Three carbon fixation strategies
C3 plants (rice, wheat, most trees) fix CO₂ directly via Rubisco in mesophyll — simple but prone to photorespiration in heat.
C4 plants (maize, sugarcane) shuttle CO₂ to bundle sheath cells, concentrating it around Rubisco — efficient in hot bright climates.
CAM plants (cacti, pineapple) open stomata at night to fix CO₂ into organic acids, then release CO₂ internally by day — minimizes water loss.
Ecological distribution
Pathway correlates with climate: C4 dominance in tropical grasslands; CAM in arid environments; C3 in temperate and shaded habitats.
Research and crop improvement
Engineering C4 traits into C3 crops is a major goal for food security under warming climates.