A Technique for Measuring CO sub(2) and Water Vapor Profiles Within and Above Plant Canopies over Short Periods

In plant canopies, the rate of photosynthesis often depends strongly on air carbon dioxide concentrations and on air humidity. A technique is described that has been developed to monitor CO sub(2) and water-vapor profiles simultaneously with an infrared gas analyzer, which cycles through the measurements for six heights in a total of 1 min. Results are presented from an analysis of the method in terms of the response time, and a comparison is presented between the multiport air-sampling apparatus and psychrometer measurements of water vapor. The sampler has been used over two seasons with good results.