Anthocyanin concentration across diverse lettuce cultivars decreases photosynthesis similarly at low and high photosynthetic photon flux density.

Anthocyanins are non-photosynthetic pigments that absorb photons and thus decrease photosynthesis. Several studies have characterized the reduction in photosynthesis from anthocyanins by comparing high and low anthocyanin genotypes under single light intensity. We hypothesized that high anthocyanin levels would result in a greater reduction in photosynthesis in low than at high PPFD because anthocyanin-induced screening would have a stronger impact under limited conditions. We quantified the reduction of light-saturated gross photosynthesis (Pg) and quantum yield of CO2 (QYCO2) across eight lettuce cultivars ranging from 3.4 to 34 mg m− 2 anthocyanins, and report the photosynthetic effects over a range of wavelengths from 400 to 700 nm. We used spectral reflectance to quantify normalized difference anthocyanin index (NDAI), which ranged from − 0.24 to + 0.12. As expected, photosynthesis decreased as anthocyanin concentration increased, but surprisingly, the photosynthetic reduction was similar over a range of PPFDs from 50 to 1500 µmol m− 2 s− 1. The positive correlation between the absorptance at green wavelengths and NDAI suggest that anthocyanins filtered primarily green photons. Due to the screening effect of the green photons by anthocyanins, Pg and QYCO2 decreased from 45 to 82% with the increase of NDAI across all PPFDs. The similarity in the slopes of light-saturated Pg and maximum QYCO2 over NDAI indicate that the screening effect of anthocyanins was similar from low to high PPFD.