Field decomposition of transgenic Bt maize residue and the impact on non-target soil invertebrates

Abstract

Genetically modified Bacillus thuringiensis Berliner (Bt) maize (Zea mays L.) expressing Cry toxins against various target pests is now grown on more than 16 million hectares worldwide, but its potential effects on the soil ecosystem need to be further investigated. In an 8-month field study, we investigated the effects of Bt maize expressing the Cry1Ab protein on both the soil community and maize residue decomposition. We used litterbags with three different mesh sizes (20, 125, and 5,000 μm) to investigate potential effects of different soil organism groups on the decomposition processes. Litterbags were incorporated into the soil in fall into a field that had previously been planted with non-Bt maize and subsamples were removed monthly. The dry weight of the remaining residue was measured for all bags. Bt and non-Bt maize decomposed similarly in large mesh bags, which allowed the whole soil organism community to enter and interact with each other. In contrast, Bt maize decomposed significantly faster than non-Bt maize at some sample dates in winter in bags with small and medium mesh sizes. At the end of the experiment in late spring, however, there was no significant difference in the amount of maize plant residues remaining for any of these three mesh sizes. Additionally, soil organisms from bags with the largest mesh size were identified. The most frequent taxa extracted were collembolans (Isotomidae, Tullbergiidae, Entomobryidae), mites (Gamasina, Oribatida), and annelids (Enchytraeidae). Three of these taxa were extracted in higher numbers from non-Bt than Bt residue (Tullbergiidae, Gamasina, Enchytraeidae), while there was no difference in the number of individuals extracted for the remaining three taxa. Our results do not show major changes in the decomposition of Bt maize residue and in the composition of the soil organism community. However, further studies are needed that assess the impact of the continuous release of Cry1Ab via root exudates and plant biomass on the soil ecosystem.

Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape

“…Additionally, 86% (n = 187) of the streams contained some form of maize detritus, such as cobs and stalks, in addition to maize leaves. However, in the case of cobs and stalks, we cannot be certain they originated from the 2006 crop year because they decompose more slowly than leaves, the latter of which were most likely from 2006 based on maize leaf decomposition studies (6,23). Stream sites containing maize leaves were prevalent and randomly distributed across the stream network ( Fig.…”

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“…Litter-bag experiments with Bt-maize (Bt11) reported by Zwahlen et al (2007) did not reveal major changes in the decomposition rate of Bt-maize residues. Similarly, but for MON810 instead of Bt11, various studies found no evidence for any effect related to the genetic modification when examining the decomposition rate of Bt-maize (Griffiths et al, 2007a,b;Hönemann et al, 2008;Lehman et al, 2008;Tarkalson et al, 2008).…”

Long-Term Consumption and Food Replacement of Near-Isogenic by Bt-Maize Alter Life-History Traits of Folsomia Candida Willem 1902 (Collembola)

“…by Birch et al (2007) and currently by Arias-Martín et al (2016). In general, no severe side-effects on soil animal (Zwahlen et al, 2007;Hönemann et al, 2008) or collembolan (Marvier et al, 2007;Comas et al, 2014) populations and coenosees were found in the field.…”