A Review of Environment Effects on Nitrate Accumulation in Leafy Vegetables Grown in Controlled Environments

Abstract

Excessive accumulation of nitrates in vegetables is a common issue that poses a potential threat to human health. The absorption, translocation, and assimilation of nitrates in vegetables are tightly regulated by the interaction of internal cues (expression of related genes and enzyme activities) and external environmental factors. In addition to global food security, food nutritional quality is recognized as being of strategic importance by most governments and other agencies. Therefore, the identification and development of sustainable, innovative, and inexpensive approaches for increasing vegetable production and concomitantly reducing nitrate concentration are extremely important. Under controlled environmental conditions, optimal fertilizer/nutrient element management and environmental regulation play vital roles in producing vegetables with low nitrate content. In this review, we present some of the recent findings concerning the effects of environmental factors (e.g., light, temperature, and CO2) and fertilizer/nutrient solution management strategies on nitrate reduction in vegetables grown under controlled environments and discuss the possible molecular mechanisms. We also highlight several perspectives for future research to optimize the yield and nutrition quality of leafy vegetables grown in controlled environments.

Reduction of Nitrate Content in Baby-Leaf Lettuce and Cichorium endivia Through the Soilless Cultivation System, Electrical Conductivity and Management of Nutrient Solution

“…With the FL system, nitrate accumulation was always higher than EF and as expected, it decreased in the early-spring conditions due to higher radiation availability (Blom-Zandstra, 1989 ). Accordingly, a rise in chloride was observed confirming its well-known replacement in vacuoles of (Bian et al, 2020 ) used for sustaining the higher plant growth ( Table 9 ).…”

“…Chloride concentration was the highest in EF and EC3.5 ( Table 4 ), and especially in the EF/EC3.5 combination ( Figure 4A ), confirming the expected accumulation of Cl − in plants exposed to saline (NaCl) stress (Wu and Li, 2019 ). Chloride showed an opposite trend to nitrate as it is well-known that salinity can reduce nitrate accumulation in leafy vegetables due to antagonism between nitrate and chloride for the same root anion channel (Bian et al, 2020 ). A linear decrease in nitrate concentration has been reported in romaine lettuce baby-leaf grown in FL with an increase in NS salinity up to 4.8 dS m −1 (Scuderi et al, 2011 ), in agreement with other experiments on leafy vegetables (Barbieri et al, 2011 ).…”

“…This experiment was performed on plants grown in EF and FL systems at 2.5 dS m −1 EC level to test the replacement of NS with freshwater before the harvest (NS withdrawal -WD) as a strategy to reduce leaf nitrate concentration. We decided to apply this treatment at the lower NS salinity in autumn and winter cycles characterized by the lower solar radiation as these are the cultivation and sunlight conditions (Bian et al, 2020 ) that favor nitrate accumulation.…”

“…Nitrate concentration significantly decreased in WD plants compared with the noWD ones whereas a significant opposite behavior was observed for chloride concentration ( Table 6 ). It is well-known that during a period of deprivation, nitrates stored in vacuoles are used to sustain plant growth (Bian et al, 2020 ) and chloride may replace as osmolyte, as reported for endive (Santamaria and Elia, 1997 ), chicory and rocket (Santamaria et al, 1998 ), especially when Cl − is added to NS (pak-choi, Zhu et al, 1997 ; cultivated cardoon, Borgognone et al, 2016 ; basil, Corrado et al, 2020 ) since a very low :Cl − ratio promotes Cl − uptake (Colmenero-Flores et al, 2019 ).…”

Beetroot, A Remarkable Vegetable: Its Nitrate and Phytochemical Contents Can be Adjusted in Novel Formulations to Benefit Health and Support Cardiovascular Disease Therapies

“…Abiotic conditions, such as atmospheric humidity, extreme temperatures, low and high, exposure time to sunlight, and brightness can affect NO 3 − accumulation in vegetables, although some agricultural management aspects, such as farming systems, soil fertilization, nutrient availability, and herbicide use must be considered to achieve this crop’s growth and development [ 16 ].…”