<p>Denitrification-dependent anaerobic methane oxidation (N-DAMO) microorganisms can reduce methane emissions from sediment, but there are few reports on the effects of biodegradable plastics on such microorganisms. In this study, a large water column reactor was constructed indoors to simulate the environment of a shallow lake so as to explore the long-term effects of two biodegradable plastics including PLA (polylactic acid) and PBAT (poly (butylene adipate-co-terephthalate)) on two microorganisms ANME-2d archaea and NC10 bacteria. The abundance of NC10 and ANME-2d microorganisms was significantly higher in the biodegradable plastic group than in the control group at day 90 and day 365 post exposure, respectively. Among three groups (control, PLA, and PBAT), the abundance of these two microorganisms in the PLA group was the highest at day 365, which was 3.43 × 10⁷ copies/g sediment for NC10 and 2.63 × 10⁷ copies/g sediment for ANME-2d, respectively. At day 90, potential release of CH₄ from sediment was significantly lower in two biodegradable plastic groups than in CK group. At day 365, potential release of N₂O in biodegradable plastics groups were also significantly lower than that in CK group, which was 0.0866 ± 0.0057mg/kg sediment (for PLA) and 0.00502 ± 0.0002 mg/kg sediment (for PBAT), respectively. The research results indicated that biodegradable plastics altered the abundance and diversity of N-DAMO microorganisms by releasing carbon/nitrogen contained organic matter, exhibiting different effects on greenhouse gas emission reduction at different time scales under seasonal variation disturbances. Our findings provide new insights into the impact of biodegradable microplastics on N–N-DAMO microorganisms.</p>