Effects of Selenium on the Chlorophylls, Gas Exchange, Antioxidant Activity and Amino Acid Composition of Lettuce Grown under an Aquaponics System

María Carmen Piñero,Josefa López-Marín,Ginés Otálora,Jacinta Collado-González,Francisco M Del Amor

doi:10.3390/horticulturae8010030

María Carmen Piñero, Josefa López-Marín + Show 3 more

Open Access

https://doi.org/10.3390/horticulturae8010030

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Abstract

Aquaponics is a sustainable technique that is respectful to the environment, as it reuses products and minimizes the consumption of new materials. The combination of this technique with the foliar application of selenium (as Na2SeO4) could lead to healthier and more sustainable products, which are increasingly requested by consumers. Lettuce (Lactuca sativa L.) plants were grown in an aquaponics system (fish water) as compared with a control (conventional soilless fertigation), and sprayed with different concentrations of selenium (0, 4, 8, and 16 µmol L−1). The results showed a reduction in the dry weight and N content of lettuce plants irrigated with the fish water mixture treatment. However, the application of Se relieved this stress, increasing the photosynthetic rate and ABTS, and reducing the content of chlorophylls, β-carotene, and several of the measured amino acids. The best results were observed with the highest concentration of Se (16 µmol L−1), as an increase in nitrogen content was observed, as shown by a greater weight of the plant. Furthermore, this treatment produced the greatest increase in ABTS and the least reduction in amino acid content. This novel study highlights the possibility of improving the efficiency of N utilization in lettuce by applying foliar selenium in combination with an aquaponics system.

Highlights

In recent years, consumers have increasingly demanded products that, in addition to being healthy, are produced with more environmentally sustainable production practices [1]
The cultured fish were tilapia fish (Orechromis niloticus). This aquaponic system is comprised of 3 fish tanks of approximately 900 L, each holding an average of 80 tilapia fish, a filter tank, a clarifier, a drainage-water collection tank, and a greenhouse
(50F/50D treatment) from 39.01 g DW to 32.77 g DW, with respect to control plants (Table 1). This reduction in the plant weight is an indicator that the plants watered with the 50% fish water + 50% drainage water (50F/50D) treatment were undergoing stress, possibly due to the lower concentration of nitrates in the irrigation water

Summary

Introduction

Consumers have increasingly demanded products that, in addition to being healthy, are produced with more environmentally sustainable production practices [1]. Aquaponics could be a good option for plant production, as it is a technique that unites all of these qualities It reuses products from aquaculture in hydroponic systems, reducing the use of synthetic fertilizers and water. This system has a biological filter which transforms fish excrement (mainly in the form of ammonia) into nitrites and into nitrates, which are assimilated by plants [4]. Other advantages of this type of system are the ability to reduce or even eliminate the leaching of nitrates to the environment, and to produce vegetables with greater nutraceutical qualities (higher phenolic content and higher antioxidant activity) due to the use of organic fertilizers [5]. Aquaponics systems have some disadvantages, such as deficiencies in some mineral nutrients, such as iron (Fe), calcium (Ca), potassium (K), phosphorus (P), or manganese (Mn), which

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