The response to your question depends on the parameter you want to measure.

If you are measuring photosynthesis (An), the stability parameters given by default in the LI-6400 are sufficient. Additionally, you can also change these stability parameters at your convenience, although it is unlikely that you need that.

However, if your interest is in measuring stomatal conductance (gs) then the stability parameters given by default by the equipment can be unsuficient.

Let me explain this better, and that can be applied to any gas exchange measuring system. While photosynthesis stabilizes quite rapidly, stomatal conductance takes much more time as it is strongly affected by many parameters.

For gs, my advise will be to wait for at least 3-5 minutes per measurement.

Finally, the stability parameters will also change if you are measuring in the field or in a growth chamber. In the former case, stability is much faster than for the latter.

I hope this can help you!!

Thanks Miquel, I am interested in Pn, so luckily it is more stable. I have also called the LICOR support center and their advise supports your recommendation. I appreciate you taking the time to give me your expert opinion.

Take care.

Just put a humid paper in the cuvette and observe the stability of the system.

I agree with the first comment.

Here is the way I do it: before i start taking measurements, I put the stability parameter (Display line e) in the new measurement mode, and right after putting the leaf in the chamber, I observe the progress in the real time graphs (go to level 4, then view graph), and I can actually see when my parameters (say Pn) are pretty stable. After that, I go back to the new measurement mode and wait for 000;0/3 (if you kept the default parameters) to become 111;3/3 before I log my data (it usually doesn't take too long, which would correspond to the stability observed in the real time graphs).

This way, I am not just relying on the stability parameters in line e, but looking at the real time graphs I know that I am not logging too soon.

Please let me know if this makes sense or if you need more details :-)

Good luck!

Saadia B.

There is a lot of great advice given here. I also would check with LI-COR techsupport (http://envsupport.licor.com, or in US 800-447-3576) or at LI-COR Forum (http://www.licor.com/env/forum ). They have had a lot of questions over the years and may know answers already.

One additional comment, you should have little problem with stable readings of conifers and evergreen species as they are usually photosynthesizing at low rates and have relatively xeric conditions (low conductance and transpiration). There may be a need to watch the graphs a lot more when measuring plants that have high conductance and transpiration such as herbaceous species with very high pn rates. C4 plants also have a strange feedback cycle at high light levels - if you are looking at saturation rates the pn values seem to stabilize for a minute or two and then continue to climb over a longer time period before saturating. Have a bit of patience with those species - and use the graph tool, it's very handy! Good luck.

Thanks to all of you for your valuable input. This is exactly what I wanted to hear, your personal experiences.

Thanks also to George and LiCOR for being sensitive to clients needs.

I recommend you to connect your laptop to LI6400 during measurement, thus, you can see the data and graphics easily, and help you to know whether the reference is stable, and the Pn, gs, et al are all stable.

In my experience, illuminating sample for 20 min in cuvette under your setting condition can insure the stability of sample, but it will last a lot of time.

THis is very interesting topic for discussion. Licor conducts  many free sessions for new people and these presentations are very important. Try to visit Licor website and follow some cources. They are free. I will attach a protocol that my people are using for Licor measurements.  

Hi. I am a Ph.D Student and conducting my experiments on physiological parameters of drought stressed cotton. My question is if for several days or weeks the weather remains cloudy because i am facing this situation since last 20 days while i have to use Li-Cor X6400 in the field, so what should i do? Either i should use the sensor head lamp as alternate source of light? Please guide me...

portable photosynthesis system LI-6400XT (LI-COR Company, USA)  is reliable . you can keep the flag leaf into chamber at least three to five minuts. and Pn values seems to be stable. you can also check it by pressing match key to check the CO2 and Ci, Ci always in positive digits. At the time of data recording, the CO2 concentration in the leaf chamber should be controlled by 400 µmol mol-1, the temperature 30˚C, and the light intensity should be 1500 µmol Em-2 S-1. 

From the experience at our lab we have also observed that Pn values tend to become stable much quicker than Gs values.

I am now trying to get a paper published in which we use Pn values and reviewers are asking for the stomatal data. We have replied that our Licor measurements were optimized towards Pn measurements and that we don't want to use the Gs data as we are not sure whether these were measured in stable conditions, but this answer doesn't seem to satisfy the reviewers. As we wanted to get as much Pn maesurements as possible for each measuring day, not waiting for stable Gs values seems to me to be a reasonable approach if the main interest is Pn.

Does anybody know about publications to which can be referred to to have a stronger case for not using the Gs data.