Abstract
Abstract • Context It has been estimated that about half of a plant’s total hydraulic resistance is located belowground, but it is not well known how temperate tree species differ in root hydraulic properties and how these traits vary with the species’ drought tolerance. • Aims We examined root anatomical and hydraulic traits in five broad-leaved tree species with different drought tolerance, analyzed the relation between root anatomy and hydraulic conductivity and root embolism, and investigated the relation of these traits to the species’ drought tolerance. • Methods In small-diameter roots (2–6 mm), we measured vessel diameters and vessel density, specific hydraulic conductivity, and the percental loss of conductivity (“native” embolism) during summer in a mixed forest. • Results Specific conductivity was positively related to vessel diameter but not to vessel density. Drought-tolerant Fraxinus showed the smallest mean vessel diameters and drought-sensitive Fagus the largest. Specific conductivity was highly variable among different similar-sized roots of the same species with a few roots apparently functioning as “high-conductivity roots”. • Conclusion The results show that coexisting tree species can differ largely in root hydraulic traits with more drought-sensitive trees apparently having larger mean vessel diameters in their roots than tolerant species. However, this difference was not related to the observed root conductivity losses due to embolism.
Highlights
A key direction of plant adaptation in terrestrial environments is to maximize carbon gain while maintaining a favorable plant water status and avoiding hydraulic failure
We found no dependence of ks on vessel density in the root xylem which is contrary to the results reported by Tyree and Ewers (1991), Cruiziat et al (2002) and Tyree and Zimmermann (2002) for the hydraulic system in trunk and branches
The five broad-leaved tree species of this study showed significant anatomical differences in their small-diameter roots that could partly be related to the assumed drought tolerance of the species with more drought-sensitive trees generally having larger mean vessel diameters in their roots than tolerant species
Summary
A key direction of plant adaptation in terrestrial environments is to maximize carbon gain while maintaining a favorable plant water status and avoiding hydraulic failure. This requires adjustment of the plant’s conducting system to maximize water uptake and to reduce water deficits (Sperry et al 1998, 2002; Maseda and Fernández 2006). The hydraulic system of a tree is composed of a network of vessels that enables the continuous supply of water from roots to shoots The conductivity of this system is mainly determined by the number, diameter, and length of the vessels along the root-to-leaf flow path. The hydraulic traits have a large influence on how the leaf water status of trees is responding to changes in soil water supply and atmospheric water demand (Eamus et al 2006)
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