Data from: 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 reliance on water transport from roots. 5. Treetop leaves of S. sempervirens absorb moisture via leaf surfaces and have potential to store more than five times the daily transpirational demand. Thus, foliar water storage may be an important adaptation that helps maintain physiological function of treetop leaves and hydraulic status of the crown, allowing this species to partially compensate for hydraulic constraints and sustain turgor for both photosynthesis and height growth.

1. 垂直水分运输的限制被视作制约树木高度生长及最大可达树高的关键因素。本研究以现存最高树种北美红杉（Sequoia sempervirens）为研究对象，提供证据表明叶片储水（foliar water storage）可作为一种代偿机制，部分抵消该限制的影响。
2. 我们于美国加利福尼亚州境内，该物种地理分布的湿润北部边界与干旱南部边界区域，对高大北美红杉的带叶枝条开展了水力性状与形态解剖特征的测定。
3. 叶片的储水能力（水力电容，hydraulic capacitance）与饱和含水量（叶片肉质性，leaf succulence）均随树高与光照可获得性的升高而提升，使得叶片对水分胁迫的耐受性——即膨压丧失时的整体叶水势——相对树高保持恒定。
4. 叶片内储水转输组织（transfusion tissue）的横截面积随树高增加而增大，而木质部组织的面积则随之减小，这意味着植株对水分储存的资源分配不断提升，对根系水分运输的依赖程度逐步降低。
5. 北美红杉的顶生叶片可通过叶表面吸收水分，其储水潜力可达每日蒸腾耗水量的五倍以上。综上，叶片储水或是一项重要的适应性性状，能够帮助维持顶生叶片的生理功能与冠层的水力稳态，从而使该物种可部分抵消水力运输限制，维持光合作用与高度生长所需的细胞膨压。