Photosynthetic energy conversion efficiency: Setting a baseline for gauging future improvements in important food and biofuel crops

The conversion efficiency (ε_c) of absorbed radiation into biomass (MJ of dry matter per MJ of absorbed photosynthetically active radiation) is a component of yield potential that has been estimated at less than half the theoretical maximum. Various strategies have been proposed to improve ε_c, but a statistical analysis to establish baseline ε_c levels across different crop functional types is lacking. Data from 164 published ε_c studies conducted in relatively unstressed growth conditions were used to determine the means, greatest contributors to variation, and genetic trends in ε_c across important food and biofuel crop species. ε_c was greatest in biofuel crops (0.049–0.066), followed by C4 food crops (0.046–0.049), C3 nonlegumes (0.036–0.041), and finally C3 legumes (0.028–0.035). Despite confining our analysis to relatively unstressed growth conditions, total incident solar radiation and average growing season temperature most often accounted for the largest portion of ε_c variability. Genetic improvements in ε_c, when present, were less than 0.7% per year, revealing the unrealized potential of improving ε_c as a promising contributing strategy to meet projected future agricultural demand.