Plant Science 188–189 (2012) 60–70 Contents lists available at SciVerse ScienceDirect Plant Science jou rn al hom epa ge: www.elsevier.com/locate/plantsci The impact of long-term CO 2 enrichment on sun and shade needles of Norway spruce (Picea abies): Photosynthetic performance, needle anatomy and phenolics accumulation Zuzana Lhotáková a,∗ , Otmar Urban b , Marianna Dubánková a , Milena Cvikrová c , Ivana Tomᡠsková b , Lucie Kubínová d , Karel Zvára e , Michal V. Marek b , Jana Albrechtová a a Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, Viniˇ cná 5, 128 44 Prague, Czech Republic b Laboratory of Plants Ecological Physiology, Global Change Research Center, Academy of Sciences of the Czech Republic, Bˇ elidla 986/4a, 603 00 Brno, Czech Republic c Laboratory of Biologically Active Compounds, Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojová 236, 165 00 Prague, Czech Republic d Department of Biomathematics, Institute of Physiology, Academy of Sciences of the Czech Republic, Víde ˇ nská, 142 20 Prague, Czech Republic e Department of Probability and Mathematical Statistics, Faculty of Mathematics and Physics, Charles University in Prague, Sokolovská 83, 186 75 Prague, Czech Republic a r t i c l e i n f o Article history: Received 30 September 2011 Received in revised form 20 February 2012 Accepted 25 February 2012 Available online 23 March 2012 Keywords: Elevated CO2 Mesophyll structure Phenolic compounds Photosynthesis Picea abies Stereological methods a b s t r a c t Norway spruce (Picea abies L. Karst) grown under ambient (365–377 mol (CO 2 ) mol -1 ; AC) and ele- vated (700 mol (CO 2 ) mol -1 ; EC) CO 2 concentrations within glass domes with automatically adjustable windows and on an open-air control site were studied after 8 years of treatment. The effect of EC on pho- tosynthesis, mesophyll structure and phenolics accumulation in sun and shade needles was examined. Photosynthetic assimilation and dark respiration rates were measured gasometrically; the structural parameters of mesophyll were determined using confocal microscopy and stereological methods. The contents of total soluble phenolics and lignin were assessed spectrophotometrically, and localizations of different phenolic groups were detected histochemically on needle cross-sections. EC enhanced the light-saturated CO 2 assimilation rate and reduced dark respiration in the current-year needles. No effects of CO 2 enrichment on mesophyll structural parameters were observed. Similarly, the accumulation and localization of phenolics and lignin remained unaffected by EC treatment. Needles differentiated into sun and shade ecotypes in the same manner and to the same extent irrespective of CO 2 treatment. Based on these results, it is apparent that the EC-induced enhancement of photosynthesis is not related to changes in the examined structural parameters of mesophyll and accumulation of phenolic compounds. © 2012 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Forest ecosystems functioning as a world carbon sink with a high and changeable capacity [1] are currently under intensive investigation. For both deciduous and evergreen tree C 3 species, Abbreviations: [CO2], carbon dioxide concentration; AC, ambient CO2 con- centration; ANmax, light-saturated CO2 assimilation rate; AQE, apparent quantum efficiency; C, current-year needles; C + 2, 3-year-old needles; EC, elevated CO2 concentration; FACE, free-air CO2 enrichment; ISD, internal surface density of meso- phyll; PAR, photosynthetically active radiation; RD, dark respiration rate; SUR, systematic uniform random; TSP, total soluble phenolics. ∗ Corresponding author. Tel.: +420 2219511693; fax: +420 221951704. E-mail addresses: zuza.lhotak@seznam.cz (Z. Lhotáková), urban.o@czechglobe.cz (O. Urban), cvikrova@ueb.cas.cz (M. Cvikrová), tomaskova.i@czechglobe.cz (I. Tomᡠsková), kubinova@biomed.cas.cz (L. Kubínová), karel.zvara@mff.cuni.cz (K. Zvára), marek.mv@czechglobe.cz (M.V. Marek), albrecht@natur.cuni.cz (J. Albrechtová). it has been shown that an elevated atmospheric CO 2 concentration ([CO 2 ]) leads to an initial stimulation of the light-saturated CO 2 assimilation rate [2]. This stimulation is mediated by an increase in the CO 2 diffusion gradient, suppressed photorespiration, and the insufficient saturation of Rubisco activity by the current atmo- spheric [CO 2 ] [3]. However, over long time periods, substantial reductions in the initial CO 2 -stimulated assimilation rate (photo- synthetic down-regulation) may occur [4]. An increase in net CO 2 assimilation rates induced by elevated [CO 2 ] (EC) can persist [5,6]. Plant responses to EC with regard to dark respiration rates have been shown to be variable and species specific [6], although a mod- erate stimulation of leaf respiration rates seems to be a general trend [7]. Generally, plant responses to EC appear to be variable depend- ing on several factors including the genotype-specific response observed even within a single genus, as shown, for example, in Betula and Populus species [8,9]. In addition, the age of studied trees is a factor affecting plant responses to EC, with younger trees 0168-9452/$ – see front matter © 2012 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2012.02.013