水蚀风蚀交错带灌丛沙堆形态演化过程的根系响应机制

Morphological succession of Nebkhas plays an important role in reflecting the change of regional erosion environment. The process of nebkhas morphological succession is usually accompanied by adaptive spatial differentiation of shrub roots. However, the response mechanism of roots in process of nebkhas morphological succession is not clear. Based on the preliminary study, which found that the presence of shrub roots could influence the morphology of slope micro-topography, the project selects the nebkhas of Artemisia ordosica and Salix psammophila in water-wind erosion crisscross region as the study object. Using field investigation and observation method and photogrammetry, this project is proposed to analyze the temporal and spatial change of root architecture (root surface area density, bifurcation ratios of roots, fractal dimension of roots) in process of nebkhas morphological succession ; In process of nebkhas morphological succession, effect of root architecture on structural stability (physical and chemical properties and microbial characteristics) of nebkhas soils will be investigated; Moreover, the project will study the interaction between root architecture and structural stability of nebkhas soils，as well as its effect on the process and mechanism of nebkhas morphological succession. This project will clarify the formation mechanism of root architecture and its characteristics in process of nebkhas morphological succession; At the same time, the effect of root architecture on structural stability of nebkhas soils will be clarified; At last, the coupling effect of root architecture and structural stability of nebkhas soils on the process and mechanism of nebkhas morphological succession will be revealed. The project proposed may provide a scientific evidence for the improvement of dynamical formation mechanism of nebkhas morphology.

灌丛沙堆形态演化对反映区域侵蚀环境变化具有重要意义。灌丛沙堆形态演化过程伴随着根系适应性的空间分化，但目前关于灌丛沙堆形态演化过程中根系的响应机制尚不明确。本项目拟在前期研究发现灌丛根系能够影响坡面微地貌形态的基础上，以水蚀风蚀交错带沙蒿和沙柳灌丛沙堆为对象，采用野外调查、定位观测以及立体摄影技术相结合的方法，研究灌丛沙堆形态演化过程中根系构型（根表面积、分枝率、分形维数）的时空变化特征；灌丛沙堆形态演化过程中根系构型对沙堆土壤结构稳定性（理化性质和微生物特征）的影响；根系构型和沙堆土壤结构稳定性的相互作用及其影响灌丛沙堆形态演化的过程和机理。阐明灌丛沙堆形态演化过程中的根系构型变化特征及其形成机理；明确灌丛沙堆形态演化过程中根系构型对沙堆土壤结构稳定性的影响；揭示根系构型与沙堆土壤结构稳定性耦合作用对灌丛沙堆形态演化过程的影响机理。为进一步完善灌丛沙堆形态-动力学形成机理提供科学依据。

灌丛沙堆形态演化对反映区域侵蚀环境变化具有重要意义。灌丛沙堆形态演化过程伴随着根系生态自适应的空间分化，该项目以水蚀风蚀交错带灌丛沙堆为对象，采用野外调查、定位观测以及立体摄影技术相结合的方法，研究灌丛沙堆形态演化过程中根系构型的时空变化特征及其对沙堆土壤结构稳定性的影响，以及根系构型和沙堆土壤结构稳定性的相互作用对灌丛沙堆形态演化过程的影响机制。主要取得以下结果：（1）明确了水蚀风蚀交错带灌丛沙堆结构特征、固沙效应和根系构型的时空变化特征。沙柳和沙蒿两种典型灌丛沙堆体积分别为63.24 m3和2.15 m3，灌丛体积与沙堆体积呈极显著正相关，沙柳灌丛沙堆固沙能力显著高于沙蒿。两种典型灌丛沙堆形态演替至稳定阶段时，根系在沙堆土壤坡面中主要呈倒金字塔形分布。垂直方向上，沙柳根系主要分布在0～160 cm 深度土层，沙蒿根系主要分布在0～40 cm 深度土层，水平方向上，沙柳主要分布在距根基0～120 cm半径范围内，沙蒿则主要分布在距根基0～60 cm半径范围内。（2）解析了灌丛沙堆形态演化过程中土壤理化性质及种子库空间分布特征。草地灌丛化一方面显著改变了沙蒿植物群落结构，降低了物种数量、多样性指数和土壤种子库密度。另一方面促进了沙堆形态演化和沙堆“营养岛”效应的形成，但同时造成灌丛沙堆丘间地土壤养分出现退化现象。（3）揭示了灌丛沙堆演化过程中根系构型对风水复合侵蚀产沙的调控机制。沙柳灌丛根系降低了近地表输沙通量，弱化了风蚀对沙堆表层土壤微地形的塑造作用，从而改变了水蚀产沙过程，减少了沙堆土壤侵蚀速率。两种风蚀水蚀交互水平下（11 m s-1×60 mm h-1和14m s-1×100 mm h-1），沙柳灌丛根系减蚀效应分别可达24.37%和39.72%。以上研究结果可为完善灌丛沙堆形态-动力学形成机理提供一定科学依据。