Effects of Exogenous Silicon on the Growth, Photosynthesis and Quality Characteristics of Lettuce

Taking ‘Italian Bolting-resistant’ lettuce（Lactuca sativa L.） as the test material, substrate culture method was used, the regulation effects of different concentrations of exogenous silicon(0,0.5,1.0,2.0,and 5.0 mmol·L^-1) on roots on the growth and quality characteristics of lettuce cultured on distiller′s grains were explored, in order to provide a reference for the promotion and application of distiller′s grains and silicon fertilizer in soilless cultivation of leafy vegetables.The results showed that when the silicon concentration was in the range of 0-1.0 mmol·L^-1,the leaf width, and yield per plant of lettuce all increased with the increase of silicon concentration.When the silicon concentration was higher than 1.0 mmol·L^-1,the related indicators decreased with the increase, and reached the maximum at 1.0 mmol·L^-1.At the same time, the leaf net photosynthetic rate（Pn）,stomatal conductance（Gs） and transpiration rate（Tr） also increased first and then decreased with the increase of the silicon level in the cultivation substrate, which were the highest when the silicon concentration was 2.0 mmol·L^-1.The contents of reducing sugar, vitamin C,in lettuce leaves also increased first and then decreased with the increase of silicon level.When the silicon concentration was 1.0 mmol·L^-1,the content of reducing sugar was the highest, and the content of vitamin C was of the highest level when the silicon concentration was 2.0 mmol·L^-1.In addition, the root application of silicon solution could significantly increase the content of Fe in lettuce and reduce the content of Na and MDA,but the effect on K content was not significant.Considering comprehensively, increasing the concentration of silicon fertilizer with a concentration of 1.0-2.0 mmol·L^-1,which is based on 20% distiller′s grains compound substrate cultivation, has a significant effect on the increase of lettuce biomass and quality.