Effect of different light intensities on water use efficiency of lettuce under controlled conditions

Light is one of the main factors regulating plant growth and development. Among different aspects of light, light intensity has a great effect on plant responses, such as plant's water relations. Light intensity in greenhouse is lower than normal in winter and excessive light intensity in the summer. The aim of this study was to evaluate the effect of light intensity on performance, evapotranspiration, water use efficiency of lettuce in a completely randomized design with four treatments and twelve replications in the Park of Science and Technology in Aburaihan campus of University of Tehran. Since blue and red spectra are the main wavebands involved in growth and gas relations, the present experiment was done by using spectra composition of red and blue with a ratio of 70 percent red and 30 percent blue with four different intensities including (T1) 75 μmol.m-2.S-1, (T2) 150 μmol.m-2.S-1, (T3) 300 μmol.m-2.S-1 and (T4) 600 μmol.m-2.S-1. The studied traits included growth characteristics associated with water use efficiency. Based on the obtained results, the highest fresh weight was obtained from T3 and the lowest fresh weight was obtained under light intensity T3 with 73.52 and 17.31 respectively. Increased light intensity caused an increase in dry weight and leaf area. Highest growth simulation was observed under T3. Furthermore, the highest and the lowest water use efficiencies were observed in plants that were grown under T4 and T1.