How does C4 photosynthesis help many grasses survive in hot and dry climates?

C4 photosynthesis provides a significant survival advantage for many grasses in hot and dry climates by allowing them to minimize water loss while maintaining efficient carbon fixation.123

In these environments, plants often close their stomata to prevent water loss, which restricts the intake of carbon dioxide. In standard C3 plants, low CO2 levels cause the enzyme Rubisco to bind with oxygen instead of carbon dioxide, a wasteful process known as photorespiration.132

C4 grasses overcome this through a specialized anatomical and biochemical mechanism:13

• Spatial Separation: Photosynthetic functions are divided between mesophyll cells and bundle-sheath cells.13
• Efficient Fixation: The enzyme PEP carboxylase, located in the mesophyll, has a much higher affinity for CO2 than Rubisco and does not react with oxygen. It captures CO2 even when stomata are partially closed.123
• Concentration Mechanism: The captured carbon is converted into four-carbon acids (such as malate) and transported to the bundle-sheath cells. There, it is released as high-concentration CO2, allowing the Calvin-Benson cycle to proceed efficiently while suppressing photorespiration.132

This adaptation enables C4 grasses to thrive and grow faster than C3 relatives in warm, arid conditions, despite the extra energy required to drive the cycle.123