Summary The first year in a tree's life is characterized by distinct morphological changes, requiring constant adjustments of the hydraulic system. Despite their importance for the natural regeneration of forests and future vegetation composition, little has been known about the hydraulics of tree seedlings. At different times across the first growing season, we analysed xylem area‐specific (Kshoot_Axyl) and leaf area‐specific (Kshoot_L) shoot hydraulic conductance, as well as embolism resistance of three temperate conifer trees, two angiosperm trees and one angiosperm shrub, and related findings to cell osmotic parameters and xylem anatomical traits. Over the first 10 wk after germination, Kshoot_Axyl and Kshoot_L sharply decreased, then remained stable until the end of the growing season. Embolism resistance was remarkably low in the youngest stages but, coupled with an increase in cell wall reinforcement, significantly increased towards autumn. Contemporaneously, water potential at turgor loss and osmotic potential at saturation decreased. Independent of lineage, species and growth form, the transition from primary to secondary xylem resulted in a less efficient but increasingly more embolism‐resistant hydraulic system, enabling stable water supply under increasing risk for low water potentials.

中文翻译：

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对敏感生命阶段的新见解：树苗在第一个生长季节的水力学


总结 树木生命的第一年的特点是明显的形态变化，需要不断调整液压系统。尽管它们对森林的自然再生和未来的植被组成很重要，但人们对树苗的水力学知之甚少。在第一个生长季节的不同时间，我们分析了三种温带针叶树、2 种被子植物树和 1 种被子植物灌木的木质部区域特异性 （Kshoot_Axyl） 和叶区域特异性 （Kshoot_L） 芽水力导度，以及栓塞性，以及与细胞渗透参数和木质部解剖特征的相关发现。在发芽后的前 10 周，Kshoot_Axyl 和 Kshoot_L 急剧下降，然后保持稳定，直到生长季节结束。在最年轻的阶段，栓塞抵抗性非常低，但随着细胞壁加固的增加，到秋季时显着增加。同时，膨胀损失时的水势和饱和时的渗透势降低。与谱系、物种和生长形式无关，从初级木质部到次级木质部的转变导致液压系统效率较低但越来越抗栓塞，从而在低水势风险增加的情况下实现稳定的供水。