Just like humans, a marijuana plant has to breathe: take in oxygen from the air.
This is used in the respiration that converts sugars and oxygen into energy, water and CO2.
The energy keeps the plant alive. It is used for instance to create proteins, to pump substances into and out of the cell and to grow.
Photosynthesis is the exact opposite of respiration. If the plant is healthy and gets enough light, photosynthesis and respiration will take place at the same time.
That’s why it may seem like the plant doesn’t use any oxygen, since it only takes CO2 from the air and no oxygen.
In practice, the plant uses the oxygen it releases itself through photosynthesis directly for respiration.
If there’s no light, the plant gets its oxygen from the air and separates the CO2.
That’s why it’s so important for weed plants in their growing phase to also have a darkness period.
Stored sugars that were produced during photosynthesis are converted into proteins to stimulate the growth.
The ideal light/darkness ratio in the growing phase is 18 hours of light and 6 hours of complete darkness.
Two types of respiration
There are two types of respiration in plants: maintenance respiration and growth respiration.
The maintenance respiration keeps the plant alive. The plant has many processes that continuously need to be kept in motion, and these require energy.
The plant also replaces parts from time to time, such as leaves, cells or enzymes in the cells.
The energy that’s required for this comes from maintenance respiration.
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Maintenance of the plant always has priority over growth, because a plant can live without growing, but not without maintaining itself.
Maintenance respiration always continues and strongly increases with temperature. You can therefore steer the maintenance respiration by adjusting the temperature.
Generally, the maintenance respiration doubles with a temperature increase of 18 degrees.
At 77 degrees, 0.1 ounces of sugar is needed to maintain 3.5 ounces of dry weight in leaf. Stems and roots take half.
These numbers decline for older plants. If your plants don’t get enough light, it’s best to lower the temperature to obtain as little maintenance respiration as possible.
The plant will then consume less of its reserves, so you won’t lose as much yield.
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Contrary to maintenance respiration, which can sometimes best be slowed down a bit by adjusting the temperature to the amount of light, you can’t really get enough growth respiration.
Growth respiration is the respiration needed to make the plant grow taller and heavier.
A plant can roughly create 2.5 ounces of leaf (dry weight) from 3.5 ounces of assimilated sugars.
So these are the energy costs for creating new leaves.
Some forms of growing require more energy, such as producing buds and seeds.
If you’re not planning on using the seeds of your weed plants, it would be a waste to let the plant produce these.
This is because this process consumes a lot of energy: a plant can roughly produce 1.4 ounces of seeds from 3.5 ounces of sugars.
This energy could better be spent on the production of more buds or leaves. So only let unfertilized females flower.
Respiration in a closed space
A higher temperature always means more maintenance respiration, something you would like to be as low as possible.
But a higher temperature can also have a favorable effect if you have a lot of light and CO2. So what’s the best temperature?
Generally spoken it’s best to keep a low temperature if there’s no light. If there is a lot of light, water and CO2, it’s no problem if the temperature rises.
Make sure you read all articles in the categories plant physiology and climate to get a good understanding of the functioning of a weed plant.