Silicon in the Soil–Plant System

To investigate the amelioration of salt-induced damage on Paeonia ostii ‘Fengdan’ by exogenous silicon, we analyzed the photosynthetic and physiological characteristics of 1.5-year-old ‘Fengdan’ seedlings under NaCl stress by applying exogenous silicon (0, 0.75, and 1.5 mmol/L). Our results showed that the contents of the photosynthetic pigments chlorophyll a, chlorophyll b, and carotene, the transpiration rate, stomatal conductance, and intercellular CO₂ were significantly enhanced under salt stress when silicon treatment was applied, implying that the net photosynthetic rate was greatly improved. In addition, the plant height, stem thickness, and above-ground dry biomass of tree peony seedlings were effectively increased under salt stress with low-concentration silicon (0.75 mmol/L) treatment, along with osmotic substance (SS, SP, and Pro) content, total polyamine (TP) contents, and the activities of antioxidant-related enzymes (SOD, POD, and CAT) and polyamine-related synthetases (ADC, ODC, and SAMDC). In the low-concentration silicon treatment, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide anions (O₂⁻) were transformed quickly, which eventually reduced cell oxidative damage and improved seedling tolerance. This is an important finding in the understanding of how exogenous low-concentration silicon can alleviate salt-induced damage and promote the growth of tree peony seedlings, thus providing a new perspective on tree peony cultivation. Full article

Ssamchoo is recently attracting attention as a household hydroponic vegetable in Korea. It has a refreshing texture and a rich content of vitamins and fiber. Ssamchoo with a wide leaf area is suitable for traditional ssam or vegetable wraps, as well as a vegetable for salads; thus, it can be used in a variety of dishes. However, Ssamchoo plants responds sensitively to the nutrient solution, and it is often difficult to secure sufficient leaf area and robust growth using a commercial nutrient solution for leafy vegetables. This study consisted of three experiments conducted to develop the nutrient solution for Ssamchoo grown in a newly developed home hydroponic cultivation system using light-emitting diodes as the sole source of light. In the first experiment, growth and development of Ssamchoo in a representative commercial nutrient solution, Peters Professional (20-20-20, The Scotts Co., Marysville, OH, USA), was compared with laboratory-prepared nutrient solutions, GNU1 and GNU2. As a result, the Ssamchoo grown in Peters Professional had a high NH₄⁺ content in the tissue, leaf yellowing, darkened root color, and suppressed root hair development. In addition, adverse effects of ammonium such as low fresh weight and shorter shoot length were observed. In the second experiment, Peters Professional was excluded, and the ratio of NO₃⁻ to NH₄⁺ in the GNU1 and GNU2 nutrient solutions was set to four levels each (100:0, 83.3:16.7, 66.7:33.3, and 50:50). As a result, the fresh weights of 83.3:16.7 and 66.7:33.3 were the greatest, and the leaf color was a healthy green. However, at 100:0 and 50:50 NO₃⁻/NH₄⁺ ratios, the fresh weight was low, and leaf yellowing, tip burn, and leaf burn appeared. The nutrient solution with a 83.3:16.7 NO₃⁻- to-NH₄⁺ ratio, which gave the greatest fresh weight in the second experiment, was chosen as the control, while the solution with a 50:50 NO₃⁻/NH₄⁺ ratio with a lower nitrate content among the two unfavorable treatments was selected as a treatment group for the next experiment. In the third experiment, NH₄⁺ was partially replaced with urea to make four different ratios of NO₃⁻ to NH₄⁺ to urea (83:17:0, 50:50:0, 50:25:25, and 50:0:50) in combination with two levels of Si (0 and 10.7 mmol·L⁻¹ Si). The greatest fresh weight was obtained in the treatment in which the NO₃⁻/NH₄⁺/urea ratio was 50:25:25. In particular, when Si was added to the solution, there was no decrease in the number of leaves, and plants with the greatest fresh weight, chlorophyll content, and leaf area were obtained. The number of leaves and leaf area are important indicators of high productivity since the Ssamchoo is used in ssam dishes. It can be concluded that a solution with a NO₃⁻/NH₄⁺/urea ratio of 50:25:25 and supplemented with 10.7 mmol·L⁻¹ Si is the most suitable nutrient solution for growing Ssamchoo in the home hydroponic system developed. Full article