January 13, 2011

Lab Testing vs. Field Work

What happens when you take something from its natural environment and place it in a new environment and then extrapolate the results back into the natural environment?

Be aware that there is a difference between what you find out in the laboratory and what actually takes place in the world. Be cautious about how laboratory data is extrapolated to natural environments.

The paper below was inspired by my own experience discovering that lab studies do not reflect 100% the natural environment. I quickly discovered there's more to growing duckweed than taking it from one place and moving it to another. The duckweed I use grows naturally here in Cache Valley on the Wellsville and Logan City wastewater treatment lagoons. They grow fine outdoors in their native environment, it's not until I bring them inside that their behavior changes and I have difficulty maintain a good healthy culture.

Future posts will address the issues I've come accross (e.g. light intensities, algae-duckweed competition, phytophagous fauna, fungi, crop densities, and pH). But as a teaser take a look at the photos below which show the effect fungi can have on duckweed. The duckweed was removed from very healthy populations; however, once they came indoors the conditions began to favor a certain fungi that within days/weeks destroys the duckweed crop.

Figure 1: Start of experiment with healthy duckweed from Cache Valley (Lemna minor species).
Also shown is the Omega pH controller (pH 7.7, later lowered to 6.5), pH probe, temp. probe, 100 L reactors with nutrient solution based on hydroponic solution explained here, high-pressue soldium lamps (HPLS) 4 ft. above supplying approx. 175ppf (16/8hrs on/off), constant temp. @ 25'C.

Figure 2: Chlorosis/necrosis setting-in causing yellowing and bleaching of some duckweed fronds. Note: similar blight patches were seen in actual duckweed covers outdoors on the wastewater lagoons in Wellsville; however, it appears there is enough duckweed to overcome the blight. An interesting article titled "Dynamics of fungal infection in duckweeds (Lemnaceae)" by Rejmankova E. (1986) talks about this phenomena and is referenced on this informative website.

Figure 3: More blight and bleaching of fronds short time after.

Figure 4: Majority of duckweed is chlorotic within a short period of time.

Figure 5: The result is a mat of chlorotic/necrotic (i.e. dead) duckweed which is submerged just below the surface of water. Perhaps the submersion actually suffocates the plants.

Figure 6: The culprit. Microrganisms are thriving all over the tissues of the unhealthy duckweed plants. These observations support an intersting article discussing why invertabrates consume decaying macrophytes rather than living ones.

Figure 7: The stringy organisms appear to be fungi which mats the duckweed together and leads to its death.

Video: "Duckweed Feast" showing duckweed tissue in varying states of decomposition due to bacteria colonies, rotifers, vorticella, and fungi.

Title: Recognizing the effect of extrapolating lab data into natural environments
Created: 30 April 2009
Author: Jon Farrell

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