The Effects of Increased Atmospheric Carbon Dioxide on Growth, Carbohydrates, and Photosynthesis in Radish, Raphanus sativus

The effects of sink capacity on the regulation of the acclimationof photosynthetic capacity to elevated levels of carbon dioxideare important from a global perspective. We investigated theeffeocts of elevated (750 µmol mol^–1) and ambient(350 µmol mol^–1) atmospheric CO₂ on growth, carbohydratelevels, and photosynthesis in radish seedlings from 15 to 46d after planting. In radish, a major sink is the storage root,and its thickening is initiated early. Elevated CO₂ increasedthe accumulation of dry matter by 111% but had no effect onthe acclimation of the rate of photosynthesis or on the levelsof carbohydrates in leaves at dawn. Elevated CO₂ increased thedry weight in storage roots by 105% by 46 d after planting,apparently enhancing the sink capacity. This enhanced capacityseemed to be responsible for absorption of elevated levels ofphotosynthate and to result in the absence of any over-accumulationof carbohydrates in source leaves and the absence of negativeacclimation of photosynthetic capacity at the elevated levelof CO₂. (Received July 4, 1997; Accepted October 16, 1997)