Dissolved organic matter derived from long-term photodegradation of plastics alters microbial methane conversion in mangrove sediments.

Highly enriched plastic debris leads to an increase in dissolved organic matter derived from the degradation of plastics (PDOM), which potentially influences the stability of methane (CH4) emissions of microorganisms in mangrove sediments. Here, microcosm incubation was conducted to reveal the impacts of two PDOM on CH4 emissions from mangrove sediments. CH4 emissions from PDOM treated sediments were reduced by 0.03-0.11 ppm within 30 days. The reduction in CH4 emissions was attributed mainly to alterations in sediment properties and bacterial communities. Phosphorus-containing lignin and proteins were the key molecular components that induce the decrease in the abundance of functional genes in the CO2 to methane pathway. The influence of PDOM on CH4 emissions may be associated with bacterial fermentation and the degradation pathways of aromatic compounds. This study enhances the understanding of the impact of PDOM on carbon cycling in mangrove ecosystems.