河西走廊沙丘下覆粘土层的水文效应及其对植被影响

The physical and chemical characteristics，as well as distribution characteristics, of clay layer underlying the sand dunes are key factors of ecological processes, which including hydrological processes and vegetation processes. While the growth and distribution of sand-fixing vegetations are directly related to the stability of the sand dunes and the health and safety of the oasis. Therefore, Hydrology effects caused by the clay layer and potential effects on the growth and distribution of sand-fixing vegetation are an important scientific questions to be solved to ecological environment construction in arid regions. The proposed project mainly focusses on clay layer underlying the sand dunes and sand-fixing vegetation in the desert region of the Hexi Corridor. By means of field trials, laboratory experiment, and theoretical analyses, we address the three key questions: (1) the physical and chemical characteristics，as well as distribution characteristics, of clay layer underlying the sand dunes in the Hexi Corridor; (2) hydrological processes are caused by the clay layer; (3) the clay layer effects on theIndividual characteristics ; (3) and on the physiological ecology and distribution of sand-fixing vegetation. By doing this, we ultimately aim to understand the heterogeneity characteristics of the clay layer underlying the sand dunes in the Hexi Corridor, to reveal the effects of water transforming patterns through the physical and chemical characteristics and distribution characteristics of the clay layer, ultimately aim to analyze the reasons and laws of the physiological ecology and distribution of sand-fixing vegetation. Ecohydrology significance of the clay layer is understood deeply and theoretical support for the restoration and construction of sand-fixing vegetation in the desert region is provided.

沙丘下覆粘土层理化性质及分布特征是导致包括水文过程及植被过程在内的生态过程变化的关键因素。而固沙植被的生长及分布特征直接关系到沙丘稳定及绿洲安全。因此，对于沙丘下覆粘土层所引起的水文效应及其对固沙植被生长和分布的影响是干旱区生态环境建设中亟待解决的重要科学问题。本项目以河西走廊荒漠区沙丘下覆粘土层及固沙植被为研究对象，通过野外试验、室内实验及理论分析相结合的方法，开展河西走廊沙丘下覆粘土层的理化性质及分布特征、水文效应及其对固沙植被个体形态及生长和分布的影响等相关研究，旨在认识绿洲边缘沙丘下覆粘土层的异质性特征，阐明粘土层的理化性质及分布特征对水分运移的影响，最终揭示粘土层对固沙植被生理生态及分布影响的原因及规律。深入理解沙丘下覆粘土层的生态水文学效应及意义，为荒漠区固沙植被的恢复和建设提供理论支持。

本项目以河西走廊荒漠区沙丘下覆粘土层及固沙植被为研究对象，通过野外试验、室内实验及理论分析相结合的方法，开展河西走廊沙丘下覆粘土层的理化性质及分布特征、水文效应及其对固沙植被的影响等相关研究。研究发现：在河西走廊绿洲边缘，含粘土层沙丘占调查沙丘的25 %左右。粘土层位于0－60 cm深处，厚达10－50 cm，呈砖红色或灰白色，黏粉粒含量高（82.37 %），容重小（1.26 g/cm3）。表层砂土容重随着粘土层埋深增加先增加后趋于稳定。粘土层通过增大黏粉粒含量，使其饱和含水量和孔隙度增大、容重减小，并使土壤水分特征曲线在低吸力段释水速率减缓。粘土层对表层砂土田间持水量、凋萎系数和有效含水量无显著影响，仅影响粘土层以下砂土的持水性能。粘土层的存在降低了沙丘土壤的导水性，剖面土壤饱和导水率随粘土层埋深减小先减小后趋于稳定，同时有效减缓土壤水分入渗和水分再分布速率，为水分短暂滞留于沙丘中提供了条件。对梭梭根系的调查发现，在垂直方向上根系生物量在接近粘土层或伸入粘土层时急剧增加，尤其是粗根生物量的增加更显著，这与粘土层的阻碍作用和粘土层较好的水分条件有关。梭梭地上部分的生长和根系的分布，即梭梭的高度和冠幅面积，以及总根系生物量与粘土层的埋深呈负相关关系，而根系深度和粘土层的深度呈正相关关系。因此粘土层存在的土壤对植物的生长发育以及固沙植被的健康发展具有积极的在作用。通过研究认识了绿洲边缘沙丘下覆粘土层的理化性质及分布特征；阐明了沙丘下覆粘土层的水文效应；揭示了沙丘下覆粘土层对固沙植被的生理生态特征及分布的影响。

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