Anything that moves has kinetic energy, the energy of motion. Atoms and molecules have kinetic energy because of their constant random motion. The faster a molecule moves, the more kinetic energy it contains. Heat is a measure of the total quantity of kinetic energy due to the molecular movement in a body of matter. Temperature measures the intensity of heat due to the average kinetic energy of the molecules.
The 3-D structure of enzymes and other proteins are sensitive to their environment. Each enzyme has conditions it works optimally in. Up to a point, the speed of an enzymatic reaction increases with increasing temperature, partly because substrates collide with active sites more frequently when molecules move rapidly. At some point, the thermal agitation of the enzyme molecule disrupts the hydrogen bonds, ionic bonds, and other weak interactions that stabilise the shape, and the protein molecule denatures. Cells may rupture if the water they contain freezes, and most organisms proteins denature above 45oC. In addition few organisms can maintain an active metabolism at very high or low temperatures.
Growth peaks occur at an average temperature of 14.3oC(range 5.6-27.5oC) for outdoor plants. For CO2-enriched plants in a greenhouse or growroom, the ideal temperature is higher at 21-27oC during the day, and 13-21oC at night.
A suitable temperature is important for optimum plant activity. For top results, the temperature must be at least 20°C. Temperatures above 30°C can cause problems with tempera-ture sensitive types, certainly when this is combined with low humidity. The temperature should be between 20°C and 30°C to avoid problems.
Good root development requires the temperature of the nutrient solution to be high (20-25°C). Below 15°C, the absorption capacity of the roots diminishes rapidly; the nutrient transport in the plant stagnates, reducing the yields. The growth of the plant slows and the root system will be less fine (fewer branches and fewer root hairs). The first visual sign that the temperature is too low is purple coloration of the leaf stems, main veins and stem. If the low tempera-tures persist for too long, leaves may also be malformed. The absorption of nitrate, phosphate, magnesium, potassium, iron and manganese is hindered most at low temperatures.
If the difference between the tem- peratures for the dark and light periods is too great, problems may arise immediately after the lamps are swit-ched on. Leaves are warmed and water will start to evaporate. However, the roots are too cold to absorb sufficient water. This will make the plant hang limply and perhaps wilt. Try to prevent major differences between night and day temperatures as much as possible (no more than a few degrees difference). Maintai-ning an optimal root temperature is a precondition for good results. An aquarium heating element with a thermostat can be used as a cheap way to maintain the temperature.