Microbial-mediated transformation shapes the molecular diversity of landfill leachate under anthropogenic and natural covariation

Extensive landfill leachate from human activities is one of the most intractable liquid waste due to the presence of stubborn leachate dissolved organic matter (LDOM) and various pollutants. However, critical driving forces regarding LDOM complexity are still unclear. This study explores relationships between LDOM chemical composition, microbial community, anthropogenic factors and climate conditions based on national-scale landfill leachates in China. The results indicate that although landfill wastes originate from human emissions, microbes dominate molecular composition diversity of LDOM, followed by climate. To further elucidate the interlink between LDOM diversity and microbial communities, a two-stage network framework is established: first constructing molecular transformation networks to clarify humification and mineralization of LDOM, succeeded by building an interaction network that links definable reactions to microbial communities. Network analyses reveal that microorganisms promote accumulation of recalcitrant components in LDOM, weakening human-induced differences. Amino acid metabolism was particularly prominent in microbial-mediated transformation of LDOM, and the potential keystone microbial species are identified. This study deepens the understanding of the evolution of organic matters in landfills, also provides a new paradigm for exploring microbial mediated molecular transformation of DOM in both artificial and natural waters.