不同林分类型对土壤团聚体稳定性及有机碳特征的影响

基于野外调查和室内分析,对人工杉木林、马尾松林、桉树林、毛竹林、天然林5种不同林分下0~20cm、20~40cm土层土壤水稳性团聚体稳定性及各粒级土壤团聚体有机碳分布特征进行研究。结果表明:1)0~20cm土层,土壤水稳性团聚体质量百分含量随粒级的减小先下降后上升,主要以0.5~0.25mm粒级最低;5种林分条件下各土层均以>0.25mm的大团聚体为主,随土层加深,大团聚体含量减少。2)各林分土壤平均质量直径(MWD)和几何平均直径(GMD)值变化趋势相似,均呈现为0~20cm土层大于20~40cm土层;林分间土壤MWD、GMD值则表现为天然林最大,桉树林最小;分形维数(D)在2个土层均以桉树最大,杉木林最小;3)5种林分各粒级团聚体中有机碳的含量均随土层的加深而减少;0~20cm土层,各林分有机碳含量随着团聚体粒级减小呈现先增大后减小再增大的趋势,最大值主要出现在5~2mm粒级,而有机碳贡献率则表现为先减小后增大的趋势。不同林分MWD、GMD差异分析结果表明,天然林土壤结构优于其他4种人工林,团聚体稳定性更高,而桉树林最低。随着土层深度变大,土壤水稳性团聚体稳定性下降;土壤团聚体有机碳含量表现为天然林最大、桉树林最小。 

Impact of different forest types on stability and organic carbon of soil aggregates

Based on the field survey and laboratory analysis, we studied the soil aggregates stability and soil organic carbon characteristics in two soil layers, i. e. , 0 -20 cm and 20 -40 cm, under five different forest types, namely Eucalyptus robusta, Pinus tabuliformis, Cunninghamia lanceolata, Phyllostachys heterocycla, and natural forestland. 1) In the 0-20 cm layer, the mass percentage of soil water stable aggregates under the five different forest types firstly decreased and then increased along with decreasing aggregate size, and particle size 0. 5 - 0. 25 mm had the lowest percentage. In both layers, soil aggregates were dominated by particle size >0. 25 mm, and the mass percentage of macro-aggregates decreased as the soil went deeper. 2) The mean weight diameter (MWD) and geometric mean diameter ( GMD) of soil in different forests had similar variation tendency: it was higher in the 0 -20 cm layer than that in the 20-40 cm layer. When comparing the MWD and GMD in the same layer, both of the factors were the highest in natural forestland, while the lowest in Eucalyptus robusta forest. However, the fractal dimension ( D ) of the soil in the Eucalyptus robusta forest was the highest, but lowest in the Cunninghamia lanceolata forest. 3) The content of organic carbon in soil aggregates of each particle size in five forest types decreased with increasing depth in soil and was distributed mainly in the grain size of 2-5 mm. In 0-20 cm soil layer, with decreasing particle size of soil aggregates, the content of organic carbon firstly increased, then decreased for the particle size of 5 -2 mm and finally increased, while contribution ratio of organic carbon firstly decreased, and increased finally. According to variance analysis of MWD and GMD of different forest types and soil layers, soil in natural forest had better structure and its soil water-stable aggregates had better stability than the other four types of plantations, while Eucalyptus robusta forest was the lowest. The stability of soil water-stable aggregate decreased with increasing depth in soil. The content of organic carbon in natural forest soil aggregates was the highest, while that in Eucalyptus robusta forest was the lowest.