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Super Rice to Match Super Atmospheric CO2 Concentrations
Volume 12, Number 4: 28 January 2009

In a research report recently published in Agriculture, Ecosystems and Environment, Yang et al. (2009) write that "rice (Oryza sativa L.) is unequivocally one of the most important food crops that feed the largest proportion of the world's population," and they say that "the demand for rice production will continue to increase in the coming decades, especially in the major rice-consuming countries of Asia, Africa and Latin America, due to the population explosion and cropland reduction." Hence, they state that "as sufficient intraspecific variation in yield response exists under field conditions, there is a pressing need to identify genotypes which would produce maximum grain yield under projected future [atmospheric] CO2 levels."

Working with this goal in mind at the National Institute for Agro-Environmental Sciences in Tsukuba, Japan, Lou et al. (2008) grew plants of four different rice cultivars -- Dular (a traditional indica variety), IR72 (an improved indica variety), Koshihikari (a temperate japonica variety), as well as IR65598 (a new variety not yet released to farmers) -- within growth chambers in submerged pots filled with a fertilized soil collected from the plough layer of a paddy field in Chiba Prefecture, Japan, at two atmospheric CO2 concentrations: ambient (~370 ppm) and elevated (~570 ppm). This protocol revealed that the extra 200 ppm of CO2 actually reduced the ultimate grain yield of Dular (but by only 0.7%), while it increased the final grain yield of IR72 by 8.0%, that of Koshihikari by 13.4%, and that of IR65598 by 17.7%.

Working at the FACE facility at Yangzhou City, Jiangsu Province, China, Yang et al. (2009) had the same goal in mind, but focused on a single two-line inter-subspecific hybrid rice variety (Liangyoupeijiu), which was produced as part of "a nationwide mega project" to develop what they call "super" hybrid cultivars that would "further break the yield ceiling." In their three-year CO2-enrichment study, which employed the same CO2 levels as the study of Lou et al., they found a much greater grain yield stimulation: a 28.4% CO2-induced increase under a low nitrogen fertility treatment of 12.5 g N m-2 and a 31.7% CO2-induced increase under a high nitrogen fertility treatment of 25 g N m-2.

In discussing their findings, Yang et al. state that their hybrid cultivar "appears to profit much more from elevated CO2 than inbred japonica cultivars," which does indeed seem to be the case, as both Japanese and Chinese FACE studies of inbred japonica cultivars have only found CO2-induced grain yield enhancements on the order of 13% for a 200-ppm increase in the air's CO2 concentration. Therefore, noting that "there is a pressing need to identify genotypes which could optimize harvestable yield as atmospheric CO2 increases," Yang et al. conclude that "on the basis of available FACE data on rice," the hybrid rice cultivar Liangyoupeijiu "appears to be particularly promising."

And indeed it is, for as we have noted multiple times on our website, unless mankind can take full advantage of the ability of the ongoing rise in the atmosphere's CO2 content to boost both the productivity and water-use efficiency of our major food crops, not only will we be in "a world of hurt" just a few short decades from now, but so also will the rest of the biosphere, as we will otherwise need to usurp most of the planet's remaining land and freshwater resources merely to grow the food we will need to sustain ourselves, leaving precious little of either of these two essential resources for earth's other life forms to utilize.

Sherwood, Keith and Craig Idso

References
Lou, Y., Inubushi, K., Mizuno, T., Hasegawa, T., Lin, Y., Sakai, H., Cheng, W. and Kobayashi, K. 2008. CH4 emission with differences in atmospheric CO2 enrichment and rice cultivars in a Japanese paddy soil. Global Change Biology 14: 2678-2687.

Yang, L., Liu, H., Wang, Y., Zhu, J., Huang, J., Liu, G., Dong, G. and Wang, Y. 2009. Yield formation of CO2-enriched inter-subspecific hybrid rice cultivar Liangyoupeijiu under fully open-air condition in a warm sub-tropical climate. Agriculture, Ecosystems and Environment 129: 193-200.