The response of Brassica juncea var. Bio‐183‐92 to elevated CO2 under increased nitrogen treatment was studied. There was an interactive effect of CO2 and nitrogen nutrition, indicating that, on the addition of more nitrogen, the plants sustained the positive effect of CO2 enrichment by utilizing additional carbohydrates for the development of new sinks. Excess carbohydrate enables plants to be flexible and responsive to additional nitrogen application to sustain the CO2 enrichment effect.

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Basmati rice (Oryza sativa L.) cultivars viz. PRH-10 (pusa rice hybrid-10) and PS-2 (Pusa Sugandh-2) were grown under two different day/night temperatures (31/24°C, 35/28°C) at ambient (370 µmol/mol) and elevated (550 µmol/ mol) carbon dioxide (CO 2 ) concentration, respectively, to characterize how an increase in CO 2 and temperature affects rice photosynthesis and carbohydrate metabolism. At elevated CO 2 , the photosynthetic rates increased under both the temperature regimes, compared with plants grown at ambient CO 2 . The photosynthetic rate, sucrose-P synthase (SPS) activity and accumulation of soluble sugars and starch were higher in PRH-10 (pusa rice hybrid-10), compared to PS-2 (Pusa Sugandh-2). Elevated temperature decreased the photosynthetic rates both under ambient and elevated CO 2 conditions. The SPS (sucrose-P synthase) activity and the accumulation of soluble sugars and starch were enhanced at elevated CO 2 under both temperature regimes compared with plants grown at ambient CO 2 . The up-regulation of SPS (sucrose-P synthase) under elevated CO 2 and temperature would be beneficial for growth and productivity of rice plants for the future climatic conditions.

There is a general concern that changes in plant productivity and composition caused by increase in atmospheric CO 2 concentration will alter the chemical composition of the grain. This review describes the impact of rising atmospheric CO 2 on the grain characteristics in wheat, rice, brassica, mungbean and soybean, which are significantly responsive to the elevated CO 2 for their growth, physiology and biochemical processes. The synthesis of the CO 2 induced changes in the chemical composition and nutritional qualities of their grains has been discussed. It was demonstrated that the rise in atmospheric CO 2 affects the nutritional and industrial application properties of the grains of crop plants. The grain proteins and other nutritionally important constituents significantly reduced, adversely affecting the nutritional and bread making quality in wheat. However, there are evidences suggesting the sustenance of the bread making properties by fertilizer application. Similarly, the CO 2 induced changes in the composition of starch in rice grains, result into easy gelatinization and higher viscosity on cooking. These grains bring firmness due to increase in amylose content. Adequately larger size of grains was the outcome of the elevated CO 2 effects, in Brassica species. It increased the oil content due to greater acetyl Co A enzyme activity and also help in regulating fatty acid biosynthesis. Some of the nutritionally undesirable fatty acids were significantly reduced in this process, making this oil less harmful for heart patients. The adequate use of fertilizer application and selection pressure of breeders may significantly contribute in developing cultivars, which will counter the adverse effect of rising atmospheric CO 2 on grain quality.

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