黄河三角洲贝壳堤优势灌木-土壤系统水分传输特征及其驱动机制

The world's shell ridge in which old and new shell ridges coexist is located in the Yellow River Delta of China, and it is the largest shell ridge in the world. The main component of the shell ridges soil is shell sand, and it has typical physical structure and water storage capacity. Water is the dominant factor impacting distribution patterns of vegetation and limit plants growth in shell ridges zones. Based on the ecological problem of the interaction and the coupling mechanism between shell sand-plant for water transport in shell ridges, our objective is to investigate the key characteristics of water transport and its driving process, such as the sources, existing forms, and utilization dynamics of soil-plant water on the shell ridges in the Yellow River Delta. . In the shell ridges of silting coastal area, the constructive species of Periploca sepium Bunge were chosen as test objects. Based on the theories and methods of the water transport via SPAC (Soil-Plant-Atmosphere Continuum) and soil particle fractal dimension characteristics, the technologies, such as laser diffraction analysis, sap flow and stable hydrogen and oxygen isotope etc. are used. This research is mainly focused on the following aspects. We will discuss the characteristics of water migration and the mechanism of fractal dimension as well as to reveal the water sources and hydrological physical processes of shell sand soil under dominant shrub stand. The transportation characteristics and dominant factor of water in P. sepium Bunge shrub will be analyzed. The water sources and water using strategy of P. sepium Bunge will be explored in the shell ridges. The interactive effects and mutual feedback of the water change process between shell sand and dominant shrub will be expressed. The driving mechanism of water transport across main interface layers in shell ridges will be clarified. . The results could provide scientific basis for the understanding of the degradation process and restoration mechanism of the shrubs in shell ridges and the recovery of damaged vegetation water habitats, and it is of great significance to reveal the water ecology mechanism of the growth and degradation of shrubs on the shell ridges in the Yellow River Delta.

黄河三角洲拥有世界上规模最大、新老并存的贝壳堤，其土壤-贝壳砂具有独特的物理结构和蓄持水分能力。在水分成为主要限制贝壳堤植物生长的背景下，针对水分运移在贝壳砂-植物之间的相互作用关系和耦合机理这一科学问题，以探明贝壳堤土壤-植物系统的水分传输特征及其利用规律为目标。本项目选取黄河三角洲贝壳堤的建群种-优势灌木杠柳为研究对象，基于SPAC系统水分传输和土壤颗粒多重分形理论与方法，综合运用激光衍射分析、植物液流信息和氢氧稳定同位素等技术，揭示杠柳林的土壤水分运移特征及其分形学机制，探讨贝壳砂的水分来源及其水文物理过程；剖析杠柳树干液流的传输特征及其关键主导因子，探明杠柳的水分来源及用水策略；明确贝壳砂与优势灌木之间水分变化过程的交互效应和互馈关系，阐明贝壳堤主要界面层水分传输的驱动机制。研究成果对揭示贝壳堤灌木生长发育及退化的水分生态机制具有重要意义，可为其植被恢复所需的水分生境提供科学依据。

黄河三角洲贝壳堤土壤-贝壳砂具有独特的物理结构和蓄持水分能力。在水分成为主要限制贝壳堤植物生长的背景下，开展了贝壳堤土壤-植物系统的水分传输特征及其利用规律方面的研究。研究发现：（1）黄河三角洲贝壳堤典型灌草群落的贝壳砂呈现非均匀分布的特性，具有明显的异质性。贝壳砂单重分形维数在1.411-2.490之间。不同灌草群落不同土层之间容量维数（D0）、信息维数（D1）、关联维数、D1/D0、D0-D1差异显著（P<0.05）。D0与贝壳砂黏粒、粉粒、极细砂粒的体积分数呈显著正相关（P<0.05）。贝壳砂的土壤质地介于砂土与黏土之间，黏粒含量高低是判断贝壳砂是否具有多重分形特征的前提。（2）随贝壳砂相对含水量（RWC）的增加，杠柳叶片气体交换、叶绿素荧光及水分生理等参数呈现显著的水分临界效应。RWC为36.61%是杠柳叶片光合作用下降由气孔限制向非气孔限制转化的水分临界点，也是维持杠柳正常光合生理过程需水量的下限。维持杠柳高光合作用和水分利用效率的水分范围为RWC为63.22%-69.98%。杠柳光合生理与水分生理过程存在显著的负反馈调节机制。（3）随着贝壳砂含量的降低，不同配比处理的土壤容重、毛管孔隙度呈现升高趋势，总孔隙度和非毛管孔隙度呈现降低趋势。贝壳砂-潮土1:1配比的混合土壤的改良性能最好。贝壳砂含量可显著影响土壤水盐运移，适宜贝壳砂含量可有效提高土壤的蓄水抑盐效应。（4）在降水较少的干旱年份，贝壳堤优势灌木柽柳倾向于利用稳定的土壤水和浅层地下水。滩脊的柽柳72.6%-95.4%水分来源于浅层地下水，以及含水量相对较高的深层土壤水(40-100 cm)；高潮线附近的柽柳则有40.7%-97.3%的水分来源于上层土壤水(0-40 cm)。研究成果对揭示贝壳堤灌木生长发育及退化的水分生态机制具有重要意义。