贝壳堤岛3种植被类型的土壤颗粒分形及水分生态特征

运用土壤粒径质量分布原理与分形学理论，以黄河三角洲贝壳堤岛的3种植被类型为研究对象，以裸地为对照，测定分析土壤颗粒分形维数、粒径组成和水分物理参数，探讨不同植被类型的土壤颗粒分形特征及其影响因素。结果表明：贝壳砂土壤中粗砂粒含量最高；其次是细砂粒，而石砾和粉粘粒含量较低。灌木林地和草地具有降低石砾、粗砂粒，增加细砂粒和粉粘粒含量的作用。不同植被类型土壤颗粒分形维数均值在1.5845－1.9157之间，大小依次为酸枣林、杠柳林和草地，表层高于20－40cm土层。酸枣林、杠柳林及草地0－40cm土壤容重均值分别比裸地低23.87%，14.51%和10.47%；总孔隙度均值分别比裸地增加16.96%，16.71%和1.31%。植被恢复措施对贝壳砂表层的孔隙结构、疏松程度改善较好，草地及灌木林地的蓄水性能均表现为0－20cm高于20－40cm。土壤颗粒分形维数与粉粘粒含量、毛管孔隙度、总孔隙度、饱和蓄水量、吸持蓄水量等呈极显著正相关，与细砂粒含量呈显著正相关，与粗砂粒含量和容重呈极显著负相关，与石砾含量、非毛管孔隙度、滞留蓄水量的相关性不大。从土壤分形维数及其水分生态特征来看，贝壳堤岛3种植被类型的改良土壤物理性质及蓄水保土功能表现为灌木林好于草地，其中酸枣林好于杠柳林，0－20cm好于20－40cm土层。

Water ecology and fractal characteristics of soil particle size distribution of three typical vegetations in Shell Island

Little information is available about soil particle-size distribution in shell ridge ecosystems. Based on the principle of quality distribution of soil particle size and fractal theory, Periploca sepium Bunge, Ziziphus jujuba var. spinosa Hu and Messerschmidia sibirica Linn. growing on Shell Island, located on the Yellow River Delta, were analyzed in contrast with bare soil to determine the fractal dimensions of soil particles, soil particle-size distribution and soil water physical characteristics, in order to explore the effects of different vegetation types on soil pore structure and hydrological physical characteristics, and the effect of fractal mechanisms of different vegetation types on soil particle composition in shell sand habitats. The results showed that: 1) In shell sand soil, the distribution of soil particles among three typical vegetations was as follows: coarse sand, fine sand, gravel and silt-clay. And the mean value of coarse, fine sand, gravel and silt-clay was 61.31%, 19.97%, 17.33%, 1.39%, respectively, indicating that grassland and shrub could decrease the particle content of gravel and coarse sand, and improve the content of soil fine sand and silt-clay, which performed well in 0-20cm soil layer. With the vegetation restoration measures, the mean value of fractal dimension of shell sand varied from 1.5845 to 1.9157. The sequence of fractal dimension was as follows: Z. jujuba var. spinosa Hu, P. sepium Bunge and Grassland, and the surface soil layer was larger than that in 20-40cm soil layer. Fractal dimension had a very significant positive correlation with silt-clay (r=0.940,P < 0.01), a significant positive correlation with fine sand (r=0.771,P < 0.05), and a very significant negative correlation with coarse sand (r=-0.947,P < 0.01), but the correlation with gravel was not obvious. 2) The mean value of soil density in 0-40cm of Z. jujuba var. spinosa Hu, P. sepium Bunge and Grassland were lower by 23.87%,14.51% and 10.47%, respectively, compared with bare land (1.48 g/cm³); the mean value of total porosity of soil increased by 16.96%,16.71%, 1.31%, respectively, compared with bare land (45.39%), and the degree of porosity in the surface soil layer was higher than that in 20-40cm soil layer. Fractal dimension had a very significant negative correlation with soil density, and a very significant positive correlation with capillary porosity and total porosity, but there was no significant correlation with non-capillary porosity. In shell sand habitats, the ventilation permeability was better with soil porosity decreasing, fractal dimension as well; but the higher soil-compacting degree, the bigger soil density, fractal dimension was lower. 3) Vegetation restoration measures could well improve pore structure of shell sand surface and the degree of porosity, as well as ventilation, pervious performance. Soil water storage capacity of grasslands and shrub land all performed better in 0-20cm than that in 20-40cm. Under shell sand habitats, fractal dimension had a very significant positive correlation with total water-storage capacity and capillary water-storage capacity, but the correlation with non-capillary water-storage capacity was not obvious. Judging from the fractal characteristics and soil hydrological physical characteristics, we concluded that the sequence of improving the capacity of soil physical properties and soil and water conservation of three typical vegetations in Shell Island was that shrub,was better than grassland, among which, Z. jujuba var. spinosa Hu was better than P. sepium Bunge, and soil layer in 0-20cm than that in 20-40cm.