Response of photosynthesis, growth, carbon isotope discrimination and osmotic tolerance of rice to elevated CO2

Four rice ( Oryza sativa L.) cultivars "IR72", "Tesanai 2", "Guichao 2" and "IIyou 4480" were grown in two plastic house ( 15 in x 3 in) with 35 mumol/mol and 60 mumol/mol CO2 concentration which was controlled by computer. As compared with rice at ambient 35 mumol/mol CO2], the changes in photosynthetic rate at elevated CO, showed up-regulation ("IR72" and "Tesanai 2"), stable (unchanged) in "Guichao 2" and down-regulation type ("IIyou 4480"). Growth rate, panicle weight, integrated water use efficiency (WUE) calculated from Delta C-13 and the capacity of scavenging DPPH ( 1, 1-(diphenyl-2-picrylhydrazyl) free radical were increased at elevated CO). An increment in total biomass was observed in three cultivars by elevated CO,, with die exception of "IIyou 4480". Ratios of panicle weight/total biomass were altered to different extents in tested cultivars by elevated CO2. When leaf segments were subjected to PEG osmotic stress, die electrolyte leakage rate from leaves grown at elevated CO2 was less than that at 35 mumol/mol CO2- Those intraspecific variations of rice imply a possibility for selecting cultivars with maximal productivity and high tolerance to stresses adapted to elevated CO2 in the future.