Organic matter (OM) is a critical factor which regulates nitrogen loss pathways of denitrification and anammox for microbes in marine ecosystems.

Recently, a research team led by Prof. SONG Jinming from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has revealed the impact of organic matter on the nitrogen loss rate of muddy and sandy sediments in the East China Sea coastal shelf, which provides new insights into the pathways and mechanisms of sediment nitrogen loss.

The study was published in Science of The Total Environment on Sept. 14.

In this study, the researchers analyzed the interaction between nitrogen loss and organic matter at the molecular level. They found that organic-rich muddy sediments showed higher nitrogen loss relative to sandy sediments. In muddy sediments, anammox-specific biomarkers of ladderane lipids were significantly greater than in sandy sediments. Simultaneously, the increase of total organic carbon content enchanted the abundance of anammox functional gene hzsB (subunit B-containing hydrazine synthase) and denitrification functional gene nosZ (nitrous oxide reductase).

Furthermore, the anammox rate and the denitrification rate were positively correlated, indicating a coupled relationship between denitrification and anammox. Organic matter in sediments can serve as a carbon source for heterotrophic denitrifying nitrogen loss, and its decomposition provides substrates for autotrophic anammox reactions.

"Conducting research on denitrification and anammox in muddy and sandy sediments can effectively reveal the crucial environmental factors that control the loss of nitrogen in coastal areas and their impact mechanisms, and provide essential empirical support for maintaining the health of offshore ecological environment," said LAI Xiaoshuang, first author of the study.

"This study is the first to combine the biomarkers ladderane lipids with microbial functional genes to elucidate the nitrogen removal rate of muddy and sandy sediments, providing a method to more effectively understand and predict the nitrogen cycle of sediments in coastal marine ecosystems," said Prof. SONG.