Manipulation of Contents of Nitrate, Phenolic Acids, Chlorophylls, and Carotenoids in Lettuce (Lactuca sativa L.) via Contrasting Responses to Nitrogen Fertilizer When Grown in a Controlled Environment

Abstract

This study aimed to use different nitrogen fertilizer regimes to produce Butterhead lettuce with such large differences in nitrate content that they could be used as treatment and placebo to study the effect of inorganic nitrate on human health. Plants were grown under controlled conditions at 27/23 °C day/night with a relatively low photosynthetically active radiation (PAR) of 150 μmol m s for 14 h day and nitrogen supplies ranging from 26 to 154 ppm of N as ammonium nitrate in the fertigation solution. This resulted in contrasting high (∼1078 mg nitrate 100 g FW) or low (∼6 mg 100 g) nitrate contents in the leaves. Contents of carotenoids and chlorophylls in fresh weight did not differ significantly between the highest and the lowest N-supply levels. However, increased nitrogen supply reduced contents of phenolic compounds from 154 to 22 mg 100 g FW, dry matter content from 8.9% to 4.6%, and fresh weight per plant from 108.52 to 47.57 g/plant FW (all P < 0.001). Thus, while fertilizer treatments can provide lettuce with substantially different nitrate contents, maintaining similar pigment contents (color), they also strongly influence the contents of phenolic acids and flavones.

Macronutrient deprivation eustress elicits differential secondary metabolites in red and green‐pigmented butterhead lettuce grown in a closed soilless system

“…Our data are also in agreement with Alberici et al ., who found a significant increase in the total phenols of lettuce cultivated in a floating raft system under a reduced nutrient solution, depending on cultivation season. Analogous increases in the concentrations of chicoric acid and chlorogenic acid in lettuce were noted by Qadir et al . and Becker et al .…”

“…Our data are also in agreement with Alberici et al, 17 who found a significant increase in the total phenols of lettuce cultivated in a floating raft system under a reduced nutrient solution, depending on cultivation season. Analogous increases in the concentrations of chicoric acid and chlorogenic acid in lettuce were noted by Qadir et al 21 and Becker et al 22 under reduced N concentration. Such results imply that N deficiency is a major mediator of phenolic acid accumulation, which is in line with Chishaki and Horiguchi, 40 who observed that the most marked effect on phenolic acid levels in rice plants was in response to N deficiency, followed by P deficiency, and finally by K deficiency, which had a minor effect.…”

“…Certain studies in controlled environments focused on nitrogen levels only, such as Quadir et al . and Becker et al ., or on nitrogen and phosphorus levels, such as Galieni et al . Nevertheless, nothing is known about the interaction between macronutrient deprivation, in the form of reduced macronutrient levels in the nutrient solution, and cultivar, in respect to lettuce PSM profiles.…”

“…Previous studies [17][18][19][20] have demonstrated the effect of reduced nutrient solution levels on yield and particular quality traits of greenhouse leafy vegetables, including lettuce. Certain studies in controlled environments focused on nitrogen levels only, such as Quadir et al 21 and Becker et al, 22 or on nitrogen and phosphorus levels, such as Galieni et al 23 Nevertheless, nothing is known about the interaction between macronutrient deprivation, in the form of reduced macronutrient levels in the nutrient solution, and cultivar, in respect to lettuce PSM profiles.…”

Variety-specific responses of lettuce grown in a gravel-film technique closed hydroponic system to N supply on yield, morphology, phytochemicals, mineral content and safety

“…Since lettuce is consumed in fresh form, high rates of N application especially in nitric form are associated with negative health related issues (Addiscott and Benjamin 2004;Qadir et al 2017). On the other hand, water resources contaminated with nitrate can result in euthrophication and limit the availability of drinking water (Daniele et al 2013).…”