Time required for photosynthesis?

Question

Do plants require direct and constant sunlight to maintain the process of photosynthesis? Is light diffused by leaves of a tree enough to produce photosynthesis in plants below? If the leaves of the tree are gently blown in such a way that the light is erratic, can the gaps between the sunlight cause the photosynthetic process to be interrupted in such a fashion that it resets?

I know there is a chemical process that requires sunlight, my question is truely about the effects of erratic or low level sunlight on that process.

Answer 1

Photosynthesis takes place in steps. It's not one chemical reaction, but many - notably photosystem II and photosystem I.

Photosynthesis cannot be "reset", as far as I can figure it. It requires certain amounts of energy to get from one intermediate to the other, but once they're there they remain there. Imagine lifting a heavy box up a flight of stairs - it takes a lot of energy to lift the box from step to step, but you can rest after the box is safely on the next step - it is secure in its position. Granted there are some intermediates that are relatively unstable, but unless you're firing off photons one by one it's not going to be hard to get to a stable intermediate.

Some plants take a full 24 hours to accomplish both the light and dark reactions of photosynthesis. CAM plants, common in xerophytic environments, take up carbon at night (when water loss is minimal and the stomata can be safely opened) and generate energy during the day. Malate is the chief intermediate for this process, which is stored in the vacuole of mesophyll cells.

Plants don't need THAT much light to grow. Granted more light means faster growth, but some plants actively start photosynthesizing before their shoots even break the soil surface.

Answer 2

There are shade adapted species of plants and actually do better in shade than in direct sunlight!  The more dense the canopy of trees the less growth you will see under the trees.  Plants in the understory often develop larger leaves than when in direct sunlight or grow tall and spindly to grow to a height that gets enough light.  Another adaptation is for plants in the understory is  to grow rapidly and early in the spring before the other trees become fully leafed.

The selective cutting of mature trees opens the canopy to allow immature trees to grow faster.

As to the question's title question, photosynthesis can be completed in seconds under ideal conditions.