The Dynamic Assimilation Technique measures photosynthetic CO2 response curves with similar fidelity as steady-state approaches in half the time.

Abstract

The net CO2 assimilation (A) response to intercellular CO2 concentration (Ci) is a fundamental measurement in photosynthesis and plant physiology research. The conventional A/Ci protocols rely on steady-state measurements and take 15-40 minute per measurement, limiting data resolution or biological replication. Additionally, there are several CO2 protocols employed across the literature, without clear consensus as to the optimal protocol or systematic biases in their estimations. We compared the non-steady state Dynamic Assimilation Technique (DAT) protocol and the three most used CO2 protocols in steady-state measurements, and tested whether different CO2 protocols lead to systematic differences in estimations of the biochemical limitations to photosynthesis. The DAT protocol reduced the measurement time by almost half without compromising estimations accuracy or precision. The monotonic protocol was the fastest steady-state method. Estimations of biochemical limitations to photosynthesis were very consistent across all CO2 protocols, with slight differences in ribulose 1·5- bisphosphate carboxylase/oxygenase carboxylation limitation. The A/Ci curves were not affected by the direction of the change of CO2 concentration but rather the time spent under TPU-limited conditions. Our results suggest that maximum rate of ribulose 1·5- bisphosphate carboxylase/oxygenase carboxylation (Vcmax), linear electron flow for NADPH supply (J) and triose phosphate utilization (TPU) measured using different protocols within the literature are comparable, or at least not systematically different based on the measurement protocol used.