Effect of different day and night nutrient solution concentrations on growth, photosynthesis, and leaf NO3- content of aeroponically grown lettuce

Abstract

Nitrate content in leafy green vegetables has raised concerns among consumers and policy makers worldwide. Several cultural practices have been evaluated to manipulate NO3 -content in fresh leaves with varying degrees of success. The present study was conducted to evaluate different concentrations of the nutrient solution applied during the day (D) and night (N) to aeroponically grown lettuce (Lactuca sativa L.) in Davis, California, USA, in the spring of 2012 with the objective of assessing the effect on growth, leaf photosynthesis, and nitrate accumulation in leaves. Two different treatments in the nighttime solution concentration (D25/N75, EC: 1.8 dS m -1 ; and D25/N50, EC: 1.2 dS m -1), a day nutrient solution of EC 0.6 dS m -1 , plus a day and night treatment with constant EC (D50/N50, EC: 1.2 dS m -1 ) were applied. Plant growth, leaf photosynthesis, and leaf nutrient content were evaluated after 3 wk of growth. Mean shoot weight was 106.3 g with no differences among treatments. Root biomass was lower with D25/N75 (0.14 vs. 0.85 g in the other treatments). The maximum rate of leaf photosynthesis was 66% lower with D25/N75 than in the other treatments. Nitrogen, P, K, Ca, and Mg were lower in leaf tissue in the treatments with different solution concentrations where leaf NO3 -content was reduced by approximately 75%. Switching nutrient solution concentration between day and night is a viable practice to reduce NO3 -in lettuce leaves with no detriment to leaf production.

Mode of Managing Nutrient Solution Based on N Use Efficiency for Lettuce (Lactuca sativa L.)

“…But our results are slightly high compared with others studies. In relation to dry matter (DM) our means were higher than those obtained by Albornozet al [6]. …”

“…Various articles show that high level of nitrate accumulation in leaves is harmful to human health [4, 6]. Overall in our experiment, the higher rate of NO 3 − accumulation in leaves was found in all of the M 3 treatments.…”

“…All results showed that pH and replacing nutrient solution modes were significant influences on NO 3 − accumulation in lettuce leaves at the level of 5% probability (Table 3), and lower pH of the nutrient solution was parallel to higher NO 3 − concentration in the leaves for adjusting EC treatments. In all treatments, NO 3 − concentration of lettuce leaves (spring-summer cultivation) did not exceed limits recommended in the European Union and the World Health Organization, which were 5,000 mg.kg −1 and 4,000 mg.kg −1 FW for winter and summer crops respectively for lettuce grown in greenhouse [6]. …”

Optimizing the Electrical Conductivity of a Nutrient Solution for Plant Growth and Bioactive Compounds of Agastache rugosa in a Plant Factory

“…CO 2 uptake is negatively affected by stomatal closure [29]. The photosynthesis rate of some plant species is decreased by stomatal closure due to the influence of salinity [8,28,30].…”

“…The leaf photosynthesis rate, stomatal conductance, leaf transpiration, and intercellular CO 2 concentration of some plants have also been seen to be significantly decreased by a higher EC of the NS in a hydroponic culture system, such as pak choi [8], lettuce [30], and papaya [16]. Coinciding with these former studies, our results also showed that leaf gas exchange parameters (P n , C i , g s , and T r ) were significantly decreased at a high EC of 8.0 dS•m −1 because the salinity stress was increased with an increasing EC of the NS.…”