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[Changes of soil aggregate size composition and organic carbon content at different succession stages of broad-leaved Korean pine forest in Changbai Mountain, China.]

The broad-leaved Korean pine forest is an important primary forest in Northeast China. Soil aggregates play important role in carbon fixation of forest ecosystem. Temporal-spatial substitution method was used in this study. We selected five forests with different succession stages: birch young forest, birch middle forest, birch mature forest, mature broad-leaved Korean pine fore-st, and over-mature broadleaved Korean pine forest. The distribution of soil aggregate particle size and agglomeration in organic carbon under different forests were investigated by wet sieving method. The results showed that soil aggregate size distributions and the proportions of soil aggregates were significantly different among succession stages. The mean mass diameter of aggregates was generally showed a unimodal trend along with the succession stages, peaking at birch mature forest stage. The organic carbon content in the aggregate of different particle-sizes in the soil increased firstly and then decreased slightly from early to late succession, and the maximum content of organic carbon in the aggregate was in broad-leaved Korean pine mature forest stage. Under the same succession stage, the content of organic carbon in the aggregate of different particle-sizes increased with the decreases of the particle size in the soil depth of 0 to 5 cm and 5 to 10 cm (except over-mature broad-leaved Korean pine forest at the end of succession), but it was the opposite in the soil depth of 10 to 20 cm. From the birch young forest at the early stage of succession to the over-mature broad-leaved Korean pine forest at the end of succession, organic carbon content in the aggregate of same particle-size had obvious vertical distribution characteristics, which significantly decreased with the increases of soil depth.