Vertical canopy gradient in photosynthesis and monoterpenoid emissions: An insight into the chemistry and physiology behind M.  Simpraga a, f, * , H. Verbeeck a, 1 , J. Bloemen a, 1 , L. Vanhaecke b , M. Demarcke c , E. Joó d , O. Pokorska d , C. Amelynck c , N. Schoon c , J. Dewulf d , H. Van Langenhove d , B. Heinesch e , M. Aubinet e , K. Steppe a a Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium b Laboratory of Chemical Analysis, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 132, 9820 Merelbeke, Belgium c Belgian Institute for Space Aeronomy, Ringlaan 3, 1100 Brussels, Belgium d Research Group Environmental Organic Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Ghent, Belgium e Unité de Physique des Biosystèmes, Gembloux Agro-Bio Tech, Université de Liège, Avenue de la Faculté d’Agronomie 8, 5030 Gembloux, Belgium f Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium highlights graphical abstract  vertical canopy gradient in mono- terpenoids, photosynthesis and leaf characteristics observed.  Unique carotenoid vs. mono- terpenoids composition.  Less monoterpenoids in sun leaves compared to semi-shaded counterparts.  Plants balance investments in mon- oterpenoids vs. carotenoids.  Differences in chemistry and physi- ology between sun and shade leaves. article info Article history: Received 28 April 2013 Received in revised form 17 July 2013 Accepted 20 July 2013 Keywords: Volatiles Photosynthesis Monoterpenoids Beech Vertical canopy gradient Carotenoids Sun and shade leaves abstract It is well known that vertical canopy gradients and varying sky conditions influence photosynthesis (Pn), specific leaf area (SLA), leaf thickness (LT) and leaf pigments (lutein, â-carotene and chlorophyll). In contrast, little is known about these effects on monoterpenoid (MT) emissions. Our study examines simultaneously measured Pn, MT emissions and the MT/Pn ratio along the canopy of an adult European beech tree (Fagus sylvatica L.) in natural forest conditions. Dynamic branch enclosure systems were used at four heights in the canopy (7, 14, 21 and 25 m) in order to establish relationships and better un- derstand the interaction between Pn and MT emissions under both sunny and cloudy sky conditions. Clear differences in Pn, MT emissions and the MT/Pn ratio were detected within the canopy. The highest Pn rates were observed in the sun leaves at 25 m due to the higher intercepted light levels, whereas MT emissions (and the MT/Pn ratio) were unexpectedly highest in the semi-shaded leaves at 21 m. The higher Pn rates and, apparently contradictory, lower MT emissions in the sun leaves may be explained by the hypothesis of Owen and Peñuelas (2005), stating synthesis of more photo-protective carotenoids may decrease the emissions of volatile isoprenoids (including MTs) because they both share the same biochemical precursors. In addition, leaf traits like SLA, LT and leaf pigments clearly differed with height * Corresponding author. Tel.: þ32 9 26 46 094. E-mail addresses: maja.simpraga@ugent.be, majasimpraga@telenet.be (M.  Simpraga). 1 Authors H. Verbeeck and K. Bloemen contributed equally to this article and have shared second author status. Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2013.07.047 Atmospheric Environment 80 (2013) 85e95