水蚀风蚀交错区沙柳根系抗侵蚀机理研究

Water-wind erosion crisscross region located in the junction of Maowusu sandy land and the hilly Loess Plateau. Water erosion and wind erosion occur superimposely in time and space, and the interplay between them aggravates the area being extremely vulnerable ecological environment. Therefore, the ‘Thirteen Five Plan’ implemented by the State Council, clearly stated that soil and water conservation is urgent in the region. Vegetation establishment is a positively efficient way in controlling soil erosion, in particular, the roots could significantly affect soil erosion and conserve soil and water. However, few research works have been done on the soil anti-erosion (water and wind erosion) caused by Psammophyte roots in the region. The project selects the native shrub of Salix as the study object, and is proposed to study the anti-erosion of roots in use of field survey, observation plots in situ, simulated rainfall, wind tunnel combined with 7Be tracer techniques. Specifically, the space distribution characteristics (stripe gradient, slope position, aspect, soil profile) of Salix roots will be investigated, and the relationship between the feature of soil erosion and Salix root parameters (root density, root surface area density, fractal dimension and branching rate) will be established. Moreover, this project will clarify the water-wind erosion-control effect caused by Salix roots, and the key influencing factors will be analyzed. At the same time, the approach of indoor simulations validated by field experiments, can reveal the mechanisms of water-wind erosion-control effect caused by Salix roots, through related root parameters. At last, the correlation model between water erosion, wind erosion as well as their interactions, and Salix root parameters, will be constructed. The project proposed may provide a scientific evidence for the establishment of desert vegetation and ecological environment in the water-wind erosion crisscross region.

黄土高原水蚀风蚀交错区地处黄土丘陵区向毛乌素沙区过渡地带，水蚀风蚀在时空上叠加，相互影响，使得该区生态环境极度脆弱，成为国家“十三五”水土保持重点加强区域之一。植被建设是控制风、水蚀积极有效的措施，尤其根系固土抗蚀功效显著，但该区沙生植被根系抗侵蚀作用机制的研究较为薄弱。本项目以该区乡土灌木沙柳根系为研究对象，采用野外调查、定位观测试验、室内模拟降雨+风洞试验，以及7Be核素示踪技术相结合的研究方法。分析水蚀风蚀交错区沙柳根系空间（南北条带梯度、坡位、坡向、土壤垂直剖面）分布特征；量化水蚀、风蚀土壤流失量与沙柳根系特征参数（根系密度、根表面积密度、分形维数、分枝率）的关系；阐明沙柳根系对土壤水蚀、风蚀的调控效应及其影响因素；野外试验验证室内模拟结果，揭示沙柳根系抗侵蚀的内在机理；构建土壤水蚀、风蚀及其交互作用与沙柳根系特征参数的关系模型。为水蚀风蚀交错区沙生植被与生态环境建设提供科学依据。

植被建设是黄土高原水蚀风蚀交错区防治土壤侵蚀最有效的措施之一。根系在植被调控土壤侵蚀中发挥着重要作用。本研究以沙柳为研究对象，在沙柳根系野外调查的基础上，通过野外定位观测、室内模拟降雨+风洞试验，系统研究了沙柳根系分布特征、根系对土壤水蚀、风蚀的调控效应，揭示了根系抗侵蚀性的内在机理，构建了土壤水蚀、风蚀及其交互作用与沙柳根系的关系方程，以期为水蚀风蚀交错区沙生植被与生态环境建设提供科学依据。主要结论包括：（1）沙柳根系在土壤剖面中呈倒金字塔形分布。根系随土壤埋深和距根基水平距离增大而减小，垂直方向上主要分布在0～40 cm 深度土层范围内，水平方向上主要分布在0～80 cm半径范围内。（2）沙柳根系改善了坡面水动力学性质，增大了土壤临界切应力，显著增强了土壤抗水蚀能力。与裸土相比，根系作用坡面土壤临界切应力平均增大4.19倍，土壤可蚀性参数平均减小50.83%；室内模拟降雨试验下，根系减沙效益最高可达66.52%，最低为11.39%，平均为35.62%，野外整个水蚀观测期内，根系减沙效益最高可达69.41%，最低为4.38%，平均为19.75%。（3）沙柳根系通过调控近地表输沙通量，显著增强了土壤抗风蚀能力。根系对输沙通量廓线以及输沙通量随地表高度的分布特征没有影响，但根系减小了地面不同高度的输沙通量，与裸土相比，根系作用坡面输沙通量在地表不同高度平均减小21.58%（11 m s-1）和39.38%（14 m s-1）；（4）沙柳根系弱化了风蚀对水蚀的影响，线性方程较好地反映了土壤侵蚀速率与根系特征参数的关系。随风蚀水蚀交互水平增大，根系对坡面入渗产流及坡面水动力参数的影响作用减弱；根系改变了坡面侵蚀率随降雨历时的变化趋势，与裸土坡面侵蚀率随降雨历时延长呈波动增大趋势不同，根系作用坡面侵蚀率随降雨历时延长先增大后减小最后趋于稳定；室内模拟风洞+降雨试验下，根系减沙效益最高可达61.56%，最低为6.53%，平均为37.21%；线性方程可较好地表达土壤侵蚀速率与根系特征参数的关系。