Effect Of Bt Transgenic Rice (KMD) On Microbial Activities And Diversity In Paddy Soil And Rhizosphere

Little is known about the potential impacts of the environmental release of Bt transgenic rice on soil microbiota and their processes. In this study, numbers of culturable microorganisms, selected enzyme activities and bacterial community composition in soil amended with Bt transgenic rice straw and rhizosphere of Bt transgenic rice cultivar KMD1 were compared to its isogenic, non-transgenic cultivar Xiushui 11.Results showed that there were only some occasional significant differences in the number of aerobic bacteria, actinomycetes, fungi, anaerobic fermentative bacteria, denitrifying bacteria, hydrogen-producing acetogenic bacteria, and methanogenic bacteria between flooded soil amended with Bt-transgenic rice straw (BTS) and with the non-Bt parental rice straw (NBTS) at the booting stage during the early stages of incubation. Significant differences were found in soil dehydrogenase activities after d 7 to 49 of incubation. There were no apparent effects of Bt-transgenic rice straw on the dynamics of soil neutral phosphatase activity. Results from DGGE analysis based on 16S rRNA gene amplification revealed that there were transient differences in the bacterial community composition between soil amended with BTS and NBTS over the soil incubation.Few significant differences in protease, phosphatase and cellulase activities between soil amended with BTS and NBTS at the maturing stage were found. None of them were persistent. However, significant differences in dehydrogenase, methanogenic, hydrogen-producing and anaerobic respiration activities between soil supplemented with BTS and NBTS were observed over the course of soil incubation. Activities of dehydrogenase, methanogensis and anaerobic respiration in soil with BTS were considerably lower from sample day 7 to day 56, but higher after sample day 56.In comparison, hydrogen-producing activities in soil with BTS were significantly lower than those in soil with NBTS after sample day 56.There were no significant differences in the CPUs of culturable bacteria, actinomycetes, fungi and in the protease, phosphatase, urease and respiration activities between soil (60% of water holding capacity) amended with BTS and NBTS at the maturing stage. Few transient differences were observed in the number of ammonifying, nitrogen-fixatiing and cellulose-decomposing bacteria over the incubation time. Dehydrogenase activities in soil amended with BTS were significantly higher than those with NBTS. However, the apparent differences in dehydrogenase activity disappeared after 63 days' incubation.Microbial abundance, activity and community composition were assessed at 4 stages in the rice developmental cycle. There were no statistically significant differences between Bt transgenic rice and non-Bt rice in the total numbers of nitrifying bacteria, fungi or actinomycetes in the rhizosphere over the crop development. The number of aerobic bacteria was significantly higher in the rhizosphere of Bt transgenic rice than that of non-Bt parental rice at the seedling stage. Significant differences in the number of spore-forming bacteria of rhizosphere between Bt and non-Bt rice were found at the seedling, heading and maturing stages. There were no significant differences in phosphatase activity, dehydrogenase activity, urease activity, or CO2 production in rhizosphere soils between Bt and non-Bt rice at all tested stages. Significant differences in CH4 producing activity between Bt-rice rhizosphere soil and non-Bt parental rice rhizosphere soil were observed at the seedling, booting and heading stages, however, there was no significant difference at the maturing stage. The analyses of DGGE fingerprints showed that there were apparent differences in the composition of the bacteria and eukaryotic microbial community between non-planted soil, flooded rhizosphere soil, and non-flooded rhizosphere soil, but there were few differences in the composition of the bacteria community between rhizosphere soil of Bt and non-Bt rice at the seedling, booting, heading and maturing stages in the...