Extractable Soil Lipids and Microbial Activity as Affected by Bt and Non Bt Maize Grown on a Silty Clay Loam Soil

Abstract

Pyrolysis-gas (Py-GC) chromatography was used to characterize extractable lipids from Bt and non-Bt maize shoots and soils collected at time of harvesting. Py-GC-MS (mass spectrometry) showed that the concentrations of total alkenes identified in non-Bt shoots and soils were 47.9 and 21.3% higher than in Bt maize shoots and soils, respectively. N-alkanes identified were of similar orders of magnitude in Bt and non-Bt maize shoots, but were 28.6% higher in Bt than in non-Bt soils. Bt maize shoots contained 29.7% more n-fatty acids than non-Bt maize shoots, whereas the concentrations of n-fatty acids in Bt soils were twice as high as those in non-Bt soils. Concentrations of unsaturated fatty acids in Bt maize shoots were 22.1% higher than those in non-Bt maize shoots, while concentrations of unsaturated fatty acids were 22.5% higher in non-Bt than in Bt soils. The cumulative CO2-C evolved from soils under Bt and non-Bt crops was 30.5% lower under Bt as compared to non-Bt crops, whereas when maize shoots were added to Bt and non-Bt soils, the decrease in CO2-C evolved were 16.5 and 23.6%, respectively. Our data showed that the cultivation of Bt maize significantly increased the saturated to unsaturated lipid ratios in soils which appeared to negatively affect microbial activity.

Bt corn plants and their straw have no apparent impact on soil microbial communities

“…By contrast, some studies have indicated that Bt corn affects microbial communities, the activities of some enzymes, and microbe-mediated processes and functions in soil (e.g., Dinel et al 2003;Castaldini et al 2005;Griffiths et al 2005Griffiths et al , 2006Turrini et al 2004;Xue et al 2005). Xue et al (2005) found that the ratio of Gram-positive to Gramnegative bacteria was lower in soil with Bt corn than in soil with near-isogenic non-Bt corn.…”

Decomposition of residues and loss of the δ-endotoxin from transgenic (Bt) corn (Zea mays L.) in soil

“…Stotzky (2000) suggested that the slower decomposition of Bt-corn (NK6800Bt) was related to its greater lignin content compared with non-Bt-corn, even though the N content of the Bt-corn was also lower than that of the non-Bt-corn. Dinel et al (2003) also reported slower C mineralization from Bt-corn (Pioneer 38W36) compared to the near-isoline non-Bt-corn (Pioneer 3893). By contrast, Escher et al (2000) claimed that lignin decomposition was faster in Bt-corn (Novartis X4334-EPR, previously Northrup King) than in the near-isoline non-Bt-corn.…”

Crop residue chemistry, decomposition rates, and CO2 evolution in Bt and non-Bt corn agroecosystems in North America: a review

“…Yet, the experimental evidence does not support this hypothesis unequivocally. Three decomposition studies with controlled-environment conditions showed lower CO 2 production in Bt compared to non-Bt corn residue amended soils (Dinel et al 2003;Castaldini et al 2005;Flores et al 2005). In contrast, field decomposition litterbag studies showed either no difference in mass loss between Bt and non-Bt corn residues buried in the field (Lehman et al 2008;Tarkalson et al 2008) or faster decomposition of Bt leaves compared to non-Bt leaves during early decomposition, after which the two hybrids levelled off at the end of the study (Zwahlen et al 2007).…”

“…It is possible that the results were influenced by corn varieties selection. Dinel et al (2003) incubated a silty clay loam soil from Sainte-Barbe in Quebec, Canada, with Bt shoots (Pioneer 38W36) and with non-Bt shoots (Pioneer 3893) and measured 30.5% more cumulative CO 2 -C production from the non-Bt amended soil after 51 days of incubation.…”