Root xylem in three woody angiosperm species is not more vulnerable to embolism than stem xylem

Min Wu,Thais Oya,Carmen Regina Marcati,Luciano Pereira,Steven Jansen,Ya Zhang

doi:10.1007/s11104-020-04525-0

Abstract

AimsSince plants are compartmentalised organisms, failure of their hydraulic transport system could differ between organs. We test here whether xylem tissue of stems and roots differ in their drought-induced embolism resistance, and whether intact roots are equally resistant to embolism than root segments.MethodsEmbolism resistance of stem and root xylem was measured based on the pneumatic technique for Acer campestre, A. pseudoplatanus and Corylus avellana, comparing also intact roots and root segments of C. avellana. Moreover, we compared anatomical features such as interconduit pit membrane between roots and stems.ResultsWe found a higher embolism resistance for roots than stems, although a significant difference was only found for A. pseudoplatanus. Interconduit pit membrane thickness was similar for both organs of the two Acer species, but pit membranes were thicker in roots than stems of C. avellana. Also, embolism resistance of an intact root network was similar to thick root segments for C. avellana.ConclusionOur observations show that root xylem is not more vulnerable to embolism than stem xylem, although more species need to be studied to test if this finding can be generalised. We also demonstrated that the pneumatic method can be applied to non-terminal plant samples.

Highlights

The plant hydraulic system is known to form a soil-plant-atmosphere continuum (Taiz and Zeiger 1998)
We found a higher embolism resistance for roots than stems, a significant difference was only found for A. pseudoplatanus
Interconduit pit membrane thickness was similar for both organs of the two Acer species, but pit membranes were thicker in roots than stems of C. avellana

Summary

Introduction

The plant hydraulic system is known to form a soil-plant-atmosphere continuum (Taiz and Zeiger 1998). The “hydraulic vulnerability segmentation hypothesis” (HVSH) suggests that distal organs (e.g. leaves and roots) are less resistant to xylem embolism than the proximal organs (e.g. stems and trunks) by means of providing hydraulic safety and protecting vital, meristematic tissues on proximal organs from dehydration (Johnson et al 2016; Tyree and Ewers 1991; Zhu et al 2016) This hypothesis is supported by some studies on angiosperms (e.g. Acer pseudoplatanus, Fagus sylvatica, Juglans regia × nigra and Juglans regia; Cochard et al 2002; Hochberg et al 2016; Losso et al 2019; Tyree et al 1993) and gymnosperms (e.g. Cupressus sempervirens and Pinus halepensis; Domec et al 2006; Froux et al 2005; Sperry and Ikeda 1997). The discrepancy between studies may be due to variation among species, potential differences in habitats and growth patterns, and/or methodological differences in the protocol

Methods

Results

Conclusion