Journal Article

Experimental evidence supporting the concept of light-mediated modulation of stem hydraulic conductance

Arne Sellin, Eele Õunapuu and Annika Karusion

Edited by Ram Oren

in Tree Physiology

Volume 30, issue 12, pages 1528-1535
Published in print December 2010 | ISSN: 0829-318X
Published online November 2010 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/tpq091
Experimental evidence supporting the concept of light-mediated modulation of stem hydraulic conductance

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It is a well-described phenomenon that plant leaves respond to changes in light intensity and duration by adjusting leaf hydraulic efficiency, and there is current consensus that up- or down-regulation of water channels (aquaporins) in the plasma membrane of the bundle sheath and mesophyll cells play a central role in the underlying mechanisms. Recently, experimental evidence has been provided also for light-mediated changes of stem hydraulic conductance (Kstem) in field-grown laurel plants. This effect was attributed to differences in potassium ion concentration of xylem sap as a function of light conditions. In the present article, we report evidence obtained in silver birch (Betula pendula Roth), supporting the concept of light-mediated modulation of Kstem. Both canopy position (long-term effect) and current photosynthetic photon flux density (PPFD; short-term effect) had a significant impact (< 0.001) on Kstem measured in shoots taken from the lower (shade shoots) and upper (sun shoots) third of the crowns of ∼25-year-old trees growing in a natural forest stand. The shade shoots responded more sensitively to light manipulation: Kstem increased by 51% in shade shoots and 26% in sun shoots when PPFD increased from 70 to 330 μmol m−2 s−1. In 4-year-old trees growing in a dense experimental plantation, Kstem, specific conductivity of branch-wood (kbw) and potassium ion concentration ([K+]) in xylem sap varied in accordance with canopy position (< 0.001). Both Kstem and kbw increased considerably with light availability, increasing within the tree crowns from bottom to top; there was a strong relationship between mean values of Kstem and [K+] in hydraulically sampled branches.

Keywords: Betula pendula; canopy position; light intensity; potassium ions; silver birch; specific hydraulic conductivity; xylem sap

Journal Article.  5515 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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