title: Testing the ecophysiological basis for the control of monoterpene concentrations along canopy profiles in thinned and unthinned balsam fir stands.
abstract: To determine which ecophysiological factors appear to control monoterpene concentrations in balsam fir foliage [Abies balsamea (L.) P. Mill.], the percentage of photosynthetically active radiation (%PAR), specific leaf area (SLA), light-saturated photosynthesis (Amax), and concentrations per unit leaf area of foliar nitrogen (N), total soluble sugars (TSS), starch and monoterpenes were measured on current-year needles from three canopy levels (upper, middle and lower) the year following a pre-commercial thinning. The thinning only modestly changed the light profile within the canopy. %PAR was negatively correlated with SLA (r2=0.62 in June, r2=0.53 in July and August) and positively correlated with foliar nitrogen concentrations (r2=0.51) within the crown profile. The positive relationship between N and Amaxwas quite weak (r2=0.15), suggesting significant variations in non-photosynthetic N within the canopies. Total monoterpenes were positively correlated with both %PAR (r2=0.29) and Amax(r2=0.27), and negatively correlated with SLA (r2=0.30). Contrary to that predicted by the carbon-nutrient balance hypothesis, total monoterpenes were negatively and only very weakly correlated with the starch/N ratio (r2=0.06) and were not significantly correlated with either the TSS/N or the [TSS+starch]/N ratios. Monoterpenes were positively correlated with both N and TSS, although the relationship varied with the phenological state of the foliage, i.e., monoterpenes were more highly correlated with TSS (r2=0.67) (immature foliage) in June, and in July and August with N (r2=0.63) (mature foliage). Thus, it appears that monoterpene concentrations may be controlled primarily by carbohydrate supply in the early growing season and later by enzymatic capacity. Data expressed on a dry weight basis showed a similar pattern.
authors.affiliation: Centre de recherche en biologie forestière, Pavillon Abitibi-Price, Université Laval, Sainte-Foy, Québec G1K 7P4, Canada, , , , , , CA.
authors.forename: M
authors.initials: M
authors.lastname: Lamontagne
authors.affiliation: Centre de recherche en biologie forestière, Pavillon Abitibi-Price, Université Laval, Sainte-Foy, Québec G1K 7P4, Canada, , , , , , CA.
authors.forename: H A
authors.initials: HA
authors.lastname: Margolis
authors.affiliation: Centre de recherche en biologie forestière, Pavillon Abitibi-Price, Université Laval, Sainte-Foy, Québec G1K 7P4, Canada, , , , , , CA.
authors.forename: É
authors.initials: É
authors.lastname: Bauce
keywords: Carbon-nutrient balance; Key words Balsam fir; Light; Monoterpenes; Photosynthesis