Department of Botany & Plant Sciences, University of California, 2150 Batchelor Hall, Riverside, CA 92521, USA.
Smithsonian Tropical Research Institute, Balboa, Ancón, Panamá 0843-03092, Republic of Panamá.
Tree Physiol. 2021 Jan 9;41(1):24-34. doi: 10.1093/treephys/tpaa106.
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 (Ψmin) 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 (πo,x). Furthermore, species with lower Ψmin showed lower P50, Ψtlp,x and πo,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.
木材密度（WD）常被用作水力特性的替代指标，例如对干旱诱导的木质部空化的脆弱性和最大水分运输能力，通常木质部密度较高的物种对干旱诱导的木质部空化的抵抗力更强，最大水分运输速率和边材电容较低。然而，在热带森林中，WD 与它们旨在预测的水力特性之间的关系尚未得到很好的建立，在热带森林中，需要建模来预测大量未测量物种的干旱响应。我们评估了 WD 与茎木质部脆弱性的关系，方法是测量巴拿马一个单一湿热带森林地点的 6 种树木和 3 种木质藤本植物的上层树冠枝条的空化曲线、边材水分释放曲线和最小季节性水势（Ψmin）。目的是更好地理解水力特性之间的协调和权衡，以及这些关系在建模中的潜在用途。我们发现，边材水分释放曲线的参数，如电容、饱和含水量和边材膨压损失点（Ψtlp,x）与 WD 相关，而茎脆弱性曲线参数则不相关。然而，水力导率损失 50%时的水势（P50）与 Ψtlp,x 和边材完全膨压时的渗透势（πo,x）相关。此外，具有较低 Ψmin 的物种表现出较低的 P50、Ψtlp,x 和 πo,x，表明抗旱性更强。我们的结果表明，WD 是一些与抗旱性相关的性状的良好、易于测量的替代指标，但不是其他性状。如果要使用 WD 值来预测没有详细生理测量的物种的干旱响应，则必须仔细检查 P50 和 Ψtlp,x 等水力特性预测死亡率的能力。
