Component-specific oyster-mediated modular nitrous oxide turnover

As an important and rapidly developing agricultural industry worldwide, oyster aquaculture helps mitigate the coastal eutrophication by denitrification, a process which produces nitrous oxide (N₂O). Yet it is not presently possible to quantify the N₂O flux associated with oyster farming in transitional water bodies. Incubations using nitrate and nitrite as the substrates complemented with functional gene screening confirm net anaerobic N₂O production in oyster digestive tract. The N₂O production rate could be positively regulated by nitrate and nitrite availabilities and temperature. Surprisingly, oyster’s digestive tract is an unexpected N₂O source due to the inability of N₂O reduction to N₂. In comparison, the oyster shell-associated biofilm and attached particulate matter (APM) can perform complete denitrification, thus offsetting net N₂O production by digestive tract. Such a net N₂O consumption is more effective under lower oxygen condition. However, high availabilities of nitrite and nitrate in the water column may lower the N₂O sink capacity, even ceasing N₂O consumption. This study elucidates a modular N₂O turnover that is specific to the compartments inside and outside of oysters, providing insights into the environmental controls about dynamic N₂O source or sink associated with shellfish-microbe interactions.