Deforestation and Photosynthesis relate in a lot of ways. One way is if there are no trees because of deforestation then there is no photosynthesis. If there is no photosynthesis then there is no oxygen. Trees play a big role in the carbon cycle. Trees that are alive take in and store carbon. Dying trees let out carbon into the atmosphere. If there are no trees then the sunlight will dry up all the moist soil and then plants can't grow. If plants can't grow there will be no photosynthesis.