Do all plants emit CO2 at night? I heard that plants do respiration all the time but in sunlight they utilises more CO2 and releases more oxygen. During day with sunlight: CO2>Oxygen. At night or plants that are in shade, they don't produce oxygen at all but produce CO2? Correct?

Also, If suppose a tree is getting light but only one part, What will be the consequence of this?

(I am okay if this question migrates to Biology if this is not suited here)

3 Answers 3


Yes, plants emit CO2 day and night. CO2 is an end product of metabolism which is the burning or oxydation of sugar that occurs in the mitocondria.

The Calvin cycle of photosynthesis can occur only in light or in daytime,if you wish. However the intake of CO2 varies across species. CAM species, of which jade (crassula ovata) is an example, take in CO2 at night and store it in malic acid. This means the stomata can be closed during the heat of the day, but the Calvin cycle can operate, unlike the common C3 species that have no means of storing CO2 and must take in CO2 during daylight as well. The third type, C4 also utilizes metabolism of malic or aspertic. Maize and sugar cane are expamples of C4 plants.

The critical piece of carbon fixation is an enzyme known as RuBisCo (an acronym for a very lengthy chemical name). RuBisCo does the actual fixing of carbon into elemental sugar. I also sometimes incorporates oxygen instead. The rate of fixation increases with temperature, however, the rate of fixing oxygen increases more rapidly than that of fixing carbon so that at temperatures near 95F (35C) and above, there is no net carbon fixing. Malic/aspertic acid in C4 and CAM plants is a mechanism of effectively blocking oxygen from RUBISCO and so allows carbon fixation to occur at higher temperatures. Hence, these are typically tropical species.

So plants continually emit CO2 because of the process of life. They emit more the hotter the environment, so this goes up and down though the course of a day. Carbon fixation occurs only via photosynthesis. Most species are C3 and will release more oxygen than carbon dioxide during the daylight hours and while the temperature is below 95F (35C). The same for C4 plants, except that there will continue to be a net fixation of carbon at yet higher temperatures. CAM, plants, however, will take in carbon at night.

SHORT VERSION: you are correct, but for plants such as crassula ovata and pineapple.


Plants respirate co2 and expire oxygen during the day. At night, the respire oxygen and expire co2, but to a much lesser degree.


Oxygen is one of the products of photosynthesis. Part of ventilation is blowing away the O2 so that CO2 is more readily available to the plant's leaves. Photosynthesis uses CO2 and the byproduct is O2. I have never heard of photosynthesis happening in the dark, nor have I ever heard CO2 is a product from photosynthesis. O2 is produced by photosynthesis while there is sufficient light. The plants use CO2 primarily for synthesis of the plant's food via photosynthesis.

A shrub or tree or any plant that has leaves that aren't doing a great job because of less light than the top leaves are actively gotten rid of by the plant. The plant won't direct nutrients towards photosynthetic leaves (stems) that aren't producing as much in relation to the leaves on top of the plant. Slow death of interior and shaded plant material. Remember photosynthesis provides the plant with FOOD. Chemicals are necessary for photosynthesis that we have to provide when too little of these chemicals exist in the soil. Plants MAKE THEIR OWN FOOD! Pruning out obviously dying branches, leaves just helps plants direct their energies more effectively. Part of the art of pruning, getting rid of plant material not helping the plant make food or thrive.

Respiration is more than O2, it is also water through the stomata...especially when temperatures are too high. Maybe I am wrong but I can't imagine that a plant would ever respire CO2. At night photosynthesis is stopped.

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