Diurnal, seasonal, and inter-annual variations of N2O fluxes from native semi-arid grassland soils of inner Mongolia

In order to investigate the diurnal, seasonal, and inter-annual variations of nitrous oxide (N2O) flux and associated microbiological mechanisms, in situ measurements of N2O Flux from unfertilized, ungrazed, and unirrigated semi-arid grassland soils in Inner Mongolia, northeast China were undertaken using a closed chamber technique from 1995 to 2003. In addition, laboratory experiments were carried out using the acetylene inhibition method (AIM) in 1998 and 2001. The results showed no significant linear relationship between soil moisture and diurnal N2O flux, or between N2O flux and temperature (i.e., temperature at 0–15 cm depth, temperature of surface soil, and temperature of inner chamber air). However, the results showed a significant influence of growing season on diurnal variations of N2O flux. N2O efflux was usually high in spring or summer, and low in winter. The mean total annual N2O fluxes was 0.73±0.52 kg N2O-N ha−1 yr−1, with a coefficient of variation of annual N2O flux of 71.6%. Based on our estimates from 5 yr of data, the total N2O emission from all of the temperate grassland soils of China was approximately 0.21 Tg N2O-N yr−1, which was about 21% of the total global flux from temperate grassland soils. It was the distribution of effective rainfall, rather than precipitation intensity, that influenced seasonal and inter-annual variations of N2O flux. Our laboratory incubation study revealed that heterotrophic nitrification was the principal source of N2O in the studied soils.