Stomata during night (respiration)
Leaves have no need to 'exhale' carbon dioxide - it gets consumed by photosynthesis.

Elsewhere in the plant, metabolic processes produce carbon dioxide. This escapes via inter-cellular gas channels that, in woody plants, terminate as lenticels (little pores) on the stem surface. Oxygen for metabolism diffuses into the plant in the same inter-cellular spaces as carbon dioxide diffuses out.

With roots, the oxygen necessary for metabolic processes is dissolved in water.

If you've meant to ask about leaf adsorption of carbon dioxide and when stomata close, it depends on what carbon fixation scheme the plant exhibits, CAM, C4, or C3.

You might want to also consult an  answer I gave to a similar question previously posed here.