Nitrification Regulates the Spatiotemporal Variability of NO Emissions in a Eutrophic Lake.

Nitrous oxide (NO) emissions from lakes exhibit significant spatiotemporal heterogeneity, and quantitative identification of the different NO production processes is greatly limited, causing the role of nitrification to be undervalued or ignored in models of a lake's NO emissions. Here, the contributions of nitrification and denitrification to NO production were quantitatively assessed in the eutrophic Lake Taihu using molecular biology and isotope mapping techniques. The NO fluxes ranged from -41.48 to 28.84 μmol m d in the lake, with lower NO concentrations being observed in spring and summer and significantly higher NO emissions being observed in autumn and winter. The N site preference and relevant isotopic evidence demonstrated that denitrification contributed approximately 90% of the lake's gross NO production during summer and autumn, 27-83% of which was simultaneously eliminated via NO reduction. Surprisingly, nitrification seemed to act as a key process promoting NO production and contributing to the lake as a source of NO emissions. A combination of NO isotopocule-based approaches and molecular techniques can be used to determine the precise characteristics of microbial NO production and consumption in eutrophic lakes. The results of this study provide a basis for accurately assessing NO emissions from lakes at the regional and global scales.