[Effects of land use type and incubation temperature on soil nitrogen transformation and greenhouse gas emission].

A laboratory experiment with the soil samples collected from China and Canada was conducted to study the effects of land use type (forestland vs. grassland) and incubation temperature (10 degrees C vs. 15 degrees C) on the soil nitrification, nitrogen mineralization, and N2O and CO2 emissions under aerobic condition. As compared with forestland soils, grassland soils had higher nitrification rate and N2O emission, with the highest nitrification rate in China grassland soil. At 10 and 15 degrees C, the average net nitrification rate of China grassland soil was 2.10 and 2.86 mg N x kg(-1) x d(-1) and the cumulative N2O emission in 15 incubation days was 10.2 and 15.4 microg N2O-N x kg(-1), respectively. Soil pH was the main factor affecting the nitrification rate and N2O emission, and there existed significant positive correlations between the soil pH and the nitrification rate and N2O emission. Forestland soils had higher nitrogen mineralization rate and CO2 emission than grassland soils, and China forestland soil had the highest nitrogen mineralization rate, with the average net mineralization rate at 10 and 15 degrees C being 3.08 and 2.87 mg N x kg(-1) x d(-1), respectively. The CO2 emission was the highest in Canada forestland soil, and the cumulative CO2 emission in 15 incubation days at 10 and 15 degrees C was 314 and 370 mg CO2-C x kg(-1), respectively. The soil organic carbon and soluble organic carbon contents had significant positive correlations with the soil nitrogen mineralization rate and CO2 emission, respectively, whereas the increasing soil temperature promoted the nitrification in grassland soils and the N2O emission from forestland soils and grassland soils. The same pronounced effects of increasing temperature were also found on the CO2 emission from forestland soils.