Erosion-reducing effects of plant roots during concentrated flow under contrasting textured soils

Abstract

The effects of plant roots on water erosion are likely to vary according to the range of root traits and soil textures. However, little is known about the erosion-reducing potential of roots under different soil textures due to the lack of sufficient texture variations which come from a comparable system. In this study, we systematically investigate how root functional traits respond to soil sand contents and their combined effects on rill erosion. Seeding of Cynodon dactylon (L.) Pers. were grown in a greenhouse under varied proportions of sand mass (ranging from 14% to 83%) by mixing silty clay soil (Ultisols derived from quaternary red clay) and engineering sand. After six months growing, the root-soil composites were subjected to concentrated flow in a hydraulic flume to obtain soil detachment capacity (Dc), then roots were separated to measure their morphology and architecture traits. The results showed that sand content significantly affected root morphology traits (e.g., RD and RLD) (p < 0.01). In contrast, root architecture traits (e.g., root fractal dimension, topological index and radius frequency distribution function) showed no significant changes with soil texture (p > 0.05). Generally, root strongly promoted soil cohesion and they mitigated rill erodibility in a coordinated way. Rill erodibility was mostly determined by soil texture even in soils with dense roots, and the erosion-reducing effects of roots were less efficient in heavy-textured soils. Moreover, no significant correlations were found between critical flow shear stress (τc) and root traits, and soil with a loam texture displayed the lowest τc. Those relationships are likely to exist elsewhere, but its strength and direction could be changed according to the root trait variability and the varied root-soil feedbacks. The results of this study would be quite relevant for soil erosion modeling and imply the bare sandy soils are more urgent to be recovered during engineering constructions. Moreover, the inclusion of plant with dense fibrous roots could be the optimal species mixtures to stable sandy slopes.