Expert: Dana Krempels, Ph.D. - 9/21/2007

Question
Hi, I am M.Sc student in Agronomy
I want to plant wheat and an annual weed in a tube, close to each other, to study root competition in deferent water treatments.At the end of season,I will open the tube and cut the soil which contains root systems, so I will have soil of each depth separately. If I omit top of wheat some days before sampling, I expect that only weed root system absorb the water because of transpiration, but the wheat root system can not absorb the water or any solution. I want to use a absorbable color with adequate solubility in water to distinguish wheat root system from weed's one. Do you know any color with these properties(non-oxidative, passive in chemical reactions, available, and specially which can be absorbed by root)? What do you think about this idea?

Answer
Dear Abbas,

This is an interesting problem, but I don't think it's going to be easy to discriminate between the root systems with a simple dye, since both plants will likely take up the dye, even if the wheat tops are cut off.  Although most water movement in plants is caused by transpiration, some is also caused at the roots via root pressure.  So I don't think there's a way for you to have only one type of the two plants take up the dye.

I wonder if there is another label you could actually inject into the *phloem* of the aboveground parts of the plant, since the phloem will bring such a substance to the roots without it being in the soil.  You could use two different types of such a marker:  one for your weed species, and one for the wheat.  Since the dye will not cross out of the roots into the soil, this might be the most reliable way to distinguish between the root systems.

I hope your thesis committee might be able to help you with ideas about such a dye marker.  I am sorry that this particular area is outside my expertise.

Good luck with your project!

Dana