If higher levels of atmospheric oxygen can lead to larger animals, can it also lead to larger plants? According to some information, in the ancient past (at least some) animals grew larger due to a higher levels of oxygen in the atmosphere. So for example there is this study regarding dragonflies. Can higher levels of atmospheric oxygen also lead to larger plants? For example, would it be possible to grow gigantic strawberries in a hermetically sealed greenhouse that maintains a higher atmospheric oxygen concentration?

Oxygen is good for animals because our basic metabolism is this:

> High energy carbon molecules + O2 → energy + H2O + CO2

Plants do that too at night, but during the day, they mostly do this:

> High energy photons + H2O + CO2 → High energy carbon molecules + O2

Rubisco, one of the most important enzymes in photosynthesis, can bind to O2, leading to less efficient photorespiration, instead of photosyntheis. Rubisco is often a bottleneck in photosynthesis, in large part for that reason. So high oxygen isn't helpful to plants. In fact, C4 plants and CAM plants have evolved more complicated physiology to minimize the effect of O2.