Impact of transgenic birch with modified nitrogen metabolism on soil properties, microbial biomass and enzymes in 4-year study

Aims The potential adverse effects of transgenic plants on soil processes get less attention than their other environmental risks. Also, there has been virtually no relevant research in transgenic plants with improved nutrient use efficiency. Methods We investigated the effect of transgenic birch ( Betula pubescens ) plants expressing the glutamine synthetase GS1 gene from pine or the marker gus gene on soil properties in a long-term pot experiment under greenhouse and natural conditions. Activity of 11 enzymes and microbial biomass (MBC, MBN, MBP), which are indicators of soil quality, were analyzed at the end of each growing season after leaf fall, and physicochemical soil properties at the end of the experiment. Results Transgenic birch plants with the GS1 gene differed in growth rate, habit, and the content of C and N in leaf tissue. The nitrogen content in their soil increased significantly, while the content of potassium ions decreased, possibly to compensate for nitrogen reassimilated via glutamine synthetase. The observed statistically significant differences in enzyme activities and microbial biomass were temporary and inconsistent, suggesting that transgenic birch plants had no harmful effects on soil microflora. Conclusion The birch plants with the neutral gus gene had a significantly weaker impact than those with the gene of nitrogen metabolism enzyme GS. In particular, GS plants showed the most stable (in 3 of 4 years) effect on nitrate reductase, an N-cycle enzyme. The obtained results may be important for assessing potential environmental risks associated with commercial cultivation of transgenic forest trees.