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Why does photorespiration become more important at high temperatures?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — photosynthesis Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

Photorespiration becomes more significant at high temperatures because of the dual nature of the enzyme ribulose 1,5-bisphosphate carboxylase (Rubisco).12

Rubisco catalyzes two competing reactions: the carboxylation of RuBP (which initiates the Calvin-Benson cycle) and the oxygenation of RuBP (which initiates photorespiration). Whether oxygenation or carboxylation is favored depends on the relative concentrations of oxygen and carbon dioxide within the chloroplasts and the leaf temperature.12

At high temperatures, plants often close their stomata to conserve water, which restricts the entry of carbon dioxide. As internal carbon dioxide levels drop, the ratio of oxygen to carbon dioxide increases, causing Rubisco to function more frequently as an oxygenase rather than a carboxylase. Consequently, the plant shifts toward the wasteful process of photorespiration, which releases carbon dioxide and reduces the efficiency of photosynthesis.3412