title: Rice grain yield and quality responses to free-air CO2 enrichment combined with soil and water warming.
abstract: Rising air temperatures are projected to reduce rice yield and quality, whereas increasing atmospheric CO2 concentrations ([CO2 ]) can increase grain yield. For irrigated rice, ponded water is an important temperature environment, but few open-field evaluations are available on the combined effects of temperature and [CO2 ], which limits our ability to predict future rice production. We conducted free-air CO2 enrichment and soil and water warming experiments, for three growing seasons to determine the yield and quality response to elevated [CO2 ] (+200 μmol mol(-1) , E-[CO2 ]) and soil and water temperatures (+2 °C, E-T). E-[CO2 ] significantly increased biomass and grain yield by approximately 14% averaged over 3 years, mainly because of increased panicle and spikelet density. E-T significantly increased biomass but had no significant effect on the grain yield. E-T decreased days from transplanting to heading by approximately 1%, but days to the maximum tiller number (MTN) stage were reduced by approximately 8%, which limited the panicle density and therefore sink capacity. On the other hand, E-[CO2 ] increased days to the MTN stage by approximately 4%, leading to a greater number of tillers. Grain appearance quality was decreased by both treatments, but E-[CO2 ] showed a much larger effect than did E-T. The significant decrease in undamaged grains (UDG) by E-[CO2 ] was mainly the result of an increased percentage of white-base grains (WBSG), which were negatively correlated with grain protein content. A significant decrease in grain protein content by E-[CO2 ] accounted in part for the increased WBSG. The dependence of WBSG on grain protein content, however, was different among years; the slope and intercept of the relationship were positively correlated with a heat dose above 26 °C. Year-to-year variation in the response of grain appearance quality demonstrated that E-[CO2 ] and rising air temperatures synergistically reduce grain appearance quality of rice.
authors.affiliation: Agro-Meteorology Division, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki, 305-8604, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Usui
authors.affiliation: Agro-Meteorology Division, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki, 305-8604, Japan.
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Sakai
authors.affiliation: Agro-Meteorology Division, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki, 305-8604, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tokida
authors.affiliation: Taiyo Keiki Co. Ltd., 1-12-3 Nakajujo, Kitaku, Tokyo, 114-0032, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Nakamura
authors.affiliation: NARO, National Agricultural Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki, 305-8666, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakagawa
authors.affiliation: Agro-Meteorology Division, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki, 305-8604, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Hasegawa
mesh_terms: D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism*; D006358:Hot Temperature; D007564:Japan; D012275:Oryza / Q000254:growth & development*; D012621:Seasons; D014867:Water / Q000032:analysis*; D014887:Weather
chemical_list: D014867:Water; D002245:Carbon Dioxide
keywords: Oryza sativa; chalky grain; free-air CO2 enrichment; grain quality; heat dose; protein content; soil and water warming