Contrasting belowground strategies between maize and sunflower to adapt to soil texture

Plant adaptive traits that regulate water transport from soil to leaf are essential for maintaining gas exchange and productivity, especially under drought conditions. Yet, how such traits respond to contrasting soil textures remains unclear. Here we grow maize (Zea mays) and sunflower (Helianthus annuus) in contrasting soil textures, namely, sand and loam. We measured transpiration rate, soil-plant hydraulic conductance and abscisic acid (ABA) concentration during soil drying. At the end of the experiment, root systems were extracted, scanned and analyzed for morphological traits. We showed that, during soil drying, maize and sunflower adopt distinct root strategies to regulate root water influx under two contrasting soil textures (sand vs. loam). In sand, maize increased root diameter by 60% without altering root length, while sunflower increased root length by threefold compared to loam. These changes moderate the flux of water into root per unit surface area, buffering soil–plant hydraulics across soil textures. Interestingly, ABA concentration decreased with increasing root length in sunflower, with higher levels in loam (shorter roots) and lower levels in sand (longer roots), whereas maize showed no substantial variation in ABA levels between soil textures. Notably sunflower exhibited three times higher transpiration, highlighting the need to adapt to soil hydraulic limitations, particularly in sand, where hydraulic conductivity declines steeply upon drying. These observed species-specific patterns underscore that root trait plasticity might be complemented by hormonal regulation of stomatal conductance in maintaining water balance under soil drying. Taken together, our findings demonstrate that contrasting root morphological adjustments can achieve functional vantage maintaining plant water balance across soil textures, highlighting the importance of root plasticity for coping with edaphic drought.