Create rapid A/C_i curves in minutes

High-speed CO₂ ramping technique for rapid A/C_i curves

For many years researchers have been regularly performing steady-state A/C_i curves on a wide variety of vegetation providing very useful information on plant status. PP Systems is excited to announce that the CIRAS-3 is capable of performing rapid A/Ci curves in just a fraction of the time it takes to perform steady-state measurements based on our innovative High-Speed CO₂ Ramping Technique. It is possible to generate A/C_i curves in less than 5 minutes with the CIRAS-3! However, the actual length of time to perform these measurements is highly dependent on user settings and parameters of interest.

What is the purpose of rapid A/Ci measurements?

The purpose of performing rapid A (Assimilation) vs. C_i (Intercellular CO₂) curves is to provide two or sometimes three parameters for photosynthetic characteristics of leaves, which are beyond those derived from any single A and C_i measurement. These parameters include:

1. Maximum capacity of the ribulose bis-phosphate carboxylase enzyme
2. Maximum rate of photosynthetic electron transport
3. Maximum rate of triose phosphate utilisation

Whether the third parameter can be quantified with this method depends on the metabolic properties of the leaf. The above three parameters, which are all temperature dependent, combined with stomatal conductance values, permit estimation of leaf photosynthesis under any combination of light, temperature, CO₂, and humidity via the Farquhar, von Caemmerer and Berry photosynthesis model.

One could obtain the same two or three parameters by doing slower, steady-state measurements of A at a range of C_i values, but that is quite time-consuming (generally at least 30 minutes, but sometimes up to one hour, as compared with possibly as little as 5 minutes per leaf with our rapid A vs. C_i method).

How does the CIRAS-3 measure rapid A/C_i?

The CIRAS-3 features a highly accurate, true differential gas analysis system for both CO₂ and H₂O. It can easily, quickly and accurately linearly ramp the CO₂ concentration in the leaf cuvette in order to produce a complete A vs. C_i curve in just minutes. Our unique stored differential balance feature allows simplified data recordings and straight-forward post-processing in Excel. Our response script editor allows users to easily generate and edit linear response scripts to meet their specific requirements.

Comparing steady state vs. non-steady state A/C_i curves

Comparison of a Non-Steady State High-Speed A/C_i Ramping (black points) to traditional point-by-point Steady State (red points) for a typical C₄ Giant Foxtail leaf with PAR of 1500 µmol m^-2 s^-1 and Cuvette Flow of 300 ml/min. Reference CO₂ ramped from 50 to 500 in 7 minutes. Each Steady State point had an approximate 2 minute acclimation time for total data recording time of 18 minutes.

Comparison of a Non-Steady State High-Speed A/C_i Ramping (black points) to traditional point-by-point Steady State (red points) for a typical C₃ Soybean leaf with PAR of 1500 µmol m^-2 s^-1 and Cuvette Flow of 300 ml/min. Reference CO₂ ramped from 100 to 1000 in 10 minutes. Each Steady State point had an approximate 2 minute acclimation time for total data recording time of 22 minutes.