February 18, 2007
Hydroponics Gardening - An Introduction To Hydroponics Gardening For Beginners (part 14) CO2
How Carbon Dioxide (CO2) Can Keep Your Plants Growing!
Carbon, Hydrogen and Oxygen make up about 90% of the dry matter in a plant. CO2 (Carbon Dioxide) in the air supplies all of the Carbon in the plant. Like animals, plants breathe in Oxygen and breathe out Carbon Dioxide all the time. The plant needs Carbon Dioxide during the hours of daylight and uses this to produce sugars. During the hours of darkness it will breathe out Carbon Dioxide, which is a waste product.
The plant uses light and Carbon Dioxide for photosynthesis. The more light there is available the greater the plant’s requirement for Carbon Dioxide, It has been found that it takes about 10 photons, (quantum units of light) during photosynthesis, to create enough energy to split one Carbon Dioxide molecule into its basic components of Carbon and Oxygen and form a sugar.
Because there are trillions of photons hitting the plant’s leaves, sufficient Carbon Dioxide is needed to convert their energy into sugars. If enough CO2 is not available, then the unused photons will bounce off the plant’s leaves and be lost. So the more light the plant is given the more Carbon Dioxide it will need to produce its maximum yield of sugars from photosynthesis.
Plants absorb different spectrums of light in differing amounts. This light is affected in different ways by a range of factors, such as distance and percentage of reflection etc. Because any unusable light is wasted, the calculation of how much useable light the plant is getting is quite complicated. It can be measured using a special PAR meter (PAR = Photosynthetically Active Radiation).
This machine takes into account the lumen level of the light striking the leaves and discounts the unusable fractions of the available light.
Plants outside, in full sunlight, will get about 5000 lumens per square foot. This means that the plant could process about 2000 ppm of CO2. It is unfortunate that the Carbon Dioxide levels outside are nowhere near this level.
Indoors, using a light level of 3000 lumens, the plant will need approximately 1500 ppm of CO2. If the light level was at 1000 lumens this would drop to around 300 ppm CO2 (city air is about 400 ppm) which is within the normal range. The lower the concentration of Carbon Dioxide the more the air has to be moved across the plant’s leaves in order for it to get sufficient exchange.
It is known that if the plant has enough CO2 and enough light it will perform to its optimum, so if we increase the light levels and up the CO2 available then we can expect a good increase in growth and subsequent yield.
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