Biodegradable Microplastics Increase Fungi-Mediated N2o Emission by Rapidly Releasing Dissolved Organic Matters

Abstract

Plastic pollution in paddy fields disrupts soil nitrogen biogeochemistry, prompting the introduction of biodegradable plastics like PBAT (poly (butylene adipate-co-terephthalate)) as a potential mitigation strategy. However, the effects of nonbiodegradable and biodegradable microplastics on the nitrogen cycle remain unclear. To clarify this, we conducted an incubation experiment, employing 15N isotopic tracing, N2O isotopocules, and molecular analysis to assess the impact of additives from PBAT and non-biodegradable (polyethylene, PE) microplastics. This study aimed to investigate their effects on N2O emission from bacterial, fungal, and chemical denitrification. The results showed that PE reduced N2O production potential from denitrification (DN2O) and bacterial denitrification (BDN2O), while PBAT increased DN2O and fungal-derived N2O (FDN2O) but decreased BDN2O. PE inhibited N2O production via bacterial denitrification due to the toxicity of plastic additives such as dibutyl phthalate and diethylhexyl phthalate. In contrast, PBAT enhanced N2O production via fungal pathways by facilitating the release of dissolved organic carbon. Bacterial denitrification accounted for 43-56% of total N2O production potential (DN2O) in PE treatments but only 28-50% in PBAT treatments. These findings highlight the short-term risks posed by biodegradable microplastics in elevating N2O emissions and reveal new dimensions of the influence of microplastics on greenhouse gas emissions from agricultural soils.

Keywords: N2O, PBAT, PE, Denitrification, plastic additives