Combined Effect of Salt Stress and Nitrogen Level on the Primary Metabolism of Two Contrasting Hydroponically Grown Cichorium spinosum L. Ecotypes

Stamnagathi (Cichorium spinosum L.) is an indigenous plant species well-known for its health-promoting properties. Salinity is a long-term issue with devastating consequences on land and farmers. Nitrogen (N) constitutes a crucial element for plant growth and development (chlorophyll, primary metabolites, etc.). Thus, it is of paramount importance to investigate the impact of salinity and N supply on plants’ metabolism. Within this context, a study was conducted aiming to assess the impact of salinity and N stress on the primary metabolism of two contrasting ecotypes of stamnagathi (montane and seaside). Both ecotypes were exposed to three different salinity levels (0.3 mM—non-saline treatment, 20 mM—medium, and 40 mM—high salinity level) combined with two different total-N supply levels: a low-N at 4 mM and a high-N at 16 mM, respectively. The differences between the two ecotypes revealed the variable responses of the plant under the applied treatments. Fluctuations were observed at the level of TCA cycle intermediates (fumarate, malate, and succinate) of the montane ecotype, while the seaside ecotype was not affected. In addition, the results showed that proline (Pro) levels increased in both ecotypes grown under a low N-supply and high salt stress, while other osmoprotectant metabolites such as γ-aminobutyric acid (GABA) exhibited variable responses under the different N supply levels. Fatty acids such as α-linolenate and linoleate also displayed variable fluctuations following plant treatments. The carbohydrate content of the plants, as indicated by the levels of glucose, fructose, α,α-trehalose, and myo-inositol, was significantly affected by the applied treatments. These findings suggest that the different adaptation mechanisms among the two contrasting ecotypes could be strongly correlated with the observed changes in their primary metabolism. This study also suggests that the seaside ecotype may have developed unique adaptation mechanisms to cope with high N supply and salinity stress, making it a promising candidate for future breeding programs aimed at developing stress tolerant varieties of C. spinosum L.

Functional Quality, Mineral Composition and Biomass Production in Hydroponic Spiny Chicory (Cichorium spinosum L.) Are Modulated Interactively by Ecotype, Salinity and Nitrogen Supply

The hydroponic cultivation of spiny chicory (Cichorium spinosum L.), also known as stamnagathi, allows the development of year-round production. In the current study, two contrasting stamnagathi ecotypes originating from a montane and a coastal-marine habitat were supplied with nutrient solution containing 4 or 16 mM total-N in combination with 0.3, 20, or 40 mM NaCl. The primary aim of the experiment was to provide insight into salinity tolerance and nutrient needs in the two ecotypes, thereby contributing to breeding of more resilient cultivars to salinity and nutrient stress. Nutritional qualities of the stamnagathi genotypes were also tested. The coastal-marine ecotype was more salt tolerant in terms of fresh shoot biomass production and contained significantly more water and macro- and micro-nutrients in the shoot per dry weight unit. The root Na⁺ concentration was markedly lower in the coastal-marine compared to the montane ecotype. The leaf Na⁺ concentration was similar in both ecotypes at external NaCl concentrations up to 20 mM, but significantly higher in the montane compared to the coastal-marine ecotype at 40 mM NaCl. However, the leaf Cl^- concentration was consistently higher in the coastal-marine than in the montane ecotype within each salinity level. The marine ecotype also exhibited significantly less total phenols, carotenoids, flavonoids, and chlorophyll compared to the montane ecotype across all treatments. Integrating all findings, it appears that at moderate salinity levels (20 mM), the higher salt tolerance of the coastal-marine ecotype is associated with mechanisms mitigating Na⁺ and Cl^- toxicity within the leaf tissues, such as salt dilution imposed through increased leaf succulence. Nevertheless, at high external NaCl levels, Na⁺ exclusion may also contribute to enhanced salt tolerance of stamnagathi. Both ecotypes exhibited a high N-use efficiency, as their shoot biomass was not restricted when the total-N supply varied from 16 to 4 mM. The leaf organic-N was not influenced by salinity, while the interaction ecotype × N-supply-level was insignificant, indicating that the mechanisms involved in the salt tolerance difference between the two ecotypes was not linked with N-acquisition or -assimilation within the plant. The current results indicate that both ecotypes are promising germplasm resources for future breeding programs.

Impact of nitrogen source and supply level on growth, yield and nutritional value of two contrasting ecotypes of Cichorium spinosum L. grown hydroponically

BACKGROUND

In the present study, two contrasting stamnagathi (Cichorium spinosum L.) ecotypes originating either from a mountainous or from a seaside habitat were grown hydroponically and supplied with a nutrient solution differing in the total-N level (4 or 16 mmol L^-1 ) and the N source (NH₄⁺ -N/total-N: 0.05, 0.25 or 0.50). The aim was to search for genotypic differences in nitrogen nutrition.

RESULTS

At commercial maturity, the dry weight of mountainous plants was higher than that of seaside plants. The shoot mineral concentrations were higher in seaside plants than in mountainous plants in both harvests. The leaf nitrate concentration was influenced by the levels of both total-N and NH₄⁺ -N/total-N at both harvests, whereas plants with a seaside origin exhibited higher nitrate concentrations than those originating from a mountainous site in all total-N and NH₄⁺ -N/total-N treatments.

CONCLUSION

The two stamnagathi ecotypes differed considerably in their responses to nitrogen nutrition and tissue nitrate content. The mountainous ecotype was superior in terms of growth, tissue nitrate concentration and antioxidant capacity, whereas the seaside ecotype accumulated more nutrient microcations in leaves. A low total-N concentration (up to 4 mmol L^-1 ) combined with a high NH₄⁺ -N/total-N ratio (up to 0.05) could minimize tissue NO₃^- concentrations without compromising yield. © 2017 Society of Chemical Industry.