Institute of Plant Sciences, Volcani Center, Agricultural Research Organization, Rishon LeZion, Israel.
Institute of Soil, Water and Environmental Sciences, Volcani Center, Agricultural Research Organization, Rishon LeZion, Israel.
Physiol Plant. 2024 Jul-Aug;176(4):e14467. doi: 10.1111/ppl.14467.
Measurements of resistance to embolism suggest that Cupressus sempervirens has a stem xylem that resists embolism at very negative water potentials, with 50% embolism (P) at water potentials of approximately -10 MPa. However, field observations in a semi-arid region suggest tree mortality occurs before 10% embolism. To explore the interplay between embolism and plant mortality, we conducted a controlled drought experiment involving two types of CS seedlings: a local seed source (S-type) and a drought-resistant clone propagated from a semi-arid forest (C-type). We measured resistance to embolism, leaf relative water content (RWC), water potential, photosynthesis, electrolyte leakage (EL), plant water loss, leaf hydraulic conductivity, and leaf non-structural carbohydrate (NSC) content during plant dehydration and before rewatering. All measured individuals were monitored for survival or mortality. While the S- and C-types differed in P, transpiration, and mortality rates, both displayed seedling mortality corresponding to threshold values of 52-55% leaf RWC, 55% and 18.5% percent loss of conductivity (PLC) in the xylem, which corresponds to 48% and 37% average EL values for S and C types, respectively. Although C-type C. sempervirens NSC content increased in response to drought, no differences were observed in NSC content between live and dead seedlings of both types. Our findings do not fully explain tree mortality in the field but they do indicate that loss of membrane integrity occurs before or at xylem water potential, leading to hydraulic failure.
栓塞阻力的测量表明，智利柏具有在非常负的水势下抵抗栓塞的茎木质部，在水势约为-10 MPa 时，栓塞率达到 50%（P）。然而，半干旱地区的实地观测表明，树木死亡率发生在 10%栓塞之前。为了探讨栓塞和植物死亡率之间的相互作用，我们进行了一项受控干旱实验，涉及两种类型的 CS 幼苗：本地种子源（S 型）和从半干旱森林繁殖的抗旱克隆（C 型）。我们在植物脱水过程中和重新浇水前测量了栓塞阻力、叶片相对含水量（RWC）、水势、光合作用、电解质泄漏（EL）、植物水分损失、叶片水力传导率和叶片非结构性碳水化合物（NSC）含量。所有测量的个体都监测其存活或死亡情况。虽然 S 型和 C 型在 P、蒸腾和死亡率方面存在差异，但两者都表现出与叶片 RWC 52-55%、木质部导率损失 55%和 18.5%（PLC）以及 S 和 C 型的平均 EL 值分别为 48%和 37%对应的阈值值的幼苗死亡率。尽管 C 型智利柏的 NSC 含量随着干旱而增加，但两种类型的活苗和死苗之间的 NSC 含量没有差异。我们的发现不能完全解释野外树木死亡率，但它们确实表明膜完整性的丧失发生在木质部水势之前或之时，导致水力衰竭。
