【摘要】 【目的】探究红桦在干旱胁迫下水力学和碳代谢特性，揭示其致死阈值与死亡机制，明晰红桦在全球气候变暖背景下生存与适应能力，也为红桦苗木培育及森林经营提供理论参考。【方法】对4年生红桦幼苗进行持续干旱胁迫，根据叶片外观及生理状态划分为4个胁迫阶段（阶段Ⅰ，达到叶片膨压损失点；阶段Ⅱ，叶片下垂；阶段Ⅲ，叶片开始干枯；阶段Ⅳ，叶片完全枯黄），到达每个胁迫阶段后进行阶段复水（1周，2周，4周），干旱胁迫期间及复水特定阶段测定：土壤体积含水量，叶凌晨水势、正午水势，叶比导水率，茎比导水率、茎导水率损失值，根、茎、叶可溶性糖及淀粉含量并计算非结构性碳水化合物（NSC）总量。【结果】1）干旱胁迫至4个阶段时，叶凌晨水势分别下降到–0.732、–1.32、–1.712、–2.23 MPa，胁迫到最终阶段，茎比导水率、叶比导水率分别下降94.5%、99.1%，导水率损失超过88%，各器官可溶性糖含量上升，淀粉含量下降，可溶性糖与淀粉比值上升，根NSC总量下降到62.6%，可溶性糖和淀粉含量与导水率损失值有显著相关性（P<0.01）。2）复水后，Ⅰ、Ⅱ、Ⅲ阶段各器官可溶性糖含量显著高于对照组（P<0.05），在此胁迫阶段红桦幼苗的水分运输能力可以得到恢复，Ⅳ阶段红桦幼苗水力学性状无法恢复，根、茎的NSC含量低于对照组水平。3) 4个阶段红桦幼苗茎导水率损失值分别为15.57%±0.61%、49.49%±5.03%、77%±2.52%、96.4%±1.11%，死亡率为0,0,33.3%,100%。【结论】干旱胁迫期间红桦幼苗水力学性状与NSC存在耦合关系，红桦幼苗通过动态调节各器官碳分配模式，将淀粉转化成可溶性糖，应对持续干旱胁迫对水分运输的影响，复水后，红桦幼苗水力学性状与NSC的恢复程度会受到前期干旱胁迫程度的影响，水力失衡和碳饥饿共同发生在植株死亡过程中，红桦幼苗的茎导水率损失值为77%时已有死亡风险。更多还原

【Abstract】 【 Objective】 Under the background of global warming, there is a lack of research on the hydraulics and carbon metabolism of Betula albo-sinensis(red birch), and the mechanism of death and lethal threshold due to persistent drought stress are still unclear. This study aims to explore the hydraulics and carbon metabolism characteristics of B. albo-sinensis under drought stress, revealing its lethal threshold and death mechanism, which is necessary for clarifying the survival and adaptive capacity of B.albo-sinensis in the context of global warming. It also provides theoretical reference for red birch seedling cultivation and forest management. 【Method】The present study was carried out on four-year-old B. albo-sinensis seedlings subjected to continuous drought stress, which was classified into four stages of stress according to the appearance of the leaf blades and physiological status(Stage Ⅰ, reaching the point of leaf turgor loss; Stage Ⅱ, leaf blade drooping prolapse; Stage Ⅲ, leaves starting to dry up; StageⅣ, leaves completely yellow). After reaching each stage, the seedlings were rehydrated for 1 week, 2 weeks, and 4 weeks. During the period of drought stress and at specific stages of rehydration, the soil volumetric water content, predawn leaf water potential,midday water potential, leaf specific conductance, stem specific hydraulic conductance, stem hydraulic conductivity loss, and soluble sugars and starch contents in roots, stems and leaves were measured, and the total amount of non-structural carbohydrates(NSC) was calculated. 【 Result】 1) The results showed that at four stages of drought stress, leaf predawn water potential decreased to –0.732, –1.32, –1.712, –2.23 MPa, respectively. In the final stage of stress, the stem specific hydraulic conductivity and leaf hydraulic conductivity decreased by 94.5% and 99.1%, respectively, and the loss of hydraulic conductivity was more than88%. The soluble sugar content in each organ rose, starch content decreased, the soluble sugar to starch ratio increased, and the total root NSC decreased to 62.6%. There was a significant correlation between the soluble sugar and starch contents and the loss of hydraulic conductivity values(P<0.01). 2) After rehydration, the soluble sugar content in various organs of seedlings that experienced stage Ⅰ, Ⅱ and Ⅲ drought stress was significantly higher than that of the control group(P<0.05), and the water transport capacity of B. albo-sinensis seedlings was able to be restored. However the hydraulic traits of B. albo-sinensis seedlings that experienced stage Ⅳ stress could not be restored, and the NSC content of roots and stems was lower than the level of the control group. 3) The loss values of stem hydraulic conductivity of B. albo-sinensis seedlings at the four stages were 15.57% ±0.61%, 49.49%± 5.03%, 77%± 2.52%, and 96.4%± 1.11%, and the mortality rates were 0, 0, 33.3%, and 100%, respectively.【Conclusion】There is a coupling relationship between the hydraulic traits and NSC of B. albo-sinensis seedlings during drought stress, and B. albo-sinensis seedlings cope with the impact of sustained drought stress on water transport by dynamically regulating the carbon allocation pattern of each organ and converse starch into soluble sugars. After rehydration, the recovery degree of the hydraulic traits and NSC of B. albo-sinensis seedlings is affected by the degree of the previous drought stress. Hydraulic failure and carbon starvation co-occur during plant death, and B. albo-sinensis seedlings are already at risk of death at a value of 77% loss of stem hydraulic conductivity.更多还原