When do root hairs matter for water uptake? Root hair traits to enhance plant water use and drought resilience under contrasting soil textures

Although root hairs (RHs) have been shown to enhance root-soil contact and soften the gradients in matric potential across the rhizosphere, our mechanistic understanding of how RH traits (length, density, and shrinkage) collectively affect water uptake and drought response remains elusive. Using a soil-plant hydraulic model, we investigated how these traits alter root water uptake dynamics in two contrasting soil textures (sandy loam and loam) and evaluated two scenarios: (1) RHs increasing the effective root radius and (2) RHs extending the effective absorption length (L eff ). In the first scenario, longer RHs enhanced effective root radius and delayed the soil hydraulic limit on transpiration, but only when RHs were shrinkage-resistant (shrinkage initiated at -0.2 MPa), with no significant difference between soil textures. In the second scenario, increased L eff improved uptake under moderate drought (soil matric potential around -0.15 MPa), mitigating declines in soil-plant hydraulic conductance. Long, dense, and shrinkage-resistant RHs broadened the moisture window for water uptake, with the largest relative gains in sandy loam. During soil drying, these trait interactions mitigated the gradients in matric potential at the root-soil interface, delayed stomatal closure, and shifted water use toward more anisohydric behavior, particularly in sandy loam. Our findings provide a step toward establishing a mechanistic basis for optimizing RH traits to enhance water uptake efficiency and drought resilience. • Root-hair traits modulate soil–plant hydraulic connectivity. • Increased effective absorption length (Leff) boosts uptake in sandy loam. • Shrinkage-resistant, long, dense hairs delay stomatal closure under drought. • Leff links measurable hair traits to crop-scale drought-resilience targets.