Why do C3 grasses tend to be more successful in cooler climates?

C3 grasses are often more successful in cooler climates because they avoid the metabolic "penalty" associated with the C4 photosynthetic pathway.

While C4 plants have evolved a specialized mechanism to concentrate carbon dioxide and minimize photorespiration—a process that reduces photosynthetic efficiency—this mechanism requires the expenditure of extra ATP to recycle the enzyme phosphoenolpyruvate (PEP). In cool environments, photorespiration is naturally insignificant, meaning the C4 pathway's energy-intensive carbon-concentrating mechanism offers little advantage.12

Consequently, in cooler conditions or environments with lower light availability, the additional energy cost of the C4 pathway becomes a disadvantage, allowing C3 plants to operate more efficiently. Conversely, C4 plants are favored in warm, arid environments where their ability to suppress photorespiration and conserve water outweighs the metabolic cost of their specialized carbon-fixation system.21