[Soil net nitrogen mineralization in the typical temperate grassland].

Soil net nitrogen mineralization rate of three types temperate grassland in Inner Mongolia, China was studied using the resin-core technique. The major results include: the net nitrogen mineralization rate of the Stipa baicalensis meadow grassland, the Aneulolepidum Chinense grassland and the Stipa krylovii grassland were 0.333 kg x (hm2 x d)(-1), 0.316 kg x (hm2 x d)(-1) and 0.211 kg x (hm2 x d)(-1) respectively during the field incubation period of July to October, 2005; Soil net nitrogen mineralization accumulation and rates was remarkably different between phase incubation and continuous incubation during the same field incubation period; Rainfall was one of the main factors affecting nitrogen mineralization. The net nitrogen mineralization rate was correlated with the change of soil moisture in all of the measured sites, the correlation coefficient was 0.80, 0.61 and 0.56.

Emission characteristics of carbon dioxide in the semiarid Stipa grandis steppe in Inner Mongolia, China.

Using the static opaque chamber method, the soil respiration rates (SR) were measured through the continuous experiments in situ in semiarid Stipa grandis steppe in Xilin River Basin of Inner Mongolia, China from June 2001 to June 2003, in parallel, the difference between the SR and the ecosystem respiration rates (TER) were compared. The results indicated that the seasonal variations of the SR and TER were obvious with higher emissions in growing season and a relatively low efflux level in non-growing season, furthermore, the negative effluxes were found in the observation site in winter; the annual CO2 efflux of total ecosystem ranged from 160.5 gC/(m2 x a) to 162.8 gC/(m2 x a) and that of soil ranged from 118.7 gC/(m2 x a) to 152.3 gC/(m2 x a). The annual SR accounted for about 74.0% to 93.5% of the annual TER, but the results of Analysis of Variance (ANOVA) indicated that the difference between the annual average TER and SR did not reach the significance level of 0.05. The TER was under similar environmental controls as SR, in growing seasons of drought years, the variations of soil moisture at 0-10 cm and 10-20 cm depth could account for 79.1%-95.6% of the changes of the SR and TER, but in non-growing season, more than 75% of the variations of the SR and TER could be explained by the changes of the ground temperature of soil surface layers.