Rice cultivar responses to elevated CO2 at two free-air CO2 enrichment (FACE) sites in Japan

There is some evidence that rice cultivars respond differently to elevated CO2 concentrations ((CO2)), but (CO2) � cultivarinteractionhasneverbeentestedunderopen-fieldconditionsacrossdifferentsites.Here,wereportontrials conducted at free-air CO2 enrichment (FACE) facilities at two sites in Japan, Shizukuishi (2007 and 2008) and Tsukuba (2010). The average growing-season air temperature was more than 5 � C warmer at Tsukuba than at Shizukuishi. For four cultivarstestedatbothsites,the(CO2) � cultivarinteractionwassignificantforbrownriceyield,buttherewasnosignificant interaction with site-year. Higher-yielding cultivars with a large sink size showed a greater (CO2) response. The Tsukuba FACEexperiment,whichincludedeightcultivars,revealedawiderrangeofyieldenhancement(3-36%)thanthemulti-site experiment. All of the tested yield components contributed to this enhancement, but there was a highly significant (CO2) � cultivar interaction for percentage of ripened spikelets. These results suggest that a large sink is a prerequisite for higher productivity under elevated (CO2), but that improving carbon allocation by increasing grain setting may also be a practical way of increasing the yield response to elevated (CO2).