When measuring small needles or leaves, they should be inserted into the sensor as shown below. This is because single needles or small leaves (including blades of grass) may not adequately cover the aperture of the sensor.
For an accurate measurement it is critical that the entire cross sectional area of the diffusion path be covered with leaf material. Sometimes it is necessary to remove the leaves/needles from the plant in order to arrange them over the opening in the diffusion path. This results in an accurate measurement as long as the measurement is completed within two minutes of leaf/needle removal, because the stomatal aperture should remain unchanged for at least that long after disturbance.
Please note that needles with a square or triangular cross-section and lots of sclerenchyma may not work with the SC-1 because they will prevent a good seal with the chamber. Needles of the genus Picea are a good example of needles for which the SC-1 is not well suited, while the flat, pliant needles common to Abies work quite well.
How long does a measurement take?
One measurement with the SC-1 takes 30 seconds (in auto mode). The time to get the relative humidity <10% between measurements varies (e.g., 30-90 seconds), but it shouldn’t take longer than 90 seconds of shaking the sensor head. If it takes longer than 90 seconds of shaking the sensor head between measurements, then check the desiccant to ensure it is blue (for Indicating Drierite, 10-20 mesh). If the problem persists, replace the teflon filter that separates the measurement chamber from the desiccant, and check the rubber seals on the porometer head.
What should I check if during the measurement period, leaf conductance declines toward zero instead of increases (as it would normally over the auto measurement period?
Double check that the units in the measurement screen are in mmol/m2s and not m2s/mmol or s/m.
Can the diffusion path of the SC-1 be horizontal, if I take the clamp off to take measurements (i.e., measuring fruit and tree trunks)?
This is not a good idea if the bead is in the diffusion path. The bead needs to be sitting down against the porous plastic membrane (Teflon disc) that retains the desiccant. If not, it could violate the assumption of 1-D vapor diffusion between the two vapor pressure sensors. That diffusion path doesn’t have to be perfectly vertical, but it needs to be vertical enough to ensure the bead is out of the way.
Can silica gel be used as desiccant in place of the Drierite, for the leaf porometer sensor head?
Silica gel works. It doesn’t last as long or scrub down as fast as the Drierite. You can use silica gel in place of the Drierite desiccant, but be prepared to need to change the silica gel more often and expect possibly longer shake down times. Non-indicating Drierite can also be used. It is safe and should work just as well as the indicating Drierite. Use 10-20 mesh size.
How often should the SC-1 be calibrated when taking readings out in the field?
Verify the measurement accuracy daily or after a change in field conditions. This is done by using the calibration plate and moist filter paper. Recalibrate when the measurement falls outside of the expected range. When calibrating in the field, wind gusts can dry out the filter paper faster, so try to perform the calibration in a sheltered area from wind. Use the SC-1 case to protect the calibration plate from drying out fast, and also turn the calibration plate upside down between calibration points, so it doesn’t dry out as quickly. As long as you have fresh desiccant and have performed any necessary maintenance, then you should expect the SC-1 system to calibrate in a stable environment. If you put the sensor head on a different SC-1 handheld, then recalibration is required. The reason is that the calibration for the sensor head is stored in the hand-held device.
What type of calibration filter paper should be used for the SC-1?
Use Whatman #3 filter paper and use a hole punch to make the correct-sized discs. If you use a different type of filter paper, then verify with the Whatman #3 that the substitute filter paper gives the same expected results.
What should I do if the SC-1 will not connect to a computer using the cable adapter?
1. Download the METER USB driver.
2. Download the Leaf Porometer Utility.
3. Connect the Serial to USB cable adapter from the hand-held to a computer.
4. Turn on the SC-1 hand-held, Open Utility, and find the appropriate communication port the drop-down menu.
5. Select Download.
Where can I purchase new desiccant?
The desiccant is Drierite 10 to 20 mesh. You can purchase new desiccant from METER or another supplier.
What should I do if the SC-1 calibration is abnormally slow (1+ hours) and the calibration is unsuccessful after multiple attempts?
1. Set the instrument and calibration supplies in measurement environment before calibrating for 10+ minutes. Replace desiccant and follow the calibration instructions in the SC-1 Calibration quick start.
2. If unsuccessful, replace Teflon filter and then try calibrating.
3. If unsuccessful still, conduct cleaning and maintenance shown in the maintenance video, and then try calibrating.
4. If unsuccessful still, contact METER for further troubleshooting or to request an RMA to send it in for repairs.
How do I put the spring back in after doing maintenance on the porometer?
Position the spring in the sensor head. Then, insert the pin to secure the spring.
I get the message “initial conductance too high” before I take a measurement. Is that normal, and what could be the cause?
The SC-1 will give you the message “initial conductance too high” between every reading. This is normal operation of the sensor. The sensor head needs approximately 30 seconds to 1.5 minutes of shaking to return to a state where it can begin another reading. It is not a problem but part of the design of the sensor. The chamber must have an RH below 10%, and the stomatal conductance must be 0 to clear the message “initial conductance too high”. When you receive that message, the stomatal conductance is not yet 0, and you must continue shaking the sensor head to equilibrate the chamber. Refer to the SC-1 quick start, SC-1 Calibration quick start, and SC-1 calibration video for operating instructions.
Do I need to put a bead in my new leaf porometer?
You do not need to replace the bead unless the screen and bead fall out. You should have spare screens in your porometer kit. Watch our maintenance video, and it will walk you through reassembling your sensor head with the proper bead and screen placement.
Why does the SC-1 sensor head and diffusion path need to be vertical when taking measurements?
If the bead is in the diffusion path, it needs to be sitting down against the porous plastic membrane that retains the desiccant. If not, it could violate the assumption of 1-D vapor diffusion between the two vapor pressure sensors. That diffusion path doesn’t have to be perfectly vertical, but it needs to be vertical enough to ensure the bead is out of the way.
Can the SC-1 provide accurate leaf temperature data?
While the leaf and sensor head come into thermal equilibrium quickly, the temperature reported by the sensor may not be a good proxy for the leaf temperature in equilibrium with the environment. The clip most likely warms the leaf slightly when the clip is placed on the leaf. This is not important for the reading of stomatal conductance because all that matters there is that the leaf and chamber are the same temperature. But it does matter if you want to use that reading to calculate transpiration. I recommend using an infrared thermometer to get a leaf temperature before placing the sensor head on the leaf for the best leaf temperature measurement.
Why doesn’t the leaf porometer output transpiration like the LI-COR used to?
The SC-1 Leaf Porometer measures the vapor flux to arrive at stomatal conductance, which on the surface gives you leaf level transpiration. However, the leaf chamber of the SC-1 forces its own environment on the leaf, so the chamber steady-state transpiration will likely differ significantly from the environment steady-state transpiration. This is fine for stomatal conductance since the reading is taken within 30 seconds, but it doesn’t work for transpiration. We recommend you use independent atmospheric vapor pressure and leaf temperature measurements coupled with an estimate of leaf boundary layer conductance to calculate transpiration from the stomatal conductance measurement made with the SC-1.