Nutrient Solution Deprivation as a Tool to Improve Hydroponics Sustainability: Yield, Physiological, and Qualitative Response of Lettuce

Michele Ciriello,Maria Giordano,Giovanna Marta Fusco,Antonio Pannico,Pasqualina Woodrow,Luigi Giuseppe Duri,Giancarlo Fascella,Christophe El-Nakhel,Beniamino Riccardo Gentile,Luigi Formisano,Youssef Rouphael,Francesco Cristofano,Petronia Carillo

doi:10.3390/agronomy11081469

Abstract

Hydroponics growing systems often contain excessive nutrients (especially nitrates), which could lead to a quality loss in ready-to-eat leafy vegetables and posing a health risk to consumers, if managed inadequately. A floating raft system was adopted to assay the production and quality performance of lettuce (Lactuca sativa L. cv ‘Maravilla De Verano Canasta’) deprived of the nutrient solution by replacement with only water, three and six days before harvest. Yield and quality parameters, mineral composition, pigments, organic acids, amino acids profile, soluble proteins, and carbohydrate content were determined. Nutrient solution deprivation six days before harvest resulted in a significant reduction in leaf nitrate (−53.3%) concomitant with 13.8% of yield loss, while plants deprived of nutrient solution three days before harvest increased total phenols content (32.5%) and total ascorbic acid (102.1%), antioxidant activity (82.7%), anthocyanins (7.9%), sucrose (38.9%), starch (19.5%), and γ-aminobutyric acid (GABA; 28.2%), with a yield reduction of 4.7%, compared to the control. Our results suggest that nutrient solution deprivation three days before harvest is a successful strategy to reduce nitrate content and increase the nutritional quality of lettuce grown in floating raft systems with negligible impact on yield. These promising results warrant further investigation of the potential effect of nutrient solution deprivation on the quality attributes of other leafy vegetables cultivated in floating raft systems and in a “cascade” growing system.

Highlights

BCAAs increased in lettuce at 6 Days of Deprivation (DD), which have been proved to actively function as antioxidants in plants, and in rats and mice by an unknown mechanism [85]. Hydroponic growing systems such as the floating raft system can facilitate the bioaccumulation of these nutritional compounds while reducing nitrate content through the possibility to apply nutritional eustress
We demonstrated that replacing nutrient solution with water three and six days before harvest reduced the nitrate content and increased the nutritional quality of ready-to-eat lettuce
The lowest nitrate content (1290 mg kg−1 fw) was obtained in plants deprived of the nutrient solution six days before harvest, the fresh yield decreased by 13.2% compared to control plants

Summary

Introduction

Lettuce (Lactuca sativa L.) was historically grown and used in the “Old Continent” (Mediterranean areas), nowadays, this tender and fresh leafy vegetable belonging to the Asteraceae has widely spread in more industrialized countries such as China and the USA [1,2]. Due to its high water content, the nutritional quality of lettuce is often undervalued [3]. Its low caloric, sodium, and fat contents have made it a well-liked and popular vegetable, electing it as a staple ingredient for fresh meals like salads [4,5]. The genetic variability of the genus Lactuca, which is the fruit of intense breeder selection over the years, provides consumers with a wide assortment of leaf typology that differs in color (red to green), morphology (smooth or curly), size, and nutritional characteristics [3,6,7]

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Results

Discussion

Conclusion