Volume 12, Number 25: 24 June 2009
In a review paper published in Plant Production Science, Peng et al. (2009) report that rice production in China more than tripled over the past half-century, due mainly to an increase in grain yield that resulted from the development of new semidwarf varieties in the 1950s and hybrid varieties in the 1970s, as well as from improved crop management practices such as nitrogen fertilization and irrigation. With respect to the future, people are hoping for more of the same. Why? Because "as its population rises," in the words of Peng et al., "China will need to produce about 20% more rice by 2030 in order to meet its domestic needs if rice consumption per capita stays at the current level." However, as they continue, they say there has been a "yield stagnation" over the past decade, and that total rice production in 2006 was actually 9% lower than it was in 1997, suggesting that the country's food future does not look good.
Further complicating the picture are several unfavorable trends, among which Peng et al. include a decline in arable land, increasing water scarcity and climate change, to which they add the problems of "overuse of fertilizers and pesticides, breakdown of irrigation infrastructure, oversimplified crop management, and a weak extension system."
So what might be done to rectify the situation and prevent what would appear to be a massive disaster-in-waiting? The three researchers highlight five plant characteristics they feel could be improved by innovative breeding techniques: yield potential, drought tolerance, heat tolerance, disease resistance, and insect resistance. However, they fail to discuss them within the context of the ongoing rise in the air's CO2 content, which is a most important oversight.
Consider, for example, the case of yield potential. Working at the National Institute for Agro-Environmental Sciences in Tsukuba, Japan, Lou et al. (2008) grew four different rice cultivars within growth chambers maintained at atmospheric CO2 concentrations of 370 and 570 ppm, finding that the extra 200 ppm of CO2 actually reduced the ultimate grain yield of one of the varieties (but by only 0.7%), while it increased the final grain yield of the other three varieties by 8.0%, 13.4% and 17.7%. Likewise, working at the FACE facility at Yangzhou City, Jiangsu Province, China, Yang et al. (2009) studied a single two-line inter-subspecific hybrid rice variety that was produced as part of a mega project to develop "super" hybrid cultivars that would "further break the yield ceiling." And in their three-year study, which employed the same CO2 levels as that of Lou et al., they found a much greater CO2-induced grain yield stimulation: 28.4% at low nitrogen fertility and 31.7% at high nitrogen fertility. Hence, they concluded "there is a pressing need to identify genotypes which could optimize harvestable yield as atmospheric CO2 increases."
The same situation exists with respect to drought and heat tolerance, and with respect to disease and insect resistance. Atmospheric CO2 enrichment generally tends to enhance all four of these important plant functions. You can read more about the first two in the materials archived on our website by going to our Subject Index and, under the general heading of Growth Response to CO2 with Other Variables, clicking on the sub-headings of Temperature (Agricultural Crops) and Water Stress (Agricultural Crops). Similarly, you can read about the role of atmospheric CO2 enrichment in helping to increase crop disease resistance by visiting Disease and clicking on Plants; and you can read how rising CO2 concentrations enhance crop resistance to insect damage by visiting Herbivory and clicking on its several sub-categories.
Clearly, just as there are species and variety differences in crop yield response to elevated CO2 concentrations, so are there species and varietal differences in the responses of crop drought and heat tolerance and crop disease and insect resistance to elevated levels of CO2. Therefore, breeding for optimum performance of these important plant functions in a high-CO2 world of the future should also be a prime objective in meeting the challenge of adequately feeding the planet's future population. And the fact that the need for this "do or die" effort is not all that far distant, only makes the work required to achieve it all that more urgent. Are we up to the task?
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.
Peng, S., Tang, Q. and Zou, Y. 2009. Current status and challenges of rice production in China. Plant Production Science 12: 3-8.
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.