Silicon Accumulation and Distribution in Petunia and Sunflower

Silicon (Si) is a beneficial element that has been shown to protect plants during periods of abiotic and biotic stress. Plant-available Si can be supplied through substrate components, substrate amendments, liquid fertilization, or foliar sprays. The objective of this study was to compare Si accumulation and distribution in plants grown in a Si-amended and non-amended substrate. The base substrate was 85 peat : 15 perlite, with incorporation of either 0% or 20% parboiled rice hulls (by volume). Seedlings of petunia (Petunia ×hybrida ‘Dreams Pink), a low-Si accumulator, and sunflower (Helianthus annuus ‘Pacino Gold’), a high Si-accumulator, were transplanted into 11.5-cm pots. Greenhouse conditions were maintained at 22 °C day/18 °C night, with a 14 h photoperiod and supplemental irradiance from high-pressure sodium lamps when ambient irradiance was less than 300 µmol∙m^-2∙s^-1 photosynthetically active radiation. Plants were irrigated as needed with 20N-4.4P-16.6K at a concentration of 150 mg∙L^-1 N. They were harvested when all had flowered, 53 and 72 days after transplant for petunia and sunflower, respectively. Leaf, stem, and root Si concentrations (mg∙kg^-1 dry weight) were higher in petunia plants grown in the rice hull-amended substrate, but flower Si concentration was similar in both treatments. Sunflowers had higher Si concentrations for all tissues (roots, leaves, stems, and flowers) when grown in the rice-hull amended substrate. Of the total plant Si accumulated in petunias grown in the rice-hull amended substrate, approximately 72% accumulated in leaves, 17% in stems, 5% in flowers, and 6% in roots. In sunflower, Si distribution in plants grown in the rice hull-amended substrate was 91% in leaves, 3% in stems, 3% in flowers, and 3% in roots.