Experimental Design and Statistical Analysis:
Bt Corn, Lignin, and ANOVAs

Part II—"Methods"

by
Eric Ribbens
Department of Biological Sciences
Western Illinois University

Read Saxena and Stotzky's description of the methods they used (information concerning the soil used is removed):

"...Seeds of ten different Bt corn hybrids (Table 1), representing three transformation events (Bt11, MON810, and 176), and their respective non-Bt isolines were planted (3 seeds/pot) and the pots were kept in a plant-growth room at 26 ± 2ºC, with a 12-h light-dark cycle...  Seeds of eight Bt hybrids (Table 2) and their non-Bt isolines were also planted in a Haven sandy soil in another site in East Marion, Long Island, New York, USA...  Plants were irrigated but not fertilized.  The plants were harvested after 97 d of growth in the plant growth room and after 90 d of growth in the field.  Uniform free-hand sections of fresh corn stems between the 3rd and the 4th node from the surface of the soil (thickness was ~11 mm for plants grown in the plant growth room and ~18 mm for field-grown plants) were examined for lignin by fluorescence microscopy at 400 nm (Hu et al., 1999) and by staining with 0.01% toluidine blue (Sylvester and Ruzin, 1994).  The content of lignin of the same portion of the stems (oven-dried, ground, and passed through an 80-mesh sieve) was determined by the acetyl bromide method (Hatfield et al., 1999)."

Questions:

  1. Based on the abstract above and on this description of the methods, modify your reconstruction of their experimental approach.  What did they do?  How did they do it?
  2. What questions do you have about their research protocol that the abstract and methods sections do not answer?
  3. Does it matter that the average thickness of the stem sections differed between the growth room and the field-grown plants?  Should lignin content be reported as an absolute value, or as a percentage of the total sampled biomass?
  4. Why did they test differences in lignin content in both the growth room and in the field?  Why might the two experiments yield different results?  What can they conclude about lignin based on performing both of these experiments that they could not conclude with a growth room test alone, or with a field test alone?


Go to Part III—"Results—Figures"



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