During repetitive defoliation events, carbon can become limiting for trees. To maintain growth and survival, the resources have to be shared more efficiently, which could result in a trade-off between the different physiological processes of a plant. The objective of this study was to assess the effect of defoliation in carbon allocation of balsam fir [Abies balsamea (L.) Mill.] to test the presence of a trade-off between allocation to growth, carbon storage, and defense. Three defoliation intensities [control (C-trees, 0% defoliation), moderately (M-trees, 41–60%), and heavily (H-trees, 61–80%) defoliated] were selected in order to monitor several variables related to stem growth (wood formation in xylem), carbon storage in stem and needle (non-structural soluble sugars and starch), and defense components in needles (terpenoids compound) from May to October 2011. The concentration of starch was drastically reduced in both wood and leaves of H-trees with a quasi-absence of carbon partitioning to storage in early summer. Fewer kinds of monoterpenes and sesquiterpenes were formed with an increasing level of defoliation indicating a lower carbon allocation for the production of defense. The carbon allocation to wood formation gradually reduced at increasing defoliation intensities, with a lower growth rate and fewer tracheids resulting in a reduced carbon sequestration in cell walls. The hypothesis of a trade-off between the allocations to defense components and to non-structural (NCS) and structural (growth) carbon was rejected as most of the measured variables decreased with increasing defoliation. The starch amount was highly indicative of the tree carbon status at different defoliation intensity and future research should focus on the mechanism of starch utilization for survival and growth following an outbreak.

Many studies have focused on the influence of needle defense compounds that are produced when trees are attacked. Spruce budworm is the most important defoliator of conifers in eastern North America causing tree mortality. Volatile components such as terpenes are of importance as they are known to be agents of defense in plants and trees against many aggressors like spruce budworm. In this study, the Static Headspace Gas Chromatography (HS-GC) method was used to evaluate volatile compounds in the foliage of balsam fir (Abies balsamea) in order to compare the results obtained with the traditional GC-MS method. An advantage of analyzing plant volatile compounds with the HS-GC was the simplicity of execution, allowing a large number of samples to be treated.The most abondant volatile molecules were identified on the HS-GC chromatogram, except for some compounds such as α-thujene, fenchone, terpin-1-en-4-ol and α-terpineol. In addition to the qualitative analysis of terpene, a quantitative analysis of β-phellandrene was done to compare the variation of this compound between a control and a defoliated site. This study suggests that β-phellandrene was released as a response to injuries when the site was heavily defoliated by spruce budworm.

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Santene; (2) Tricyclene; (3) a-thujene; (4) a-ptnene; (5) Camphene; (6) p-pinene; (7) , 1996;Tuomi & et al, 1988;Wagner & et al, 1985). Les metabolites secondaires peuvent être classés en trois groupes bien distincts; terpènes, composés phénoliques et les composés contenant de l'azote (Taiz & Zeiger, 2006; Waksmundzka-Hajnos & et al, 2008). L'origine des metabolites secondaires mise en relation avec la voie métabolique de base est illustrée à la figure 1.1. Cette figure démontre bien que tous les produits de la plante dérivent de 24 la production des glucides en provenance de la photosynthèse et que l'acétyl-Co est le point central des voies de synthèses des divers composés de défense. Les terpenesLes terpenes représentent la classe la plus large et vaste de produits secondaires générés par les plantes. Chez les conifères, les terpenes s'accumulent en général au niveau des tissus des aiguilles, surtout en grande quantité dans les trichomes glandulaires de la face supérieure des aiguilles et ils sont également nombreux dans la résine présente dans le tronc (xylème et phloème) des conifères (B..Miller & al, 2005; Phytochemical Society of Europe, 1991). Selon certaines études, la quantité présente des composés terpéniques dans les aiguilles serait directement influencée (dépendante) par la quantité de sucres solubles totaux (SST) présents lors de la saison de croissance des arbres (Gershenzon & et al, 1989;. (Gîonest, 1999;Maclean & Lidstone, 1982).L'analyse des composés chimiques et de la croissance se divisera en trois sections qui porteront sur :• La quantification des metabolites secondaires (monoterpènes et sesquiterpènes) servant de composés de défense contre la tordeuse des bourgeons de l'épinette.• La quantification des sucres solubles totaux et des réserves d'amidon contenus dans les aiguilles des sapins sélectionnés ainsi que les réserves d'amidon contenus dans le xylème.