Microbial Respiration and Bt Leaching in Agricultural Streams

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Microbial Respiration and Bt Leaching in
Agricultural Streams

• Therese Frauendorf
• 10. Nov. 2006

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Carbon Sources in Agricultural Streams
Forested Stream Light Litter Fall Allochthonous
Agricultural Stream Light Litter
Fall Autochthonous
Allochthonous Carbon input by corn byproducts
Allochthonous and Autochthonous Relative
components of Carbon Spiraling
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Central Questions

• Does Bt leach out of corn leaves over short time
  period of eight hours?
• What is the heterotrophic respiration along a
  stream, is it different among streams, and does
  it change with temperature?

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Bt (Bacillus thuringiensis)

• 35 of corn planted in the US was genetically
  modified to express Bacillus thuringiensis
• (Bt) d-endotoxin proteins
• Gut poison spilling of gut content into
  hemolymph
• Target species Coleoptera (Corn Borer) and
  Lepidoptera (Root Borer)
• Effect on non-target species Monarchs and
  Caddisflies

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Bt Leaching

• Bt Leaching determine the degree of the effect
  on aquatic organism
• Question How fast does Bt leach out of corn
  leaves?
• Long-term leaching
• (Shredders and up the food web)
• Short-term leaching
• (Filterers and water column)

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Bt Methods

• Field
• DITCH 2005 site Brost
• 5 litter bags 15g dried corn leaves
• Take 0.5g of leaves out every half hour
• Total leaching time 8 hours
• Lab
• Add PBST extraction buffer (1g50ml)
• Homogenize centrifuge
• SDI Cyr1AB ELISA Plate
• read at 450nm and 650nm absorbance

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Bt Results
Average of 5 replicates every half hour for eight
hours
Results suggest that short-term leaching occurs
mostly within the first hour

• Each of the 5 replicates every half hour for
  eight hours
• Linear Regression
• Showed a significant negative deviation from zero
  
• (F-ratio 23.379, plt 0.001)

Fine-print Time zero was done on a completely
different plate at a different time
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Central Questions

• Does Bt leach out of corn leaves over short time
  period of eight hours?
• What is the heterotrophic respiration along a
  stream, is it different among streams, and does
  it change with temperature?

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Carbon Spiraling

• Carbon Budget generally used, shows the total
  benthic and transported carbon present, not know
  where it is taken up and released
• Carbon Spiraling can outline the cycling
  pathway more detailed and apply to Carbon
  Spiraling Indices

• Voc TOC x Q
• (m/day) BOC x w
• Koc Rhet
• (per day) BOC (TOC x z)
• Soc Voc
• (m) Koc

Voc (net longitudinal velocity of organic
carbon TOC (total transported organic carbon
concentration Q (discharge) BOC (total organic
carbon benthic standing stock w (mean river
width) Koc (the biotic turnover rate) Rhet
(heterotrophic respiration) z (mean water
depth) Soc (organic carbon turnover length)
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Carbon Cycling
Measurement of heterotrophic respiration -
Oxygen consumption by microbial communities -
Measurement of microbial communities of
sediments ? substrate with most
microbial
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Respiration Methods

• Collected Fine Benthic Organic Matter of a 60 ml
  test tube area (5.27cm2)- filled to lip
• 40 test tubes for four streams (DITCH 2006 sites
  2A, 2B, 2D, 2F)
• Tubes filled with water airtight and incubated
  2hours in dark at 20C and 10C (incubator at
  constant temperature)
• Temperature and DO measured before and after
  incubation
• Substrate collected for AFDM

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Respiration Result

• There is a significant difference in microbial
  respiration per grams of AFDM (mg O2/g AFDM/h)
  between sites and between the two temperatures
• - 2-way ANOVA
• (Site F-ratio 14.835 plt 0.001, Temperature
  F-ratio 40.776 plt0.001, Site x Temperature
  F-ratio2.800 p0.04)
• Hill et. al. 2000 0 0.621 mg O2/g AFDM/h
  (Central Appalachians, Southern Rockies, Central
  Valley)
• There is a significant difference in microbial
  respiration per cm2 (mg O2/ cm2/h) between sites
  and between the two temperatures
• - 2-way ANOVA
• (Site F-ratio 22.534 plt0.001, Temperature
  F-ratio 44.441 plt0.001, Site x Temperature
  F-ratio 4.783 p0.003)

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Conclusion

• Bt-corn Short-term leaching
• - there is a significant decrease of Bt in corn
  over eight hours suggesting a higher appearance
  in the water column
• - the most significant decrease is during the
  first hour
• - More to come repeat experiment, conduct a
  short-term experiment for one hour with shorter
  sample intervals
• Microbial Respiration
• - there is a significant difference in
  respiration between sites, which should be taken
  into account when calculating the turnover rate
  and length (high Rhet higher Koc and lower Soc)
• - there is a significant difference in
  respiration between temperatures, suggesting that
  the carbon spiraling indices are temperature
  sensitive
• - More to come repeat experiment in
  post-harvest season and compare to pre-harvest
  respiration

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Many Thanks!

• Jen Tank
• Natalie!
• Mia
• And the Tank Lab

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Questions