Effect of elevated CO2 on monoterpene emission of young Quercus ilex treesand its relation to structural and ecophysiological parameters

We investigated growth, leaf monoterpene emission, gas exchange, leaf struc ture and leaf chemical composition of 1-year-old Quercus ilex L. seedlings grown in ambient (350 mul l(-1)) and elevated (700 mul l(-1)) CO2 concentra tions ([CO2]). Monoterpene emission and gas exchange were determined at con stant temperature and irradiance (25 degreesC and 1000 mu mol m(-2) s(-1) o f photosynthetically active radiation) at an assay [CO2] of 350 or 700 mul l(-1). Measurements were made on intact shoots after the end of the growing season between mid-October and mid-February. On average, plants grown in e levated [CO2] had significantly increased foliage biomass (about 50%). Leav es in the elevated [CO2] treatment were significantly thicker and had signi ficantly higher concentrations of cellulose and lignin and significantly lo wer concentrations of nitrogen and minerals than leaves in the ambient [CO2 ] treatment. Leaf dry matter density and leaf concentrations of starch, sol uble sugars, lipids and hemi-cellulose were not significantly affected by g rowth in elevated [CO2]. Monoterpene emissions of seedlings were significan tly increased by elevated [CO2] but were insensitive to short-term changes in assay [CO2]. On average, plants grown in elevated [CO2] had 1.8-fold hig her monoterpene emissions irrespective of the assay [CO2]. Conversely, assa y [CO2] rapidly affected photosynthetic rate, but there was no apparent lon g-term acclimation of photosynthesis to growth in elevated [CO2]. Regardles s of growth [CO2]. photosynthetic rates of all plants almost doubled when t he assay [CO2] was switched from 350 to 700 mul l(-1). At the same assay [C O2], mean photosynthetic rates of seedlings in the two growth CO2 treatment s were similar. The percentage of assimilated carbon lost as monoterpenes w as not significantly altered by CO2 enrichment. Leaf emission rates were co rrelated with leaf thickness, leaf concentrations of cellulose, lignin and nitrogen, and total plant leaf area. In all plants, monoterpene emissions s trongly declined during the winter independently of CO2 treatment. The resu lts are discussed in the context of the acquisition and allocation of resou rces by e. ilex seedlings and evaluated in terms of emission predictions.