Effects of genetically modified Bt maize on earthworms and Collembola functional groups.
Debeljak, Marko*,1, Demsar, Damjan1, Cortet, Jérôme 2, Dzeroski, Saso1, Krogh, Paul Henning 3, 1 Jozef Stefan Institute, Ljubljana, Slovenia2 Institut Mediterraneen d'Ecologie et Paleoecologie, Aix en Provence, France3 National Environmental Research Institute, Silkeborg, Denmark
ABSTRACT- The population dynamics of soil organisms under agricultural field conditions are influenced by many factors, including farming practices such as crop type, tillage and pesticides. It is thus necessary to rank the influence of all of these parameters to assess the real effects of farming practices on soil organisms. Bt maize (Zea mays L.), as a crop recently introduced in to farming practice, is a genetically modified maize with the cry1Ab gene which produces a protein considered to be toxic to specific lepidopteran insect pests. In order to assess the effects of Bt maize on non target soil organisms we conducted research with real crop systems. We focused on populations of springtails (Order Collembola) and earthworms (Class Oligochaeta) sampled at one site during two consecutive years. Samples were taken at the beginning and at the end of the maize crop-growing season. The study site was located in Foulum (Denmark) with a loamy sand soil containing 6.4% organic matter. Farming practices, soil parameters, the biological structure of soil communities, and the type and age of the crop at the sampling dates, were used as attributes to predict the total biomass of springtails and earthworms in general, and their biomass per particular functional groups (epigeic, endogeic and anecic groups for earthworms, and eu-, eu to hemi-, hemi-, hemi to epi- and epiedaphic groups for Collembola). Predictive models were build with data mining tools, i.e., regression trees that predict the value of a dependent variable from the set of values of independent variables. Regression trees were constructed with the data mining system M5. The models were evaluated by qualitative and quantitative measures of performance. The total earthworms (r2=0.73) as well as anecic worms (r2=0.83) showed preferences for less clay and more silt soil with medium pH, while they were not influenced directly by farming practices. The biomass of earthworms was greater in early autumn as compared to spring or late autumn. Hemi-epiedaphic collembolan (r2=0.83) were increased at the end of the maize growing season, while higher organic matter content and higher pH tended to increase their biomass also in spring. A greater abundance of collembolan was also noted in early autumn if the crop was non-Bt maize.
Key words: genetically modified Bt maize, soil functional groups, springtails and earthworms, data mining
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