Photosynthesis, growth and productivity of rice under elevated CO₂

A field experiment was conducted to compare the changes in photosynthesis, growth and productivity of rice at elevated CO₂ concentration with that of the plants grown under ambient CO₂ and field conditions. Thirty-five days old seedlings of rice (Oryza sativa) cv. BRRIdhan 39 were transplanted in three growing environments - (i) open top chamber (OTC) with elevated CO₂ (570 ± 50 ppm), (ii) OTC with ambient CO₂ (−360 ppm) and (iii) in the open field. Leaf photosynthesis rate (Pn) of rice was measured at successive growth stages viz. vegetative, panicle initiation, flowering, early maturity, mid-maturity and maturity stages. It was observed that Pn increased from vegetative stage to flowering stage and then declined gradually towards the maturity stage in this cultivar. Elevated CO₂ profoundly increased the Pn rates at all growth stages of rice, the highest Pn (40.02 μmol m⁻² S⁻¹) being observed at flowering stage. Elevated CO₂ also enhanced biomass accumulation resulting in nearly 38% and 35% higher dry matter than ambient and field-grown rice, respectively. Compared to the plants grown in OTC at ambient CO₂ or grown in the field, elevated CO₂ treated plants had more favourable partitioning of dry matter into panicles. Consequently, plants with elevated CO₂ produced higher seed yield (19.624 g hill⁻¹) than the ambient (15.543 g hill⁻¹) and field (15.682 g hill⁻¹) grown rice.