Key message

Resilience to xylem embolism and the accumulation of cyclitols are promising criteria for the selection of drought-resilient Eucalyptus species.

Abstract

Due to the aridity of the climate in the southern Mediterranean region, the choice of suitable species for afforestation projects is crucial. The present study aims to compare resilience mechanisms against drought in two frequently used Eucalyptus species (E. camaldulensis and E. torquata). Two-year-old self-rooted cuttings of the two species were grown in sand-filled pots and subjected to a dehydration period followed by rehydration. At regular intervals, water relations, gas exchange, chlorophyll fluorescence and xylem embolism were measured on these plants. In addition, carbohydrates and cyclitols were quantified in their leaves. The results revealed that E. camaldulensis was more resilient to drought than E. torquata. During the dehydration phase, plant water status, cell turgor, net photosynthetic rate (P_n) and photosynthetic machinery integrity were less affected in E. camaldulensis than E. torquata. After rehydration, these variables were at levels similar to those of control plants in the case of E. camaldulensis, but not in the case of E. torquata. The restoration rate was 96% and 88% for predawn leaf water potential (Ψ_pd), and it was 98% and 77% for P_n in E. camaldulensis and E. torquata, respectively. The resilience of E. camaldulensis against drought may be due to the efficiency of two determinant survival mechanisms: osmotic adjustment and resistance to xylem embolism. Indeed, E. camaldulensis was less vulnerable to drought-induced xylem embolism and more able to repair embolized xylem vessels than E. torquata. Xylem refilling reduced embolism rate (percent loss of conductivity) to 15% in E. camaldulensis, compared to 22% in E. torquata. Furthermore, E. camaldulensis was found capable of efficient osmotic adjustment than E. torquata by accumulating soluble carbohydrates, especially cyclitols. Indeed, under severe drought (Ψ_pd of − 7 MPa), E. camaldulensis accumulated 9.27 mg g^− 1 DW of quercitol and 3.81 mg g^− 1 DW of pinitol; it also had three times more myo-inositol in its leaves than E. torquata. We suggest the use of resilience to xylem embolism and the accumulation of cyclitols to screen Eucalyptus germplasm for drought resistance.

中文翻译：

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经历脱水-脱水循环的两种桉树（Camaldulensis和E. torquata）的水分关系，光合作用，木质部栓塞以及碳水化合物和环醇的积累

关键信息

对木质部栓塞的抵抗力和环醇的积累是选择抗旱桉树物种的有希望的标准。

抽象

由于南部地中海地区气候干旱，为造林项目选择合适的物种至关重要。本研究旨在比较两种常用桉树物种（E. camaldulensis和E. torquata）的抗旱机制。将这两个物种的两年生的自生根插枝放在装满沙子的盆中，进行脱水，然后再补水。在这些植物上定期测量水关系，气体交换，叶绿素荧光和木质部栓塞。另外，在其叶片中定量了碳水化合物和环糖醇。结果表明，卡玛杜兰E. camaldulensis比干旱E. toquata具有更强的抗旱能力。在脱水阶段，与E. torquata相比，Camaldulensis对E. camaldulensis的植物水分状况，细胞膨大，净光合速率（P _n）和光合机械完整性的影响较小。补液后，这些变量的水平与对照植物的水平相似，对于卡氏大肠杆菌（E. camaldulensis）而言，但对to水（E. torquata）而言则不同。恢复率为96％，对于黎明前叶水势（88％Ψ _PD），它是98％和77％P _Ñ在赤桉和E. torquata分别。大肠杆菌的弹性抗干旱可能是由于两个决定性生存机制的有效性：渗透调节和对木质部栓塞的抵抗力。事实上，赤桉是干旱引起的木质部栓塞那么脆弱，更能够修复栓塞木质部导管比E. torquata。木质部充填使camaldulensis的栓塞率（电导率损失百分比）降低至15％，而E. torquata的栓塞率为22％。此外，赤桉，发现能够有效地渗透调节比E. torquata通过累积可溶性碳水化合物，尤其是环多醇。事实上，严重干旱下（Ψ_概率pd - 7兆帕），赤桉累积9.27 mg g ^{− 1} DW的槲皮醇和3.81 mg g ^{− 1} DW的松醇; 它也有三倍多的肌醇肌醇在它的叶子比E. torquata。我们建议使用对木质部栓塞的回弹力和环糖醇的积累来筛选桉树种质的抗旱性。