Answer:
Tropical rainforests such as the Amazon have been said to produce so much of Earth's oxygen when in fact this is not necessarily true.
Plants do indeed use Carbon dioxide during photosynthesis and the end product is Oxygen. The amount of oxygen produced however is more or less equivalent to the amount of Carbon dioxide taken in as atoms cannot be multiplied. With Carbon dioxide comprising only 0.04% of air, the oxygen produced is not as much as one would think.
After these trees produce Oxygen, they will also use it during respiration to produce energy which means that they would be sucking in most of the oxygen that they created. This would therefore reduce the net oxygen coming from these trees.
Another thing is that when plant life dies and is decomposed, the carbon dioxide that it stored from will be released back into the atmosphere. Leaves falling and fruits eaten will have this effect as well and since this happens a lot in tropical rainforests, their net oxygen production decreases.
