Plants use carbon dioxide (CO2) during the process of photosynthesis to create new biomass for their growth, and energy for their metabolism. The enzyme that assists in this process, for many plants, is called D-ribulose-1,5-bisphosphate carboxylase/oxygenase (abbreviated as Rubisco). Rubisco is the most abundant protein/enzyme on earth. One reason for this is that it is not very efficient as an enzyme and, thus, each plant needs a relatively large amount of it. Rubisco can capture both CO2 and O2 molecules, but carbon dioxide is the only molecule useful for creating new biomass. A molecule of oxygen that a molecule of Rubisco captures prevents CO2 capture for an instant and reduces overall enzyme cycle efficiency.
Scientists have found that by adding CO2 to the air that C3 plants are exposed to, the plants grow faster as long as other required inputs (such as light) are in adequate supply. The supplemental CO2 is captured by some Rubisco proteins that would have otherwise captured the useless O2. Supplemental CO2 levels of approximately 1000 ppm have been shown to increase growth by 50%.
At Cornell, we have used a combination of CO2 and daily light integral control as a means to make light (PAR) more effective for growth (Ferentinos, et al., 2000). The goal is not to achieve faster growth, but to achieve the same growth using less supplemental lighting - to save energy and cost. The deliberate application of a combination of both supplemental light and CO2 helps to ensure an unvarying supply of biomass during even the coldest and darkest days of winter; situations that are normally not conducive to plant growth. Consistent year-round plant growth can help to market products because the seller can assure the buyer that a constant amount (and quality) of product will be available to meet consumer demand.
Optimal Light Integral and Carbon Dioxide Concentration Combinations for Lettuce in Ventilated Greenhouses. K. P. Ferentinos, L. D. Albright, and D. V. Ramani. J. agric. Engng Res., 2000, 77(3), 309-315.
