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The Variable Response of Rice Cultivars to Atmospheric CO2 Enrichment
Reference
Ziska, L.H., Manalo, P.A. and Ordonez, R.A. 1996. Intraspecific variation in the response of rice (Oryza sativa L.) to increased CO2 and temperature: growth and yield response of 17 cultivars. Journal of Experimental Botany 47: 1353-1359.

What was done
The authors grew well watered and fertilized plants of 17 different cultivars of rice (Oryza sativa L.) from seed to maturity within glasshouses maintained at atmospheric CO2 concentrations of either 373 ppm (ambient) or 664 ppm (elevated) in 24-l pots filled with local soil at two different sets of day/night temperatures (29/21C and 37/29C), after which they measured both total plant biomass and grain biomass.

What was learned
Overall, the degree of CO2-induced enhancement of total plant biomass and the number of cultivars showing significant enhancement with elevated CO2 decreased at the higher and more stressful set of growth temperatures, dropping from 12 out of 17 cultivars with an average biomass stimulation of 70% at the lower set of temperatures to 8 out of 17 cultivars with a mean biomass stimulation of 23% at the higher set of temperatures.

With respect to both total plant biomass and grain biomass production under the more standard lower set of temperatures, a few cultivars exhibited no significant changes in response to the specific degree of atmospheric CO2 enrichment employed in the study, while the most responsive cultivar - a tropical japonica type from Brazil - exhibited a whopping 265% increase in total plant biomass and an astounding 350% increase in grain biomass.

What it means
In light of the huge range in the degree of productivity enhancement exhibited in response to atmospheric CO2 enrichment by the 17 cultivars of rice examined in this experiment, it would appear there is a tremendous potential to select rice varieties to best take advantage of the aerial fertilization effect of the ongoing rise in the air's CO2 content, which endeavor, in the words of the researchers who conducted the study, "could maximize productivity as CO2 concentration increases." In fact, just such a selection process will likely be an essential element of the race to feed humanity in the year 2050 without usurping vast tracts of tropical and temperate forests, savannas and grasslands - as well as most of the planet's remaining freshwater resources - and thereby destroying most of what little remains of "wild nature."

For more on this incredibly important, but largely ignored, latter topic, see The CO2-Induced Preservation of Terrestrial Species (p. 17-19) in our critique of James Hansen's 26 April 2007 U.S. House of Representatives testimony.

Reviewed 22 August 2007