No, that happens at night.
Flowering plants open and close their stomata during the daytime in response to changing conditions, such as light intensity, humidity, and carbon dioxide concentration. It is not entirely certain how these responses work. However, the basic mechanism involves regulation of osmotic pressure.
When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity), a proton pump drives protons (H+) from the guard cells. This means that the cells' electrical potential becomes increasingly negative, and so an uptake of potassium ions (K+) occurs. This in turn increases the osmotic pressure inside the cell, drawing in water through osmosis. This increases the cell's volume and turgor pressure. Then, because the wall of the guard cell facing the stomatal pore is less elastic (more rigid) than the wall on the opposite side of the cell, the two guard cells bow apart from one another, creating an open pore through which gas can move.
When the roots begin to sense a water shortage in the soil, abscisic acid (ABA) is released. ABA binds to certain receptors in the guard cells' plasma membranes, which first raises the pH of the cytosol of the cells and cause the concentration of free Ca2+ to increase in the cytosol due to influx from outside the cell and release of Ca2+ from internal stores such as the endoplasmic reticulum and vacuoles. This causes the chloride (Cl-) and inorganic ions to exit the cells. Secondly, this stops the uptake of any further K+ into the cells and subsequentally the loss of K+. The loss of these solutes causes a reduction in osmotic pressure, thus making the cell flaccid and so closing the stomatal pores. When the stama become flaccid some water is lost to the environment. This loss of water is called transpiration and is essential in the water cycle.