Journal Article

Nitrogen allocation and the fate of absorbed light in 21-year-old <i>Pinus radiata</i>

Sabine Posch, Charles R. Warren, Jörg Kruse, Helmut Guttenberger and Mark A. Adams

in Tree Physiology

Volume 28, issue 3, pages 375-384
Published in print March 2008 | ISSN: 0829-318X
Published online March 2008 | e-ISSN: 1758-4469 | DOI:
Nitrogen allocation and the fate of absorbed light in 21-year-old Pinus radiata

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We investigated effects of nitrogen (N) fertilizer and canopy position on the allocation of N to Rubisco and chlorophyll as well as the distribution of absorbed light among thermal energy dissipation, photochemistry, net CO2 assimilation and alternative electron sinks such as the Mehler reaction and photorespiration. The relative reduction state of the primary quinone receptor of photosystem II (QA) was used as a surrogate for photosystem II (PSII) vulnerability to photoinactivation. Measurements were made on needles from the lower, mid and upper canopy of 21-year-old Pinus radiata D. Don trees grown with (N+) and without (N0) added N fertilizer. Rubisco was 45 to 60% higher in needles of N+ trees than in needles of N0 trees at all canopy positions. Chlorophyll was ∼80% higher in lower- and mid-canopy needles of N+ trees than of N0 trees, but only ∼20% higher in upper-canopy needles. Physiological differences between N+ and N0 trees were found only in the lower- and mid- canopy positions. Needles of N+ trees dissipated up to 30% less light energy as heat than needles of N0 trees and had correspondingly more reduced QA. Net CO2 assimilation and the proportions of electrons used by alternative electron sinks such as the Mehler reaction and photorespiration were unaffected by N treatment regardless of canopy position. We conclude that the application of N fertilizer mainly affected the biochemistry and light-use physiology in lower- and mid-canopy needles by increasing the amount of chlorophyll and hence the amount of light harvested. This, however, did not improve photochemistry or safe dissipation, but increased PSII vulnerability to photoinactivation, an effect with likely significant consequences during sunflecks or sudden gap formation.

Keywords: canopy; chlorophyll; N fertilizer; photoprotection; photosynthesis; Rubisco

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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