Effects Of Bt Maize On Soil Microbial Activity And Fertility

The breed and application of transgenic crops are important approaches to increase crop production and quality,for the advantages of high yield,good quality and resistance to adverse environments. As the potential safety for both food and environment of GMO are concerned recently,transgenic maize has been ready to be commercial released since the beginning of it in 1989.Transgenic Bt maize can release Bt protein into soil through root exudates, pollens, plant residues and straw decomposition, along with the field planting and straw back to the soil. Simultaneity, the agronomic characters and chemical constituents of maize plant can be changed because of the insertion of Bt gene. These differentia may both affect the soil activities and fertilities, resulting in changes of soil fertility quality.At present, a few research reports have been published to evaluate the effects of Bt maize on soil fertility quality. In order to study the effects of Bt maize on the ecological safety,especially the safety of soil ecosystem,the transgenic Bt maize MON810 and its parental non-transgenic maize were planted in field conditions for two years in 2008 and 2009.At different stages, such as seedling stage, jointing stage, bell mouthed stage, tasseling stage, silking stage, milky stage and straw returned, soil activities and fertilities were analyzed. Correlation was analyzed also,to investigate the potential ecological risk of Bt maize. The results are as follows:1.Results of soil activities showed that,the sucrase activity was significant higher in Bt maize soil, compared to non-Bt parental maize soil. However, an inconsistent trend existed in the whole growth period. There was no significant differences on soil protease activity, with a similar impact regularity. A diversification of effects on soil urease and acid phosphatase activity were engendered between Bt maize and non-Bt maize. After straw returned, soil sucrase and urease activities in soil of Bt maize were significant higher than that of non-Bt maize, but soil protease and acid phosphatase activities were opposite.2.According to the selected index of soil fertility,the effects of transgenic Bt maize and its parental non-Bt maize at different periods of growth were investigated. There were significant differences in the soil organic matter and available potassium,with inconsistent impact trend in two years. The soil available nitrogen and total phosphorus were reduced in some periods of maize growth. However, the soil slowly available potassium content was about 1100-1300mg·kg^-1 stability.3.Based on the measurements of soil activities,the correlation analysis showed that there was a positive correlation between the soil sucrase and acid phosphatase activity in soil of Bt maize, in conformity with its parental non-Bt maize. The highest correlation coefficient was 0.9763 in non-Bt maize in 2008, and the lowest 0.6948 in Bt maize in 2009. The relationship between soil urease and acid phosphatase activity reached extremely correlation level soil of non-Bt maize. There were no significant correlations between the other various enzymes.4.In the case of soil fertility index, there were different correlations between Bt maize and non-Bt maize. In soil of non-Bt maize, the relationship between soil organic matter and total nitrogen,available nitrogen, total phosphorus, available potassium reached negative level. There was positive level between soil total nitrogen and total phosphorus, available potassium, and the same as that between total phosphorus and available potassium. However, in soil of Bt maize, the relationship between available potassium and total nitrogen, phosphorus reached positive level, total nitrogen and potassium had the same relationship. The relationship between slowly available potassium and available nitrogen, available phosphorus reached extremely negative level. In addition, the planting and straw returning of Bt maize resulted in the reduction of the correlation variety between fertility factors, with less index reached extremely significant or significant level.5.Correlation analysis showed that there was weak Correlation between soil activity and fertility than that merely between soil activities or soil fertilities. This trend changed following the planting years. The correlation between soil activity and fertility was affected significantly in Bt maize soil, which could reach diametrically opposite results between some indicators.