Carbon Dioxide

Plants produced in greenhouses consist mostly of water on the average around 90% of their fresh weight. Of the remaining 10%, about half that 10% is carbon. This carbon is derived from the carbon dioxide (CO₂) in the air, which has a very low concentration of about 340 ppm or 34 Pa (0.034%). More common is measuring the CO₂ concentration in the air under suitable conditions. Determination of the photosynthetic rate in plants requires a measure of the CO₂ depletion that occurs under suitable radiant energy, or how much CO₂ that must be injected to maintain a specific CO₂ level. There are numerous methods for measuring CO₂. These include chemical absorption, thermal conductivity, infrared spectroscopy, gas chromatography, and electrical conductivity. Responses to elevated CO₂ will obviously vary with water availability, nutritional status of the crop and the possibility of disease. Assuming sufficient energy, particularly at high CO₂ levels, the biochemical process becomes limiting. Temperature becomes an increasingly important factor.