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by Dr . Lynette Morgan
Q
Would there be any connection to my CO 2 levels going down when my lights go on ? Thanks for any insight you can provide !
— Paul J . a
Yes , there is a connection to CO 2 levels in a growroom dropping when the lights come on . This is caused by the plants switching on photosynthesis as soon as there is sufficient light to power this process . As the plants sense the light , the stomata become fully open and are able to rapidly absorb the carbon dioxide from the surrounding air required for photosynthesis to occur . Plants use this CO 2 absorbed via the leaf surface , combined with water from within the plant and PAR ( photosynthetically active radiation which your lights provide ) to photosynthesise and produce assimilate ( sugars ) for growth and development . As a byproduct during the light phase , the plants release oxygen from the leaf surface . This only occurs in the light , so the plants don ’ t take up CO 2 in the dark when the lights are off and additional CO 2 does not need to be supplied until the lights come on . The drop in CO 2 levels as the lights come on can occur surprisingly fast , particularly if the plants are large , grown at a high density , or in quite a limited room volume with minimal air exchange . This can also be seen in greenhouses when vents are closed to conserve heat in the early morning , sunlight powering photosynthesis can actually crop the ambient CO 2 to levels low enough to restrict photosynthesis and retard growth somewhat . The best way to counter this drop in CO 2 as the lights come on is to either rapidly vent and draw fresh air in from outside ( ambient CO 2 levels in the atmosphere these days are now over 400ppm ) and ideally the growroom doesn ’ t want CO 2 to fall much below this while plants are actively photosynthesising , so this may require a fairly rapid rate of air intake and venting out stale , CO 2 depleted air . A more common approach in a growroom is to enrich with additional CO 2 so the plants are given an extra boost to increase the rate of photosynthesis rather than just making sure CO 2 depletion doesn ’ t occur . CO 2 can be enriched to 1,000-1,500ppm for many fast growing crops under warm growing conditions and good light . CO 2 enrichment has been well proven to increase growth rates and yields significantly and is widely used in controlled environment agriculture . Plants will make the most efficient use of CO 2 if they also have warm temperatures which are required to boost photosynthesis . To prevent the CO 2 levels suddenly dropping as the lights come on , it ’ s a good idea to start CO 2 enrichment just before photosynthesis is triggered so that the environment is up to a good level as the lights fire up , this prevents any lag in photosynthesis which may otherwise occur if CO 2 drops rapidly during this time . Monitoring CO 2 levels in your growroom is also a good was to not only ensure the CO 2 depletion does not occur , but to also monitor the rate of plant growth — healthy plants , growing rapidly under good conditions will consume large amounts of CO 2 .
Lynette Morgan Suntec International Hydroponic Consultants
LM
Dr . Lynette Morgan holds a B . Hort . Tech . degree and a PhD in hydroponic greenhouse production from Massey University , New Zealand and is a partner in SUNTEC International Hydroponic Consultants . She has authored six hydroponic technical books .
18 Maximum Yield