Effects of exogenous silicon on growth and physiological characteristics of lily under alkali stress

Bulbs of Siberian lily (Lilium 'Siberia') were employed as the experimental material in a pot experiment. The plants were treated with 240 mmol·L⁻¹ Na₂CO₃ to simulate alkaline stress, and five concentrations of K₂SiO₃ (0, 0.5, 1.0, 1.5, and 2.0 mmol·L⁻¹) were applied to the roots. The effects of different silicon concentrations on plant growth indicators, root morphology, plasma membrane permeability, osmotic adjustment substances, and ion content under alkaline stress were analyzed. The results showed that the application of potassium silicate (K₂SiO₃) could promote the root morphology and shoot (plant height, ground diameter, leaf area) growth of lily under alkaline stress. With the increase of silicon concentration, the contents of soluble protein (SP), soluble sugar (SS), proline (Pro) and K ⁺ , Si^{4 +} in leaves increased. At the same time, the ratio of K ⁺ / Na ⁺ increased, while the content of Na ⁺ , relative conductivity (RC) and malondialdehyde (MDA) decreased. Moreover, compared with alkaline stress, the root morphology (root length, root surface area, root average diameter, root volume, K ⁺ content) and leaf (SP, SS, Pro) were significantly increased under 2.0 mmol·L⁻¹ silicon concentration treatment. However, the contents of MDA, RC and Na ⁺ (ANa ⁺ ) in aboveground and underground parts were significantly decreased. The results of correlation analysis indicated that exogenous silicon had significant effects on all indexes of lily under alkali stress. Principal component analysis (PCA) showed that MDA, RC, ANa ⁺ and underground Na ⁺ content (UNa ⁺ ) could be used as the characteristic indexes of alleviating effect of 0.5～1.0 mmol·L⁻¹ exogenous silicon on lily under alkali treatment. Leaf area (LA), osmotic adjustment substances, K ⁺ content in aboveground and underground parts, K ⁺ /Na ⁺ ratio and root morphological indexes could be used as the characteristic indexes of lily alleviation under 1.5～2.0 mmol·L⁻¹ exogenous silicon treatment. Moreover, Membership function analysis revealed that the 2.0 mmol·L⁻¹ silicon treatment achieved the highest membership function value.