Effect of ozone treatment and light colour on photosynthesis and yield of lettuce
2017
Kleiber, Tomasz | Borowiak, Klaudia | Schroeter-Zakrzewska, Anita | Budka, Anna | Osiecki, Szymon
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 O3-I and O3-II) and light colour (white, blue, and white+blue 50:50) on photosynthesis and yield of lettuce (Lactuca sativa L. ‘Subyana F1’) grown in a hydroponic system. During the experiments the following conditions were maintained: photoperiod 12h; temperature 22°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 70μmolm−2s−1. Plants were fertigated with a standard nutrient solution with the following chemical composition (mgdm−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 1.8mScm−1. The analysed factors significantly modified photosynthetic activity, growth, yield, chlorophyll content (SPAD measurements) and chemical composition of plants. The highest net photosynthesis rate (PN) was recorded in plants cultivated with O3-I under W+B light, while the lowest was observed for O3-II under B light. In the case of O3-II 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 O3-I plants, while O3-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 O3-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.
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