关键词: 压力–体积曲线, 屈服点, 质壁分离点

Abstract: Aims Pressure–volume (PV) curves are widely used to characterize leaf water relations, yet the turgor-decline segment (D2) is often treated as a single linear and reversible process, potentially overlooking a transition from elastic to elastoplastic behavior. We aimed to (i) identify the yield point (P_y) via segmented fitting as a physiological marker of this transition, and (ii) test how P_y and the turgor loss point (Ψ_tlp) bound the upper limit of rehydration capacity, thereby evaluating their drought relevance. Methods Leaves of Platanus occidentalis (isohydric-leaning) and Fraxinus chinensis (anisohydric-leaning) were measured. P_y was identified by continuous segmented fitting of PV data. After the first PV run, the same leaves were rehydrated in darkness for ~30 h to obtain the maximum fresh mass, which was compared with fresh-mass estimates back-calculated at P_y and Ψ_tlp. Species differences in Ψ_sat, Ψ_tlp, and P_y were analyzed. Important findings The maximum fresh mass consistently fell between estimates at P_y and Ψ_tlp; it reached 92.6% ± 5.0% (P. occidentalis) and 86.4% ± 3.5% (F. chinensis) relative to P_y, and 109% ± 4.0% and 99% ± 4.0% relative to Ψ_tlp. Ψ_sat and Ψ_tlp differed significantly between species (higher in the isohydric species), whereas P_y did not. Interspecific differences were captured by the position of the rehydrated maximum within the (P_y, Ψ_tlp) interval rather than by the absolute values of P_y or Ψ_tlp. These results indicate that P_y marks the mechanical transition of cell walls, and that P_y together with Ψ_tlp bounds rehydration capacity in detached leaves; the rehydration window (P_y–Ψ_tlp) and its position metric hold promise as diagnostic indicators of drought tolerance.

Key words: pressure–volume (PV) curve, yield point (Py), turgor loss point (Ψtlp)