Energy utilization and carbon metabolism in mediterranean scurb vegetation of Chile and California : I. Methods: A transportable cuvette field photosynthesis and data acquisition system and representative results for Ceanothus greggii.

A transportable system for field and laboratory measurement of plant CO2 exchange and transpiration is described. A computer based data acquisition system which controls data-logging has been successfully proven in mediterranean zones of central Chile and southern California and in the taiga of central Alaska. Six Peltier-effect cooled acrylic plastic chambers are utilized in an open infrared gas analysis system for continuous monitoring of CO2 exchange. Chamber air temperatures automatically track ambient air temperatures or can be preset to maintain a constant temperature. Use of Peltier-effect cooling modules and electric cartridge heaters result in light-weight chambers and heat exchange units with low power requirements. No refrigeration or liquid coolant is required under most operating conditions. A unique sampling method using natural illumination and six chambers allows highly replicated determinations of the temperature and light dependence of photosynthesis and/or respiration to be made over the course of a 6-d sampling period. Measurements are made continuously 24 h/day. Diurnal CO2 exchange patterns are determined from one chamber that tracks the ambient air temperature. The other five chambers have air temperatures fixed at distinct levels over a 35° C range. Each day the chambers are changed to another temperature level according to a randomized sampling pattern. All the data are pooled at the end of the 6-d run to construct the light and temperature response surfaces of CO2 exchange typical of the individuals sampled. Simultaneous determinations of conductance, leaf temperature, air temperature, and light are made.