Bt leaching from corn detritus and the effects on stream sediment respiration

1
Bt leaching from corn detritus and the effects on
stream sediment respiration
T.C. Frauendorf1, N.A. Griffiths1, J.L. Tank1,
M.A. Evans-White2, E.J. Rosi-Marshall3, T.V.
Royer4, and M.R. Whiles5
1Univ. of Notre Dame, Notre Dame, IN. 2Kansas
State Univ., Manhattan, KS. 3Loyola Univ.,
Chicago, IL. 4Indiana Univ., Bloomington, IN.
5Southern Illinois Univ., Carbondale, IL.
Introduction
Results Microbial Respiration
Methods Bt Leaching

• 40 of corn planted in the US has been
  genetically modified to express Bacillus
  thuringiensis (Bt) derived crystal (cry) proteins
  (National Agriculture Statistics Service).
• Cry1Ab, a 67kDa protein, targets the European
  corn borer (lepidopteran pest) and may adversely
  affect related non-target species (e.g. monarch
  butterflies, caddisflies).
• Streams draining corn fields in the
  agricultural Midwest receive significant inputs
  of corn harvest byproducts (leaves, cobs, stalks,
  husks) that continue to express Cry1Ab.
• Little is known about the fate of Cry1Ab in
  corn detritus once they enter stream ecosystems
  (Fig. 1).

• Microbial respiration was significantly higher
  on FBOM pre-harvest (Plt0.001), but was
  significantly lower on sediments from Bt streams
  post-harvest (Plt0.001) (Fig. 4).
• Lower sediment respiration in Bt streams
  post-harvest was not driven by differences in
  stream temperature (P0.94)

• We measured short-term (8 hrs) and long-term
  (70 days) leaching of Cry1Ab from corn leaves by
  placing litterbags (n3 short-term, n5
  long-term) with dried corn leaves in each of 4
  streams (Fig. 2b).
• We removed 0.5 g from each bag (short-term
  sampled every 30 min for 8 hrs long-term on days
  3, 7, 13, 25, 37, 70).
• We used a double sandwich ELISA to determine
  Cry1Ab concentration in corn leaves (Fig. 2c).

Methods Microbial Respiration

• We collected 40 sediment samples of fine
  benthic organic matter (FBOM) before (October)
  and after (December) corn harvest in 4 streams (2
  draining Bt fields, 2 draining nonBt fields). In
  the lab, using microcosms, we measured microbial
  respiration at 20ºC (Hill et al. 2000).

Results Bt Leaching
Conclusions

• Short-term Leaching 61 of the Cry1Ab leached
  from corn leaves within 1 hr (Fig. 3 inset).
• Long-term Leaching Cry1Ab leached
  exponentially through time, with 18 of Cry1Ab
  remaining in corn leaves after 70 days (Fig. 3).

• Once corn leaves enter streams, Cry1Ab rapidly
  leaches into the water column, but significant
  amounts remain in the leaves as they decompose.
• Lower sediment respiration rates in Bt streams
  post-harvest suggest that leached Cry1Ab may
  negatively affect benthic microbes.
• However, previous research on soil microbes
  (Saxena and Stotzky 2001) and microbes associated
  with submerged corn leaves (Griffiths et al.
  unpublished) were not influenced by the presence
  of Cry1Ab.
• More research on the fate of Cry1Ab in the
  water column (downstream transport, degradation,
  sediment adsorption) is needed.

Research Questions
1) How fast does Cry1Ab leach from submerged corn
leaves? 2) Does leached Cry1Ab affect sediment
microbial respiration?
Study Sites

• We chose headwater streams draining Bt and
  nonBt corn fields in Benton County, Indiana (Fig.
  2a).

References

• Griffiths, N.A., Chambers, C.P., Frauendorf,
  T.C., Tank, J.L, Evans-White, M.A.,
  Rosi-Marshall, E.J., Royer, T.V. and M.R. Whiles.
  Microbial respiration and decomposition of corn
  detritus in Midwestern agricultural streams. In
  Preparation
• Hill, B.H., Hall, R.K., Husby, P., Herlihy, A.T.
  and M. Dunne. 2000. Interregional comparisons of
  sediment microbial respiration in streams.
  Freshwater Biology 44213-220
• National Agriculture Statistics Service,
  http//www.nass.usda.gov/idex.asp
• Saxena, D. and G. Stotzky. 2001. Bacillus
  thuringiensis (Bt) toxin released from root
  exudates and biomass of Bt corn has no apparent
  effect on earthworms, nematodes, protozoa,
  bacteria, and fungi in soil. Soil Biology
  Biochemistry 331225-1230

Acknowledgments This project was funded by the
NSF-DEB 0415984. We thank the McDowell laboratory
at Notre Dame and Ashley Burtner for technical
support. Contact
Information tfrauendorf_at_gmail.com