Measurements of photosynthesis in the field: utility of the CO₂ depletion technique

A portable system for the rapid measurement of photosynthetic rates in the field is described and evaluated. The measurement of photosynthesis is based on extraction of volumes of air from a closed system cuvette containing a leaf over a set time interval. CO 2 content of the gas volumes is determined with an infrared gas analyser, and photosynthetic rate is calculated from the cuvette CO 2 concentration depletion rate. The magnitudes of sources of error with this system were analysed and methods of reducing the errors discussed. Representative examples of data obtainable with this technique are presented. From the inlet and outlet ports of a cuvette for measurements of Sorghum bicolor dark respiration rates in the laboratory. We have modified their technique and report the utility of the CO 2 depletion technique for measurements of photosynthesis on plants in the field, far from laboratory facilities. The technique is reliable and easy to operate in the field. A description of the technique, as well as an analysis of the sources of error and examples of the data which can be obtained with it are presented.