Luminescent light shifting film affects lettuce pigments and yield in a season- and cultivar-dependent manner

Innovative glasshouse films that reduce light quantity and alter spectral quality show great potential to increase light use efficiency in protected cropping. While crop responses to these films vary according to the cultivar and season, underlying mechanisms by which plants respond is not fully understood. This study evaluated the performance of a light-shifting film (LSF) on growth, pigments, and physiology of two lettuce cultivars, butterhead and green cos, grown for two crop cycles during the early and late autumn season. We postulated that overall light intensity reduction, combined with higher red-light levels under LSF, would trigger photo acclimation and stimulate yield via increased leaf expansion under light limiting conditions. Comparing control plants, both cultivars showed reduction in leaf number (-30 to -37%) and yield (-16 to -17%) due to lower light availability in late relative to early autumn, yet only butterhead showed declines in total chlorophyll (-52%) and carotenoid (-54%) content. The LSF reduced light intensity (∼ -20%) and shifted light wavelengths in the green towards red spectrum and affected foliar pigments and lettuce yield in a season and cultivar dependent manner. The LSF significantly reduced foliar pigment (- 14 to -58%) parameters in early autumn and increased yield (+14%) in late autumn, particularly in butterhead cultivar, without changes in light-saturated photosynthesis ( A ₛₐₜ) revealing some degree of photo acclimation. In conclusion, the LSF offsets moderate PAR reductions maintaining and significantly enhancing lettuce biomass particularly when grown in seasons of lower light, and in a cultivar-dependent manner. The increased biomass correlated with enhanced leaf area rather than photosynthetic capacity highlighting that LSFs engineered to enhance the red-light wavelengths offer potential not only to offset yield reductions under low-light conditions, but also to actively improve photosynthetic efficiency and crop performance.