Paper Reviewed
Nakano, H., Yoshinaga, S., Takai, T., Arai-Sanoh, Y., Kondo, K., Yamamoto, T., Sakai, H., Tokida, T., Usui, Y., Nakamura, H., Hasegawa, T. and Kondo, M. 2017. Quantitative trait loci for large sink capacity enhance rice grain yield under free-air CO2 enrichment conditions. Scientific Reports 7: 1827, doi:10.1038/s41598-017-01690-8.

Introducing the rationale for their study, Nakano et al. (2017) reference the global food security dilemma, where there is an urgent need to increase global food production to feed the ever-increasing population of the planet. And in this regard, they note the importance of increasing crop yields per unit area given present limits to arable land.

One way to accomplish the objective of increasing food production per unit area is, in the words of Nakano et al., to formulate "a strategy that can be used to develop high-yielding [crop] varieties under increased atmospheric CO2 concentrations, such as those predicted in the near future." Clearly, as numerous studies have shown (see our Plant Growth Data section of our website), plant growth and yield do indeed respond positively to the aerial fertilization effect of atmospheric CO2. Thus, it is important for scientists to identify which genotypes of a given crop species will respond with the greatest yield increases for a given increment increase in CO2.

Such was the ultimate goal of Nakano et al., who grew three rice genotypes under ambient (383 ppm) and elevated (577) ppm CO2 in an outdoor Free-Air CO2 Enrichment (FACE) study located in Tsukubamirai, Japan, over two growing seasons (2012 and 2013). The three rice genotypes included (a) Koshihikari, a conventional variety in Japan, (b) a chromosome segment substitution line (CSSL) containing quantitative trait loci GN1a, which favors the production of more spikelets per panicle of rice, and (c) a near-isogenic line (NIL) with allele APO1, which also produces a higher number of spikelets per panicle.

So which genotype performed the best under elevated CO2?

Using grain yield as the measure of interest, CSSL had the highest yield, experiencing a 21 percent increase at the elevated levels of CO2, followed by NIL at 19 percent and Koshihikari at eight percent. According to the authors, the improved yields at the higher CO2 concentration in the CSSL and NIL genotypes occurred because of their higher number of spikelets per panicle, their increased capability to translocate carbohydrates into the panicle, and their ability to enhance the sink capacity of the grains. Given such findings, Nakano et al. say that, "consequently, to develop varieties which can contribute a stable and high production of rice under increased atmospheric CO2 concentrations in the near future, introducing alleles to conventional varieties that enhance sink capacity represents a useful strategy." And that seems like a winning strategy to us!