Effects of elevated CO2 concentration on photosynthetic acclimation and productivity of two potato cultivars grown in open-top chambers

In two subsequent years, an early maturing potato cultivar with low leaf area index (LAI) and a late culti- var with high LAI were grown at concentrations of 350 and 700 µL CO2 L -1 in open-top chambers. The average increase of tuber dry matter yield by elevated CO2 was 27% in 1995 and 49% in 1996. During the first weeks after planting, elevated CO2 stimulated the light-saturated rate of photosynthesis (Amax) of both cultivars by 80%. However, Amax under elevated CO2 declined to the level of the low-CO2 treatment in the course of the growing season. In 1995 this convergence due to acclimation of photosynthesis was completed within 6 weeks, but in 1996, accli- mation proceeded until the end of the growing season. Photosynthetic acclimation was accompanied by a reduced Rubisco content, and was correlated more closely with accumulation of sucrose than of starch. From fluorescence measurements it was concluded that, in contrast to the carboxylation efficiency, the efficiency of photosynthetic reactions centers was not affected by acclimation to elevated CO2. The faster photosynthetic acclimation in 1995 coincided with overall lower values of Amax, crop growth rate and growth response to elevated CO2. It is shown that the indeterminate growth pattern of potato with its large sink capacity does not preclude acclimation. The effect of acclimation on yield was quantified by computer simulations. The simulated results indicated that photosynthetic acclimation reduced the positive effect of elevated CO2 on tuber yield by 50%.