黑河流域荒漠地区梭梭人工林地土壤水分动态研究

Soil Water Regime under the Shrubberies of Haloxylon ammodendron in the Desert Regions of the Heihe River watershed

梭梭林地土壤剖面的含水量与裸沙地含水量显著不同 ,裸沙地土壤含水量随深度增加而增加 ,林地在 30～ 12 0cm范围内有较高的含水量 ;林地 0～ 30cm的上层土壤含水量受降雨及蒸发的剧烈影响 ,30～ 2 0 0cm范围内的林地土壤各测量层平均含水量与其标准差有二次函数的关系 ;降雨对每月的 0～ 2 0 0cm的土壤贮水量没有明显的影响 ,说明降雨多数在当月就被蒸散和深层渗漏所消耗 ;认为梭梭人工林这种脆弱生态系统能够在严酷的环境条件下存在 。

The eco-environmental degradation has been paid more and more attention to in the semiarid and arid regions in China. It is becoming a challenge for scientists to find the effective measures to tackle the ecoenvironmental problems. Afforestation is one of the methods used for preventing wind-erosion and controlling desertification, and large areas of trees and shrubs including Haloxylon ammodendron have been planted in the Linze desert regions, Gansu Province, where the mean annual precipiation is 113.8mm. However, the main limitation of planting trees and shrubs in the desert regions shortage of water.Because of influence from human activities,the ground water level is declined, which has made the trees and shrubs in a large area in the regions die.Therefore, it is necessary to investigate and assess the relationship between shrub growth and soil water content. The present study is undertaken for a native and sand fixed shrub species, Haloxylon ammodendron. The soil water content in the sand land covered by shrubberies and the vegetation-uncovered sand soil is measured. We found that:(1) The water content in vegetation-uncovered soil increased as the depth of soil profile increased, and the soil water content in the land covered by shrubberies is higher in soil depth of 30～120cm than that of 120～200cm, and is significantly affected by rainfall and evaporation in the soil depth of 0～30cm; (2)The relationship between the average values of water contents in measured soil layers of 30～200cm in the land covered by shrubberies and their standard deviations can be described by a quadric function; (3) Rainfall does not significantly influence the soil water storage in the depth of 0～200cm, which means that rainfall is completely consumed by evapotranspiration and seepage at the same time; (4)Although the growth of artificially-planted shrubberies is closely related to the soil water content, the soil moisture partitioning in the soil depth of 0～200cm may not be much important for the maintenance of species during different seasons in the regions, which assumes that the shrubs are able to send roots deeper than 200cm in soil, and to tap water from permanent water table for survivorship. The functional significance of deep roots for water flux in arid ecosystems under high evaporation has been shown regarding the 'hydraulic lift' mechanism. At night roots take up water from deep soil, which is released from shallow roots back to the soil in the upper layers. The water is reabsorbed next day by the same plants. This mechanism has an important ecological significance, allowing plants to maintain high transpiration rate during dry periods. In conclusion, it is considered that the redistribution of soil water and groundwater by the shrub root systems is one of the important factors that affect the survival of Haloxylon ammodendron from severe environmental conditions.