Hydraulic safety margins and air-seeding thresholds in roots, trunks, branches and petioles of four northern hardwood trees

Publication Title

New Phytologist

Document Type

Article

Department or Program

Biology

Publication Date

4-16-2018

Keywords

Acer rubrum, air-seeding threshold, embolism, Fagus grandifolia, Fraxinus americana, Quercus rubra, segmentation, xylem

Abstract

During drought, xylem sap pressures can approach or exceed critical thresholds where gas embolisms form and propagate through the xylem network, leading to systemic hydraulic dysfunction. The vulnerability segmentation hypothesis (VSH) predicts that low-investment organs (e.g. leaf petioles) should be more vulnerable to embolism spread compared to high-investment, perennial organs (e.g. trunks, stems), as a means of mitigating embolism spread and excessive negative pressures in the perennial organs. We tested this hypothesis by measuring air-seeding thresholds using the single-vessel air-injection method and calculating hydraulic safety margins in four northern hardwood tree species of the northeastern United States, in both saplings and canopy height trees, and at five points along the soil–plant–atmosphere continuum. Acer rubrum was the most resistant to air-seeding and generally supported the VSH. However, Fagus grandifolia, Fraxinus americana and Quercus rubra showed little to no variation in air-seeding thresholds across organ types within each species. Leaf-petiole xylem operated at water potentials close to or exceeding their hydraulic safety margins in all species, whereas roots, trunks and stems of A. rubrum, F. grandifolia and Q. rubra operated within their safety margins, even during the third-driest summer in the last 100 yr.

Comments

Original version is available from the publisher at: https://doi.org/10.1111/nph.15135

PubMed ID

29663388

Copyright Note

© 2018 The Authors

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