Abstract

Parenchyma is an important component of the secondary xylem. It has multiple functions and its fraction is known to vary substantially across angiosperm species. However, the physiological significance of this variation is not yet fully understood. Here, we examined how different types of parenchyma (ray parenchyma [RP], axial parenchyma [AP] and AP in direct contact with vessels [APV]) are coordinated with three essential xylem functions: water conduction, storage of non-structural carbohydrate (NSC) and mechanical support. Using branch sapwood of 15 co-occurring drought-adapted woody species from the subtropical Bonin Islands, Japan, we quantified 10 xylem anatomical traits and examined their linkages to hydraulic properties, storage of soluble sugars and starch and sapwood density. The fractions of APV and AP in the xylem transverse sections were positively correlated with the percentage loss of conductivity in the native condition, whereas that of RP was negatively correlated with the maximum conductivity across species. Axial and ray parenchyma fractions were positively associated with concentrations of starch and NSC. The fraction of parenchyma was independent of sapwood density, regardless of parenchyma type. We also identified a negative relationship between hydraulic conductivity and NSC storage and sapwood density, mirroring the negative relationship between the fractions of parenchyma and vessels. These results suggest that parenchyma fraction underlies species variation in xylem hydraulic and carbon use strategies, wherein xylem with a high fraction of AP may adopt an embolism repair strategy through an increased starch storage with low cavitation resistance.

中文翻译：

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薄壁组织是日本亚热带岛屿 15 种木本植物木质部水力学和碳储存的种间变异的基础

摘要

薄壁组织是次生木质部的重要组成部分。它具有多种功能，并且已知其比例在被子植物物种中差异很大。然而，这种变异的生理意义尚未完全了解。在这里，我们检查了不同类型的实质（射线实质 [RP]、轴向实质 [AP] 和与血管直接接触的 AP [APV]）如何与三个基本的木质部功能相协调：水传导、非结构性碳水化合物的储存。 NSC）和机械支撑。我们使用来自日本亚热带 Bonin 群岛的 15 种共同发生的适应干旱的木本植物的枝边材，量化了 10 种木质部解剖特征，并检查了它们与水力特性、可溶性糖和淀粉的储存以及边材密度的联系。木质部横截面中 APV 和 AP 的比例与原生条件下的电导率损失百分比呈正相关，而 RP 的比例与物种间的最大电导率呈负相关。轴向和射线薄壁组织部分与淀粉和 NSC 的浓度呈正相关。薄壁组织的比例与边材密度无关，与薄壁组织类型无关。我们还确定了导水率与 NSC 储存和边材密度之间的负相关关系，反映了薄壁组织和血管部分之间的负相关关系。这些结果表明，实质部分是木质部水力和碳利用策略中物种变异的基础，