Effects Of Transgenic Soybeans On The Rhizospheric Soil Microbial Communities And Their Diversity Indices Measurement

Soil microbial community plays important roles in land ecological system. Any minute change of the environmental factors could lead to the variation of the structural, genetic and functional diversities of soil microbial community. The approach to soil microbial community possesses a great potential significance. As regards such a hot issue as ecological safety of transgenic plants, this study, in combination with several methods, focuses on the effects of the transgenic soybeans planted in the rhizoboxes on the soil microbial communities.After going into the soil, the litter, residues and root exudates from transgenic soybeans will, in varying degrees, affect soil quality (including soil water-holding capacity, pH values, carbon&nitrogen content, metal element content, enzymatic activities and the structural, genetic and functional diversities of soil microbial community). In this experiment conducted in2010, two different soybean groups were planted in the rhizoboxes, i.e. Group A (with one recipient variety, Nannong88-1as CK-1, and its3transgenic lines OE-8, OE-7, RNAi-3), and Group B (containing another recipient variety, N2899as CK-2, and its3transgenic lines Gagal17-4, Gagal21-8, Gagal57). In comparison with those of CK, the variation in the soil physic-chemical properties and enzymatic activities was observed; in addition, by means of phospholipid fatty acid (PLFA) and Biolog analyses, the effects of the transgenic soybean on the structural and functional diversities of the rhizopheric soil microbial communities were also examined. The main results were as follows:1) The rhizospheric soil water-holding capacities of transgenic lines and their recipients were significantly different with genotype, growth period and transgenic line.2) The pH assay indicated that during the growth process, the H+accumulation effects imposed by Line Gagal17-4and Line Gagal57on their rhizospheric soils were significantly greater than those by Line Gagal21-8and Group A.3) During florescence stage, there was no significant difference in carbon and nitrogen contents between the rhizospheric soils of CKs and the corresponding transgenic lines. By the florescence stage, the root system of the transgenic lines of Group A assimilated more sulphur element than that of CK-1, causing the decline of sulphur content within their rhizospheric soils; but for Group B, the sulphur content within Line Gagal57rhizospheric soil was significantly raised compared with that of CK-2, implying that more probably, the assimilation power of sulphur element in soil by the transgenic soybean lines differed with growth period, genotype, assimilation manner or metabolic pathway. The assimilation ability of calcium element in soil by Line RNAi-3was much higher, whereas the root systems of Line Gagal57and Line Gagal21-8evolved a much lower assimilation power of Ba, Co, Fe, V and Zn.4) During florescence stage, there occurred no significant difference in the activities of both acid phosphatase and alkaline phosphatase between the rhizospheric soils of CKs and the corresponding transgenic lines. Neither significant effect appeared of the transgenic lines on the activities of invertase or FDA hydrolase within the rhizospheric soils. The urease activity determination implied that the proportions of nitrogen occurring in urea and NH4+form occupying total nitrogen content in the rhizospheric soils of Group B transgenic lines, were significantly higher than that of CK-2, with those of Group A exceeding those of Group B. The arylsulfatase activity determination suggested that before the florescence stage of Group A soybeans, the proportions of sulphur occurring in inorganic form in the rhizospheric soils of the transgenic lines, were significantly higher than that of CK-1, and much of inorganic sulphur had been absorbed better, leading to the proportions of organic sulphur in the rhizospheric soils of the transgenic lines to be mineralized by arylsulfatase dropping by florescence stage. This result illustrated that3transgenic lines (characteristic of enriching S-amino acids) in Group A physiologically proceeded an active sulphur amassment mainly before the florescence stage.5) As for PLFA contents with GP bacteria feature of overall bacteria and soil samples, Line OE-8in Group A got significantly higher than CK-1and Line Gagal17-4and Gagal57in Group B also significantly higher than CK-2. The PCAs of the single PLFA content showed that, at soybean florescence stage, the structure of the rhizospheric soil microbial community altered, with Line OE-7, Line RNAi-3,Line Gagal17-4and Line Gagal57in greater degrees compared with their CKs.6) Biolog results showed that in GP2, GN2, FF MicroPlates and EcoPlate, for Group A the activities reflected by average well color development (AWCDs) of the rhizospheric soil microbial community of Line RNAi-3were significantly lower or even highly significantly lower than those of CK-1. And the diversity indices of AWCD revelation in the4MicroPlates meant that the richness, diversity and evenness related to Line RNAi-3were all significantly lower or even highly significantly lower than those of CK-1; and the richness and evenness related to Line OE-7were significantly lower than those of CK-1; for Group B the richness, diversity and evenness related to Line Gagal57and Line Gagal17-4were all significantly lower or even highly significantly lower than those of CK-2.In order to determine the diversity indices for measuring the transgenic soybean rhizospheric soil microbial community, this study addresses the diversity analysis of the experimental data obtained from PLFA, Biolog and PCR-DGGE methods applied to the rhizospheric soils in which the same two soybean groups were planted in an agricultural field in2009as well. After making investigation into the advantage and disadvantage of each index, the following measures could be recommended in analyzing the microbial community diversity in the soil affected by the soybean transgenic lines:1) At PLFA level-relationship between diversity indices and soil microbial communities, Gini index to Group A and McIntosh index to Group B should be used.-Correlation between diversity indices, Gini index, Shannon index, Simpson index, Simpson1-D to Group A, and Simpson index, Simpson1-D,1/D to Group B should be used.-Correlation between diversity indices and soil factors, Simpson index, Simpsonl-D,1/D to Group A, and McIntosh evenness to Group B should be used.2) At Biolog-GN level-relationship between diversity indices and soil microbial communities, McIntosh index to Group A and Shannon evenness to Group B should be used.-Correlation between diversity indices, Shannon index to Group A, and Shannon index, McIntosh evenness to Group B should be used.-Correlation between diversity indices and soil factors, Gini index to Group A, and Shannon evenness, Simpsonl-D, McIntosh evenness to Group B should be used.3) At Biolog-GP level-relationship between diversity indices and soil microbial communities, all the indices to both Group A and Group B should be used. Correlation between diversity indices, Gini index, Shannon index&evenness to Group A, and Shannon index to Group B should be used.-Correlation between diversity indices and soil factors, Gini index, Shannon index, McIntosh evenness to Group A, and Simpson index, Simpson1-D, McIntosh index to Group B should be used.4) At Biolog-FF level-relationship between diversity indices and soil microbial communities, Shannon index to Group A and McIntosh index to Group B should be used.-Correlation between diversity indices, Simpson index, McIntosh index&evenness to Group A, and Gini index to Group B should be used.-Correlation between diversity indices and soil factors, all the indices to Group A, and Shannon index&evenness, Simpson1/D to Group B should be used.5) At Biolog-ECO level-relationship between diversity indices and soil microbial communities, Shannon index to Group A, and all the indices to Group B should be used.-Correlation between diversity indices, Shannon index&evenness, McIntosh index to Group A, and Gini index, Shannon index&evenness, McIntosh index&evenness to Group B should be used.-Correlation between diversity indices and soil factors, Simpson index and Simpson1-D, McIntosh evenness to Group A, and Shannon index, McIntosh index to Group B should be used.6) At PCR-DGGE level-relationship between diversity indices and soil microbial communities, McIntosh evenness to both Group A and Group B should be used.-Correlation between diversity indices, Gini index, Shannon index&evenness, Simpson index and Simpson1/D to Group A, and Simpson index and Simpson1-D to Group B should be used.-Correlation between diversity indices and soil factors, Shannon evenness to Group A, and Gini index, Shannon index, McIntosh index&evenness to Group B should be used.7) Using the same index to respectively analyse the data obtained by Biolog GN, Biolog GP, Biolog FF, Biolog ECO, PCR-DGGE and PLFA methods, only Shannon Index showed the highest of number of significant difference between different treatments with the different methods to Group A (except Biolog GN and Biolog GP); and only McIntosh index showed the highest of number of significant difference between different treatments with the different methods to Group B (except Biolog GP and Biolog ECO).This study assessed of the effects of the transgenic soybeans on soil system in several respects. Being part of the research in soil microbiology, the results of this study are of positive significance for further assessing the risk of transgenic crops.