It is known by all that plants, during the day, produce oxygen and consume carbon dioxide from the atmosphere thanks to the reaction called photosynthesis , dependent on sunlight. However, plants are still aerobic living beings, that is, they breathe, and therefore, although to a much lesser extent, they also absorb part of that oxygen to release carbon dioxide again . As long as there is light, the balance between photosynthesis and respiration is extraordinarily asymmetric in favor of the former. But during the night, the light disappears, photosynthesis stops working, and the plant just breathes, consuming oxygen and expelling carbon dioxide.
That is why it is common knowledge that sleeping with plants is dangerous, because they steal the oxygen from the environment.
The truth is that the matter is not so simple. To be able to break it down, we must first remember that plants breathe through organs that they have in the epidermis of leaves, floral pieces and green stems, called stomata , and through lenticels , which are openings that run through the woody stems and roots.
When do the stomata open?
This kind of valves that are the stomata are not permanently open, they open or close depending on various factors and the type of plant. And one of those factors is the way they metabolize atmospheric carbon, where we find three types.
The so-called C3 and C4 absorb carbon dioxide during the day, to carry out photosynthesis —direct in the first case, indirect in the second—. So they open their stomata during the day and close them at night . The third group is made up of CAM plants , which accumulate carbon dioxide at night, and store it until, during the day, they use it in photosynthesis. These plants, which usually live in dry and sunny areas, keep their stomata closed during the day and prevent water loss through evaporation. Since these plants capture carbon at night, they do not cause any problems.
In principle, C3 and C4 plants should not be problematic either, because at night, their stomata remain practically closed . However, plants not only breathe through the leaves, but also through the stem and roots , through lenticels , and those do not close. Therefore, they breathe during the day, in light, and also in the dark of night .
How much oxygen does a plant consume during one night?
The question is not easy to answer . There are many variables that can affect the answer. To begin with, the size of the plant . It is clear that a majestic 20 meter tall oak will consume a lot more oxygen than a pot of petunias overnight. Other influencing factors are temperature or atmospheric pressure . However, for practical purposes, the problem is unrealistic for several reasons.
In the first place, a bedroom is not exactly a sealed compartment, it always has a certain amount of air renewal ; but even if it were, the plant has produced far more oxygen during the day than it has consumed—and will consume all night. The net balance of carbon and oxygen in the 24 hours of the day is, and with great advantage, in favor of oxygen .
If the respiration of a plant at night inside a room were a real problem, then a forest at night would be a huge oxygen sink that would endanger the lives of the animals that live in it. More problematic would be a deciduous forest all winter long, with whole months of plants breathing, and no leaves to photosynthesize.
In reality, the amount of oxygen consumed by a plant in one night is negligible compared to the consumption of human beings. There is no plant that fits in a room capable of consuming in one night the amount of oxygen consumed by a medium-sized, warm-blooded animal, such as the dog that sleeps at our feet or the couple that sleeps next to us.
An adult person consumes around 100 liters of oxygen during the eight hours of night sleep. Under normal conditions of pressure and temperature, a pot whose petunias weigh 5 kilos consumes, in the same time, around 10 milliliters .
REFERENCES:
Álvarez Nogal, R. 2015. Citología e histología de las plantas. Eolas.
Hunt, S. 2003. Measurements of photosynthesis and respiration in plants. Physiologia Plantarum, 117(3), 314-325. DOI: 10.1034/j.1399-3054.2003.00055.x
O’Leary, B. M. et al. 2017. Variation in Leaf Respiration Rates at Night Correlates with Carbohydrate and Amino Acid Supply. Plant Physiology, 174(4), 2261-2273. DOI: 10.1104/pp.17.00610
Thornley, J. H. M. 1970. Respiration, Growth and Maintenance in Plants. Nature, 227(5255), 304-305. DOI: 10.1038/227304b0
