贝壳堤岛3种植被类型的土壤颗粒分形及水分生态特征

Abstract

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,P0. 01),a significant positive correlation with fine sand( r = 0. 771,P0. 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.