Abstract:

Objective: Monitoring of biosafety of adult transgenic trees of Populus alba ×P. berolinensis in a field trial for successive years and assessment of possible ecological risks caused by transgenic P. alba ×P. berolinensis were conducted to provide a basis for evaluating the biosafety of transgenic poplar and soil environment of transgenic plants. Method: 11 years old transgenic trees of P. alba ×P. berolinensis, non-transgenic P. alba ×P. berolinensis(control), weeds and soil in the field trial established in Fangshan District of Beijing, leaves of seedlings under the roadside poplar beside the trial, and Kanamycin-resistant strain screened out from the soil were used for PCR amplification to detect stability and horizontal transfer potential of JERF 36 gene. The dilution plate method was used to quantify the soil microbes (including bacteria, actinomycetes and fungi) respectively for the 9-11 years old transgenic and non-transgenic poplars in the trial. Result: The exogenous gene, JERF 36 , was stable in the transgenic poplar, and no target gene fragment was detected in the weeds and soil in the trial, the roadside poplar trees, and the Kanamycin-resistant strain. There was no significant difference in the total number of microorganisms in the soil between the 9-11 years old transgenic and non-transgenic poplar trees. There were slight differences in the number of soil microorganisms of transgenic and the non-transgenic poplar trees among different years, with the same rank from June to August in 9 years old > 10 years old >11 years old. The number of bacteria, fungi and actinomycetes had no significant difference between transgenic and the non-transgenic poplar trees, with the same change tendency from 9 to 11 years old, i.e. rising first followed by falling in growing season. The total amount of microbial peaked in July and August, significantly higher than other months, and the number of bacteria and actinomycetes both peaked in August, while the fungi peaked in August (9-10 years old) or July (11 years old). Proportions of the three types of microorganisms in the soil of transgenic poplar trees were similar to that of the non-transgenic trees for all the years, in an order from the highest to the lowest of bacteria, actinomycetes and fungi. The proportions of the three types of microorganisms were slightly different among each other in different years, with no sudden increase or sharp decrease, indicating that the balance among the main microbial types was not broken by the transgenic poplar trees. Environmental changes such as differences in rainfall might be the main reasons for the differences in the quantity of microorganisms in different years. Conclusion: The exogenous gene stably exists in the transgenic trees of Populus alba ×P. berolinensis 11 years after planting, with no horizontal transfer to the surrounding environment, also no significant impact on the number or variety balance of soil microorganisms. Environmental change may be the major influential factor for the quantity difference. The slight differences of microbial quantity between the transgenic and non-transgenic poplar trees needs further studies by considering environmental factors.

Key words: Populus alba × P. berolinensis, transgenic poplar, gene stability, soil microorganisms, horizontal gene transfer