Light is needed in the process. Plants create O2 during the process and release CO2 at night reversing the process.
Photosynthesis occurs in the presence of sunlight, CO2, water, chlorophyll and at night there's no sunlight for the plants to carry on photosynthesis. Though I've heard that... Never mind. The site admins will probably delete this answer if I mention it.
What food is stored in plant in a process of photosynthesis