Quercus suber is found growing in drought-prone regions around the Mediterranean basin. In hot, dry areas such as these, some species exhibit a daily suppression in photosynthesis around noon, at the hottest part of the day. This is known as the ‘midday depression’, when the plant closes its stomata to reduce water loss.
This closure can cause other short-term effects to the plant. Gas exchange through stomata is important for cooling, so leaves with closed stomata can overheat. Additionally, the suppression of photosynthesis means the light energy cannot be used as normal, and the energy surplus can damage cells within the plant. However, water loss would be more catastrophic to the plant than either overheating or problems caused by high light, and there are rhythmic repair processes which deal with the damage.
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