Agricultural studies of GM maize and the field experimental infrastructure of ECOGEN

Within the ECOGEN project, long-term field experiments with genetically modified maize, Zea mays L. were conducted to study agro-ecological effects on the soil fauna and agro-economic implications of the technology. Here, we describe the study-sites, experimental layout and results of agro-economic relevance. Experiments were conducted during 2002–2005 in Denmark (Foulum), northern France (Varois) and the Midi-Pyrenees region of southern France (Narbons). MON810 Bacillus thuringiensis (Bt)-varieties expressing the Cry1Ab protein, and a T25 glufosinate-ammonium (Basta) tolerant variety expressing the pat-gene encoding phosphinotrinacetyl-transferase were compared with near-isogenic non-Bt varieties, and conventional maize varieties. At Foulum, the maize was harvested for silage. There were no significant differences in yield between Bt-maize and a near-isogenic non-Bt variety, while a small difference in N-concentration of dry matter was detected in 1 year in a range of a measured quality parameters. Similar yield and quality were found in ploughed and reduced tillage treatments in all varieties. At Varois, the maize was harvested at ripeness and no significant differences in grain yield between Bt-maize and near-isogenic non-Bt varieties were found. These results were expected, as only Narbons harbours significant corn-borer populations. At Narbons, the number of Sesamia and Ostrinia corn-borer larvae were significantly lower in the Bt-maize than in a near-isogenic non-Bt variety and for Sesamia even less than in conventional varieties sprayed with pesticides to control corn-borer infestation. Here, Bt-maize produced a higher grain yield and grain size than a near-isogenic non-Bt variety or allowed a significant reduction in pesticide use. Concentrations of Cry1Ab in the Bt-varieties were sufficient to effectively control corn-borer larvae. In soil, Cry1Ab was close to the limit of detection and the protein did not accumulate in the soil year on year.     

Evaluation of effects of transgenic Bt maize on microarthropods in a European multi-site experiment

The effects of maize expressing the Bacillus thuringiensis Cry1Ab protein (Bt maize) on soil microarthropods were assessed in the field at four European locations (two in Denmark and two in France) that differ in their climatic conditions or soil properties. Each site was considered as a separate experiment, with separate statistical comparison. Effects of farming practices using Bt maize were compared with conventional farming practices using near-isogenic non-Bt maize and also (at some of the sites) other conventional varieties. Furthermore, at one field site (Foulum, Denmark), the effects of Bt crops were studied in both conventional tillage and reduced tillage contexts. At another field site (Askov, Denmark), Bt maize effects were also compared to the effects of the chemical insecticide dimethoate. Moreover, at three of the field sites (all except Narbons, France), the possibility of a localised Bt effect around the rhizosphere compared to the bulk soil was assessed by sampling within and between maize rows. There were some significant negative effects of Bt maize on microarthropods in soils with a high clay content. Significant differences of the same magnitude also occurred between different conventional varieties of maize, but the effect of dimethoate appeared clearly greater than Bt effects. It is thus debatable if the Bt maize effect is an effect of the Bt toxin or just an effect of the maize variety. Based on the results, it can be concluded that the effect of Bt maize on soil microarthropods was small and within the normal variation expected in conventional agricultural systems.     

Microbial and microfaunal community structure in cropping systems with genetically modified plants

Soils from field sites at Foulum (DK), Narbons (FR) and Varois (FR) planted with genetically modified maize expressing either the insecticidal Bacillus thuringiensis protein (Bt) or herbicide tolerance (HT), as described elsewhere in this volume, were analysed for nematodes, protozoa and microbial community structure. These analyses were mirrored in single-species testing and in mesocosm experiments, and were coordinated with field samples taken for microarthropods, enchytraeids and earthworms so allowing for cross-comparison and a better understanding of the results observed in the field. Over the first 2 years of the field experiments (in 2002 and 2003), the effect of Bt-maize was within the normal variation expected in these agricultural systems. Sampling in 2004 and 2005 was expanded to include the effects of tillage (i.e. reduced tillage versus conventional tillage) and also the use of HT-maize. Tillage had major effects regardless of soil type (Varois or Foulum), with reduced-tillage plots having a greater abundance of microfauna and a different microbial community structure (measured both by phospholipid fatty-acid analysis (PLFA) and by community-level physiological profiling (CLPP)) from conventionally tilled plots. Grass, as a contrasting cropping system to maize, also had an effect regardless of soil type and resulted in greater microfaunal abundance and an altered microbial community structure. Differences in crop management, which for the Bt-maize was removal of the insecticide used to control European corn borer and for HT-maize was a change in herbicide formulation, were only tested at single sites. There were differences in microbial community structure (CLPP but not PLFA) and sporadic increases in protozoan abundance under the Bt-crop management. The HT-maize cropping system, which covered a shorter period and only one site, showed little change from the conventional system other than an altered microbial community structure (as measured by PLFA only) at the final harvest. The Bt-trait had a minimal impact, with fewer amoebae at Foulum in May 2003, fewer nematodes at Foulum in May 2004 but more protozoa at Varois in October 2002 and an altered microbial community structure (PLFA) at Foulum in August 2005. These were not persistent effects and could not be distinguished from varietal effects. Based on the field evaluations of microfauna and microorganisms, we conclude that there were no soil ecological consequences for these communities associated with the use of Bt- or HT-maize in place of conventional varieties. Other land management options, such as tillage, crop type and pest management regime, had significantly larger effects on the biology of the soil than the type of maize grown.     

Adsorption and Desorption of Cry1Ab Proteins on Differently Textured Paddy Soils

In recent years, selected cry genes from Bacillus thuringiensis (Bt) encoding the production of Cry proteins (Bt toxins) have been engineered into crop plants (Bt-crops). Through the cultivation of Bt crops and the application of Bt pesticides, Cry proteins could be introduced into arable soils. The interaction between the proteins and soils was analyzed in this study to investigate the affinity of Cry proteins in paddy soil ecosystems. Four Paddy soils were selected to represent different soil textures. Cry proteins were spiked in soils, and the amount of protein adsorbed was measured over 24 h. Desorption of Cry1Ab proteins from paddy soils was performed by washing with sterile Milli-Q water (H₂O_MQ), and subsequently extracted with an extraction buffer. The paddy soils had a strong affinity for Cry1Ab proteins. Most of the Cry1Ab proteins added (> 98%) were rapidly adsorbed on the paddy soils tested. More Cry1Ab proteins were adsorbed on non-sterile soils than on sterile soils. Less than 2% of the adsorbed Cry1Ab proteins were desorbed using H₂O_MQ, while a considerable proportion of the adsorbed proteins could be desorbed with the buffer, ranging from 20% to 40%. The amount of proteins desorbed increased with the increases in the initial amount of Cry1Ab proteins added to the paddy soils. The concentration of Cry1Ab proteins desorbed from the paddy soils was higher for sterile soils than non-sterile ones. Our results indicate that Bt toxins released via the cultivation of Bt crops, the application of Bt pesticides can be adsorbed on paddy soils, and soil texture could impose an impact on the adsorption capability.     

Hierarchical classification of environmental factors and agricultural practices affecting soil fauna under cropping systems using Bt maize

The population dynamics of soil organisms under agricultural field conditions are influenced by many factors, such as pedology and climate, but also farming practices such as crop type, tillage and the use of pesticides. To assess the real effects of farming practices on soil organisms it is necessary to rank the influence of all of these parameters. Bt maize (Zea mays L.), as a crop recently introduced into farming practices, is a genetically modified maize with the Cry1Ab gene which produces a protein toxic to specific lepidopteran insect pests. To assess the effects of Bt maize on non-target soil organisms, we conducted research at a field site in Foulum (Denmark) with a loamy sand soil containing 6.4% organic matter. The study focused on populations of springtails (Collembola) and earthworms (Oligochaeta) from samples taken at the beginning and at the end of the maize crop-growing season during 2 consecutive years. Farming practices, soil parameters, the biological structure of soil communities, and the type and age of the crop at the time of sampling, were used as attributes to predict the total abundance of springtails and biomass of earthworms in general and the abundance or biomass for specific 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 built with data mining tools, such as regression trees that predict the value of a dependent variable from a set of independent variables. Regression trees were constructed with the data mining system M5′. The models were evaluated by qualitative and quantitative measures of performance and two models were selected for further interpretation: anecic worms and hemi-epiedaphic Collembola. The anecic worms (r²=0.83) showed preferences for less clay and more silt soil with medium pH but were not influenced directly by farming practices. The biomass of earthworms was greater in early autumn than in spring or late autumn. Biomass of hemi-epiedaphic Collembola (r²=0.59) increased at the end of the maize growing season, while higher organic matter content and pH tended to increase their biomass in spring. Greater abundance of Collembola was also noted in early autumn if the crop was non-Bt maize. The models assessed by this research did not find any effects of the Bt maize cropping system on functional groups of soil fauna.     

Responses by earthworms to reduced tillage in herbicide tolerant maize and Bt maize cropping systems

Genetically modified (GM) crops may affect earthworms either directly through the plant, its root exudates and litter, or indirectly through the agricultural management changes that are associated with GM plant production. In order to investigate such possible effects, we established two field studies of Bacillus thuringiensis (Bt) maize and a glufosinate ammonium tolerant maize and included a reduced tillage (RT) treatment and a conventional tillage (CT) treatment as examples of a likely concomitant change in the agricultural practise. At a French study site at Varois, (Bourgogne), a field grown with the Bt-toxin producing transgenic maize line MON810 was studied for 1 year. At a Danish study site, Foulum (Jutland), 1 year of Bt maize was followed by 2 years of herbicide tolerant (HT) maize. At the French study site, the most prominent effects observed were due to the tillage method where RT significantly reduced the earthworm populations to levels about half of CT. At the Danish study site effects of CT complied with known reduction of anecic earthworms due to this technique and likewise effects of RT were observed for endogeic earthworms. Earthworm populations were diminished with the HT crop, probably due to exposure to the herbicide Basta^® during the two consecutive autumn seasons. This study confirms the importance of including the tillage techniques and pesticide usage when evaluating the environmental effects of new agricultural technologies.     

Effects of Bt-maize material on the life cycle of the land snail Cantareus aspersus

Insect resistant Bt-maize (MON 810) expresses active Cry1Ab endotoxin derived from Bacillus thuringiensis (Bt). Snails constitute non-target soil species potentially exposed to Bt-toxin through consumption of plant material and soil in fields where transgenic plants have been grown. We studied the effect of the Cry1Ab toxin on survival, growth and egg hatchability of the snail Cantareus aspersus. From the age of 4 to 88 weeks, snails were fed either powdered Bt-maize or non-Bt-maize and exposed to soil samples collected after harvesting either the Bt-maize or non-Bt-maize. We applied four treatments: non-Bt soil + non-Bt-maize (MM); Bt soil + Bt-maize (BB), non-Bt soil + Bt-maize (MB), Bt soil + non-Bt-maize (BM). Eggs laid by snails not exposed to Bt-toxin were also exposed to the two types of soils (Bt and non-Bt soil).At the end of growth (47 weeks of exposure), snails exposed to Bt-toxin in food and soil (BB) had a growth coefficient (GC) 25% lower than unexposed snails (MM). After the first period of reproduction (68 weeks) a significant difference remained for body mass GC between the BB and MM treatments. Differences in body mass were not significant at the end of exposure (88 weeks). For snails not previously exposed to Bt material, hatchability of eggs was similar in the soils tested. The outcome of the experiments indicates that, in growing snails, long-term exposure is needed to reveal an effect of Bt-maize. The hazard analysis of Bt-maize which we performed, based on a worst-case scenario, i.e. snails having no food choice, should now be complemented by other simple measurements, e.g. food intake, to understand the underlying mechanisms involved.     

Fate and effects of insect-resistant Bt crops in soil ecosystems

Recent applications of biotechnology, especially genetic engineering, have revolutionized crop improvement and increased the availability of valuable new traits. A current example is the use of the insecticidal Cry proteins from the bacterium, Bacillus thuringiensis (Bt), to improve crops, known as Bt crops, by reducing injury from various crop pests. The adoption of genetically modified (GM) crops has increased dramatically in the last 11 years. However, the introduction of GM plants into agricultural ecosystems has raised a number of questions, including the ecological impact of these plants on soil ecosystems. Crop residues are the primary source of carbon in soil, and root exudates govern which organisms reside in the rhizosphere. Therefore, any change to the quality of crop residues and rhizosphere inputs could modify the dynamics of the composition and activity of organisms in soil. Insect-resistant Bt crops have the potential to change the microbial dynamics, biodiversity, and essential ecosystem functions in soil, because they usually produce insecticidal Cry proteins through all parts of the plant. It is crucial that risk assessment studies on the commercial use of Bt crops consider the impacts on organisms in soil. In general, few or no toxic effects of Cry proteins on woodlice, collembolans, mites, earthworms, nematodes, protozoa, and the activity of various enzymes in soil have been reported. Although some effects, ranging from no effect to minor and significant effects, of Bt plants on microbial communities in soil have been reported, using both culturing and molecular techniques, they were mostly the result of differences in geography, temperature, plant variety, and soil type and, in general, were transient and not related to the presence of the Cry proteins. The respiration (i.e., CO₂ evolution) of soils cultivated with Bt maize or amended with biomass of Bt maize and other Bt crops was generally lower than from soils cultivated with or amended with biomass of the respective non-Bt isolines, which may have been a result of differences in chemical composition (e.g., the content of starch, soluble N, proteins, carbohydrates, lignin) between Bt plants and their near-isogenic counterparts. Laboratory and field studies have shown differences in the persistence of the Cry proteins in soil, which appear to be the result primarily of differences in microbial activity, which, in turn, is dependent on soil type (e.g., pH, clay mineral composition, other physicochemical characteristics), season (e.g., temperature, water tension), crop species (e.g., chemical composition, C:N ratio, plant part), crop management practices (e.g., till vs. no-till), and other environmental factors that vary with location and climate zones. This review discusses the available data on the effects of Cry proteins on below-ground organisms, the fate of these proteins in soil, the techniques and indicators that are available to study these aspects, and future directions.     

Decomposition processes under Bt (Bacillus thuringiensis) maize: Results of a multi-site experiment

The effects of maize expressing the Bacillus thuringiensis Cry1Ab protein (Bt maize) on decomposition processes under three different European climatic conditions were assessed in the field. Farming practices using Bt maize were compared with conventional farming practices using near-isogenic non-Bt maize lines under realistic agricultural practices. The litter-bag method was used to study litter decomposition and nitrogen mineralization dynamics of wheat straw. After 4 months incubation in the field, decomposition and mineralization were mainly influenced by climatic conditions with no negative effect of the Bt toxin on decomposition processes.     

Earthworm populations in a northern U.S. Cornbelt soil are not affected by long-term cultivation of Bt maize expressing Cry1Ab and Cry3Bb1 proteins

Earthworms, which play a key role in biogeochemical processes in soil ecosystems, could be negatively affected by the cultivation of transgenic Bt crops. Studies to date have found few effects of Bt maize on earthworm species. If adverse effects occur, they are likely to be chronic or sub-lethal and expressed over large spatial and temporal scales. Our objective in the present study was to investigate potential effects on earthworm populations in soil cultivated with Bt maize in a large multiple-year field study. We surveyed the earthworm populations in 0.16-ha experimental field plots of two varieties of Cry1Ab Bt maize, one variety of Cry3Bb1 Bt maize, and three non-transgenic control varieties cultivated for four years. Four earthworm species were found in our sample: Aporrectodea caliginosa, Aporrectodea trapezoides, Aporrectodea tuberculata (collectively, the A. caliginosa species complex), and Lumbricus terrestris. We found no significant differences in the biomass of juveniles and adults for all four species between Bt and non-Bt maize varieties. From this and previous studies, we conclude that the effects of Cry1Ab and Cry3Bb1 Bt maize on the A. caliginosa species complex and L. terrestris are small. Nonetheless, general conclusions about the effects of Bt maize on earthworm populations are not warranted due to the small number of species tested. In future laboratory studies, earthworm species should be selected according to their association with a Bt crop and the impact of that species to valued soil ecosystem processes.     

The Maximum Incremental Social Tolerable Irreversible Costs (MISTICs) and other benefits and costs of introducing transgenic maize in the EU-15

The decision to release a new transgenic crop variety for planting in the European Union (EU) is a decision under irreversibility and uncertainty. We use a real option model to assess the ex-ante incremental benefits and costs of the decision to release Bt maize and HT maize in the EU-15 member states. The analysis uses Eurostat data for modelling the benefits and costs of non-transgenic maize using partial equilibrium models. The farm-level benefits and costs of Bt maize and HT maize are derived from field trials conducted within the EU-funded ECOGEN project in combination with secondary data sources. Adoption curves, hurdle rates and Maximum Incremental Social Tolerable Irreversible Costs (MISTICs) are calculated at country level for selected EU-15 member states. In general, the results show that the MISTICs on a per capita level are very small confirming previous results calculated in values for the year 1995. The MISTICs per farm are much larger. This indicates a problem for decision makers.     

Earthworms of different functional groups affect the fate of the Bt-toxin Cry1Ab from transgenic maize in soil

The fate of the insecticidal Cry1Ab protein from crop residues (leaves and roots) of the transgenic maize variety MON810 was studied in the presence and absence of two earthworm species (Lumbricus terrestris, Aporrectodea caliginosa; separate incubations) in soil microcosms. The recombinant Cry1Ab protein was quantified using a highly sensitive ELISA. Control microcosms received corresponding non-transgenic plant material. All earthworms survived in the microcosms over a period of 5 weeks, irrespective of whether they received MON810 or non-transgenic plant material. Weight loss was observed for both earthworm species, independent of the plant material or transgenic modification. A strong decline of immunoreactive Cry1Ab in plant residues (mean initial concentration approx. 5000 ng g⁻¹) of MON810 was observed in all treatments, but in microcosms with earthworms this decline was significantly higher with less than 10% of the initial Cry1Ab concentration remaining after 5 weeks. Cry1Ab concentrations in casts were only 0.1% of those found in remaining plant material of the respective microcosms. No immunoreactive Cry1Ab proteins were found in earthworm tissues (threshold of detection: 0.58 ng g⁻¹ fresh weight). No further decline was found for Cry1Ab concentrations in casts of A. caliginosa during a subsequent period of 3 months of incubation in bulk soil (<0.1 ng g⁻¹) after removal of the earthworms from the microcosms, while in casts of L. terrestris the concentration decreased from 0.4 to below 0.1 ng g⁻¹. In conclusion, this study demonstrates that earthworms enhance the decline of immunoreactive Cry1Ab proteins from maize residues.     

Exposure and effects assessments of Bt-maize on non-target organisms (gastropods, microarthropods, mycorrhizal fungi) in microcosms

Potential differences between Bt-maize (MEB307 expressing the insecticidal Cry1Ab protein) and a near-isogenic non-Bt variety (Monumental) in their influence on the garden snail (Helix aspersa), soil microarthropods (Collembola, Actinedida, Acaridida, Gamasida and Oribatida) and mycorrhizal fungi were studied. Growing snails were caged in microcosms allowing the development of Bt or non-Bt-maize (Zea mays L.) on a sandy loam soil. After 3 months exposure, survival and growth of snails were similar in both treatments. Cry1Ab protein was detected in the Bt-maize leaves (22–42.2 μg Bt protein g⁻¹ dry wt), in the snail tissues (0.04–0.11 μg Bt-protein g⁻¹ dry wt) and in their faeces (0.034–5 μg Bt-protein g⁻¹ dry wt). Total soil microarthropod abundance and diversity were similar between control (non-Bt-maize) and the genetically modified (GM) Bt-maize microcosms. The mycorrhizal colonization of roots did not differ between Bt and non-Bt-maize (frequency of mycorrhizal roots was 88.7% and 83.3% respectively). The mycorrhizal infectivity of soils, expressed as MI₅₀ (minimum soil dry weight required to colonize 50% of plants) was measured using red clover. MI₅₀ was similar for soils where Bt or non-Bt-maize was cultivated for 4 months. The detection of Cry1Ab protein in the viscera and faeces of H. aspersa exposed to Bt-maize indicates that snails contribute to the transfer of the Bt-protein from plant to soil or snail predators. This may constitute an alternative route of exposure for Bt-protein in soil, but this was without a negative influence on mycorrhizal fungi or microarthropods. Results showed that Bt-maize was not toxic for the selected non-target species exposed for 3 or 4 months. The microcosms and analyses used in this study represent new methods for assessing effects of chronic exposure to GM plants of several diverse, yet ecologically and temporally associated species. As the soil organisms we studied can also be used in standardized ecotoxicological tests (XP X31-205-2 for mycorrhizal fungi, ISO 11267 for Collembola and ISO 15952 for snails), microcosm exposures represent a way to link laboratory and field methods for the ecotoxicological evaluation of GM plants.     

Are survival and reproduction of Enchytraeus albidus (Annelida: Enchytraeidae) at risk by feeding on Bt-maize litter?

Enchytraeids are saprophagous soil organisms, appearing in high abundances and contributing to ecological processes within the soil. For decades they have been used as model species for biological research. In the framework of research on genetically modified plants, however, they have not been considered to date. Following the ISO/DIS guideline, survival and reproduction of Enchytraeus albidus, fed with diets containing Bt-maize (N4640Bt Cry1Ab, DKC5143Bt Cry3Bb1) leaf material were analysed. For comparison, diets with the corresponding untransformed near-isolines (N4640, DKC5143) were examined. Additionally a high quality control diet (oat flakes) was included. Survival and reproduction showed no significant differences between the Cry3Bb1 treatment and the treatment with the untransformed counterpart. For the Cry1Ab treatment survival was significantly higher than for the treatment with the corresponding near-isoline. In contrast, reproduction was significantly lower for the Cry1Ab treatment compared to that for the isoline. For the Cry3Bb1 treatment, no effect was shown on survival or reproduction. For the Cry1Ab variety and its untransformed counterpart, a contrasting result was detected, which is unlikely to be caused by the Bt-protein but rather by differences in other plant components. Overall survival and reproduction were highest for the control.     

Cry1Ab Adsorption and Transport in Humic Acid-Coated Geological Formation of Alumino-Silica Clays

Genetically modified agricultural products have been introduced to increase food supply by enhancing their resistance to pests and diseases, along with easily adapting to environmental conditions. Due to the modification of DNA, public objections are prevalent, including concerns on the impact on the ecosystem. In this research, adsorption and transport of Cry1Ab, a toxin exuded by the transgenic Bt maize in alumino-silica clays, were evaluated in laboratory columns under steady-state flow conditions. Since Cry1Ab fate and transport were very responsive to animal waste field applications, during which humic acids were released, Cry1Ab adsorption and transport in humic acid-coated alumino-silica clays were also investigated. Cry1Ab breakthrough curves were simulated using the convection-dispersion transport models. It was discovered that the humic acid coating increased Cry1Ab deposition during the transport. Based on analysis of the breakthrough curves, adsorption isotherms of Cry1Ab in alumino-silica clays were obtained and compared with those of batch experiments. The humic acid coating changed the bonding energy between Cry1Ab and the adsorption receptor sites on alumino-silica clay surfaces, thereby changing Cry1Ab partition between the aqueous phase and the solid phase.     

Release of the recombinant Cry3Bb1 protein of Bt maize MON88017 into field soil and detection of effects on the diversity of rhizosphere bacteria

A three-year experimental field study with a genetically engineered Bt maize (event MON88017) and three conventionally bred cultivars was conducted to quantify the recombinant Cry3Bb1 protein released into soil and detect effects on the diversity of soil bacteria. Protein extraction and an enzyme-linked immunosorbent assay (ELISA) allowed a threshold detection of 0.01 ng Cry3Bb1 g^?1 soil. The maximum amount found in field plots with Bt maize was 1.0 ng Cry3Bb1 g^?1 rhizosphere soil. Average concentrations during the growing seasons varied between years from 0.07 to 0.29 ng g^?1. No accumulation of Cry3Bb1 in soil occurred over the three growing seasons. Four weeks after harvest, the major Cry3Bb1 reservoirs on the field were the remaining root stubbles, but their Cry3Bb1 concentration declined by 98.30–99.99% in the following seven months. During the three consecutive years of study there were never significant differences between the rhizosphere bacterial community structure of the Bt maize and the other cultivars, as detected by cultivation independent profiling of PCR-amplified 16S rRNA genes. The low concentrations of soil extractable Cry3Bb1, its degradation in decaying roots, and the lack of effects on rhizosphere bacteria give no indications of adverse effects of MON88017 cultivation on soil ecology.     

Effects of conventionally bred and <Emphasis Type="BoldItalic">Bacillus thuringiensis</Emphasis> (<Emphasis Type="BoldItalic">Bt</Emphasis>) maize varieties on soil microbial biomass and activity

Genetically modified (GM) maize containing genes from the soil bacterium Bacillus thuringiensis (Bt) was cultivated on 29% of the total maize production area worldwide in 2009. Most studies to date compare Bt-maize varieties with their near isogenic lines; however, there is little information on the variability of conventional maize breeding lines and how the effects of Bt varieties are ranked within. In our study on the potential risks of Bt-maize varieties, we analyzed tissue quality and compared the effects of ten conventional and GM maize varieties on soil microbiological properties in a replicated climate chamber experiment. All maize varieties were cultivated twice in the same soil microcosm. Shoot yields and soluble C in leaf tissue of Bt varieties were higher than the ones of non-Bt. Soil dehydrogenase activity was reduced by 5% under Bt varieties compared to non-Bt, while most of the other soil microbial properties (soil microbial biomass, basal respiration) showed no significant differences between Bt and non-Bt varieties. The leaves and roots of one Bt variety were decomposed to a greater extent than the ones of its near isogenic line; the conventional breeding lines also showed higher values. Changes in crop and soil parameters were found when comparing the first and the second crops, but the effects of repeated cropping were the same for all tested varieties. For the studied parameters, the variation among non-Bt-maize varieties was similar to the difference between Bt and non-Bt varieties.     

南非冬闲期表施和混施入Bt层玉米落叶和Cry1Ab蛋白的分解研究

Unintended effects of genetic modification on chemical composition of Bt maize leaf litter may have impacts on its decomposition. In most agricultural systems in South Africa, maize litter is either left on the soil surface or incorporated into the soil during tillage. A litterbag experiment, using leaf litter of three maize hybrids （DKC80-12B, DKC80-10 and DKC6-125）, was carried out at the University of Fort Hare Research Farm, South Africa, to determine the effects of genetic modification on decomposition of maize leaf litter when left on the soil surface under field conditions between July and November, the normal fallow period, in 2008. Another litterbag experiment was conducted at the University of Fort Hare Research Farm and Zanyokwe Irrigation Scheme, South Africa, using leaf ~itter of two maize hybrids genetically modified with the erylAb gene （MONS10）, DKC75-15B and PAN6Q-3OSB, and their corresponding near isolines, CRN3505 and PAN6Q-121. The degradation of CrylAb protein in the litter, both surface-applied and soil-incorporated, was also investigated. Decomposition of Bt maize litter was similar to that of non-Bt maize litter both when applied on the surface and when incorporated into soil. Soil-incorporated litter, as well as its CrylAb protein, decomposed faster than that applied on the surface. The leaf litter C：N ratios of PAN6Q-308B and PAN6Q-121 were similar throughout the study, whereas those of DKC75-15B and CRN3505 declined by similar amounts during a 12-week period. These findings suggested that decomposition of leaf litter of Bt maize, with the MON810 event, was not affected by maize genetic modification, and that the CrylAb protein broke down together with plant leaf litter during the winter fallow regardless of whether the litter was applied on the soil surface or incorporated into soil.     

Effects of physical and chemical properties of soils on adsorption of the insecticidal protein (Cry1Ab) from Bacillus thuringiensis at Cry1Ab protein concentrations relevant for experimental field sites

The adsorption of the insecticidal Cry1Ab protein of Bacillus thuringiensis (Bt) on Na-montmorillonite (M-Na) and soil clay fractions was studied. The aim of this study was not to find the adsorption capacity of the soils from the experimental field site, where Bt corn (MON810) was cultivated, but rather to characterize the adsorption behavior of the Cry1Ab protein at concentrations typically found at experimental field sites. In kinetic experiments, the Cry1Ab protein adsorbed rapidly (<60 min) on M-Na. As the concentration of M-Na was varied and the added Cry1Ab protein concentration was kept constant (20 and 45 ng ml⁻¹), the adsorption per unit weight of Cry1Ab protein decreased with increasing concentrations of M-Na. Adsorption of Cry1Ab protein on M-Na decreased as the pH value of the suspension increased. All adsorption isotherms could be described mathematically by a linear regression with the parameter k, the distribution coefficient, being the slope of the regression line. Although their mineralogical composition was nearly identical, the soil clay fractions showed different k values. The different k values were correlated with the physical and chemical properties of the soil clay fractions, such as the organic carbon content, the specific external surface area, and the electrokinetic charge of the external surfaces of the clays, as well as with the external surface charge density. An increase in the amount of soil organic matter, as well as an increase in the electrokinetic external surface charge of the soil clays, decreased the distribution coefficient k. An increase of the specific external surface areas of the soil clays resulted in a higher distribution coefficient k.Less than 10% of adsorbed Cry1Ab protein was reversibly adsorbed on the soil clays and, thus, desorbed. The desorption efficiency of distilled water was higher than that of a solution of CaCl₂ (2.25 mmol) and of dissolved organic carbon (50 mg C l⁻¹).     

Decomposition of Bacillus thuringiensis (Bt) transgenic rice residues (straw and roots) in paddy fields

Background, aim, and scope  

Genetic modification of commercial crops may affect their decomposition and nutrient cycling processes in agricultural ecosystems. Intensive rice cultivation under partially submerged conditions (paddy rice) is an important and widespread cropping system, particularly in the tropics, yet there is little data on the decomposition of Bt rice residue under field conditions. We investigated straw and root decomposition of rice modified to express the Cry1Ab protein of Bacillus thuringiensis (Bt) to kill lepidopteran pests, compared with a parental non-Bt isoline. The objective of this study was to assess the possible impacts of cry gene transformation of rice on residue decomposition under intensive rice cultivation with long period of submergence.