植物根系对崩积体侵蚀产沙和土壤分离速率的影响机理

Soil and water loss is the severest in colluvial deposits in granite Benggang. Vegetation restoration is the most effective method of water and soil conservation, and plant roots play important roles in reducing soil erosion. Four types of runoff plots, with the whole plant, with living roots, with dead roots and without plant and roots, are designed to investigate the reduction of sediment yield caused by plants roots by observing their runoff and sediment under natural rainfall. Root characteristic, changes of soil properties as well as flow hydraulic characteristic is to be compared to reveal the effect of plant roots. Five types of soils, with living roots, with dead roots, with simulation roots and with root exudates are subjected to concentrated flow using a hydraulic flume in the laboratory to evaluate the relative contribution of physical consolidation of soil, including net-link and soil-root bond functions, and root biochemistry effect especially the effect of root exudates, to soil detachment. The influences of root density and flow rates on the partitioning the reduction of soil erosion are also to be analyzed. This study is important for understanding the effect of roots on soil water erosion process and in revealing the mechanism of plants roots reducing soil detachment capacity. It also would contribute to soil and water conservation monitoring, as well as to selection of the proper species for soil and water conservation in granite red soil area.

崩岗崩积体是华南花岗岩红壤区水土流失重灾区，恢复植被是水土保持最有效的方法，植物根系在减少土壤侵蚀方面具有重要作用。本研究将选择深根系和浅根系草本各一种，通过设置含完整植被、含活根、含死根和不含根系径流小区，分析根系特征和土壤理化性质，对比观测坡面产流产沙过程和径流水动力学特征，研究根系的减沙效应及其机理；通过开展含活根、死根、模拟根系、根系分泌物的土壤的径流冲刷实验，定量分析根系网络串联和根土粘结等物理固结作用以及根系分泌物作用等生物化学作用在降低土壤分离速率的贡献，探讨冲刷流量和根系密度对根系减少土壤分离速率的影响。本研究将对于理解根系影响土壤水蚀过程，揭示根系减少土壤侵蚀的机理具有重要科学意义，可以为水土流失监测、筛选适合红壤地区的水土保持物种提供理论依据。

本项目通过模拟降雨实验，分析并揭示了两种水保植物冠层、根系和生物结皮对减少坡面侵蚀产沙的贡献及其对坡面径流水动力的影响，定量分析了根系减沙作用占完整植株和结皮总体减沙作用的比例以及其增加坡面粗糙度和降低坡面径流流速的作用。一年生的糖蜜草和香根草分别可以减少98.1%和86.63%的坡面产沙，其中根系分别能减少45.02%和36.64％。两者的根系能分别降低土壤可蚀性Ki63.3%和54.4%，分别增加坡面粗糙度0.80和0.70倍，分别降低坡面流速17.65%和17.39%。根系通过模拟冲刷实验，分析并揭示了根系的影响土壤分离速率的物理固结作用和生物化学作用的比例，尤其是根系分泌物的作用。根系的物理固结作用占据了绝对的贡献，在不同流量的冲刷下都超过87.3%以上，而根系的生物化学作用则介于4.8%至12.7%之间。单独利用根系分泌物培养的土壤的减沙效率在3.8和7.6 L min-1流量下能够达到56.6%和60.5%，但是在11.4 L min-1流量下则减少到15.8%；这表明在超过7.6 L min-1流量的时候径流的作用力可能远超过了分泌物的作用，造成分泌物不再起作用。研究结果对南方强降雨、陡坡的水土流失防治具有参考价值。