Mechanoadaptive root growth in Medicago sativa under controlled microhydrodynamic environments

Plant roots are essential organs that anchor plants in the soil and absorb water and other nutrients. Studying root growth contributes to the enhancement of plant growth. In this study, we designed a microfluidic platform to investigate the effects of microhydrodynamic stimulation on plant root growth. A wide range of microfluidic flow rates was applied to Medicago sativa seedling roots using a syringe pump. Higher inlet flow rates promoted main root elongation by 60.7% and suppressed root hair growth by 65.7%. A threshold response of root growth was observed between the inlet flow rates of 0.1 and 1 μL min^-1. The normalized distribution pattern of root hair lengths shifted from a sigmoid pattern at low flow rates to an exponential pattern at high flow rates. Computational fluid dynamics was used to investigate the direct and indirect hydrodynamic stimulation of the roots. Higher maximum wall shear and bending stresses were observed at higher flow rates and longer root hairs. The Péclet number of the secreted ethylene was larger at higher flow rates and had minor differences depending on root hair length. These results suggest that M. sativa tends to promote main root elongation rather than root hair elongation in mechanically stressful and advection-dominant environments. The microfluidic system and analytical method used in this study provides a mechanistic understanding of the effects of fluid dynamics on plant root growth and has the potential to be valuable tools for future research, ultimately contributing to improve crop productivity and addressing future food security concerns.