Nitrate concentration in lettuce leaves depending on photosynthetic photon flux and nitrate concentration in the nutrient solution

Abstract

The nitrate accumulation in plant tissues can occur due to low light availability. However, published studies have not linked nitrate accumulation to photosynthetic photon flux (PPF) measured during the growing period. This study aimed to evaluate the effect of the reduction of photosynthetic photon flux and the concentration of nitrate in the nutrient solution on agronomic characteristics and accumulation of nitrate in lettuce grown in hydroponics. The trial design was entirely randomized in a factorial scheme (4 x 2) with three repetitions, and four shading levels: 0, 30, 50, and 80% and two nitrate levels in nutrient solution: 5 and 10 mmol L-1. The dry matter production decreased directly and linearly with the reduction of light. The lowest level in nitrate solution also led to reduction in dry mass yield. The maximum accumulation of nitrate reached 966.3 mg kg-1 fresh mass, with PPF of 118 μmol/m²/s and 140 mg L-1 of N-NO3-1 (below the maximum levels recommended by the European Union), and the minimum of 200 mg kg-1 with PPF of 455 μmol/m²/s and 70 mg L-1 of N-NO3-1 in the nutrient solution. The reduction of nitrate in the nutrient solution from 140 to 70 mg L-1 led to the reduction of nitrate accumulation in shoots, but also caused a decrease in the production of phytomass of shoots, as well as reduced leaf area significantly.

Yield and nutritional quality of greenhouse lettuce as affected by shading and cultivation season

“…Lettuce leaves are usually consumed raw and without any restriction to daily intake. However, lettuce is characterized by its great ability to accumulate nitrate in leaves which can be harmful to human health (Cometti et al, 2011). Thus, nitrate concentration in lettuce is considered one of the more important quality parameters.…”

“…Besides nitrates, ascorbic acid concentration is also considered as an important quality indicator in lettuces which is also influenced by both abiotic and biotic parameters (Cometti et al, 2011). However, the effects of different light intensities in ascorbic acid concentration in lettuces remained more or less obscure.…”

Amelioration of an open soilless cultivation system for microgardening spinach (Spinacia oleracea L.)

“…Crop demand for N is also dependent on dry matter accumulation and therefore vegetables such as lettuce shows increase in fresh and dry biomass with the increase in NO 3 application and its accumulation in the leaves (Cometti et al, 2011). A correlation between TOC, TSS and D m suggests an increase in carbon assimilation which then boosts the production of carbohydrates and plant biomass.…”

Nitrate Content in Minimally Processed Lettuce (Lactuca sativa L.) as Affected by Fluorescent Light Exposure During Storage

“…In lettuce production, nitrogen fertilization is commonly used for proper green pigment retention and leaf growth. However, lettuce is characterized by its ability to accumulate high level of nitrate [1]. Indeed, the higher amount of nitrate accumulation is noticed in butter head lettuce [2].…”

“…Accumulation of nitrates in lettuce also has been observed to be affected by light intensity. Lettuce grown in the lower light intensity accumulates the higher level of nitrate [1,5,6]. The increased nitrate at low light intensity is due to reduced activity of nitrate reductase [7].…”