Abstract
Nitric oxide (NO) is a highly reactive trace gas affecting atmospheric chemistry and air quality. Although forest soils have been recognized as an important source of atmospheric NO, there are large uncertainties in global forest soil NO emission inventories (ranged from 0.03 to 8.00 kg N ha−1, averaged 1.34 ± 0.28 kg N ha−1), partly due to the paucity of high-frequency monitoring from unmanaged forests. In this study, we used an automated sampling system to measure NO fluxes with a high temporal resolution over two years (daily measurements from January 2019 to December 2020) in a mixed forest in Northeast China. We found that the mean annual NO emission was 0.42 ± 0.04 kg N ha−1, being 31% of the global forest average. The contribution of NO emission during the growing season was 92% of the yearly NO flux. Soil temperature was the most important edaphic factor in regulating NO emission, explaining 90–92% of the seasonal variation. The apparent temperature sensitivity (Q10) of NO flux was 3.67. In the growing season, NO emission was also influenced by soil moisture, with optimum soil moisture of 37% WFPS. By providing a detailed measurement of diurnal, seasonal, and annual dynamics of NO emissions and their environmental controls from forest soils, our data are useful to develop more accurate biogeochemical models that will improve upscaled global NO budgets.
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