School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia.
Am J Bot. 2013 Aug;100(8):1483-93. doi: 10.3732/ajb.1200471. Epub 2013 Aug 8.
The mechanisms by which plants tolerate water deficit are only just becoming clear. One key factor in drought tolerance is the ability to maintain the capacity to conduct water through the leaves in conditions of water stress. Recent work has shown that a simple feature of the leaf xylem cells, the cube of the thickness of cell walls divided by the lumen width (t/b)(3), is strongly correlated with this ability.
Using ecologically, phylogenetically, and anatomically diverse members of Proteaceae, we tested the relationships between (t/b)(3) and climate, leaf mass per unit area, leaf area, and vein density. To test relationships at high phylogenetic levels (mostly genus), we used phylogenetic and nonphylogenetic single and multiple regressions based on data from 50 species. We also used 14 within-genus species pairs to test for relationships at lower phylogenetic levels.
All analyses revealed that climate, especially mean annual precipitation, was the best predictor of (t/b)(3). The variation in (t/b)(3) was driven by variation in both lumen diameter and wall thickness, implying active control of these dimensions. Total vein density was weakly related to (t/b)(3) but unrelated to either leaf area or climate.
We conclude that xylem reinforcement is a fundamental adaptation for water stress tolerance and, among evergreen woody plants, drives a strong association between rainfall and xylem anatomy. The strong association between (t/b)(3) and climate cannot be explained by autocorrelation with other aspects of leaf form and anatomy that vary along precipitation gradients.
植物耐受水分亏缺的机制尚不清楚。耐旱能力的一个关键因素是在水分胁迫条件下维持通过叶片输水的能力。最近的研究表明，叶片木质部细胞的一个简单特征，即细胞壁厚度的立方除以腔宽(t/b)(3)，与这种能力密切相关。
我们使用生态、系统发育和解剖学上多样化的 Proteaceae 成员来测试(t/b)(3)与气候、单位叶面积的叶质量、叶面积和叶脉密度之间的关系。为了在高系统发育水平（主要是属）上测试关系，我们使用了基于 50 个物种数据的系统发育和非系统发育的单因素和多因素回归。我们还使用了 14 个属内种对来测试较低系统发育水平上的关系。
所有分析都表明，气候，特别是年平均降水量，是(t/b)(3)的最佳预测因子。(t/b)(3)的变化是由腔直径和壁厚度的变化驱动的，这意味着对这些尺寸的主动控制。总叶脉密度与(t/b)(3)弱相关，但与叶面积或气候无关。
我们得出结论，木质部强化是对水分胁迫耐受的基本适应，在常绿木本植物中，强烈地将降雨与木质部解剖结构联系起来。(t/b)(3)与气候之间的强烈关联不能用与沿降水梯度变化的叶片形态和解剖结构的其他方面的自相关来解释。
