Principles of Biochemistry Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
Photosynthesis
Photorespiration is a major challenge for agriculture in temperate zones

Although the exact Biological Role of Photorespiration remains to be fully understood, it clearly warrants serious attention, as it reduces the productivity of C₃ plants—namely, The rate of plant biomass accumulation—in temperate zones. On a hot, windless day in a C₃ crop canopy, the concentration of CO₂ in the surrounding air may drop to 0.005% (compared to the normal level of 0.03%) due to the rapid consumption of CO₂ during Photosynthesis. As a result, the CO₂/O₂ ratio in the air above the plants decreases, meaning that oxygen begins to compete more effectively with CO₂ in the ribulose bisphosphate carboxylase reaction. Consequently, CO₂ fixation slows down, while the "wasteful" process of photorespiration is intensified. Photorespiration can reduce the actual biomass production in C₃ plants by as much as 50%.

Currently, researchers are exploring ways to inhibit photorespiration in C₃ plants, thereby enhancing CO₂ fixation and, consequently, biomass accumulation. One such approach involves inhibiting the Enzymes that catalyze glycolate oxidation. Another strategy relies on breeding and cultivating varieties characterized by a low rate of photorespiration. However, it is quite possible that nature will solve this problem for us: due to the massive combustion of fossil fuels, the concentration of atmospheric CO₂ is steadily rising (Section 13.1).