Paper Reviewed
Chen, C., Jiang, Q., Ziska, L.H., Zhu, J., Liu, G., Zhang, J., Ni, K., Seneweera, S. and Zhu, C. 2015. Seed vigor of contrasting rice cultivars in response to elevated carbon dioxide. Field Crops Research 178: 63-68.

Writing as background for their work, Chen et al. (2015) note that although numerous studies have examined the effects of CO2 on the growth and yield of rice, "to date, no information is available with respect to whether [CO2] alters seed germination and/or seedling vigor, and whether such variation is the basis for cultivar variation in growth or yield" in response to atmospheric CO2 enrichment. Seeking to remedy this lack of knowledge, the international team of nine researchers performed a free-air CO2 enrichment (FACE) study on six rice cultivars (Koshihikari, Yangdao 6Hao, IIY084, Zhonghua14, Wuyunjing21 and Takanari) at the Zongcun village FACE facility (32.58°N, 119.70°E), Jiangsu province, China during the 2012 and 2013 growing seasons. Specifically, their objective was to determine the effects of a 200-ppm increase in atmospheric CO2 above ambient conditions on various seed characteristics of rice, including seed vigor, germination rate and energy, seedling fresh and dry weight and seed coat permeability.

The results of this experiment indicated a positive, though varied, response of elevated CO2 on seed yield that ranged from 4 to 37 percent among the six cultivars. In contrast, elevated CO2 had no effect on seed germination rate or germination energy, nor on 1000-grain weight, seed specific gravity, hull thickness, conductivity of electrolyte leakage, or soluble protein in seed leakage among any of the cultivars. There was, however, a significant interaction between CO2 and soluble sugar in seed leakage (SSL); but the authors report that "these changes had no effect on seed germination rate and germination energy," indicating they were of little importance. In addition, in two of the six cultivars elevated CO2 induced a significant reduction in grain nitrogen and protein concentration; but once again the decline was determined to have had "no effect on either germination rate or energy." Consequently, given such findings, the authors write in the concluding sentence of their paper's abstract that "no clear indication of quantitative effects of elevated [CO2] on rice germination was found." And because seed germination "is an essential aspect of crop establishment," as characterized by Chen et al., it would appear that the growth-enhancing benefits of atmospheric CO2 enrichment on rice yields will continue into the future, as seeds from today's cultivars germinate and sprout anew -- without detriment -- into the harvests of tomorrow.