Leaf cell wall mechanics reveal contrasting patterns of structural persistence and tissue plasticity in two temperate...

It remains unclear whether drought-induced cell wall softening reflects a functional adjustment or structural impairment after severe water stress. To address this question, we combined pressure-volume curve analysis, non-linear constitutive modeling, anatomical measurements, and species-level biogeographical context in two temperate deciduous tree species, Fraxinus pennsylvanica and Platanus occidentalis. The two species exhibited contrasting mechanical responses after dehydration-rehydration. F. pennsylvanica retained a more stable pressure-volume curve morphology and higher residual stiffness, despite a reduction in maximum bulk elastic modulus. In contrast, P. occidentalis showed a marked shift in constitutive behavior, including loss of the initial linear elastic phase, a strong decline in elastic modulus, increased hydraulic capacitance, and a higher symplastic relative water deficit at turgor loss. Anatomical comparisons further showed that P. occidentalis had thicker but more compliant cell walls, whereas F. pennsylvanica had thinner but mechanically stiffer tissues. Cleaned species-level occurrence records indicated broadly overlapping climatic distributions, providing ecological context rather than evidence for strict climatic niche separation. Together, these results suggest that drought-induced wall softening is not a uniform response, but may reflect species-specific differences in the coordination between cell wall mechanics and leaf hydraulic function. This framework provides a mechanistic basis for future tests of how micro-scale wall properties contribute to drought response strategies across broader plant functional types.