缙云山4种森林植被土壤团聚体有机碳分布特征

以重庆市缙云山的竹林、阔叶林、针叶林和针阔叶混交林这4种亚热带森林植被为研究对象,分析不同林分下土壤团聚体及团聚体有机碳在0～20、20～40、40～60和60～100 cm土壤剖面上的分布规律.结果表明,阔叶林土壤 2 mm粒级团聚体含量、平均重量直径(MWD)、几何平均直径(GMD)及 0. 25 mm团聚体含量(R0. 25)均随土层深度的增加而降低,而其他林分在整个土层中则无明显规律.在各土层中,竹林以 2 mm粒级团聚体为主(30. 73%～53. 08%);阔叶林和混交林的2～0. 25 mm粒级团聚体含量较高,为36. 27%～44. 67%和48. 69%～52. 44%;针叶林的优势粒径为2～0. 25 mm和0. 053 mm.总体上,在各土层中,竹林团聚体的MWD、GMD、R0. 25值均高于其他林分,且其分形维数(D)低于其他林分,可见竹林的土壤团聚体稳定性较好.随着土层深度的增加,不同林分(除针叶林外)土壤团聚体有机碳含量逐渐降低,其中竹林团聚体有机碳含量最高,显著高于针叶林和混交林.就不同团聚体粒级而言,4种林分土壤团聚体有机碳在整个土壤剖面上无明显规律,但各土层均以2～0. 25 mm和0. 053 mm粒级团聚体有机碳含量较高.不同林分下土壤团聚体有机碳相对贡献率存在显著差异,其中针叶林中0. 053 mm粒级团聚体有机碳贡献率最高;竹林的 2 mm粒级团聚体有机碳贡献率高达27. 44%～53. 47%;而阔叶林和混交林则以2～0. 25 mm粒级团聚体有机碳贡献率最高.缙云山的4种林分中,竹林的土壤团聚体稳定性较好,而针叶林的较差;在各土层中,竹林土壤各粒级团聚体有机碳含量最高,针叶林最低.

Distribution of Organic Carbon in Soil Aggregates from Four Kinds of Forest Vegetation on Jinyun Mountain

This study was intended to explore the distribution and stability of soil aggregates and the organic carbon for different forest types and to provide a scientific basis for the efficient management of soil carbon pools in subtropical forest ecosystems. Four subtropical forest types, including bamboo forest, broad-leaf forest, coniferous forest, and a mixed coniferous and broad-leaf forest on Jinyun Mountain (Chongqing Municipality), were selected as research subjects to explore the distribution of soil aggregates and organic carbon in different layers (depths of 0-20, 20-40, 40-60, and 60-100 cm). The results showed:The content of >2 mm aggregates and mean weight diameter (MWD), geometric mean diameter (GMD), and >0.25 mm aggregate content (R_0.25) in broad-leaf forests decreased with soil depth, while other forests did not have a similar distribution pattern. In each soil layer, bamboo forest soils were mainly composed of >2 mm fractions of aggregates, which made up 30.73%-53.08% of the total content; The content of 2-0.25 mm particle size aggregates of broad-leaf and mixed forest soils was higher than that for other sizes, and its content ranged from 36.27% to 44.67% and 48.69% to 52.44%, respectively. The 2-0.25 mm and <0.053 mm fractions of aggregates dominated conifer soils. In general, the MWD, GMD, and R_0.25 of bamboo aggregates were higher than for other stands in each soil layer, and the fractal dimension (D) was lower than for other stands. This indicated that the soil aggregates of bamboo forest have better stability. As the soil layer deepened, the organic carbon content of soil aggregates in forest types, except for coniferous forest, gradually decreased. Among them all, bamboo forest aggregates had the highest organic carbon content, and this was significantly higher than that of coniferous forest and mixed forest. In the whole soil profile, as far as different aggregate size is concerned, there was no obvious regularity about organic carbon in the four forest types soil aggregates; the organic carbon content of the 2-0.25 mm and <0.053 mm fractions of aggregates was high in every soil layer. There was a significant difference in the relative contribution of organic carbon in soil aggregates for different forest stands, among these contributions, the contribution rate of organic carbon in the <0.053 mm fraction of aggregates in the coniferous forest was the highest. The organic carbon contribution rate of the >2 mm fraction of bamboo forest aggregates was as high as 27.44%-53.47%. Broad-leaf forests and mixed forests had the highest contribution to the organic carbon of the 2-0.25 mm fractions of soil aggregates. Among the four forest types on Jinyun Mountain, the soil aggregates in bamboo forest have better stability, but the stability of aggregates in coniferous forests is poor. In each soil layer, the content of bamboo forest organic carbon in the various aggregates was the highest, and that of coniferous forest was the lowest.