# Ratio of oxygen produced / consumed by plants

Related questions:

How long can a plant generate oxygen from its own carbon dioxide, produced during nighttime?

Are plants actual oxygen factories?

But the actual question I'm interested in is:

What is the ratio of oxygen produced during the day vs. consumed at night.

Even ballpark numbers are sufficient, as this came up in a conversation about a Mars colony game where a tree produced 2 units of oxygen during the day and consumed 1 at night (with the game-night being half the length of a game-day because...reasons). Colonists would then need about 1 to 1.5 oxygen per full day/night cycle.

My friend and I were like "this ratio does not sound right" and haven't been able to find any any decent numbers to back up our opinion...or refute it.

Obviously the chemical reactions involved are mirrors of each other, and the output depends on the amount of light, and so forth...But wouldn't trees just be...less active at night in order to conserve energy, while more active during the day?

• define plant, the answer is vastly different for cacti, trees, grass, or algae.
– John
Mar 7, 2018 at 18:31
• @John Given the context of what my friend and I were discussing: Trees. If you want more specific than that, I don't honestly care, pick one. Mar 7, 2018 at 18:42
• well it depends on what your colony is using, algae is the best at producing oxygen, about 1.9grams per cubic meter of algae , sciencedirect.com/science/article/pii/0043135488901054
– John
Mar 7, 2018 at 23:14
• @John 1.92g is a net value. For all I know it could produce 1g per hour of daylight and consume 0.84g per hour of nighttime for a ratio of 1.2:1. Or it might be that it produces 0.2g per hour of sunlight and consumes 0.04g per hour of night for a ratio of 5:1, that's the number I'm interested in. Mar 7, 2018 at 23:21