Using a macro to calculate stomatal conductance.

Technical Support and Questions

Default avatar

Patrick S.

Dec 2017

I'm looking to use the MultispeQ to measure stomatal conductance since existing protocols claim that they can estimate stomatal conductance via changes in air humidity and leaf temperature.

I was looking at using the following protocol: https://photosynq.org/protocols/rides1_3_1 The corresponding macro is: https://photosynq.org/macros/rides1_3_1

I was wondering how I can use the macro since when i setup a new project it only allows me to attach the protocol with no option of implementing the macro. I don't have any experience in coding so I was wondering how I could use this macro.

Alternatively, is there a way of finding out what calculations can be be done to work out the estimate of stomatal conductance using the data-set obtained from using the RIDES131 protocol.

Attached is the data I got from using the RIDES131 so is there a way for me to calculate stomatal conductance from this data-set?

Cheers,

Patrick

Thumb dave in cap img 4615

David M. Kramer

6 days ago

...thought I'd add that, based on what we see in the data sets, the leaf temperature differential correlates pretty well with stomatal conductance. In practice, this is a good qualitative indicator of changes in gs. I would prefer to add a more robust theoretical bases for the calculations in the macro...maybe this is something you have some ideas about.

Dave

Thumb dave in cap img 4615

David M. Kramer

6 days ago

Hi Patrick S.! Thanks for your comments. The new MultispeQ can measure (quite sensitively) humidity changes associated with transpiration. In principle, measuring these changes together with the leaf temperature and air temperature and humidity can yield estimates of stomatal conductance. However, to make this work, you need to have the air flow at very specific rates to carry the transpired water from the leaf to the detector. I am happy to report that we have a prototype pump that, so far, is doing this very nicely. We plan to release this with the new version of the MultispeQ. In the meantime, if you are interested in helping us beta test the system, please let me know.

Dave

Default avatar

David Alm

6 days ago

Hi Dave Kramer,

Is it doable/advisable to attach our own pump and flow meter to the MultispeQ and then use the rides131 protocol to get gs?

We want to see if there are differences after chilling a susceptible (it wilts) vs. tolerant (it doesn't) variety of eggplant. (Going to measure root hydraulic conductivity, too.)

Mostly interested in comparing the species (and their hybrid), so if absolute accuracy is not guaranteed, that's not critical yet, as long as precision is there for the comparison. If that makes sense.

The above is for the 3 university instruments; also, I have my own (personal) instrument and would be interested in beta testing if you're still doing it this summer.

Thanks,

David Alm

Thumb dave in cap img 4615

David M. Kramer

6 days ago

*First, it's a problem of an open platform that you saw the RIDES11` before we were really comfortable with the results ;-)

Yes and no. Let me explain. Typically, in a gas exchange system like Li-Cor, there is a long time required to achieve stable, steady-state conditions where the differential humidity would be a reliable indicator of gs. We want to do this in our given time limit of ~20s! In a field-deployable, inexpensive and easy-t-use instrument. So, what we've done is develop a computer-controlled pump that changes it flow rate over time. This allows us to eliminate much of the effects of drift and get a much higher sensitivity.

My students have been testing the beta units and we are, I think, pretty close to sending some out for outside tests. The main limitation is in my schedule... But I will keep you up to date.

Default avatar

David Alm

2 days ago

Thanks, that clarifies a lot.

In the interim, could we possible do the following? (I'm asking because, we have no Li-Cor or similar gs capability):

To get a qualitative comparison of eggplant varieties, pump a slow, constant air stream to the cuvette, and use the standard protocol's RH diff and a manual flow rate readout to approximate transpiration?

If the answer is "yes," what would be a good flow rate? (And which port is "in"?)

If "no," thats ok, I have a humidity sensor and we'll rig something up.

David

Thumb dave in cap img 4615

David M. Kramer

2 days ago

Hi David, Actually, that is what we planned. In fact, it is a bit more involved than that. Turns out that the drifts and fluctuations were too large for that approach. We came up with a new plan that kinetically distinguished between drifts and signal, and this seems to be much better. What is the time frame for your measurements? It might be we will have something useful in time... Dave

Default avatar

David Alm

1 day ago

Approximately 4 weeks from now.

Note: This is just a small student experiment for a plant phys class. 24 plants, repeated measures, before and after chilling.

Thanks for your help.

(My "plan B" is a humidity cell and flow-through leaf chamber that we made, years back, from a pair of vice grips, and Dr. Scholl's bunion pads for gaskets :-)

Hi David! Can I update V1 and add air flow pump? What kind of pump do you use?

Thumb dave in cap img 4615

David M. Kramer

6 days ago

Another great question!

The short answer is yes, but you might need to make at least one modification to the add-on case (the bottom part of the clamp). We designed V. 1.0 to accommodate the pump, but as we continually added improvements in the measuring technique, we needed to change the air flow. The change is small, and I think it will not be a huge problem to upgrade that part. When we are a bit closer to releasing, we will describe how to make the changes, or provide an upgrade service of some kind (like swapping the part out). Dave

Thumb nationalzoo

Craig Whippo

5 days ago

The ability to modify the bottom part of the V 1.0 clamp to accommodate the pump is wonderful news. It is also good to know that leaf-temperature differential tracks gs fairly well in your trials. I'm waiting to update my firmware to 1.22 until the update is official, but all of the testing you are doing on these changes is appreciated.

Thumb dave in cap img 4615

David M. Kramer

5 days ago

Hi Craig, Your comments are much appreciated! I think you will like the new version of the firmware ;-) Dave

Hi David. You wrote, "... to sending some out for outside tests." Do you plan to send these modules for beta testing outside the United States?

Thumb dave in cap img 4615

David M. Kramer

2 days ago

Hi, Sure! The only criterion is that we can validate and improve the devices. Dave

Default avatar

Sean

Dec 2017

Hey Patrick,

Good questions and I think I have some answers for you. You inquired about how to use the macro with the protocol you selected, and the good news is that they are automatically attached to one another. When someone makes a protocol, they attach a macro to it to turn their traces and other inputs to interpretable data. So during your project creation when you chose the RIDES131 protocol, you are also choosing the corresponding macro at the same time.

Concerning measuring stomatal conductance, you will need an additional air pump that can attach to the MultispeQ. To inquire more about this pump email support@photosynq.org

Best, Sean @ PhotosynQ

Also, your data was not attached to this comment, probably something on our end, so I will investigate. However I did look at your "wheat under pathogen stress 2" project, and you will see the parameter "air flow". With the pump you will see a more curvy line that can help estimate stomatal conductance.