Non-invasive imaging reveals convergence in root and stem vulnerability to cavitation across five tree species

Abstract

Root vulnerability to cavitation is challenging to measure and under-represented in current datasets. This gap limits the precision of models used to predict plant responses to drought because roots comprise the critical interface between plant and soil. In this study we measured vulnerability to drought induced cavitation in woody roots and stems of five tree species (Acacia aneura, Cedrus deodara, Eucalyptus crebra, Eucalytus saligna, and Quercus palustris) with a wide range of xylem anatomies. X-ray microtomography was used to visualize the accumulation of xylem embolism in stems and roots of intact plants that were naturally dehydrated to varying levels of water stress. Vulnerability to cavitation, defined as the water potential causing a 50% loss of hydraulic function (P50), varied broadly among the species (-4.51 to -11.93 MPa in stems and -3.13 to -9.64 MPa in roots). The P50 of roots and stems was significantly related across species, with species that had more vulnerable stems also having more vulnerable roots. While there was strong convergence in root and stem vulnerability to cavitation, the P50 of roots was significantly higher than the P50 of stems in three species. However, the difference in root and stem vulnerability for these species was small; between 1% to 31% of stem P50. Thus, while some differences existed between organs, roots were not dramatically more vulnerable to embolism than stems and the differences observed were less than those reported in previous studies. Further study is required to evaluate the vulnerability across root orders and to extend these conclusions to a greater number of species and xylem functional types.

Mechanisms of xylem hydraulic recovery after drought in Eucalyptus saligna

“…The strong correlation between PLV and PLC is supported by numerous studies (Gauthey et al, 2020; Li et al, 2020; Peters et al, 2020) which suggests that loss of conductivity in this species can be approximated by counting gas filled vessels, especially if vessel diameter remains relatively constant within the stem.…”

Unlocking Drought-Induced Tree Mortality: Physiological Mechanisms to Modeling

“…This assumption is supported by some early studies showing that roots are often more vulnerable to embolism than stems or leaves ( Johnson et al, 2016 ; Wason et al, 2018 ). However, some recent findings suggest that roots are comparably or even more tolerant to drought-induced embolism compared with other organs in some species ( Rodriguez-Dominguez et al, 2018 ; Peters et al, 2020 ; Lübbe et al, 2021 ). Clearly, more studies are required to confirm the spatial pattern of vulnerability to embolism within plants, particularly within the root system and rhizosphere.…”

High variation in hydraulic efficiency but not xylem safety between roots and branches in four temperate broad‐leaved tree species

“…In line with this main result, a growing number of recent studies using different techniques have confirmed that roots are notably more embolism resistant than previously thought. These studies used the micro‐CT technique and the optical method, both direct and non‐invasive methods applied on intact plants (Losso et al., 2019; Peters et al, 2020; Rodriguez‐Dominguez et al., 2018; Skelton et al., 2017), the rehydration kinetics technique (Creek et al., 2018), the single‐vessel air‐injection method (Wason et al., 2018) and the pneumatic method (Wu et al., 2020). Together with our study, the results from six independent methods are largely in contradiction with the majority of former comparative studies, which found the root xylem to be the most vulnerable organ along the hydraulic pathway in a wide range of species from different environments (e.g.…”