Abstract
AbstractInstrumentation has been developed for measuring absolute simultaneous assimilation of carbon dioxide and evolution of oxygen by photosynthetic systems in anaerobic atmospheres under flow conditions. Time‐dependent photosynthetic quotients (PSQ) have bccn obtained. A detailed description of the instrument, including how it was constructed, calibrated and uscd for photosynthesis measurements, is presented. An important factor in the measurements was a clear understanding of the response time of the instrument. As with any flow system, flow rate, forward void volume and relative position of the O2 and CO2 sensors in the gas train were crucial to performance. Response time was measured by step‐function calibrations mimicking PSQ of unity. Oxygen was generated using an in‐line electrolysis cell driven by a programmable constant current source. Carbon dioxide assimilation was mimicked with the use of a programmable electronic gas blending system. Simultaneous step functions of these two key photosynthetic parameters fully characterized the response time and sensitivity of the instrument. In this report, time‐dependent PSQ for spinach leaf disks and the microalga Scenedesmus D3 are reported. It is explicitly demonstrated that the transient approach to steady state is different for the two systems. Whereas the time‐dependent PSQ for spinach depended on illumination history and reached a steady‐state value less than 1, this was not the case for Scenedesmus.
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