Hello,

Specialized cells known as guard cells surround stomata and function to open and close stomatal pores.Stomata allows a plant to take in carbon dioxide, which is needed for photosynthesis. They also help to reduce water loss by closing when conditions are hot or dry.
Carbon dioxide CO2 is an essential part of the cycle of life.Without a source of CO2,plants will die off.
Plants release carbon dioxide during the but it does not released out because carbon dioxide generated during daytime is used by the plants in the process of photosynthesis. While using CO2 in the presence of sunlight,they produce glucose and oxygen thus counter balancing CO2 release.
Plants close stomata in response to their environment; for example, most plants close their stomata at night. Under drought,plants may also close their stomata to limit the amount of water that evaporates from their leaves.


I hope this helps.