crucial for accurate greenhouse gas inventories and mitigation strategies.
• The study highlights the complex interactions between aged MPs, soil microbes, and carbon cycling.