[Dynamics of CO and NO in Seasonal Frozen Soil Profiles for a Typical Steppe in Inner Mongolia].

In order to evaluate the effect of grazing on the mechanism for greenhouse gas emissions in the seasonal frozen soils for a typical steppe in Inner Mongolia, variations of NO and CO concentrations in different soil layers were monitored by an in situ gas collection system. Three conditions were selected:ungrazed since 1979 (UG79), ungrazed since 1999 (UG99), and continuously grazed (CG). The results showed that the profile soil NO and CO concentrations demonstrated a significant spatio-temporal distribution. ① The average concentrations of CO in the soil profile of the three conditions were:CO in the growth period > in the freezing-thawing period > in the freezing period. The CO concentrations in the growing period were much higher than in the freezing-thawing period and freezing period. The CO concentration was the highest in the UG79, and the lowest was in the CG. The concentration of CO in different soil layers was ordered as 20 cm ≥ 50 cm ≥ 35 cm ≥ 10 cm ≥ 5 cm at the UG79 and UG99 sites, and 50 cm ≥ 35 cm ≥ 20 cm ≥ 10 cm ≥ 5 cm at the CG site. ② The spatial and temporal variation of NO concentration in the soil profile was different from that of CO. While the UG79 and UG99 sites showed a "single peak type" change, the CG site had a "bimodal" pattern. The NO concentration of the three conditions increased sharply during the soil freezing-thawing period, and the NO was also released weakly during the growing season at the CG site (<0.05). The average NO concentration of the CG was significantly higher than that of UG79 and UG99 (<0.05). The results show that the concentration of NO in different soil layers was ordered as follows:UG79:20 cm ≥ 50 cm ≥ 35 cm ≥ 10 cm ≥ 5 cm; CG:50 cm ≥ 35 cm ≥ 20 cm ≥ 10 cm ≥ 5 cm, and UG99:35 cm ≥ 50 cm ≥ 20 cm ≥ 10 cm ≥ 5 cm. The results concluded that grazing decreased the profiled soil CO concentration and increased NO concentration, which provides a basis for the accurate estimation of greenhouse gas emissions in the seasonal frozen soil in grasslands.