Trophic status strongly regulates nitrous oxide but not methane production in global freshwater lake sediments

Freshwater lakes are globally significant sources of potent greenhouse gases (GHGs), but how their GHGs emissions respond to changing nutrient levels remains unclear. Here, we demonstrated that nitrous oxide (N₂O) production pathways in lake sediments are tightly linked to trophic state, whereas methane (CH₄) production appears to be multifactorial Through global metagenomics and controlled batch experiments. In eutrophic sediments, N₂O is efficiently removed through complete denitrification, with nitrification serving as the main production pathway, whereas oligotrophic sediments produce N₂O primarily via incomplete denitrification. By simulating nutrient transitions using an innovative cross-inoculation experiment, we further revealed that lake sediments systematically shift between these N₂O production pathways as their trophic state changes, from denitrification-driven to nitrification-dominated during eutrophication, with the inverse pattern during oligotrophication. Consequently, N₂O emissions can be effectively mitigated by inhibiting nitrification in eutrophic lakes and restricting incomplete denitrification in oligotrophic ones. Our findings establish trophic status as a key driver of N₂O production sources in lake sediments.