Carbon dioxide fertilization involves increasing carbon dioxide levels in greenhouses to improve plant growth and yields. Higher CO2 levels shift the activity of the enzyme rubisco to favor carbon fixation during photosynthesis. On average, yields increase 33% when CO2 is doubled. Commercial greenhouse operations commonly use natural gas, propane, or boiler flue gases to maintain CO2 levels between 1000 ppm for sunny conditions to 700 ppm for young plants or lower for cloudy days with more ventilation. Higher CO2 leads to increased sugar levels in fruits and vegetables, improving taste, growth rates, and time to flowering for some ornamental crops.

1. Carbon Dioxide Fertilization

2. Energy Relationship of Photosynthesis and Respiration Carbohydrate Respiration Photosynthesis CO + H O 2 2 2 O 1_2 LOW HIGH Energy 2H + 2H + 2 O 1_2

3. C 3 - Photosynthesis

4. Carbon Dioxide and Plants Atmospheric CO 2 is the source of all carbon accumulation in plants C3 plants benefit significantly from increased CO 2 concentration in the greenhouse. Carbon Dioxide Fertilization is common practice in many ornamental and food crop commercial greenhouse operations

5. Effect of CO 2 Shifts the activity of RUBISCO in favor of the carboxylation reaction On average yields should increase by 33% with a doubling of CO 2 That average based on entire plant life cycle, but increases in growth result in juvenile and mature tissues when CO 2 levels are increased.

6. Carbon Dioxide Fertilization Normally present at about 300 ppm During daylight hours CO 2 may be rapidly depleted during crop production Depletion may be exacerbated during winter production when there is less ventilation

7. CO 2 Greenhouse Levels 1,000 ppm or more have shown to increase tomato yields economically However, you must adjust based on plant maturity and environmental conditions Bright, sunny weather 1000 ppm Cloudy weather 750 ppm Young plants 700 ppm During moderate ventilation 350-400 ppm Less needed as temperature and ventilation rates increase

8. Producing CO 2 for Commercial Greenhouse Production Natural Gas Propane Flue gases from hot water boiler Compressed CO 2

11. Other Impacts Increased sugars (fruit crops) Reduced acid:sugar ratio (fruit crops) Taste improvement noticeable by consumers (fruit crops) Improved growth rates (fruit and ornamental) Shorter times to flowering for certain ornamental crops.

12. Impacts on Sustainable Design Heat and carbon dioxide are also released as part of the composting process Pilot tested at the New Alchemy Institute in Massachusetts. Potential for these system exists, but rare on a commercial scale.

13. Good Sources of Information http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/gtp_pages/co2.html Trembley and Gosselin. 1998. Effect of carbon dioxide and light. HortTechnology. 8(4). http://oregonstate.edu/Dept/NWREC/tomatogh.htm http://www.ejpau.media.pl/series/volume4/issue2/horticulture/art-03.html http://www.attra.org/attra-pub/ghveg.html