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Effects of Rising Atmospheric CO2 and Warming on Rice Growth

Reference
Roy, K.S., Bhattacharyya, P., Neogi, S., Rao, K.S. and Adhya, T.K. 2012. Combined effect of elevated CO2 and temperature on dry matter production, net assimilation rate, C and N allocations in tropical rice (Oryza sativa L.). Field Crops Research 139: 71-79.
New research out of India suggests that rising atmospheric CO2 and temperature may have significant positive impacts on this important agricultural crop.

Writing as background for their work, authors Roy et al. (2012) state that "an average annual increase in grain production of 44 million metric tons is required to meet the food demands of the world by 2050," citing Tester and Langridge (2010); and they also note that "the predicted 2.0°C increase in air temperature by the end of 2050 (IPCC, 2007) might lead to a 20-40% decrease in cereal yields [italics added]," citing Lele (2010), all of which paints a truly bleak picture of humanity's future. But is this truly so?

To assess this situation from an experiment-based perspective, the five researchers from the Central Rice Research Institute of India conducted a three-year open-top-chamber field study to observe the effects of elevated atmospheric CO2 concentration (550 vs. an ambient 390 ppm), and elevated temperature (2°C above ambient temperature), focusing on how increases in these two parameters will affect dry matter production, carbon and nitrogen concentrations in plant parts, and their allocation in a tropical rice cultivar (cv. Naveen).

Results of the experiment revealed the following responses in the elevated CO2/normal temperature treatment:
     (1) Dry matter accumulation in the aboveground portion of the rice plants was enhanced by 17.7% at maturity.
     (2) Root biomass, leaf area index and net carbon assimilation rates increased significantly by 28, 19 and 40%, respectively.
     (3) Grain yield was significantly higher (22.6%) in the CO2-enriched treatment.
     (4) The net carbon yield increased by 23.3%.
     (5) Nitrogen allocation increased significantly in leaf (13%), stem (14%) and panicle (17%) at maturity.

Results of the experiment revealed the following responses in the elevated CO2/elevated temperature treatment:
     (1) Dry matter accumulation in the aboveground portion of the rice plants was enhanced by 18.1% at maturity.
     (2) Root biomass, leaf area index and net carbon assimilation rates also increased significantly.
     (3) Grain yield was significantly higher (19.6%) in the CO2-enriched treatment.
     (4) The net carbon yield increased by 24.2%.
     (5) Nitrogen allocation increased significantly in leaf (13%), stem (14%) and panicle (17%) at maturity.

In considering such findings, and focusing on food production, perhaps things might not be nearly as bad as they are projected to be at mid-century and beyond, in terms of feeding the world's anticipated larger population at that point in time. In fact, they might even be much better than they are today, thanks in part to both rising atmospheric CO2 and warmer temperatures.

Additional References
IPCC. 2007. Climate Change 2007: Impacts, Adaptation and Vulnerability. IPCC Secretariat, Geneva, Switzerland.

Lele, U. 2010. Food security for a billion poor. Science 326: 1554.

Tester, M. and Langridge, P. 2010. Breeding technologies to increase crop production in a changing world. Science 327: 818-822.

Archived 24 April 2013