Diurnal and spatial variations of soil NOx fluxes in the northern steppe of China

Short-term effect of nitrogen addition on nitric oxide emissions from an alpine meadow in the Tibetan Plateau

Little information is available on nitric oxide (NO) fluxes from alpine ecosystems. We measured NO fluxes in control and nitrogen (N) addition (NH4NO3, 6 g N m(-2) year(-1)) plots from early June through October 2013 in an alpine meadow on the Tibetan Plateau, China. During the sample period, NO fluxes varied from -0.71 to 3.12 ug m(-2) h(-1) and -0.46 to 7.54 ug m(-2) h(-1) for control and N treatment plots. The mean NO emission in N addition plots (1.68 ug m(-2) h(-1)) was 2.15 times higher than the control plots (0.78 ug m(-2) h(-1)), indicating that alpine meadows may be a source of atmospheric NO, and N additions stimulated NO flux. A positive correlation was found between NO flux and soil temperature, water-filled pore space (WFPS), nitrate (NO3 (-)-N) content but no correlation with soil ammonium (NH4 (+)-N). These results suggest that denitrification is a principal process producing NO flux from alpine meadows.