Effects of the cultivation of genetically modified Bt crops on nontarget soil organisms - Microbial Ecology in Sustainable Agroecosystems - page 153

and Saxena, 2009). Since the commercial introduction of GM plants, the acreage dedicated
to GM crop cultivation has increased each year, such that the majority of all major crop
plants grown in the United States—soybean, cotton, and maize—are genetically engi-
neered (U.S. Department of Agriculture [USDA], 2010). Developing countries also continue
to increase their share of global GM crop production and now account for almost half (46%)
of the global hectarage of GM crops (James, 2010). This rapid and widespread adoption of
GM crops has led to a dramatic shift in the agricultural landscape since the mid-1990s and
has raised questions about the impact of agricultural biotechnology on nontarget organ-
isms in the soil environment.
Although some GM crops can provide a variety of agricultural benefits, there may also
be potential risks to nontarget organisms. Some of the key scientific concerns regarding the
widespread cultivation of GM crops include (1) the potential for gene flow from transgenic
plants to related species (e.g., Mercer and Wainwright, 2008; Pineyro-Nelson et al., 2009);
(2) persistence of GM plant material in the environment (e.g., Saxena and Stotzky, 2001b;
Zwahlen, Hilbeck, Gugerli, et al., 2003; Stotzky, 2004; Flores et al., 2005; Tarkalson et al.,
2008); (3) the evolution of pest resistance (e.g., Gould et al., 2002; Abel and Adamczyk, 2004;
Huang et al., 2007; Gao et al., 2010); (4) risks to the environment associated with changes in
the agricultural landscape or farming practices associated with the adoption of GM crops
(e.g., Krogh et al., 2007; Lupwayi et al., 2007; Watrud et al., 2011); and (5) the risk to nontarget
organisms, including mammals, birds, fish, insects, and soil organisms (e.g., Stotzky, 2000;
Adamczyk and Hardee, 2002; Kowalchuk et al., 2002; Clark et al., 2005; Rosi-Marshall et
al., 2007; Thies and Devare, 2007; Icoz and Stotzky, 2008b; Lang and Otto, 2010; Then, 2010;
Gatehouse et al., 2011).
This chapter summarizes the environmental risk assessment research of Bt crops to
date in soil and offers suggestions on how to examine and understand better the effects
of these types of GM crops on soil organisms. The chapter includes discussion of the fol-
lowing: an introduction to Bt crops (what they are, where they are grown, how they are
engineered, etc.); how Bt and other transgenic crops are regulated in the United States; the
fate of Bt plant material in soil (how Bt toxin enters soil, binding properties, potential dif-
ferences in degradation rates of transgenic plant material, etc.); effects of Bt crops on soil
organisms, including bacteria, fungi, protozoa, nematodes, and soil invertebrates (earth-
worms, microarthropods, insects); and a brief discussion of the escape and introgression
of transgenes as this could also have nontarget effects on soil organisms. The question of
whether Bt crops can contribute to the sustainability of agroecosystems is also discussed.
The chapter concludes with a summary and recommendations for future research direc-
tions. The information here follows many excellent reviews evaluating effects of trans-
genic crop cultivation on nontarget organisms in the soil environment (e.g., Stotzky, 2000,
2002, 2004; Giovannetti, 2003; Kowalchuk et al., 2003; Saxena and Stotzky, 2003; Motavalli
et al., 2004; Giovannetti et al., 2005; Liu et al., 2005; O'Callaghan et al., 2005; Thies and
Devare, 2007; Icoz and Stotzky, 2008b; Liu, 2010; Saxena et al., 2010). Although herbicide
tolerance is often incorporated into Bt cultivars as a stacked trait, nontarget effects of GM
herbicide-tolerant (HT) crops on soil organisms are not included in this review because the
genetic insertion has been shown to have no direct effect on soil organisms (although the
use of this technology may have indirect effects on soil organisms as a result of changes
in agricultural practices) (e.g., Siciliano and Germida, 1999; Dunfield and Germida, 2003,
2004; Kowalchuk et al., 2003; Krogh et al., 2007; Griffiths et al., 2008; reviewed by Lundgren
et al., 2009; Watrud et al., 2011).