草地演替中土壤结构演变与降雨—入渗过程的互作机理

Implementation of vegetation restoration measures for improving soil structure and functions, fulfilling the significant regulatory role of soil water reservoir, and effectively utilizing precipitation resources is an important strategy for eco-environmental control and management on the Loess Plateau. Grassland vegetation succession drives soil structure optimization and thus inevitably influences precipitation-infiltration process. Presently, systematic research that combines grassland vegetation succession-driven soil structure evolution and precipitation-infiltration process is lacking. In particular, there are lacks of quantitative description for dynamic characteristics of soil pores during precipitation and quantitative description for their influence on rainwater infiltration. In this study, a successional chronosequence of fenced grasslands is established in the Yunwushan National Nature Reserve in semiarid region of Loess Plateau. Based on field investigation and laboratory analysis, a combination of CT scanning and image processing, and mercury intrusion porosimetry for pore size analysis, and indoor artificial rainfall simulation is used to reveal the evolutionary characteristics of soil aggregates and pores driven by grassland vegetation succession, and to analyze dynamic changes in soil pores under different precipitation conditions as well as their influence on rainwater infiltration. A soil structure-precipitation-infiltration model is established to clarify the mechanism of the interaction between soil structure evolution and precipitation-interaction processes in relation to grassland vegetation succession. This study will provide scientific evidence for functional evaluation of soil water reservoir and accurate simulation of water cycling in grassland ecosystems in semiarid regions on the Loess Plateau.

通过植被恢复措施以提升土壤结构功能、发挥土壤水库巨大调节作用、有效利用降水资源，是黄土高原生态环境治理的重要策略。草地植被演替驱动土壤结构优化必然影响降雨-入渗过程。目前将草地演替中土壤结构演变与降雨-入渗过程相结合的系统研究不足，尤其缺乏降雨过程中土壤孔隙特征动态定量描述及其对入渗过程影响的定量表征。本研究利用黄土高原半干旱区云雾山国家草地自然保护区建立的草地封育演替年代序列，采用野外调查和室内分析，结合CT扫描图像处理和压汞仪孔隙测定技术及室内人工模拟降雨方法，揭示草地演替过程中土壤团聚体及孔隙特征演变过程，分析不同降雨条件下土壤孔隙动态变化特征及其对入渗过程的影响，并构建土壤结构-降雨入渗模型，阐明土壤结构演变与降雨入渗过程的互作机理，以期为黄土高原半干旱区草地土壤水库功能评价和草地生态系统的水循环过程的精确模拟提供科学证据。

本研究利用黄土高原半干旱区云雾山国家草地自然保护区建立的草地封育演替年代序列，采用野外调查和室内分析，结合CT扫描及室内人工模拟降雨方法，揭示草地演替过程中土壤团聚体及孔隙特征演变过程，分析了不同降雨条件下土壤孔隙动态变化特征及其对入渗过程的影响，阐明土壤结构演变与降雨入渗过程的互作机理。研究表明，（1）团聚体和CT扫描孔隙相结合能更好地定量表征土壤结构特征，草地植被演替过程中土壤结构稳定性表现出明显的时空动态变化过程，植被恢复22前提升显著，且主要在0-40 cm土层；（2）基于同步辐射光源微型CT技术分析了土壤大团聚体微尺度（> 3.25 μm）下土壤孔隙的体积和形状特征，植被恢复有利于团聚体总孔隙度的提高，尤其是>100 μm通气孔隙，增加了团聚体狭长孔隙的孔隙度。（3）植被演替改变了土壤的水力性质，有利于土壤持水、供水和导水能力的提升，与土壤团聚体稳定性和有机碳有显著相关性。（4）植被恢复提升了土壤结构稳定性，增加不同降雨入渗阶段的入渗速率，其实质是减缓表土对降雨作用的物理性结皮形成，从而减少土壤孔隙度降低幅度，土壤大孔隙特征与降雨入渗速率有显著相关性。研究可为黄土高原半干旱区草地土壤水库功能评价和草地生态系统的水循环过程的精确模拟提供科学证据。