Influence of Cambial Age and Axial Height on the Spatial Patterns of Xylem Traits in Catalpa bungei, a Ring-Porous Tree Species Native to China

Shan Li,Roman Link,Xiaomei Jiang,Jingming Zheng,Shuang Li,Liping Deng,Rongjun Zhao,Yafang Yin,Bernhard Schuldt,Xin Li,Ren Li

doi:10.3390/f10080662

Abstract

Studying how cambial age and axial height affects wood anatomical traits may improve our understanding of xylem hydraulics, heartwood formation and axial growth. Radial strips were collected from six different heights (0–11.3 m) along the main trunk of three Manchurian catalpa (Catalpa bungei) trees, yielding 88 samples. In total, thirteen wood anatomical vessel and fiber traits were observed usinglight microscopy (LM) and scanning electron microscopy (SEM), and linear models were used to analyse the combined effect of axial height, cambial age and their interaction. Vessel diameter differed by about one order of magnitude between early- and latewood, and increased significantly with both cambial age and axial height in latewood, while it was positively affected by cambial age and independent of height in earlywood. Vertical position further had a positive effect on earlywood vessel density, and negative effects on fibre wall thickness, wall thickness to diameter ratio and length. Cambial age had positive effects on the pit membrane diameter and vessel element length, while the annual diameter growth decreased with both cambial age and axial position. In contrast, early- and latewood fiber diameter were unaffected by both cambial age and axial height. We further observed an increasing amount of tyloses from sapwood to heartwood, accompanied by an increase of warty layers and amorphous deposits on cell walls, bordered pit membranes and pit apertures. This study highlights the significant effects of cambial age and vertical position on xylem anatomical traits, and confirms earlier work that cautions to take into account xylem spatial position when interpreting wood anatomical structures, and thus, xylem hydraulic functioning.

Highlights

The xylem structure is a complex and delicate multicellular network, which simultaneously fulfils three key functions, namely water transport, mechanical support, and water and nutrient storage [1]
Vessel lumen diameter differed by about one order of magnitude between earlywood and latewood, and vessel lumen diameter distribution patterns varied among tree individuals
Vessel density was significantly affected by axial height, and vessel element length and earlywood pit membrane diameter were positively influenced by cambial age

Summary

Introduction

The xylem structure is a complex and delicate multicellular network, which simultaneously fulfils three key functions, namely water transport, mechanical support, and water and nutrient storage [1]. Vessels and fibres account for the largest fractions of vascular structures, while vessels function as the main water conducting cells of the xylem hydraulic architecture [2]. The largest vessels are found in roots and vessel lumen diameters becomes acropetally tapered, i.e., small conduits tend to distribute in distal parts of trees such as the apical positions. According to the hydraulic segmentation hypothesis [2], distal positions in plants are more embolism-resistant, and given that larger conduits are more vulnerable to embolism [3], smaller conduits in apical parts might be a biological compensation for increased hydraulic resistance with axial height [4,5]

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Results

Discussion

Conclusion