Effects Of Long-term Planting Of Transgenic Cotton On Soil Quality

With the increasing variety and quantity of genetically modified crops,their potential ecological risks have attracted much attention.This study regard salt-tolerant cotton "013018",disease-resistant cotton "HN6",drought-tolerant cotton "013011",transgenic(Bt+Cp TI)cotton "SGK321" and their parental conventional cotton "Qinben","Zhong 24","TH2" and "Shiyuan 321" as research project.The effects of long-term planting of transgenic cotton on soil physical and chemical properties,enzyme activities and bacterial community structure were analyzed at seedling stage,budding stage,flowering and boll-setting stages and boll opening stage.It provided technical support for soil environmental safety assessment of genetically modified crops.The main results are as follows:(1)There were no significant differences in soil p H,moisture,total nitrogen,total phosphorus,organic matter content between the four transgenic cotton varieties and their parents' conventional cotton at the same growth stage(P>0.05).However,there was no significant difference in available phosphorus content between transgenic cotton 013018 and 0130111 in four growth stages and their parents' conventional cotton(P>0.05).The content of available phosphorus in soil of transgenic cotton HN6 and SGK321 was significantly lower than that of their parents' conventional cotton only at flowering and boll-setting stage(P<0.05).The content of ammonium nitrogen in soil of four transgenic cotton varieties was significantly lower than that of their parents' conventional cotton at seedling stage,flowering and boll-setting stages or boll opening stage(P<0.05).and the nitrate nitrogen in soil of four transgenic cotton varieties was significantly different with their parents only at seedling stage and budding stage(P<0.05).During different growth stages,soil total nitrogen and phosphorus contents were significantly different between transgenic cotton 013018,HN6,013011 and conventional cotton TH2(P<0.05).Soil p H,water content,organic matter,available phosphorus,ammonium nitrogen and nitrate nitrogen were significantly different between the four transgenic cotton varieties and their parents' conventional cotton(P<0.05).(2)At the same growth period,there was no significant difference in soil catalase activity between the four transgenic cotton varieties and their parents' conventional cotton varieties(P>0.05).There was no significant difference in soil alkaline phosphatase activity between the other three transgenic cottons and their parents' conventional cotton except SGK321(P>0.05).There was no significant difference in soil urease activity between transgenic cotton 013018 and 013011 and their parents' conventional cotton(P>0.05),but the soil urease activity of transgenic cotton HN6 was significantly higher than that of its parents' conventional cotton at bud and boll stages(P<0.05).The soil urease activity of transgenic cotton SGK321 was significantly higher than that of conventional cotton at four growth stages(P<0.05).During different growth stages,soil urease activities were significantly different between four transgenic cotton and their parents' conventional cotton(P<0.05).Alkaline phosphatase activities were significantly different between transgenic cotton 013018,013011 and SGK321(P<0.05).However,catalase activities were significantly different between transgenic cotton 013018,HN6 and SGK321(P>0.05).(3)Through correlation analysis and two-factor analysis of soil physical and chemical properties and enzyme activity,we found that different varieties and different growth stages were the main factors affecting soil physical and chemical properties and enzyme activity compared with transgenic cotton planting;However,compared with transgenic cotton planting,cotton growth stages has more significant effects on soil physical and chemical properties and enzyme activities.(4)We used high-throughput sequencing technology to analyze the community structure of soil bacteria.It was found that Proteobacteria,Actinobacteria and Acidobacteria were the dominant bacterial phyla in the soil bacterial community of four transgenic cotton and their parents' conventional cotton.By analyzing the abundance of dominant phylum,we found that there was no significant difference in the abundance of Proteobacteria among transgenic cotton 013018,013011 and parents' conventional cotton(P>0.05).The abundances of Actinobacteria and Acidobacteria in soils of four transgenic cotton varieties were significantly different with parents' conventional cotton varieties at seedling stage,budding stage or flowering and boll-setting stages(P<0.05).And during different growth stages,there were significant differences in soil Actinobacteria abundance among three transgenic cotton varieties(HN6,013011,SGK321)(P<0.05),the abundance of soil Acidobacteria in three transgenic cotton(013018,HN6,013011)and soil Proteobacteria in four transgenic cotton were also significantly different(P<0.05).LEf Se analysis showed that cotton growth stages were the main factor affecting soil bacterial community structure compared with transgenic cotton planting.The results showed that the cultivation of different varieties of transgenic cotton only changed the abundance of individual bacteria,but did not change the composition of soil bacterial community.In conclusion,compared with conventional cotton parents,long-term planting of transgenic cotton did not affect soil p H,water content,total nitrogen,total phosphorus,organic matter content and soil catalase activity,but significantly changed soil available nutrient content,soil urease and alkaline phosphatase activity at individual growth.It also did not change the species composition and quantity of soil bacterial community structure,but changed the abundance of individual bacterial phyla.Compared with transgenic cotton planting,the effect of cotton growth stages on soil quality is more significant.