Body of Abstract: Traditionally, gas exchange measurements have relied on the steady-state method, assuming that both the instrument and biology reach a stable state and that assimilation by plants remains constant under specific environmental conditions. However, this method is problematic when studying transient responses or when high throughput is required. To address these limitations, LI-COR has developed the Dynamic Assimilation Technique (DAT), which allows gas exchange measurements under non-steady-state conditions.
In our study, we conducted survey measurements on sunflower leaves using both steady-state and non-steady-state methods. We tested conditions where chamber controls matched the ambient environment and conditions where specific chamber controls (light, CO2, air moisture, and temperature) were not matched to ambient.
Our results show that the LI-6800 gas exchange system, which implements both dynamic and steady-state mass balance, allows real-time observation of the differences between the two approaches. Dynamic assimilation equations eliminate the wait time for the chamber to flush, enabling rapid assessment of biological response to an environmental change. Differentiation between instrument and biological non-stability, facilitates the study of plant acclimation processes. Empty chamber measurements confirm that the dynamic assimilation value quickly returns to the expected zero value for assimilation.
When the instrument reaches a steady state, the transient term in the dynamic mass balance becomes zero, indicating convergence between dynamic and steady state calculations. This convergence serves as a useful indicator of stability, especially for new users, instilling confidence in the timing of data recording. Simultaneously utilizing both approaches allows users to differentiate instrument response from biological response, which is valuable for diagnostic purposes and for studying transient responses of biological processes.
Additionally, our study emphasizes the importance of matching chamber controls to ambient conditions when conducting survey measurements.