Effect of ozone treatment and light colour on photosynthesis and yield of lettuce

Between factors which may influence on plant growth are light conditions and chemical composition of atmosphere. The objective of this study was to investigate the effect of ozone treatment (at the stage of seeds and seeds + seedlings, described as O-3-1 and O-3-II) and light colour (white, blue, and white + blue 50:50) on photosynthesis and yield of lettuce (Lactuca sativa L 'Subyana F-1') grown in a hydroponic system. During the experiments the following conditions were maintained: photoperiod 12 h; temperature 22 degrees C; relative humidity (RH) 65-70%. LED lamps emitted the following light colours: white, blue and white + blue (50:50) (described as W, B and W + B). For all colours, quantum irradiance was 70 awl m(-2) s(-1). Plants were fertigated with a standard nutrient solution with the following chemical composition (mg dm(-3)): N-NH4 < 10, N-NO3 150, P-PO4 50, K 150, Ca 150, Mg 50, Fe 3.00, Mn 0.5, Zn 0.44, Cu 0.03, B 0.01; pH 5.50, EC 1.8 mS cm(-1). The analysed factors significantly modified photosynthetic activity, growth, yield, chlorophyll content (SPAD measurements) and chemical composition of plants. The highest net photosynthesis rate (P-N) was recorded in plants cultivated with 03-I under W + B light, while the lowest was observed for 03-11 under B light. In the case of O3-11 a highly significant increase of mean N content in leaves was observed, together with decreases of P, Ca, Mg, Na, Fe and Mn contents in comparison to control plants. An improvement of yield (although not statistically significant) was found in O-3-1 plants, while O-3-II application caused a decrease of the yield, for B light by about -27.87%, for W -53.74% and for W + B -46.51%. Similar observations were noted for the number of leaves. Moreover, a significant effect of O-3-I on chlorophyll content was noted, excluding plants cultivated under W light. It seems that ozonization of seeds improves their germination and some other growth and physiological processes, while a second ozonization impairs the condition of plants and has a similar effect as tropospheric ozone in outside conditions. From the practical point of view, it would be interesting to investigate the effect of ozonization and other light colours on different crop species. (C) 2017 Elsevier B.V. All rights reserved.