红壤丘陵区不同植被类型土壤颗粒分形与水分物理特征

Soil particle fractal dimension and soil moisture physical properties in different forest stands in hilly red soil region

为探明红壤丘陵区不同植被对土壤分形结构及水分物理特征的改良作用与机制,运用土壤分形学和水文物理学原理与方法,以南方红壤丘陵区福建省长汀县为例,研究经济林、针阔混交林、乔灌混交林及针叶林4种植被类型土壤颗粒组成、分形维数、水分物理参数及其相关性。结果表明:1)红壤丘陵区不同植被类型土壤中以粗砂粒质量含量最高,细砂粒和石砾质量含量次之,粉黏粒质量含量较低,与裸地相比,不同植被类型具有显著提高土壤细砂砾和粉黏粒质量含量的作用,并且混交林作用程度高于纯林;2)红壤丘陵区不同植被类型具有降低土壤密度、增加土壤孔隙度的功能,针阔混交林、乔灌混交林、针叶林、经济林土壤的饱和蓄水量分别是裸地的1.20、1.16、1.14和1.10倍,表土层(0～20 cm)贮水能力好于表下土层(20～40 cm);3)土壤颗粒分形维数与土壤粉黏粒、总孔隙度、饱和蓄水量、孔隙比呈极显著正相关,与石砾质量含量、土壤密度呈极显著负相关,红壤丘陵区4种植被类型土壤均为不均匀性良好的土壤,以混交林土壤粒径分布结构较好,尤其是以针阔混交林的最好,其次是纯林的,针叶林好于经济林,表土层(0～20 cm)大于20～40 cm土层。

Based on the theory of soil fractals and physical hydrology,we investigated soil particle size distribution（PSD）,fractal dimension,soil water physical parameters and related affecting factors of four typical vegetations in hilly red soil region of Changding County,Fujian Province.Our aims are to explore the improving effect and the mechanism of the forest vegetation to soil fractal structure and soil moisture physical property.The results indicated that： 1） in hilly red soil region,the mass fraction sequence of soil particles among all kinds of forests was given as follows： coarsefine sand and gravel particlessilt and clay.Forests could improve the contents of soil fine sand and silt and clay,compared with bare land,and the mixed forest has better improving effects than pure forest.2）Vegetation restoration could decrease the soil bulk density and increase soil porosity.The sequence of soil total porosity and capillary porosity was given as follows： conifer-broadleaf forest landarbor mixed with shrub landconifer forest landeconomic forest landbare land.The soil saturated water content of conifer-broadleaf forest land,arbor mixed with shrub land,conifer forest land,and economic forest land was 1.20,1.16,1.14,1.10 times higher than that of bare land,respectively.The capacity of soil water storage in 0-20 cm soil layer was larger than that in 20-40 cm soil layer.3）The sequence of soil fractal dimension was given as follows： conifer-broadleaf forest landarbor mixed with shrub landconifer forest landeconomic forest landbare land.Soil fractal dimension in 0-20 cm soil layer was larger than that in 20-40 cm.Fractal dimension had significantly positive correlation with soil silt and clay,total porosity,soil saturated water content and void ratio,and had negative correlation with the mass fraction of gravel,soil density.But there was no significant correlation with non-capillary porosity,non-capillary porosity water-holding content,and soil total absorption precipitation and effective precipitation.The soil of four typical forest stands were good structural soil with uneven coefficient in hilly red soil region.Mixed forest has better soil particle distribution,particularly,conifer-broadleaf forest soil.The improving effect of forest vegetation on soil fractal structure and soil moisture physical property was followed as this order： conifer-broadleaf forest landarbor mixed with shrub landconifer forest landeconomic forest land.The fractal geometry mechanism of improved soil fractal structure and soil moisture property with forest communities was to increase the soil fractal dimension by raising the content of fine-grained soil particles,thereby improving aggregate structure,pore structure,soil texture uniformity and soil moisture physical property.The results of this study could provide reference for scientific selection and distribution of water conservation vegetation types in hilly red soil region.