Annual N 2 O emissions from conventionally grazed typical alpine grass meadows in the eastern Qinghai-Tibetan Plateau.

Annual nitrous oxide (N2 O) emissions from high-altitude alpine meadow grasslands have not been effectively characterized because of the scarcity of whole-year measurements. The authors performed a year-round measurement of N2 O fluxes from three conventionally grazed alpine meadows that represent the typical meadow landscape in the eastern Qinghai-Tibetan Plateau (QTP). The results showed that annual N2 O emissions averaged 0.123±0.053 (2SD, i.e., the double standard deviation indicating the 95% confidence interval) kgNha-1 yr-1 across the three meadow sites. N2 O flux pulses during the spring freezing-thawing period (FTP) were observed at only one site, indicating a large spatial variability in association with soil moisture differences. Approximately 34-57% (mean: 46%) of the annual N2 O emissions occurred in the non-growing season, highlighting the substantial importance of accurate flux observations during this period. The simultaneous observations showed conservative, marginal nitric oxide (NO) fluxes of 0.058±0.032 (2SD) kgNha-1 yr-1 . The N2 O fluxes across the three field sites correlated negatively with the soil nitrate concentrations during the entire year-round period (P<0.05). Furthermore, a significant joint regulatory effect of topsoil temperature and moisture on the N2 O and NO fluxes was observed during the relatively warm periods. Based on the results of the present and previous studies, a simple extrapolation roughly estimated the annual total N2 O emission from Chinese grasslands to be 73±15 (2SD) GgNyr-1 (1Gg=109 g). A linear dependence of the annual N2 O fluxes on the aboveground net primary productivity (ANPP) was also found. This result may provide a simple approach for estimating the N2 O emission inventories of frigid alpine or temperate grasslands that are ungrazed either in the summer or year round. However, further confirmation of this relationship with a wider ANPP range is still needed in the future studies.