Assessment of the Effect of Silicon On the Morphology and Physiology of Petunia Plants Grown in the Presence of Varying Salt Concentrations.

Silicon (Si) supplemental to substrates low in available silicic acid can improve plant response to biotic and abiotic stresses. Our objective was to test whether Si supplementation to a soilless substrate would improve the salt tolerance of petunia, a low Si accumulator. The experiment combined 4 irrigation water treatments (0, 20, 40 or 80 mM NaCl supplemented to a commercial complete water soluble fertilizer) by 3 Si treatments (0, 2 or 4 mM potassium silicate supplied as weekly drenches). Petunia (Petunia hybrida ‘Mitchell’) seedlings were transplanted into containers with a peat-based soilless substrate grown in a greenhouse at 22 °C. Salt treatments began 2 weeks after transplanting and plants were evaluated for morphological and physiological response after 7 weeks of salt treatments. NaCl, but not Si, had a significant effect on both shoot length and average leaf area: shoot length was decreased at all salt concentrations (68, 61 and 42 cm for increasing salt concentrations), as compared to that of control plants (81 cm), and average leaf area was significantly reduced at the greatest NaCl treatment as compared with controls. Yellowing of lower leaves was evident at the greatest salt concentration. Chlorophyll index averaged across all treatments was 40, 37, and 25 for upper, middle, and lower leaves, respectively. NaCl and Si treatments had a significant interaction. There was no significant difference in chlorophyll index among the three control treatments (0, 2 or 4mM Si with 0 mM NaCl). In the absence of Si, only 80 mM NaCl caused a significant reduction in leaf chlorophyll index. The chlorophyll index of Si supplemented plants exposed to 80mM Si was comparable with control plants. We further examined whether chlorophyll index results were reflected in photosynthesis efficiency or photosystem II fluorescence. Though there were no statistically significant differences, some interesting trends suggest follow up.