Photosystem II efficiency in response to diurnal and seasonal variations in photon flux density and air temperature for green, yellow-green, and purple-leaved cultivars of sweet potato [ (L.) Lam].

This study aimed to investigate the impact of diurnal and seasonal variations in photon flux density (PPFD) and air temperature on PSII efficiency in three sweet potato leaf-color cultivars: green (G), yellow-green (Y), and purple (P). The cultivars were exposed to full sunlight and measurements were taken from November to March. The maximal quantum yield of PSII photochemistry for the dark-adapted state (F/F) indicated Y's increased sensitivity to low temperatures at predawn, followed by G and P. Both quantum yield of PSII photochemistry for the dark and light-adapted state (ΔF/F') depressions were correlated with increased PPFD, with regression slopes in the order of Y > G > P. On high-light and low-temperature days, F/F values deviated below regression lines, with differences ranked as Y > G > P. These findings suggest that Y exhibits the highest sensitivity to high light and low temperatures, followed by G and then P in terms of PSII efficiency.