Potassium Silicate Supplementation Enhances Heat Tolerance of Petunia xhybrida ‘Mitchell Diploid'

Silicon (Si) supplementation to plants has been reported to mitigate several abiotic stresses, including: drought, salinity, extreme temperatures, and heavy metal toxicity.  While the beneficial effects of Si have been long documented, obstacles to the realization of the potential of Si in greenhouse crop production include limited knowledge regarding the regulatory pathways underlying Si accumulation by plants and subsequent mode of action. Our objective was to determine if silicon supplementation to Petunia during greenhouse production could ameliorate subsequent response to heat stress. Greenhouse grown petunia plants received either 0 (control), 0.5, or 2 mM Si from potassium silicate supplemented to the standard daily fertilizer regime. Potassium chloride was also supplemented so that all plants received the same amount of potassium. After several weeks plants were moved to controlled environment chambers. Following acclimation to the chambers, plants received 40 °C heat stress treatments for three days followed by a return to 24 °C. Plants were well watered in the chamber experiment. Si treatment led to a visual improvement in plants exposed to heat stress. Plants receiving 2 mM Si exhibited less wilting and leaf yellowing than control plants. With 24 h of heat stress, net photosynthesis (Pn) of control plants was reduced by about 50% while 0.5 and 2 mM Si plants exhibited only a 30% decrease in Pn.  Transpiration (E) of 2 mM Si plants was greater than control plants in response to 24 and 72 h of heat stress. Silicon treated plants did not exhibit a decrease in chlorophyll fluorescence (Fv/Fm) in response to heat stress; whereas for control plants, Fv/Fm decreased from 0.83 prior to stress to 0.45 following 48 hours of stress. Stress induced silicon accumulation (SISA) was observed. Leaf Si concentration prior to heat stress was 78, 352, and 897 mg kg^-1 for 0, 0.5, and 2 mM Si treatments, respectively. Following heat stress, leaf Si concentration had increased by more than two-fold to 208, 1161, and 2360 mg kg^-1 for 0, 0.5, and 2 mM Si treatments, respectively. Our results demonstrate that Si supplementation partially ameliorates 40 °C heat stress in Petunia. Future work should explore the landscape performance of Si-amended greenhouse grown petunias and further explore the mechanisms underlying Si-mediated heat tolerance.