Peter Motavalli

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ENVIRONMENTAL IMPACT OF GENETICALLY-MODIFIED CROP
S AND THEIR MANAGEMENT
Non-transgenic corn
Transgenic Bt corn
Peter Motavalli Environmental Soil Science
Program Email motavallip_at_missouri.edu
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CONTROVERSY OVER GM CROPS

• LATEST ARTICLES ON GM FOODS IN NEW SCIENTIST
• GM FOOD SAFETY FEAR BASED ON DISTORTION (25
  Jun 03)
• GENETIC ENGINEERS DECAFFEINATE COFFEE (18 Jun
  03)
• SEEDS MORE RISKY THAN POLLEN FOR GM ESCAPE (18
  Jun 03)
• GM CROP EXPERIMENT LACKS STATISTICAL POWER (18
  Jun 03)
• ALTERED BEET OFFERS A TASTE OF THE FUTURE (15
  Mar 03)
• GENE SILENCING COULD WIPE OUT FARM PESTS (10 Mar
  03)
• KWAZULU FARMERS BOOSTED BY GM COTTON (7 Mar 03)
• FIGHTING OVER PHARMING (1 Mar 03)
• BRITAIN MAY FORCE DNA BARCODES FOR GM FOODS (13
  Feb 03)

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WHAT ARE GM CROPS?

• A genetically-modified (GM) or transgenic crop
  plant contains a gene or genes which have been
  artificially inserted instead of the plant
  acquiring them through pollination.

• The inserted gene sequence (known as the
  transgene) may come from another unrelated plant,
  or from a completely different species
  transgenic Bt corn, for example, which produces
  its own insecticide, contains a gene from a soil
  bacterium.

Source Center for Life Sciences and Department
of Soil and Crop Sciences at Colorado State
University
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IMPORTANCE OF GM CROPS

• In 2002, 22 of global land (145 million acres)
  under cultivation grown to GM crops.

Source Pew Initiative on Food and Biotechnology,
2003
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IMPORTANCE OF GM CROPS

• In 2002, 66 of global land planted to GM crops
  are in the U.S. Other three countries with
  largest acreage are Argentina, Canada and China.

• Major commercially-released GM crops have
  herbicide, insect and disease resistance.
  Herbicide-resistant soybeans (e.g. Roundup-Ready)
  represent 62 of the global GM cropped area for
  all crops. Insect resistant Bt corn 13 of
  cropped area herbicide-resistant canola 5 of
  cropped area Bt cotton 4 of cropped area

Source Pew Initiative on Food and Biotechnology,
2003
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Soybeans
Eleven states account for 84 to 85 of the GM
corn and soybeans planted in 2002 in the U.S.
In Missouri, 42 of the corn and 83 of the
soybeans planted in 2002 were GM
Corn
Source Pew Initiative on Food and
Biotechnology, 2003
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IMPORTANCE OF GM CROPS

• Global market value for GM crops is expected to
  rise from 500 million in 1996 to 20 billion by
  2010.
• New GM crops being developed include plants
  containing modifications for- Improved
  resistance to stress conditions- Plants with
  better nutritional qualities and vitamins-
  Plants with enhanced N fixation and
  photosynthesis- Plants that produce industrial
  products or precursors, such as bioplastics,
  pharmaceutical proteins and vaccines.

Source Nottingham, 2002
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POTENTIAL ENVIRONMENTAL IMPACTS

• Dispersal and invasiveness of the GM plant into
  ecosystems
• Movement of transgenes in the environment through
  pollen dispersal to other non-GM plants or gene
  transfer to microorganisms
• Reductions in the biodiversity and activity of
  non-target organisms including both flora and
  fauna
• Development of resistance in target organisms
• Environmental effects of changes in soil and crop
  management practices for GM crops, such as
  changes in pesticide and tillage practices.

Source NRC, 2002 Motavalli et al., 2003
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SOIL FLORA AND FAUNA
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SOIL BIOLOGICAL FUNCTIONS

• Nutrient cycling
• Decomposition of organic materials
• Biological nitrogen fixation
• Pesticide detoxification
• Oxidation-reduction reactions
• Alteration of soil physical properties (e.g.
  aggregation)

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DIRECT AND INDIRECT EFFECTS

• Direct Effects

• Root exudates
• Herbicide and insecticide applications
• Gene transfer

Indirect Effects

• Crop residues (quantity and composition)
• Animal and other agricultural processing wastes
• Soil erosion and runoff
• Use of marginal lands

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POTENTIAL IMPACTS
Transgenic Crop
Management practices
Climate
Pesticides
Tillage
Fertilization
(Animal waste)
Nutrient export
Crop residues
Root exudates
Soil properties

• Clay type and content
• pH
• Soil structure
• Soil organic matter

Rhizosphere
Microbially-mediated nutrient transformations
Gene transfer

• Mineralization/immobilization
• Oxidation/reduction
• Fixation/gaseous loss
• Solubilization

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Cry gene for Bt endotoxin in corn
Example of an indirect effect of a transgenic
crop Crop residues
Reduced corn borer damage
Greater production of undamaged residues
Slower decomposition of residues
Decreased rate of nutrient release
Nutrient availability????
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DIFFICULTIES TO ASSESS EFFECTS OF GM CROPS ON
SOIL BIOLOGICAL PROCESSES AND FUNCTIONS

• Lack of sufficient long-term baseline information
  on the variation in soil microbial diversity and
  activity in diverse agroecosystems to compare
  with agroecosystems in which transgenic crops
  have been introduced.
• Information on effects of changes in soil
  microbial diversity and activity on environmental
  processes is limited.
• Research results showing significant negative
  effects of GM crops on soil biological activity
  obtained under laboratory or greenhouse
  conditions may not be as clearly manifested under
  field conditions.

Source Motavalli et al., 2003
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DIFFICULTIES TO ASSESS EFFECTS OF GM CROPS ON
SOIL BIOLOGICAL PROCESSES AND FUNCTIONS

• when science moves into a policy realm, the
  very uncertainty that is a natural product of the
  scientific process frustrates efforts to put
  policies into place (Scully, 2003)
• Scientific research characterized by being slow
  and often incomplete.
• Negative findings may be followed by subsequent
  research studies that discounts or clarifies
  initial results.

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http//www.whybiotech.com/main.html
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http//www.greenpeaceusa.org/ge/
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U.S. REGISTRATION PROCESS

• In U.S. EPA, FDA and APHIS (Animal and Plant
  Health Inspection Service USDA) are primary
  government agencies regulating biotechnology

• No provision for effects on microbial diversity,
  rhizosphere ecology, and other soil biological
  functions and processes. Also, tests run
  under limited environmental conditions (e.g.
  soil characteristics).

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DIRECT EFFECTS ROOT EXUDATES

• Effects of Bt toxin (also viaresidues and
  pollen)

• Bind rapidly on clay minerals (e.g.
  montmorillonite and kaolinite), humic acids and
  organomineral complexes (Saxena et al., 1999).
• Toxin retains insecticidal activity and protected
  against microbial degradation for 234 d.

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DIRECT EFFECTS ROOT EXUDATES

• Effects of Bt toxin (continued)

• No apparent effect on populations of earthworms,
  nematodes, protozoa, bacteria and fungi in soil
  but effects on composition and diversity need to
  be studied (Saxena and Stotzky, 2001).
• Aerobic bacterial and fungal populations, fungal
  species diversity and abundance in soil planted
  to Bt potatoes differed minimally from soil
  planted with control plants (Donegan et al.,
  1995).

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DIRECT EFFECTS HERBICIDE APPLICATIONS

• Effects of glyphosate application

• Glyphosate applied at a rate of 0.54 kg a.i. ha-1
  to a sandy loam soil significantly decreased
  fungal and bacterial counts 2 mo after treatment.
• Growth of 5 species of ectomycorrhizal fungi in
  medium was reduced with glyphosate concentrations
  above 50 ?l L-1 (Chakravarty and Chatarpaul,
  1990).

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DIRECT EFFECTS HERBICIDE APPLICATIONS

• Other effects of glyphosate application

• Early application of glyphosate at 1.68 kg a.i.
  ha-1 delayed N2 fixation and decreased biomass
  and N accumulation in glyphosate-tolerant
  soybean, especially under soil moisture stress.
• Plants recovered by 40 d after emergence when
  soil water content was optimal.
• N uptake of added soil N was also inhibited by
  applied glyphosate (King et al., 2001).

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INDIRECT EFFECTS CROP RESIDUES

• Bt corn may have a higher lignin content in
  residues that would reduce rate of decomposition
  and feed quality but also possibly reduce erosion
  (Saxena and Stotzky, 2001).
• Two of three Bt cotton residues added to soil
  caused transient increases in levels of
  culturable aerobic bacteria and fungi, possibly
  due to other plant characteristics besides the
  intended Bt toxin production (Donegan et al.,
  1995).

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INDIRECT EFFECTS CROP RESIDUES

• 73 of soybean growers and 26 of canola growers
  are now leaving more crop residues on the soil
  surface than they previously did before
  transgenic crops were introduced (1995 to 1996)
  due to increased use of conservation tillage.
• Conservation tillage reduces soil erosion and
  nutrient loss (Amer. Soybean Assoc., 2001 Canola
  Council of Canada, 2001)

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CONCLUSIONS

• Little current research in the literature on the
  long-term impact of transgenic crops and
  associated management practices on soil microbial
  diversity and activity.
• The potential effects of transgenic crops on soil
  biological processes and functions are large
  considering the increasing land area cultivated
  with transgenic crops and the possible direct and
  indirect effects of altering crop traits on soil
  processes.

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CONCLUSIONS (Continued)

• However, no direct evidence exists that currently
  released transgenic crops are causing significant
  changes in soil biological properties under field
  conditions.
• Further consideration of the effects of a wide
  range of soil properties, including clay type and
  mineralogy, pH, soil structure, and soil organic
  matter, is needed in evaluating the ecological
  impact of transgenic crops.