Effects of regulating hydroponic, solution temperature on plant growth, accumulation of nutrients and other metabolites

Abstract

The experiment was conducted with the objectives of establishing effects of regulating hydroponic solution temperatures on the chlorophyll content and photosynthesis processes, accumulation of anthocyanins and flavonoids, nutrient uptake and growth and development of pregnant onion (Ornithogalum longibracteatum L.) in the glasshouse during winter periods in 2009 and 2010. The plants were exposed to four hydroponic solution temperatures (control (10 - 15°C), 26°C, 30°C and 34°C). The treatments were arranged in a complete randomized design.Results from this study conducted in the glasshouse in 2009 and verified in 2010 showed that photosynthesis rate (A) and the gas exchange parameters [stomata conductance (gs), intercellular CO2 concentration (Ci) and transpiration (E)] were significantly increased by elevating the hydroponic solution temperatures to 26-30°C compared with the control and then decreased significantly at 34°C. Furthermore, increasing hydroponics solution temperature from 26°C to 34°C significantly increased the levels of flavonoids and anthocyanins in roots, bulbs, shoots and flowers of O. longibracteatum in both years 2009 and 2010.Warming of the hydroponic solution to 26, 30 and 34oC significantly increased the uptake of (N, P, K, Ca, Mg, S, Na Fe, Cu Zn, Mn and B and Mo) in organs of O. longibracteatum (root, bulbs shoot, and whole plant) in 2009 and verified in 2010. The control treatments 10/15°C (day/night) had the lowest uptake of most nutrients.Results from the two years study also showed that plant growth parameters such as number of bulbs per plant, bulb circumference, flower stalk length, flower length, and dry and fresh weights of root, bulb, shoot and flower respectively were significantly increased by warming the hydroponic solution. Elevating the hydroponic solution temperature to a range of 26 - 30°C induced best growth and produced the highest dry matter yield in O. longibracteatum under glasshouse conditions whereas further increase to 34°C resulted in reduced growth and yield.