Autumn has arrived, and more water potential measurements

August 24, 2012 by · Leave a Comment
Filed under: CPCRW, Field Work 

It’s already August and autumn is setting in at the watershed. We can see the colors change at small and large scales.

But, the plants are still active, so I’m still out measuring them every 10 days or so. As I mentioned before, one measurement I make pretty regularly is plant moisture stress. This measurement tells us about the water demand of a plant. This measurement integrates a lot of information (seeĀ for a good description. Smaller numbers (more negative numbers) means that the water demand or water stress of a plant is fairly high. The water stress of a plant shows diurnal and seasonal variation, and there is variation between species. I do these measurements on black spruce and on birch trees. The spruce tend to be more stressed than the birch trees.

Step 1: Get a branch down.

Step 2: Get the pressure chamber off the four wheeler and set it up.

Step 3: Cut a stem and put it in the holder so that the cut part is facing you, and then crank the holder onto the chamber.

Step 4: Turn on the compressed gas, get out the magnifying glass, hunch over it and wait for the stem to change color (so that it looks wet). When the color changes, the pressure in the chamber and the pressure in the plant have been equalized. Read the pressure on the gauge (15 Bars in this case).

If you see bubbles of water coming out of the stem, you waited too long to take the reading and you have to start over with another stem.