Influence of Root Diameter and Soil Depth on the Xylem Anatomy of Fine- to Medium-Sized Roots of Mature Beech Trees in the Top- and Subsoil

Abstract

Despite their importance for water uptake and transport, the xylem anatomical and hydraulic properties of tree roots have only rarely been studied in the field. We measured mean vessel diameter (D), vessel density (VD), relative vessel lumen area (lumen area per xylem area) and derived potential hydraulic conductivity (Kp) in the xylem of 197 fine- to medium-diameter roots (1–10 mm) in the topsoil and subsoil (0–200 cm) of a mature European beech forest on sandy soil for examining the influence of root diameter and soil depth on xylem anatomical and derived hydraulic traits. All anatomical and functional traits showed strong dependence on root diameter and thus root age but no significant relation to soil depth. Averaged over topsoil and deep soil and variable flow path lengths in the roots, D increased linearly with root diameter from ∼50 μm in the smallest diameter class (1–2 mm) to ∼70 μm in 6–7 mm roots (corresponding to a mean root age of ∼12 years), but remained invariant in roots >7 mm. D never exceeded ∼82 μm in the 1–10 mm roots, probably in order to control the risk of frost- or drought-induced cavitation. This pattern was overlain by a high variability in xylem anatomy among similar-sized roots with Kp showing a higher variance component within than between root diameter classes. With 8% of the roots exceeding average Kp in their diameter class by 50–700%, we obtained evidence of the existence of ‘high-conductivity roots’ indicating functional differentiation among similar-sized roots. We conclude that the hydraulic properties of small to medium diameter roots of beech are mainly determined by root age, rendering root diameter a suitable predictor of hydraulic functioning, while soil depth – without referring to path length – had a negligible effect.

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

“…Increased vessel lumen diameter with cambial age was in line with previous below- [63] and aboveground studies [12,28,64]. Increased early-and latewood vessel lumen diameter, as well as increased vessel element length with cambial age, improves water transport efficiency.…”

Lack of effect of admixture proportion and tree density on water acquisition depth for European beech (Fagus sylvatica L.) and sycamore maple (Acer pseudoplatanus L.)

“…Indeed, the fine root morphology, anatomy and water flow resistance do vary with depth in woody species (McElrone et al 2004;Wang et al 2015). However, no such information is available for sycamore maple, and the xylem anatomical and hydraulic properties of beech fine roots were not significantly influenced by soil depth in the study conducted by Kirfel et al (2017). Studies focusing on water Fig.…”

Geogenic organic carbon in terrestrial sediments and its contribution to total soil carbon

“…The calculated GOC contribution for Miocene sand was comparatively low (29 %-77 %) compared with the contribution for Red Sandstone and loess, especially at 5 m depth. Compared with the Red Sandstone, this could be due to deep biogenic carbon inputs, such as roots and root exudates from the trees John et al, 2016;Kirfel et al, 2017;Tückmantel et al, 2017), since the loosely bedded Miocene sand allows for deep infiltration compared with the Red Sandstone site with its shallow bedrock as a root-restricting layer (Schneider and Don, 2019). Although it was not possible to define the exact rooting depth for Miocene sand, this depth probably does not exceed 4 m, according to Schenk and Jackson (2005).…”

“…This type of carbon is considered a highly stable carbon pool due to its apparently high 14 C ages (Mathieu et al, 2015;Schrumpf et al, 2013). However, another explanation for this could be the contribution of geogenic organic carbon (GOC), which is defined here as OC that originates from deposition during sedimentation and rock formation and may increasingly influence subsoil OC with depth (Graz et al, 2010;Kögel-Knabner et al, 2008;Schrumpf et al, 2013;Trumbore, 2009). GOC, in most cases, is devoid of 14 C and, thus, may lead to an overestimation of ancient OC sources, although a number of studies showed the importance of root-derived young OC inputs to subsoils (Angst et al, 2016;Crow et al, 2009).…”