Duration of CO2 Enrichment Influences Growth, Yield, and Gas Exchange of Two Tomato Species

Lycopersicon esculentum Mill. cv . Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO 2 concentrations (330 or 900 μmol·m -3 ) for 10 weeks. The elevated CO 2 concentration increased the relative growth rate (RGR) of L. esculentum and L. chmielewskii by 18% and 30%, respectively, after 2 weeks of treatment. This increase was not maintained as the plant matured. Net assimilation rate (NAR) and specific leaf weight (SLW) were always higher in C0 2 -enriched plants, suggesting that assimilates were preferentially accumulated in the leaves as reserves rather than contributing to leaf expansion. Carbon dioxide enrichment increased early and total yields of L. esculentum by 80% and 22%, respectively. Carbon exchange rates (CER) increased during the first few weeks, but thereafter decreased as tomato plants acclimated to high atmospheric CO 2 . The relatively constant concentration of internal C0 with time suggests that reduced stomatal conductance under high CO 2 does not explain lower photosynthetic rates of tomato plants grown under high atmospheric CO 2 concentrations. Leaves 5 and 9 responded equally to high CO 2 enrichment throughout plant growth. Consequently, acclimation of CO 2 -enriched plants was not entirely due to the age of the tissue. After 10 weeks of treatment, leaf 5, which had been exposed to high CO 2 for only 10 days, showed the greatest acclimation of the experiment. We conclude that the duration of exposure of the whole plant to elevated CO 2 concentration, rather than the age of the tissue, governs the acclimation to high CO 2 concentrations.