How is C4 photosynthesis different from C3 photosynthesis in grasses?

In the context of the Poaceae family, the primary difference between C3 and C4 photosynthetic pathways lies in their anatomical structure and the mechanism used to fix carbon dioxide.1

Key Differences

• Anatomy: C4 grasses possess specialized, thick-walled photosynthetic cells in sheaths surrounding their vascular bundles. C3 grasses lack this specific bundle-sheath anatomy.1
• Carbon Fixation: C3 plants fix carbon dioxide directly into a three-carbon compound. In contrast, C4 plants utilize an additional step: they first fix carbon dioxide into a four-carbon compound (oxaloacetate) within the mesophyll cells. This compound is then transferred to the bundle-sheath cells, where carbon dioxide is released and refixed via the standard C3 cycle.21
• Efficiency and Environment: While the C4 cycle requires more ATP, it concentrates carbon dioxide in the bundle sheaths, which minimizes photorespiration. This makes C4 grasses significantly more efficient in hot, dry, or low-carbon environments, whereas C3 grasses are often more efficient in cooler climates where photorespiration is less of a factor.231