Bioengineering agricultural giant Monsanto has touted the safety of genetically modified crops, but a new study has found that insecticide-containing corn can be harmful to the overall health of soil ecosystems.

Genetically modified corn has been linked to a decrease in a subterranean fungus that forms a symbiotic bond with plant roots, allowing them to draw in more nutrients and water from the surrounding soil in exchange for carbon.

Researchers at Portland State University conducted a study to examine the effects of corn genetically engineered with the bacteria-derived insecticidal toxin, Bacillus thuringiensis, or Bt, on growth of arbuscular mycorrhizal fungi (AMF).

AMF is important for the overall health and fertility of soil ecosystems, and was found to form less bonds with the roots of Bt corn than with non-Bt corn.

Because these fungi rely on a plant host for nutrition and reproduction, they may be sensitive to genetic changes within a plant, such as insect-resistant Bt corn, Tanya Cheeke, a PhD student in biology at Portland State, told the American Journal of Botany.

Cheeke conducted the study as part of her doctoral research into the impact of genetically modified crops on soil ecosystems.

What makes our study unique is that we evaluated AMF colonization in 14 different lines of Bt and non-Bt corn under consistent experimental conditions in a greenhouse using locally collected agricultural field soil as the AMF inoculum, Cheeke told AJB.

Cheeke planted corn seeds containing the Bt gene and without it into soil containing AMF to simulate agricultural conditions on modern industrial farms.

Cheeke also tested AMF growth with other crops in soil formerly planted with both Bt and non-Bt corn. With soybeans planted in both soils, AMF root bonding was not harmed, leading Cheeke to conclude that the Bt gene was not directly toxic to AMF, but that its only known damage is to root bonding with Bt corn.

According to Cheeke, in 2011, 88 percent of corn cultivated in the U.S. was genetically modified with insecticides like Bt.