Free Air CO2 Enrichment of Potato (Solanum tuberosum L.): photosynthetic capacity of leaves

Photosynthetic capacity of potato (Solanum tuberosum L.) leaves was investigated to- gether with the impact of elevated atmospheric CO2 concentration on assimilation during leaf senescence in a FACE (Free Air CO2 Enrichment) experiment. METHODS. Potato plants were grown in the field un- der ambient (about 360 ?mol mol-1) and elevated (460, 560, 660 ?mol mol-1) atmospheric CO2 concen- trations. A/Ci curves, carbon uptake in the field, to- tal non-structural carbohydrates, temperature and re- flectance were measured on leaves during summer. RESULTS. Photosynthetic capacity was not affected by elevated CO2 as shown by the response of Vcmax and Jmax calculated from A/Ci curves and this lack of ac- climation response was due to the existence of a large carbohydrate sink (tuber). Nevertheless, a temporary accumulation of total non-structural carbohydrate (TNC) occurred in the leaves of plants grown under elevated CO2, which reflected a transient imbalance between CO2 fixation and carbohydrate export from the leaves. Elevated CO2 increased the rate of leaf senescence and led to a faster decrease in photosyn- thetic capacity of leaves. It is hypothesised that ear- lier leaf senescence occurred either as a result of higher leaf temperature measured in the FACE plants or by the more rapid depletion of carbohydrate stor- age capacity in the tubers, or both. CONCLUSIONS. Overall, the FACE experiment showed that photosynthetic capacity of potato leaves is not directly affected by rising atmospheric CO2 concen- trations. Decreased photosynthetic capacity is instead caused in plants exposed to elevated CO2 by the oc- currence of earlier senescence.