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 ar ea index (LAI) and a late cultivar with high LAI were grown at concentratio ns of 350 and 700 muL 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. Du ring the first weeks after planting, elevated CO2 stimulated the light-satu rated rate of photosynthesis (A(max)) of both cultivars by 80%. However, A( max) under elevated CO2 declined to the level of the low-CO2 treatment in t he course of the growing season. In 1995 this convergence due to acclimatio n of photosynthesis was completed within 6 weeks, but in 1996, acclimation proceeded until the end of the growing season. Photosynthetic acclimation w as accompanied by a reduced Rubisco content, and was correlated more closel y with accumulation of sucrose than of starch. From fluorescence measuremen ts it was concluded that, in contrast to the carboxylation efficiency, the efficiency of photosynthetic reactions centers was not affected by acclimat ion to elevated CO2. The faster photosynthetic acclimation in 1995 coincide d with overall lower values of A(max), crop growth rate and growth response to elevated CO2. It is shown that the indeterminate growth pattern of pota to with its large sink capacity does not preclude acclimation. The effect o f acclimation on yield was quantified by computer simulations. The simulate d results indicated that photosynthetic acclimation reduced the positive ef fect of elevated CO2 on tuber yield by 50%.