Effects of nutrient deficiency and abiotic environmental stresses on yield, phenolic compounds and antiradical activity in lettuce (Lactuca sativa L.)

Plants of lettuce were subjected to four abiotic limiting growing conditions, i.e. no phosphorus fertilization (0_P), no nitrogen fertilization (0_N), limitation of the photosynthetic active radiation (PAR, range from 400 to 700 nm) (LR) and water availability constraint (WR). Yield, yield components, root growth, bound and soluble phenolic compounds accumulation and their antiradical activity were investigated. Leaf length decreased by 21% in 0_N while increased by 57% in LR with respect to CONTROL plants. Yield reduced by 74% and 57% in 0_N and WR, respectively, which also induced a reduction in roots FW, resulting in a significant increase in roots/leaves ratio (0.47 and 0.33 for 0_N and WR, respectively). Conversely, LR favoured the highest leaves fresh weight (FW) (99.89 g plant−1) and the lowest root biomass FW (7.50 g plant−1); consequently, the roots/leaves ratio was strongly constrained (0.07). The limitation of PAR availability reduced both soluble and bound phenolic compounds as well as antiradical activity. 0_N allowed to obtain the highest total polyphenols content (4.27 mg GAE g−1 FW) and antiradical activity (13.91 μmol TE g−1 FW), although no differences were found in terms of the main phenolic compounds. WR improved the accumulation of caffeic, caftaric and chicoric acids in the bound forms (0.64, 300.85 and 67.38 mg 100 g−1 FW, respectively). PCA analysis significantly explored the correlation between the limiting growing conditions with lettuce yield and quality traits and indicated that water and N fertilization management as the more effective to manipulate the accumulation of plant-based phytochemicals which play an important role in human well-being