LI-6400XT Instrument Software

Viewing Data in the Field

OPEN uses the console's backlit 8 x 40 character graphical display to show any 12 experimental variables at once, on three user-defined lines. The display is quickly changed by moving a cursor to the line you wish to change and pressing a letter key corresponding to a display set or using the left and right arrows to scroll through all of the variables.

Real-time graphics allow you to carefully examine the approach to steady state for up to 24 variables with 3 plots per graph set. This avoids the difficulty in determining whether steady state has been achieved when viewing in text mode. Measured or computed variables can be used in plots or strip charts. Up to 8 sets of plots can be defined and stored.

Data Logging

Any or all of the default 13 computed and 55 measured variables may be logged manually by pressing a button on the sensor head or keypad. Data can be logged to non-volatile flash memory, removable compact flash cards, or output to the RS-232 port. Data can be logged manually or automatically using an AutoProgram.

For example, if you wanted to automatically collect A-Ci data, you would first set the desired chamber environmental conditions for temperature, humidity, light (if using the 6400-02B or 6400-40) and starting CO₂. Once the leaf is acclimated to these conditions, start the A-Ci Curve AutoProgram. This Auto-Program prompts for the CO₂ concentrations at which measurements will be logged, the minimum and maximum time between measurements, and the stability parameter(s) that must be achieved before each measurement is auto-matically logged. These parameters can be standard deviation, coefficient of variation, and/or slope of any set of variables. From then on, it's all automatic: for each of the specified set points, the leaf chamber is brought to that concentration. After the minimum wait time has elapsed, the system starts checking for stability. Once that occurs (or the maximum time elapses), the data are logged, and the cycle repeats for the next set point. All the while, the other environmental controls are maintaining their set points, providing stable conditions for your experiment.

Flexible Software

Virtually any type of calculation may be done with each measurement. In addition to standard gas exchange parameters, equations are included for computing leaf surface humidity, leaf surface CO2 mole fraction, Ball-Berry Index and others.

Programs and data are stored in readable ASCII format. Using the on-board editor, you can open an existing list of computations, for example, modify it to suit your needs, and then save it under a new name.

Software updates are always free and can be downloaded to your LI-6400XT. This makes the continued software development straightforward and guarantees that your LI-6400XT will stay current.

Multi-Level Flash Option for the 6400-40 Leaf Chamber Fluorometer

For users of the 6400-40 Leaf Chamber Fluorometer, OPEN 5.3 and above enables a multi-intensity flash option for the saturating pulse.  

Assessing Fv in either light- or dark-adapted measurements requires application of a saturating flash of light to fully reduce QA, the primary acceptor of PSII.  It is known that some field-grown, light-adapted leaves are especially difficult to saturate, even with 20,000 μmol photons m-2 s-1 PPFD.  An alternative solution exists to estimate the true Fm' under non-saturating conditions, which was introduced by Markgraf and Berry in 1990(1), and more recently by Earl and Ennahli in 2004(2).  

With Version 5.3 OPEN software and above, the LI-6400/6400-40 System supports two types of saturating flashes; single or multiple intensity. A single intensity flash provides a saturating pulse of light for a short duration, and the software looks for the maximum value of fluorescence during that pulse. The multiple intensity flash method applies three intensities within a single flash of 1.5 to 2 s in length. Flash intensities and length are user-defined. After the multiple intensity flash is applied, the software computes the fluorescence at saturation from the y-intercept of a plot of fluorescence vs. 1/ intensity. Earl and Ennahli’s(3) method separates the saturating flashes of different intensities by minutes, and does not apply them within a single flash. This new multiple intensity flash method is currently under scientific evaluation. To determine if this technique is right for your plant material, we recommend you compare the results of this method to that of Earl and Ennahli’s. If there is no difference, then this method should be appropriate.

(1) Markgraf, T. and J. Berry. 1990. Measurement of photochemical and non-photochemical quenching: correction for turnover of PS2 during steady-state photosynthesis. Curr. Res. Photosynth. 4:279-282.

(2) Earl, H.J. and S. Ennahli. 2004. Estimating photosynthesis electron transport via chlorophyll fluorometry without photosystem II light saturation. Photosynth. Res. 82:177-186.
(3) Ibid, 82:177-186.