Fixation of oxygen occur instead of carbondioxide.
Explanation:
If the stomata remain closed due to water loss, the concentration of carbondioxide decreases and oxygen increases in the leaf because of the fixation of oxygen instead of carbondioxide by rubisco. The plant takes carbondioxide from the atmosphere when the stomata is open so when the stomata is closed there is no other way for getting carbondioxide into the leave so the oxygen is now being fixed by our rubisco enzyme to that five-carbon compound instead of carbon dioxide.
