Nitrification Regulates the Spatiotemporal Variability of N 2 O Emissions in a Eutrophic Lake.

Nitrous oxide (N 2 O) emissions from lakes exhibit significant spatiotemporal heterogeneity, and quantitative identification of the different N 2 O production processes is greatly limited, causing the role of nitrification to be undervalued or ignored in models of a lake's N 2 O emissions. Here, the contributions of nitrification and denitrification to N 2 O production were quantitatively assessed in the eutrophic Lake Taihu using molecular biology and isotope mapping techniques. The N 2 O fluxes ranged from -41.48 to 28.84 μmol m -2 d -1 in the lake, with lower N 2 O concentrations being observed in spring and summer and significantly higher N 2 O emissions being observed in autumn and winter. The 15 N site preference and relevant isotopic evidence demonstrated that denitrification contributed approximately 90% of the lake's gross N 2 O production during summer and autumn, 27-83% of which was simultaneously eliminated via N 2 O reduction. Surprisingly, nitrification seemed to act as a key process promoting N 2 O production and contributing to the lake as a source of N 2 O emissions. A combination of N 2 O isotopocule-based approaches and molecular techniques can be used to determine the precise characteristics of microbial N 2 O production and consumption in eutrophic lakes. The results of this study provide a basis for accurately assessing N 2 O emissions from lakes at the regional and global scales.