Abstract

Wood density (WD) is often used as a proxy for hydraulic traits such as vulnerability to drought-induced xylem cavitation and maximum water transport capacity, with dense-wooded species generally being more resistant to drought-induced xylem cavitation, having lower rates of maximum water transport and lower sapwood capacitance than light-wooded species. However, relationships between WD and the hydraulic traits that they aim to predict have not been well established in tropical forests, where modeling is necessary to predict drought responses for a high diversity of unmeasured species. We evaluated WD and relationships with stem xylem vulnerability by measuring cavitation curves, sapwood water release curves and minimum seasonal water potential (Ψ_min) on upper canopy branches of six tree species and three liana species from a single wet tropical forest site in Panama. The objective was to better understand coordination and trade-offs among hydraulic traits and the potential utility of these relationships for modeling purposes. We found that parameters from sapwood water release curves such as capacitance, saturated water content and sapwood turgor loss point (Ψtlp,x) were related to WD, whereas stem vulnerability curve parameters were not. However, the water potential corresponding to 50% loss of hydraulic conductivity (P₅₀) was related to Ψtlp,x and sapwood osmotic potential at full turgor (π_o,x). Furthermore, species with lower Ψ_min showed lower P₅₀, Ψtlp,x and π_o,x suggesting greater drought resistance. Our results indicate that WD is a good easy-to-measure proxy for some traits related to drought resistance, but not others. The ability of hydraulic traits such as P₅₀ and Ψtlp,x to predict mortality must be carefully examined if WD values are to be used to predict drought responses in species without detailed physiological measurements.

中文翻译：

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新热带冠层藤本植物和树木种类在广泛的木材密度中的水力特征：用模型预测干旱死亡率的意义。

摘要

木材密度（WD）通常用作水力性状的替代指标，例如对干旱引起的木质部空化的脆弱性和最大的输水能力，茂密的树木通常对干旱引起的木质部空化具有更强的抵抗力，最高的发生率较低水分传输和边材电容比轻木树种低。但是，在热带森林中，WD与它们旨在预测的水力性状之间的关系尚未得到很好的建立，在热带森林中，必须进行建模才能预测大量未测物种的干旱响应。我们评估WD，并用干木质部漏洞关系通过测量空化的曲线，边材水释放曲线和最小季节性水势（Ψ_分钟）来自巴拿马一个湿热带林地的6种树种和3种藤本植物的上层树冠分支。目的是更好地理解水力性状之间的协调和权衡，以及这些关系在建模中的潜在效用。我们发现边材水分释放曲线的参数，如电容，饱和水含量和边材膨松损失点（Ψtlp，x）与WD相关，而茎杆脆弱性曲线参数与WD无关。但是，与水力传导率损失50％（P ₅₀）相对应的水势与tlp，x和边坡全渗透（p _{o ，x}）的边材渗透势有关。此外，较低的物种Ψ_分钟显示出较低的P ₅₀，Ψtlp中，x和π _{ö ，X}表明更大的抗旱性。我们的结果表明，WD对于某些与抗旱性有关的性状是易于测量的良好替代，而对于其他一些则不是。如果将WD值用于预测物种的干旱反应而没有详细的生理测量，则必须仔细检查水力性状（如P ₅₀和Ψtlp，x）预测死亡率的能力。