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The cultivation of genetically modified (GM) plants has raised several environmental concerns. One of these concerns regards non-target soil fauna organisms, which play an important role in the decomposition of organic matter and hence are largely exposed to GM plant residues. Soil fauna may be directly affected by transgene products or indirectly by pleiotropic effects such as a modified plant metabolism. Thus, ecosystem services and functioning might be affected negatively. In a litterbag experiment in the field we analysed the decomposition process and the soil fauna community involved. Therefore, we used four experimental GM wheat varieties, two with a race-specific antifungal resistance against powdery mildew (Pm3b) and two with an unspecific antifungal resistance based on the expression of chitinase and glucanase. We compared them with two non-GM isolines and six conventional cereal varieties. To elucidate the mechanisms that cause differences in plant decomposition, structural plant components (i.e. C∶N ratio, lignin, cellulose, hemicellulose) were examined and soil properties, temperature and precipitation were monitored. The most frequent taxa extracted from decaying plant material were mites (Cryptostigmata, Gamasina and Uropodina), springtails (Isotomidae), annelids (Enchytraeidae) and Diptera (Cecidomyiidae larvae). Despite a single significant transgenic/month interaction for Cecidomyiidae larvae, which is probably random, we detected no impact of the GM wheat on the soil fauna community. However, soil fauna differences among conventional cereal varieties were more pronounced than between GM and non-GM wheat. While leaf residue decomposition in GM and non-GM wheat was similar, differences among conventional cereals were evident. Furthermore, sampling date and location were found to greatly influence soil fauna community and decomposition processes. The results give no indication of ecologically relevant adverse effects of antifungal GM wheat on the composition and the activity of the soil fauna community.

Two independent food choice experiments were conducted in the laboratory to study the effects of four transgenic and five non‐GM fungicidal wheat varieties on the food selection behaviour of the woodlouse Porcellio scaber. In general, woodlice did not avoid GM wheat as a food source and we detected no adverse effects of GM wheat on the non‐target P. scaber. Moreover, we found a food preference of the woodlouse for one of the four GM varieties, Pm3b1, but not for the closely related GM Pm3b2 or for their non‐GM isolines. We assume either a pleiotropic effect like lower lignin content or more suitable leaf litter coverage by microorganisms that may cause this preference and thus increasing palatability or digestibility. We discuss that this effect is ecologically not relevant.

Abstract:Since the first introduction of genetically engineered (GE) plants, one of the major concerns has been their potential effects on non-target organisms and ecosystem services. We focused in this study on the earthworm species Lumbricus terrestris as important ecosystem engineer and studied its performance when feeding on GE antifungal wheat. We compared litter consumption, weight change and mortality of individuals feeding on GE wheat with either specific resistance against powdery mildew (Blumeria graminis) or unspecific resistance against fungi via chitinase and glucanase expression with individuals feeding on non-GE wheat or other conventional crops. We did not find detrimental direct or indirect effects of GE wheat on L. terrestris and overall L. terrrestris tended to cope even better with GE wheat varieties. Concluding from our experiment the transgene products do not harm the soil key species L. terrestris and ecosystem services like decomposition, organic matter turnover and nutrient cycling are unlikely to be affected detrimentally.