Functional relationships between wood density and measures of xylem hydraulic safety and efficiency are ambiguous, especially in wet tropical forests. In this meta-analysis, we move beyond wood density per se and identify relationships between xylem allocated to fibers, parenchyma, and vessels and measures of hydraulic safety and efficiency. We analyzed published data of xylem traits, hydraulic properties and measures of drought resistance from neotropical tree species retrieved from 346 sources. We found that xylem volume allocation to fiber walls increases embolism resistance, but at the expense of specific conductivity and sapwood capacitance. Xylem volume investment in fiber lumen increases capacitance, while investment in axial parenchyma is associated with higher specific conductivity. Dominant tree taxa from wet forests prioritize xylem allocation to axial parenchyma at the expense of fiber walls, resulting in a low embolism resistance for a given wood density and a high vulnerability to drought-induced mortality. We conclude that strong trade-offs between xylem allocation to fiber walls, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees. Moreover, the benefits of xylem allocation to axial parenchyma in wet tropical trees might not outweigh the consequential low embolism resistance under more frequent and severe droughts in a changing climate.

中文翻译：

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纤维壁、纤维腔和轴向薄壁组织之间的木材分配权衡推动了新热带树木的抗旱性。

木材密度与木质部水力安全和效率测量之间的函数关系并不明确，特别是在潮湿的热带森林中。在这项荟萃分析中，我们超越了木材密度本身，并确定了分配给纤维、薄壁组织和血管的木质部与水力安全和效率措施之间的关系。我们分析了从 346 个来源检索到的新热带树种的木质部特征、水力特性和抗旱措施的已发表数据。我们发现，纤维壁的木质部体积分配增加了抗栓塞性，但以牺牲比电导率和边材电容为代价。纤维管腔中的木质部体积投资增加了电容，而轴向薄壁组织中的投资与更高的比电导率相关。来自潮湿森林的优势树类群优先将木质部分配给轴向薄壁组织，但牺牲了纤维壁，导致给定木材密度的栓塞抵抗力较低，并且很容易遭受干旱引起的死亡。我们得出的结论是，木质部分配给纤维壁、纤维腔和轴向薄壁组织之间的强烈权衡推动了新热带树木的抗旱性。此外，在潮湿的热带树木中，木质部分配到轴向薄壁组织的好处可能不会超过在气候变化的更频繁和严重的干旱下随之而来的低栓塞抵抗力。