Photosynthetic Energy Conversion Efficiency: Setting a Baseline for Gauging Future Improvements in Important Food and Biofuel Crops

The conversion efficiency (epsilon(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 epsilon(c), but a statistical analysis to establish baseline epsilon(c) levels across different crop functional types is lacking. Data from 164 published epsilon(c) studies conducted in relatively unstressed growth conditions were used to determine the means, greatest contributors to variation, and genetic trends in epsilon(c) across important food and biofuel crop species. epsilon(c) was greatest in biofuel crops (0.049-0.066), followed by C-4 food crops (0.046-0.049), C-3 nonlegumes (0.036-0.041), and finally C-3 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 epsilon(c) variability. Genetic improvements in epsilon(c), when present, were less than 0.7% per year, revealing the unrealized potential of improving epsilon(c) as a promising contributing strategy to meet projected future agricultural demand.