Acclimation of Two Tomato Species to High Atmospheric CO(2): I. Sugar and Starch Concentrations

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO(2) concentrations (330 or 900 microliters per liter) for 10 weeks. Tomato plants grown at 900 microliters per liter contained more starch and more sugars than the control. However, we found no significant accumulation of starch and sugars in the young leaves of L. esculentum exposed to high CO(2). Carbon exchange rates were significantly higher in CO(2)-enriched plants for the first few weeks of treatment but thereafter decreased as tomato plants acclimated to high atmospheric CO(2). This indicates that the long-term decline of photosynthetic efficiency of leaf 5 cannot be attributed to an accumulation of sugar and/or starch. The average concentration of starch in leaves 5 and 9 was always higher in L. esculentum than in L. chmielewskii (151.7% higher). A higher proportion of photosynthates was directed into starch for L. esculentum than for L. chmielewskii. However, these characteristics did not improve the long-term photosynthetic efficiency of L. chmielewskii grown at high CO(2) when compared with L. esculentum. The chloroplasts of tomato plants exposed to the higher CO(2) concentration exhibited a marked accumulation of starch. The results reported here suggest that starch and/or sugar accumulation under high CO(2) cannot entirely explain the loss of photosynthetic efficiency of high CO(2)-grown plants.