[Forest soil organic matter delta 13C along a altitudinal transect on northern slope of Changbai Mountains under effects of simulated warming].

The litters, bulk soils, and soil particle-size fractions were sampled from three typical natural forests, i.e., broadleaf Korean pine (Pinus koraiensis) mixed forest (PB, altitude 740 m), spruce-fir (Picea asperata-Abies nephrolepis) forest (SF, altitude 1350 m), and Erman's birch (Betula ermanii) forest (EB, altitude 1996 m), on the northern slope of Changbai Mountains to analyze their organic matter delta13C values, and the intact soil cores (20 cm depth) from EB (high altitude) were relocated to PB and SF (low altitudes) for a year to study the responses of the delta13C values to simulated warming. It was shown that the litters had a significantly lower delta13C value than the soils, and the delta13C values of the litters and soils increased downward through the litter- and soil layers in all the three typical forest types. Soil particle-size fractions had an increased delta13C value with decreasing particle size fractions. The delta13C value of the litters was in the order of SF (-28.3 per thousand) >PB (-29.0 per thousand) >EB (-29.6 per thousand), while that of the soils was in the order of EB (-25.5 per thousand) >PB (-25.8 per thousand) >SF (-26.2 per thousand). Over one-year soil warming (an increment of 0.7 degrees C - 2.9 degrees C) , the delta13C values of the bulk soils and soil particle-size fractions all presented a decreasing trend, and the decrement of the delta13C value was larger in <2 microm (0.48 per thousand) and 2-63 microm fractions (0.47 per thousand) than in >63 microm fraction (0.33 per thousand). The results suggested that climate warming could have great effects on the older organic carbon associated with fine soil particle-size fractions.

[Dynamics of organic C in black soil of Northeast China, simulated by CENTURY model I. Accumulation of soil organic carbon under natural conditions].

By using CENTURY model, this paper simulated the dynamics of organic carbon and its fractions, including active, slow and passive pools, in black soils under natural condition at Nenjiang, Beian, Hailun and Harbin in Heilongjiang Province and at Gongzhuling in Jilin Province. The results showed that soil organic carbon had increased for a long time, and tended to reach the steady state. In the steady state, soil organic carbon reached 7914.72-11672.78 g x m(-2), which decreased from north to south in geperal. The active, slow and passive fractions were 3.36%-4.62%, 50.54%-55.47% and 36.47%-41.95% of soil organic carbon pool, respectively, which indicated that slow and passive fraction were the main body of soil organic carbon in native ecosystem. The simulated results were in agreement with some observed results, which can be used as the original data in the study on the dynamics of soil organic matter after cultivation.

[Comparison of soil organic matter models].

Soil organic matter is a soil carbon pool, and its content and dynamics is very important to global C cycling, soil fertility, and soil quality. SOM models can simulate soil organic matter dynamics and predict its content, especially for which some of data are difficult or impossible to obtain by experiential hypotheses and existing data. Therefore, SOM models have become the most important quantitative means to study SOM decomposition and accumulation, and can help us to identify the mechanism about SOM dynamics. SOM models can also predict CO2 emission and plant growth, and evaluate agricultural management practices. Several SOM models, especially RothC model and CENTURY model, were summarized and analyzed in this paper.