Effects of Growth under Elevated CO₂ on the Capacity of Photosynthesis in Two Radish Cultivars Differing in Capacity of Storage Root

抄録

The effect of growth under elevated CO₂ on the capacity of photosynthesis was assessed in two cultivars of radish, Raphanus sativus L. cv White Cherrish and Kosena, with a large and small storage root, respectively. Plants were grown under ambient (ca. 350 mmol CO₂ mol^-1) and elevated (ca. 750 mmol CO₂ mol^-1) CO₂ and the first leaf of the plants at various ages, were examined for chlorophyll fluorescence, the maximum photosynthetic rates under saturated CO₂ (photosynthetic capacity) and the rates of transpiration simultaneously. Elevated CO₂ did not significantly reduce the capacity of photosynthesis, transpiration, quantum yield of electron transport from photosystem II (ΦPSII), and the maximum intrinsic yield of photosystem II at any developmental stage in both cultivars. In other words, growth under elevated CO₂ had no effect on the capacity of photosynthesis in either cultivar. These results suggested that not only the storage root but also vigorously growing young leaves play an important role as a sink in utilizing increased photosynthate under elevated CO₂. The elevated CO₂ accelerated ontogeny and caused a slightly earlier decline in the capacity of photosynthesis. The capacity of carbon metabolism and the photochemical capacity decreased coordinately with advancing age accompanied with the decline of photosynthetic activity under both ambient and elevated CO₂.