Measurement of CO2 Evolution In a Multiplexed Flask System

Carbon dioxide flux serves as a measure of metabolic activity in many organisms, and is directly linked to respiratory processes and photosynthetic assimilation. The measurement of CO₂ flux requires instrumentation capable of making precise determination of CO₂ concentration in air. For small samples, such as individual fruit, insects or plant tissues, CO₂ flux is determined from chamber-based measurements utilizing an open differential or closed transient approach. Measurement systems using an open differential approach are well suited for tracking temporal variation in CO₂ flux, as the sample has little influence over chamber conditions. However, these systems have difficulty measuring small fluxes from small samples. Systems using a closed approach are able to resolve much smaller fluxes from small samples, but are typically limited in measurement length due to transient chamber conditions and instrument stability. The LI-8100 Automated Soil CO₂ Flux System with the LI-8150 Multiplexer is designed to measure soil CO₂ flux from up to sixteen chambers. We describe the underlying theory of, and modifications to, the LI-8100 Analyzer Control Unit and LI-8150 that allow them to measure CO₂ fluxes from discrete samples in a multiplexed flask arrangement. These modifications take advantage of the key benefits of both open and closed systems. Measurements are made using closed transient approach, allowing small fluxes to be resolved from minimal sample material. Between each measurement, chambers are continuously flushed with ambient air maintaining chamber CO₂ concentration at or near ambient. This allows for autonomous measurement of fluxes from multiple samples over extended time periods. Data will be presented demonstrating respiration measurements from detached fruit using this system.