Expert: Dana Krempels, Ph.D. - 5/7/2011

Question
QUESTION: hi i need help on my project.my project is comparative study on the effect of cigarette and firewood residue in soil on the growth of plants.the procedure i used is taking 3 potted plants of the same kind and adding equal amount of cigarette residue and wood residue into the soil of 2 of the plants everyday.all the three plants are provided with same amount of water and sunlight.1 week has passed.the plant having cigarette residue is as healthy as the one which is in normal soil but my hypothesis is that cigarette residue effects the plant.should there be a change in the procedure or do i have to wait longer to get better results?i am not able to find info in any of the search engines.

ANSWER: Dear Akhila,

I suspect you will not see a difference in growth between your treatment and control plants.  The complex alkaloids in tobacco are not likely to be able to enter the roots, as the endodermis will generally filter out most everything except inorganic compounds.

An exception would be things like lipid-containing pesticides and other compounds that can sneak through the plasma membrane of the endodermal cells.  But I doubt that the compounds in tobacco that are harmful to humans are also harmful to plants.  The receptors are just very different.

I suggest you do a review of plant anatomy (especially the roots!) and physiology, and use this to explain why you don't see a difference.  The most important thing is that you learn something from this project.  :)

Good luck!

Dana

---------- FOLLOW-UP ----------

QUESTION: hello
i have decided to redo my experiment so when i removed the plant out of the soil, the roots of the plant in the soil containing tobacco ash was much thicker than the roots of the plant in normal soil.the plant i used is tulsi(Ocimum tenuiflorum) which is very common in india.is it possible that the alkaline soil (due to presence of tobacco ash the soil becomes alkaline) has helped in the growth of plant.thank you for answering the previous question and reading this one.any advice would be much appreciated.

Answer
Dear Akhila,

Potassium is an important plant nutrient, and if there is potash in the tobacco ash, then this could be a possible explanation.

If you suspect the difference in pH to be a factor, then you might want to try growing the plants in identical soil, but water them with buffered solutions of different pH.

Hope this helps.

Dana