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Natural Science Forum / Biology / Botany / June 2005Duckweed Growth Experiment
I'm a high school junior and am interested in performing an experiment with duckweed (Lemna minor). I am hoping to submit the project to the Miami-Dade County Science Fair in the fall. My objective is to measure the growth rate of the duckweed population in solutions high in certain nutrients (N-P-K-Micronutrients). I am looking for advice on what methods would be best. I have already done a pre-test of sorts with very poor results. Commercial fertilizers and problems with water quality impeded growth. I am very interested in any scholarly journals, internet sites, references, etc. which could be of help. Advice is welcome, particularly on the experimental setup and procedure, which I am having a lot of trouble with. I also want to relate the experiment to what actually happens in ecosystems where nutrient runoff from agriculture polute waterways and cause eutrophication. Any and all help will be sincerely appreciated. Regular fertilizers, such as Miracle-Gro, contain too much ammonium and urea and lack certain of the essential mineral nutrients, particularly calcium. The ammonium causes the solution pH to drop too low. If your water quality is poor, you may need to used distilled or deionized water. You might wish to try a hydroponic fertilizer at a reduced rate, say 10% of the recommended strength, to get good growth. If your school has a well-equipped chemistry lab, you may be able to prepare your own nutrient solutions. Once you have a solution that works well, modify that for your other treatments. One common hydroponic experiment is to obtain deficiencies of each essential element, such as nitrogen, phosphorus and potassium. You can also measure how plants change the nutrient solution pH. It usually goes down with a little to a lot of the nitrogen as ammonium and up with all nitrogen as nitrate. Growing the plants under fluorescent light might be desirable for reproducible conditions. I've not grown a lot of aquatic plants in hydroponics but algae growth can be a problem. As per the 1932 reference below, you might wish to count the increase in humber of fronds as a measure of growth rate. David R. Hershey The following articles/websites should be useful: Hershey, D.R. 1994. Solution culture hydroponics: History and inexpensive equipment. American Biology Teacher 56:111-118. http://www.angelfire.com/ab6/hershey/hydro.pdf Hershey, D.R. 1993. Evaluation of irrigation water quality. American Biology Teacher 55:228-232. http://www.angelfire.com/ab6/hershey/water.pdf Hershey, D.R. 1990. Pardon me, but your roots are showing. Science Teacher 57(2):42-45. http://www.angelfire.com/ab6/hershey/sthydro.pdf Synthetic Media for Growing Duckweeds http://www.mobot.org/jwcross/duckweed/media.htm Essential Elements for Plant Growth http://www.soils.wisc.edu/~barak/soilscience326/essentl.htm Fluorescent lighting systems for plant growth http://www.fastplants.org/instructions/lighting_systems.html DUCKWEED AQUACULTURE http://www.p2pays.org/ref/09/08875.htm Peterson, H.G., M. Moody, 1997. Limited Report: Effluent toxicity testing using Lemna minor. SRC Publication No: R-1640-20-E-97. Contact author: http://www.safewater.org/aboutus/Resumes/hans.htm McHargue J.S and Calfee, R.K. 1932. MANGANESE ESSENTIAL FOR THE GROWTH OF LEMNA MAJOR. Plant Physiol. 7(4): 697-703. http://www.pubmedcentral.gov/picrender.fcgi?tool=pmcentrez&blobtype=pdf&artid=440182 |
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