Question: Are there any particular trees that put out more oxygen than others?

Jon Copley answered on 17 Jun 2010:

Yes – trees that have more leaves on their branches, and bigger trees. But there’s also more to it than that, if we think about plants in general and not just trees.

Plants come in three different types for the different ways that they carry out photosynthesis: there are “C3” plants, “C4” plants and “CAM” plants (which stands for something called “crassulacean acid metabolism”).

The amount of oxygen that a plant produces depends on a balance between two things: the amount of oxygen that it creates by splitting water in photosynthesis, and the amount of oxygen that it uses in its respiration.

That last one is what’s important, because plants can suffer from a reaction called “photorespiration” under high light and high temperature conditions, where they actually use up oxygen in their photosynthesis reactions and produce carbon dioxide, rather than the other way around (and that’s in addition to the other “normal” respiration reactions always going on in their cells, which also use oxygen and make CO2). So plants than can minimise photorespiration should be more efficient at putting out oxygen.

Photorespiration is a potential problem for “C3” plants, which are the most common type of plants. But “C4” plants have evolved some tricks to minimise photorespiration. Although only 1% of plant species are “C4” plants, they carry out 30% of all the photosynthesis by plants on land. Maize and sugar cane are “C4” plants.

But the best plants at avoiding photorespiration (and so, arguably, the most efficient oxygen producers) are the “CAM” plants (which also use the least water). Around 7% of plant species are “CAM” plants, and they are nearly all plants that grow in hot and / or dry places.

The aloe plant, which people often keep in pots in houses, is a “CAM” plant. So are pineapples. One of the quirks of “CAM” plants is that, because of their different form of photosynthesis, they have sour-tasting leaves when it is light during the day, but their leaves become sweet-tasting in the dark at night.