Lignite Substrate and EC Modulates Positive Eustress in Cucumber at Hydroponic Cultivation

Radosław Łaźny,Waldemar Kowalczyk,Janina Gajc-Wolska,Stanisław Kalisz,Monika Niedzińska,Jarosław L Przybył,Katarzyna Kowalczyk,Jacek S Nowak,Małgorzata Mirgos

doi:10.3390/agronomy12030608

Radosław Łaźny, Waldemar Kowalczyk + Show 7 more

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https://doi.org/10.3390/agronomy12030608

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Abstract

Hydroponic cultivation using organic, fully biodegradable substrates that provide the right physical properties for plant growth and development is now the future of soilless production. Despite the high productivity and strict control of production conditions in this method, excessive salinity of the substrate often occurs. However, recent research results indicate that salinity at a high enough threshold can improve yield quality, while prolonged exposure to too high EC, or exceeding the safe EC threshold for a given species, leads to reduced quality and reduced or even no yield. The aim of this study was to determine the effect of biodegradable lignite substrate (L) and eustressor in the form of high EC nutrient solution (7.0 dS·m−1) on morphological and physiological parameters, as well as the quality and yield of cucumber (Cucumis sativus L.) in hydroponic cultivation compared to the mineral wool substrate (MW). The MW/high EC combination showed a significant reduction in shoot diameter by nearly 6% compared to the MW/control EC combination. The stomatal conductance (gs) and the transpiration rate (E) were also significantly reduced in this combination. The present study indicates that the effects of eustressor application vary depending on the growing medium used, and more favorable effects in terms of yield quality were obtained using biodegradable lignite substrate. The high EC of nutrient solution combined with lignite substrate (L/high EC) significantly increased in cucumber fruit the content of β-carotene, lutein, chlorophyll a, chlorophyll b and the sum of chlorophyll a + b by 33.3%, 40%, 28.6%, 26.3% and 26.7%, respectively, as compared to MW/high EC combination.

Highlights

IntroductionCucumber (Cucumis sativus L.) is the second most economically important and widely grown species in hydroponic systems after tomato [1,2], but it is one of the vegetables sensitive to high salt concentrations in the medium
There were no significant differences in weekly shoot length growth between the combinations, at the high EC of the nutrient solution a significant shortening of the total length of shoot was observed in mineral wool substrate (MW)/high EC cucumber plants by nearly 2.6% (Table 1), this combination recorded a smaller cucumber shoot diameter by nearly
Plants fertilized with the high EC nutrient solution and grown in lignite medium had the smallest width of the tenth leaf, compared to the control

Summary

Introduction

Cucumber (Cucumis sativus L.) is the second most economically important and widely grown species in hydroponic systems after tomato [1,2], but it is one of the vegetables sensitive to high salt concentrations in the medium. According to Chen et al [2], cucumber plants tolerate electrical conductivity up to a value of 2.5 dS·m−1 , and an increase by each unit of electrical conductivity results in a decrease in the yield of more than 10%. In addition to direct effects on plant architecture and yield loss, salinity stress affects plant photosynthetic pigments (chlorophyll a and b) and chlorophyll synthesis [3–5] and leads to disruption of primary and secondary metabolite fluxes [3,6]. A decrease in photosynthetic pigment synthesis under salinity stress has been observed in plants of the genus Pisum [7], in the species

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