Influence of Hydrodynamic Forces on Root Development of Vegetation Cuttings

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Abstract
This paper investigates the development of azimuthal root asymmetry in riparian plant cuttings as a response to hydrodynamic forces, a novel tropism response that we refer to as “dynamotropism.” Laboratory experiments were performed within an experimental flume using Salix fragilis cuttings growing in rhizoboxes filled with quartz sand and undergoing different treatment conditions. These aimed to isolate and differentiate the effects that hydrodynamic forces acting on the stem exert on the root vertical biomass development from that of hyporheic flow. Results reveal that in response to an applied external (drag) force acting on the stem, root biomass increases significantly in the upstream direction, opposite the drag force, resulting in approximately 30% greater total biomass upstream than downstream. This suggests a structural adaptation of the below‐ground biomass to resist mechanical loading of the aboveground part of the cutting. While the effect of force seems to influence overall root production, the effect of hyporheic flow does not affect the total biomass in either directions. Hyporheic flow, in particular, tends to enhance root growth toward the downstream side at higher depth than in the top soil layers. Hence, flow and force appear to promote opposing patterns of root development along the sediment depth, whose evidence is maximized when both stimuli are applied simultaneously. When acting together, the relative magnitudes of such stimuli become crucial in determining the final root architecture where mechanical force dominated over flow stimulus. The results of this work path the way to novel plant nursing strategies for bioengineering applications.

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