Journal of Experimental Botany

Predictions suggest that current crop production needs to double by 2050 to meet global food and energy demands. Based on theory and experimental studies, overexpression of the photosynthetic enzyme sedoheptulose-1,7-bisphosphatase (SBPase) is expected to enhance C₃ crop photosynthesis and yields. Here we test how expression of the cyanobacterial, bifunctional fructose-1,6/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) affects carbon assimilation and seed yield (SY) in a major crop (soybean, Glycine max). For three growing seasons, wild-type (WT) and FBP/SBPase-expressing (FS) plants were grown in the field under ambient (400 μmol mol⁻¹) and elevated (600 μmol mol⁻¹) CO₂ concentrations [CO₂] and under ambient and elevated temperatures (+2.7 °C during daytime, +3.4 °C at night) at the SoyFACE research site. Across treatments, FS plants had significantly higher carbon assimilation (4–14%), V_c,max (5–8%), and J_max (4–8%). Under ambient [CO₂], elevated temperature led to significant reductions of SY of both genotypes by 19–31%. However, under elevated [CO₂] and elevated temperature, FS plants maintained SY levels, while the WT showed significant reductions between 11% and 22% compared with plants under elevated [CO₂] alone. These results show that the manipulation of the photosynthetic carbon reduction cycle can mitigate the effects of future high CO₂ and high temperature environments on soybean yield.