Target and non-target effects of genetically modified trees

Uncertainties of realized benefits and the potential for environmental effects of genetically modified (GM) trees may comprise an obstacle for an environmentally safe deployment and social acceptance of such products. Through a series of studies I explored target and non-target effects of GM trees in an objective to increase our knowledge of both benefits and environmental effects of these products. In these studies I used two Populus hybrid lines, modified for altered lignin synthesis and Bacillus thuringiensis mediated insect resistance against Coleopteran insects. The studies range from bioassays and controlled microcosm studies in the greenhouse to studies using potted plants in the field and studies designed to address environmental effects of leaf litter from GM trees on aquatic ecosystems. Results show a strong support of realized benefits in terms of resistance effectiveness of the insect resistant trees. Damage levels of relevant herbivorous insects were reduced both in the greenhouse and in the field. However, it is also indicated that benefits in term of growth may be conditionally determined and depend on environmental context, herbivore loads and interactions with non-target herbivores. In this respect, unexpected changes in innate resistance as shown here may be of importance for realized benefits. It is further shown how leaf litter from GM trees may cause effects that cross ecosystem boundaries. For example, lignin modification affected leaf litter quality and the decomposition of litter from one lignin modified line was significantly decreased. Further, leaf litter from insect resistant trees did not affect litter quality but did cause significant changes in the community composition of insects colonizing the litter. Given the signs of environmental control over realized benefits I believe that the field performance of these products needs further confirmation. Studies designed to target different aspects of environmental variability that may occur throughout the lifetime of a trees may be needed for a proper judgment of realized benefits. In such assessments effects on non-target organisms and environments need to be considered and the cause of environmental effects explained. Eventually assessments of GM trees need to relate costs and risks of these products to the costs associated with alternative management measures