Water potential isotherms reveal different but coordinated responses at leaf and root levels under controlled drought

Understanding how leaves and roots modulate their water relations under drought is critical for predicting plant stress resistance/resilience. We investigated whether these organs adopt distinct or coordinated hydraulic strategies by comparing pressure–volume (PV)-derived traits in ten species under well-watered and mild drought conditions. Measured traits included turgor loss point (Ψtlp), osmotic potential at full turgor (πo), cell wall stiffness (ε), hydraulic capacitance, and structural traits such as dry matter content and saturated water content. Roots consistently showed higher Ψtlp and πo, lower ε, and greater hydraulic capacitance than leaves, highlighting organ-specific strategies in terms of tissue water relations. Under drought, both organs primarily adjusted PV traits via osmotic modification, while changes in ε were stronger in leaves, indicating greater plasticity. Roots also showed increased dry matter content and reduced water storage capacity. Across species, Ψtlp strongly correlated with πo in roots, underscoring the dominant role of osmotic adjustment also in this organ. Moreover, species with inherently lower leaf Ψtlp displayed greater divergence between leaf and root turgor thresholds, suggesting a strategic partitioning of hydraulic risk. Overall, leaves and roots contribute complementary and coordinated strategies to drought resistance/resilience. By integrating organ-level hydraulic traits and species-specific differences, this study provides novel insight into the mechanisms by which plants manage water stress and emphasizes the importance of considering root water relations when investigating plant responses to drought.