Abstract
ABSTRACTAtmospheric CO2 concentrations ([CO2]) have increased by more than 100 μmol mol−1 over the last century and are projected to rise further. Breeding cultivars with a greater response to elevated [CO2] (E-[CO2]) can be an effective adaptation to global climate change. We wondered whether E-[CO2]-responsive cultivars have been unintentionally selected through empirical breeding as [CO2] has increased. If so, modern cultivars may respond better to E-[CO2] than old ones. We conducted free-air CO2 enrichment (FACE) experiments in 2 years to examine whether rice cultivars bred in different eras differ in response to E-[CO2] and to determine any associated traits. We tested five Japanese cultivars: Aikoku (released in 1882), Norin 8 (1934), Koshihikari (1956), Akihikari (1976) and Akidawara (2009). The yields of Aikoku and Norin 8 increased by 19.3% and 30.3%, respectively, under E-[CO2], while those of Koshihikari and Akihikari increased by 15.9% and 3.4%, respectively. However, that of Akidawara, the newest cultivar, also increased by 19.0%. Norin 8’s strong response to E-[CO2] was associated with increases in both spikelet density and percentage of ripened grains, both of which were closely related to nitrogen uptake. These results suggest that breeding has not necessarily improved cultivars’ response to E-[CO2], and that selection for traits such as sink capacity and nitrogen uptake can be effective to improve rice productivity under E-[CO2].
Highlights
Atmospheric CO2 concentrations ([CO2]) have increased by more than 100 μmol mol−1 from approximately 280 μmol mol−1 in pre-industrial times mainly through anthropogenic CO2 emissions and are projected to reach as high as 936 μmol mol−1 by the end of this century (IPCC, 2013)
We previously reported that the yield response of rice to E-[CO2] varied widely among cultivars including some old and new cultivars in a free-air CO2 enrichment (FACE) experiment under open-field conditions in a single season (Hasegawa et al, 2013)
During 30 days before heading (DBH) and after heading (DAH), which correspond to panicle formation and grain-filling periods, respectively, the mean air temperature differed among the cultivars by up to 1.1°C and 0.9°C, respectively
Summary
Atmospheric CO2 concentrations ([CO2]) have increased by more than 100 μmol mol−1 from approximately 280 μmol mol−1 in pre-industrial times mainly through anthropogenic CO2 emissions and are projected to reach as high as 936 μmol mol−1 by the end of this century (IPCC, 2013). Global warming and change of precipitation patterns resulting from this rise will have mainly negative effects on crop production (Semenov & Porter, 1995; Zhao et al, 2017). Significant intraspecific variation in the yield response to elevated [CO2] (E-[CO2]) was found in major food crops (Ziska, Manalo & Ordonez, 1996; Shimono et al, 2009; Hasegawa et al, 2013 for rice; Seneweera et al, 2010 for wheat; Bishop et al, 2015 for soybean). Screening for or breeding E-[CO2]-responsive cultivars offers an effective way to adapt crops to global climate change (Ziska et al, 2012). Continuing efforts in breeding, along with intensification of culture, resulted in rapid increases in yield (Chen, 2018; Horie et al, 2005) until the 1970s, when Japan achieved rice self-sufficiency. In the last few decades, breeders have returned their attention to productivity to reduce costs and have developed high-yielding cultivars by introducing indica genes (Yoshinaga et al, 2018)
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