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

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.

Eustress and Plants: A Synthesis with Prospects for Cannabis sativa Cultivation

“…With respect to the soil cultivation of C. sativa, it will be interesting to explore the interaction between salinity eustress and organic substrates. In cucumber, the combination of nutrient solution with high electrical conductivity and lignite substrate resulted in fruits with high content of β-carotene and lutein [85]. The combination of abiotic eustress and growth in the presence of humic acids (HAs) is also worth future investigation; HAs indeed act as chemical eustressors, since they can interact as aggregates with the root surface and cause a rise in ROS, which in turn activate scavenging enzymes by working as signaling molecules [86].…”

Nutritional and microbiological effects of vermicompost tea in hydroponic cultivation of maple peas (Pisum sativum var. arvense L.)

“…Hydroponic cultivation has been the focal point for urban soilless agriculture in the wake of land scarcity and a growing population (Łaźny et al, 2022 ), and continues to gain popularity due not only to avoidance of contaminated soils while taking active control of plant nutrition and health (Vinci & Rapa, 2019 ; Walters & Stoelzle Midden, 2018 ), but also to save water and to reduce weight load on building structures (Arcas‐Pilz et al, 2022 ). However, the adverse impacts resulting from hydroponic production on surrounding natural ecosystems cannot be overlooked, namely the production, extraction, application, and disposal of fertilizers employed to secure direct plant nutrient uptake (Rufí‐Salís et al, 2020 ; Sanjuan‐Delmás et al, 2018 ).…”

“…However, the adverse impacts resulting from hydroponic production on surrounding natural ecosystems cannot be overlooked, namely the production, extraction, application, and disposal of fertilizers employed to secure direct plant nutrient uptake (Rufí‐Salís et al, 2020 ; Sanjuan‐Delmás et al, 2018 ). For instance, salt accumulation can occur in irrigation water even with a completely closed hydroponic system (Savvas et al, 2005 ); mineral wool, a solid substrate most widely used in hydroponic cultivation of tomato, bell pepper, and cucumber, emits substantial amount of CO 2 into the environment while resulting in considerable burdens during disposal (Łaźny et al, 2022 ). There remains a dire need to search for alternative organic, biodegradable substrates that will provide the needed nutrients in support of improving plant growth without the aforementioned adversity.…”