Evaluating the potential of up-regulating stomatal conductance to enhance yield and nutritional quality for paddy rice under elevated CO2

Context or problem: Rice grown under projected concentrations of atmospheric carbon dioxide ([CO2]) often exhibits enhanced yield and decreased nutritional quality. However, rice yield increases are often lower than the theoretical extent of photosynthetic stimulation and the basis for the nutritional deterioration is unclear. Objective or research question: The objective was to evaluate the potential of up-regulating stomatal conductance to enhance rice productivity and mitigate nutrient decline at elevated [CO2]. Methods: Here we used gmo rice lines with overexpression of ZmK2.1 or OsKAT3 to test and compare the quantitative and qualitative metrics relative to their non-gmo counterpart in a free-air carbon dioxide enrichment (FACE) platform. Results: Quantitatively, all gmo lines generally showed a significantly higher yield enhancement relative to the non-gmo line at elevated [CO2]. Such responses were associated with greater increases in aboveground nitrogen uptake and photosynthetic stimulation. The gmo lines mitigated the declines of leaf nitrogen and Rubisco content due to elevated [CO2]. Qualitatively, gmo lines with overexpression of ZmK2.1 or OsKAT3 did not show nutritional degradation for iron, zinc and protein relative to the non-gmo rice line under elevated [CO2]. Conclusions: Overall, these findings provide initial evidence that overexpression of ZmK2.1 or OsKAT3 could be an effective means to further increase rice yield without sacrificing nutritional quality at elevated [CO2]. Implications or significance: Given the global importance of rice, upregulation of stomatal conductance may be one of a series of steps essential in selection and breeding efforts to provide positive adaption of rice to climate change.