Stem water storage capacity and hydraulic capacitance (C_S) play a crucial role in tree survival under drought‐stress. To investigate whether C_S adjusts to increasing water deficit, variation in stem water content (StWC) was monitored in vivo for 2 years and related to periodical measurements of tree water potential in Mediterranean Quercus ilex trees subjected either to permanent throughfall exclusion (TE) or to control conditions. Seasonal reductions in StWC were larger in TE trees relative to control ones, resulting in greater seasonal C_S (154 and 80 kg m⁻³ MPa⁻¹, respectively), but only during the first phase of the desorption curve, when predawn water potential was above −1.1 MPa. Below this point, C_S decreased substantially and did not differ between treatments (<20 kg m⁻³ MPa⁻¹). The allometric relationship between tree diameter and sapwood area, measured via electrical resistivity tomography, was not affected by TE. Our results suggest that (a) C_S response to water deficit in the drought‐tolerant Q. ilex might be more important to optimize carbon gain during well‐hydrated periods than to prevent drought‐induced embolism formation during severe drought stress, and (b) enhanced C_S during early summer does not result from proportional increases in sapwood volume, but mostly from increased elastic water.

中文翻译：

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地中海橡树的水力驯化受到永久的穿透瀑布的排斥，导致茎的水力容量增加。

在干旱胁迫下，树干的蓄水量和水力电容（C _S）在树木生存中起着至关重要的作用。为了调查是否Ç_小号调节水分亏缺不断增加，在茎的含水量（STWC）的变化在体内监测2年，在地中海与树水势定期测量冬青栎要么遭受永久性穿透排斥（TE）的树木或控制条件。与对照相比，TE树木中StWC的季节性减少幅度更大，导致季节性C _S更大（154和80 kg m ^-3 MPa ^-1），但仅在解吸曲线的第一阶段时，黎明前的水势高于-1.1 MPa。在该点以下，C _S显着降低并且在两次处理之间没有差异（<20 kg m ^-3 MPa ^-1）。通过电阻层析成像测量的树木直径与边材面积之间的异形关系不受TE影响。我们的结果表明（a）耐旱Q.冬青属对水分亏缺的C _S响应可能比在严重干旱胁迫下防止干旱引起的栓塞形成更重要，这对于充分水合时期的碳吸收最重要，和（b ）增强C _S 初夏不是边材体积成比例增加的结果，而是主要原因是弹性水的增加。