Food Production

Inside a glasshouse the grower can deliberately raise both the carbon dioxide concentration and the temperature, and each affects yield through its effect on photosynthesis.

Increased carbon dioxide

• Outdoor air is only about 0.04 % CO₂, so carbon dioxide is often the limiting factor for photosynthesis.
• Pumping extra CO₂ into the glasshouse (for example from a burner) raises the rate of photosynthesis, so the plants make more glucose and grow faster, giving a higher yield.
• The benefit only continues while CO₂ is the limiting factor. Once CO₂ is plentiful, light or temperature becomes the new bottleneck and adding still more CO₂ has no further effect.

Increased temperature

• Photosynthesis and the other reactions of growth are controlled by enzymes. As temperature rises towards the optimum, the molecules gain kinetic energy, collide more often, and the reactions speed up, so yield rises.
• Above the optimum the enzymes begin to denature: their active sites change shape, and the rate of photosynthesis falls, so pushing the temperature too high actually reduces yield.
• Warmth also lengthens the growing season, letting growers harvest crops earlier or out of season when they sell for more.

The grower aims for the combination of CO₂, temperature and light that keeps all three close to their optimum, because the yield is set by whichever factor is in shortest supply.