Before preparing any duckweed medium, read the section on troublshooting.  Adjusting the pH of the medium is important.

Duckweeds in nature

Before deciding on a growth medium for the laboratory, it is useful to understand how duckweeds grow in nature.

Elias Landolt did extensive investigtions of duckweed ecology.  He found that duckweeds grow under a wide variety of conditions.  However, he did find some generalities.  Duckweeds generally are not found in oligotrophic water (water in which nutrients are in low supply).  They also are rare on lakes drained by granitic soils and limestone and on very old soils that are poor in most nutrients.  "Exceptions are waters heavily contaminated by waste water.  On the other hand extensive eutrophication may lead to the dissappearance or more sensitivie species, e.g. L. trisulca in Finland (TOIVONEN, 1985) or Wolffiella species in California (own observations)." (Landolt, 1986, p149).

The Table below shows the range of minerals found in waters supporting the natural growth of duckweeds.

Range of nutrient content in waters with Lemnaceae  (chemical elements in mg/l, conductivity in uS/cm)
range of 95% of   the samples	absolute range	range of 95% of the samples
pH conductivity Ca Mg Na K N p HCO3 Cl S	3.5—10.4 10 — 10900 0.1 — 365 0.1—230 l.3—>l000 0.5—100 0.003—43 0.000—56 8—500 0.1—4650 0.03—350	5.0—9.5  50 — 2000 1.0 — 80  0.5—50  2.5—300  1.0—30  0.02—10  0.003—2  10—200 1—2000 1—200

Table reproduced from Landolt, 1986, p 150, summarizing data from various sources.
 

Lowest yearly mean of some nutrients in waters of Central Europe with Lemnaceae species 46 waters were investigated for three years. The Lemnaceae cover of the water was noted and the water analyzed from March to October once each month. In addition, 33 waters were observed less intensively. The number of occurrences of each species are as follows: S. polyrrhiza 18 times, L. gibba 16 times, L. minor 59 times, L. trisulca 15 times, and L. mi- nuscula 28 times.
nutrients in mg/L	Spirodela polyrrhiza	Lemna gibba	Lemna minor	Lemna trisulca	Lemna minuscula
P N K Ca Mg	0.007 0.04 1.3 18.8 1.1	0.027 0.22 2.6 23.7 4.5	0.006 0.04 0.9 11.6 1.1	0.01 0.04 2 40 4.6	0.012 0.18 1.5 18.6 1.1

Data above from Lueoend, 1983, V. Geobot. Inst. ETH, Stiftun Rubel, 80:116 pp., cited in Landolt, 1986, p. 150.
 

Hoagland's E-Medium

The most-commonly recommended medium is Hoagland's E-Medium.  First, read these comments.  There are different formulations of Hoagland's medium in the literature.  It was originally developed for hydroponic growth of terrestrial plants, not for the growth of duckweeds.

[ UTCC Formulation ] [ Cleland and Briggs Formulation ]

This formulation was provided by Judy Acreman, Department of Botany, University of Toronto. Another formulation (ASTM STP 1027) is provided below.

• Adjust the pH to 5.8 with NaOH or HCI.
• Sucrose may be added as 10 g/l if the culture is axenic.
• Autoclave medium.

Preparation of Fe·EDTA Solution
 

•  Dissolve completely and make up to 250 mL
• After autoclaving medium, add Fe·EDTA solution aseptically.
• For final medium, use 3.0 mL of Fe·EDTA stock to 150 mL of Hoaglands.

Reference:  Cowgill, U.M. and Milazzo, D.P. "The culturing and testing of two species of duckweed," Aquatic Toxicology and Hazard Assessment: 12th Volume, ASTM STP 1027, U.M. Cowgill and L.R. Williams, Eds. American Society for Testing and materials, Phila. 1989, pp. 379-391.  This article references Cleland and Briggs for this revision.  Cowgill and Milazzo also recommend addition of traces of Se, Co, Sn and V for optimal growth of one or more Lemna species.  In many cases, these trace elements are likely supplied by impurities in the other mineral components of these media, in the water used in their preparation, or leached from the glass walls of culture vessels.

TABLE 2-Chemical composition of Hoagland's E+ medium.
 

• To Make E-Medium omit yeast extract and bactotryptone.
• Make growth medium up to 1.0 L with glass distilled water. Adjust the pH to 4.60 with KOH/HCl. Autoclave 20 min at 121 C and 124.1 kPa.
• NOTE: EDTA = ethylenediamine tetraacetic acid.
• A nearly identical formulation is used by Janet Slovin (USDA Climate Stress Lab, Beltsville, MD).  Her formula states that higher levels of CuSO₄·5H₂O (4 mg/L final concentration) will inhibit flowering in Lemna gibba.  Optionally, she uses NaK·tartrate (564 mg/100 mL) instead of tartaric acid.  She also indicates that addition of kinetin (3 mL/L of a 1 mM stock solution, 21.5 g/L of kinetin or 25.2 g/L of kinetin·HCl) will allow L. gibba to grow in intermittent red light.

Schenk and Hildebrandt Medium

Reference:  Schenk, R. U. and A. C. Hildebrandt, 1972, Medium and Techniques for Induction and Growth of Monocotyledonous and Dicotyledonous Plant Cell Cultures, Can. J. Bot. 50:199-204.
 
 

Other Media

Regulatory agencies require specific defined media for phytotoxicity testing in Lemna.   The LemnaTec company details several of these formations (Steinberg, OECD, and ASTM media) on their website.

Wayne Armstrong recommends using 20% Hutner's solution solidified with agar for growth of duckweeds on a gelled medium.  There are several patents using duckweeds [ available on-line ], that reference synthetic media, including Nickell's Medium, and various commercial formulations, such as Nutricol No. 3 (Fertilizers and Chemical, Haifa, Israel) and Solu-Spray (Leffingwell Chemical Company).  These advantages of these, if any, are unclear.  The pH of these media should be adjusted, as for any medium.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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Last revised:  August 17, 2001