Pushing the limits to tree height: could foliar water storage compensate for hydraulic constraints in Sequoia sempervirens

1. The constraint on vertical water transport is considered an important factor limiting height growth and maximum attainable height of trees. Here we show evidence of foliar water storage as a mechanism that could partially compensate for this constraint in Sequoia sempervirens, the tallest species. 2. We measured hydraulic and morpho-anatomical characteristics of foliated shoots of tall S. sempervirens trees near the wet, northern and dry, southern limits of its geographic distribution in California, USA. 3. The ability to store water (hydraulic capacitance) and saturated water content (leaf succulence) of foliage both increased with height and light availability, maintaining tolerance of leaves to water stress (bulk leaf water potential at turgor loss) constant relative to height. 4. Transverse-sectional area of water-storing, transfusion tissue in leaves increased with height, while the area of xylem tissue decreased, indicating increasing allocation to water storage and decreasing ...1. 垂直水分运输的限制被认为是制约树木高度生长及最大可达树高的重要因子。本研究以现存最高树种北美红杉（Sequoia sempervirens）为材料，证实叶片储水（foliar water storage）可作为一种机制，部分抵消该限制效应。 2. 我们在美国加利福尼亚州该物种地理分布的湿润北部边界与干旱南部边界区域，测定了高大北美红杉带叶枝条的水力特性与形态解剖学特征。 3. 叶片的储水能力（水力容蓄度，hydraulic capacitance）与饱和含水量（叶片肉质性，leaf succulence）均随树高与光照可利用性的提升而升高，使得叶片的水分胁迫耐受性（膨压丧失时的总叶水势）随树高保持相对恒定。 4. 叶片内储水转输组织（transfusion tissue）的横截面积随树高升高而增大，而木质部组织的面积则随之减小，这表明植株对储水结构的资源分配不断提升，对木质部的分配则逐渐……