Tuesday, June 5, 2007
477

The rate of Bt leaching from corn detritus and the effects on microbial respiration on stream sediments

Therese C. Frauendorf1, Natalie A. Griffiths1, Jennifer L. Tank, PhD1, Michelle A. Evans-White, PhD2, Emma J. Rosi-Marshall3, Todd V. Royer4, and Matt R. Whiles5. (1) Biological Sciences, University of Notre Dame, Department of Biological Sciences, Galvin Life Science Center, Notre Dame, IN 46556, (2) Biology, Kansas State University, Division of Biology, Manhattan, KS 66506, (3) Biology, Loyola University Chicago, Chicago, IL 60626, (4) School of Public and Environmental Affairs, Indiana University, 1315 East Tenth Street, Bloomington, IN 47405, (5) Department of Zoology and Center for Ecology, Southern Illinois University, Life Science II, Carbondale, IL 62901

In the Midwestern US, 35% of planted corn has been genetically modified to express Bacillus thuringiensis (Bt) δ–endotoxins.  After harvest, corn represents a significant allochthonous input to agricultural streams, yet the effects of Bt-corn in streams have not been fully investigated.  First, we quantified the rate of Bt leaching from corn leaves and then examined the potential influence of Bt-corn on benthic microbial respiration.  After anchoring 5 replicate litterbags to the benthos, we retrieved corn leaves every 30min for an 8hr period.  Bt δ-endotoxin concentration in leaves was measured using an Enzyme-Linked ImmunoSorbent Assay.  Within 1hr, 61% of the Bt δ-endotoxin leached from the leaves and then remained constant for the next 7hrs.  To assess whether Bt-corn leachate affects stream biofilms, we measured microbial respiration on 40 sediment cores taken along 200m reaches in 6 streams, of which 3 drained Bt-corn fields, before and after corn harvest. While microbial respiration was higher on sediments in Bt streams compared to non-Bt streams before harvest (0.42mgO2/gAFDM/h vs. 0.34mgO2/gAFDM/h; p=0.02), respiration was lower in Bt streams after harvest (0.11mgO2/gAFDM/h vs. 0.20mgO2/gAFDM/h; p<0.001).  These results suggest that leached Bt δ-endotoxin has the potential to reduce microbial respiration in streams.  

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