Effects of Silicon on water use efficiency in sunflower with solution culture

Effects of silicon on growth and water use efficiency (WUE) in sunflower(Helianthus annuus L. cv. G101) plants were studied with hydroponic experiment. The objectives of this study were to find the effect of silicon on water use efficiency of sunflower plants, which is mainly through water loss from leaves and water transport in xylem. Under hydro- ponic experimental condition, water use efficiency was calculated in terms of dry matter produced per unit of water con- sumption. The transpiration rate and leaf conductance of plants with (1.5 mmol/L silicic acid) or without Si application were measured using LI-1600 steady state prometer. Flow rate of xylem sap was evaluated by calculating the volume of xylem sap per hour. The results showed that WUE of plants treated with 1.5 mmol/L silicic acid was 34% higher than that of plants without Si application. Silicon application did not significantly improve plant growth and leaf area, but sig- nificantly increase the SPAD value of the largest leaf. Silicon application significantly decreased the transpiration and leaf conductance of abaxial leaf epidermis, but had no effect on that of adaxial leaf epidermis. Comparing the flow rate of so- lutes in xylem vessels in plants treated with and without Si found that the flow rates in Si-treated plants was much lower than that in plants without treated with Si, which was due to the increase of affinity for water in xylem vessels induced by silica deposits in vessels. These results indicated that the increase of WUE was mainly resulted from the reduction of leaf transpiration and flow rate of xylem sap in xylem vessels induced by Si application.