Interacting effects of high light and elevated CO2 on the nutraceutical quality of two differently pigmented Lactuca sativa cultivars (Blonde of Paris Batavia and Oak Leaf)

• Green and red lettuces respond differently to short periods of environmental stresses.
• High light intensity provokes increases in biomass production without mineral reduction.
• High light intensity results in the active synthesis of health-promoting compounds.
• High light intensity and elevated CO2 levels promote growth without a loss of nutritional quality.
• The best lettuce growing practice depends on the cultivar and the traits that are targeted for improvement.

This study presents changes in the nutraceutical quality and biomass production of two differently pigmented Lactuca sativa (L.) cultivars grown under various combinations of high light (700 μmol photons m−2 s−1) and elevated CO2 (700 μmol mol−1) conditions. In an ambient CO2 atmosphere, high light intensity increased biomass production in the green cultivar (Blonde of Paris Batavia) but not in the red cultivar (Oak Leaf). In both cultivars, high light intensity increased the concentration of soluble proteins and sugars. High light intensities also increased the levels of carotenoids, glutathione, total phenols and anthocyanins, which was most likely due to oxidative stress. Conversely, the levels of almost all minerals remained unchanged compared with the values detected for control light intensity and ambient CO2 conditions. When a high light intensity was applied at elevated CO2 conditions, the biomass production increased in both cultivars. The concentrations of minerals (except Fe and Mg), glutathione and ascorbate remained constant compared with the high light and ambient CO2 conditions, which indicated that these components and biomass accumulated at comparable rates. The decreases in the levels of Chl-a, carotenoids, total phenols and anthocyanins in response to elevated CO2 levels at high light conditions could indicate a relief of oxidative stress due to an improved balance between ATP and NADPH production and consumption at elevated CO2 levels. These results demonstrate that the biomass production and the nutritional quality of lettuce can be improved, but the response is cultivar-specific, and the choice of the best cultivation practice (using high light intensity alone or in combination with elevated CO2 levels) depends on the attributes that are targeted for improvement.