Abstract:

The black soil samples from three different land use types in the Songnen Plain were incubated for 90 days in the laboratory. It was found that after reaching a maximum value at the initial stage, the rates of soil respiration declined continuously and then stabilized. At the four different temperature conditions(5 ℃, 15 ℃, 25 ℃ and 35 ℃), the rates of soil respiration simultaneously increased with increasing temperatures. At the same temperature conditions, intensity sequence of soil respiration rates of the different samples was as followed: black soil from the paddy field>black soil from the grassland>black soil from the dry land. The values of temperature sensitivity coefficient Q10 of soil respiration decreased with increasing temperatures, which means that the feedback of soil organic carbon to the climate warming would be more sensitive at the colder regions. Soil respiration dynamics was fitted with the firstorder kinetic equation. It was showed that among the three types of black soils, black soil from the paddy field had the highest content of active organic carbon, followed by that from the dry land and then that from the grassland; as to the proportion of active organic carbon to total organic carbon, black soil from the grassland was the highest, followed by that from the dry land and then that from the paddy field. Light fraction and heavy fraction of organic carbon in the samples were divided by the density separation, and it was found that more than 95% of total organic carbon in the samples was in the form of heavy fraction, which was much higher than the amount  of light fraction. The result from the density separation coincides with that from the model fitting, and the proportion of light fraction (active carbon) to total organic carbon was arranged as followed: black soil from the grassland>black soil from dry land>black soil from paddy field, while that of heavy fraction (slow carbon) was the opposite.

Key words: Songnen Plain, black soil, soil respiration, temperature sensitivity coefficient, active organic carbon