|MadSci Network: Botany|
Many student projects water plants with coffee or soda pop containing caffeine to see if caffeine reduces plant growth. The problem with those experiments is that both coffee and soda pop contain a lot of other ingredients which may also affect plant growth. Therefore, you cannot tell if caffeine alone is affecting plant growth. Some students find that plants watered with coffee grow better than control plants receiving water. A possible explanation is that mineral nutrients in coffee, such as potassium or phosphorus improve plant growth. To determine if caffeine is toxic to plants, a pure source of caffeine should be used instead of coffee or soda pop. Several caffeine concentrations should be used if possible. There are at least two ideas of the role of caffeine in plants. One hypothesis is that caffeine protects plants from insect or fungal attacks (Frischknecht et al., 1985). Another hypothesis is that caffeine is excreted by the plant into the soil and reduces growth of competing plants and bacteria (Friedman and Waller,1983a and b). Plants producing chemicals to inhibit growth of competing plants is called allelopathy. Alleopathy is often difficult to demonstrate under natural conditions but easy to demonstrate under laboratory conditions. The dose under lab conditions is often much higher than under natural conditions. Also, under natural conditions, chemicals released by the plant may be quickly inactivated by the soil. References The effects of caffeine in Coffea arabica L. Friedman, J., and Waller, G.R.. 1983a. Caffeine hazards and their prevention in germinating seeds of coffee (Coffea arabica L.). J. Chem. Ecol. 9:1099-1106. Friedman, J., and Waller, G.R.. 1983b. Seeds as allelopathic agents. J. Chem. Ecol. 9:1107-1115. Frischknecht, P.M., et al. 1985. Purine alkaloid formation in buds and developing leaflets of Coffea arabica: expression of an optimal defense strategy?? Phytochemistry. 3:613-616.
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