Water stored in tree stems (i.e., trunks and branches) is an important contributor to transpiration that can improve photosynthetic carbon gain and reduce the probability of cavitation. However, in tall trees the capacity to store water may decline with height because of chronically low water potentials associated with the gravitational potential gradient. We quantified the importance of elastic stem water storage in the top 5 to 6 m of large (4.2–5.0 m DBH, 82.1–86.3 m tall) Sequoiadendron giganteum (Lindley) J. Buchholz (giant sequoia) trees using a combination of architectural measurements and automated sensors that monitored summertime diel rhythms in sap flow, stem diameter, and water potential. Stem water storage contributed 1.5 to 1.8% of water transpired at the tree tops, and hydraulic capacitance ranged from 2.6 to 4.1 L MPa⁻¹ m⁻³. These values, which are considerably smaller than reported for shorter trees, may be associated with persistently low water potentials imposed by gravity and could indicate a trend of decreasing water storage dynamics with height in tree. Branch diameter contraction and expansion consistently and substantially lagged behind fluxes in water potential and sap flow, which occurred in sync. This lag suggests that the inner bark, which consists mostly of live secondary phloem tissue, was an important hydraulic capacitor, and that hydraulic resistance between xylem and phloem retards water transfer between these tissues. We also measured tree-base sap flux, which lagged behind that measured in trunks near the tree tops, indicating additional storage in the large trunks between these measurement positions. Whole-tree sap flow ranged from 2,227 to 3,752 L day⁻¹, corroborating previous records for similar-sized giant sequoia and representing the largest yet reported for any individual tree. Despite such extraordinarily high daily water use, we estimate that water stored in tree-top stems contributes minimally to transpiration on typical summer days.

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地球上最大的树木——巨杉树顶部的干水储存动态

储存在树干（即树干和树枝）中的水是蒸腾作用的重要贡献者，可以提高光合碳增益并降低空化的可能性。然而，在高大的树木中，由于与重力势梯度相关的长期低水势，储水能力可能随高度而下降。我们量化了大型红杉（4.2-5.0 m DBH， 82.1-86.3 m 高）顶部 5 到 6 m 的弹性茎蓄水的重要性(Lindley) J. Buchholz（巨型红杉）树使用建筑测量和自动传感器的组合来监测夏季液流、茎直径和水势的昼夜节律。茎蓄水贡献了树顶蒸腾水的 1.5% 至 1.8%，水力电容范围为 2.6 至 4.1 L MPa ^-1  m ^-3. 这些值远小于所报告的较短树木的​​值，可能与重力施加的持续低水势有关，并且可能表明蓄水动态随着树木高度而减少的趋势。分支直径收缩和扩张始终且大大落后于同步发生的水势和液流通量。这种滞后表明，主要由活的次生韧皮部组织组成的内部树皮是一个重要的水力电容器，木质部和韧皮部之间的水力阻力阻碍了这些组织之间的水分转移。我们还测量了树基液流通量，它落后于在树顶附近的树干中测量的值，这表明在这些测量位置之间的大树干中有额外的存储量。全树液流从 2,227 到 3，^-1，证实了类似大小的巨型红杉的先前记录，并代表了迄今为止报告的任何单棵树的最大记录。尽管日常用水量如此之高，但我们估计，储存在树顶茎中的水在典型的夏季对蒸腾作用的贡献微乎其微。