Abstract
During the past decades, the effects of the transgenic crops on soil microbial communities have aroused widespread interest of scientists, which was mainly related to the health and growth of plants. In this study, the maize root-associated bacterial communities of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) transgenic glyphosate-tolerant (GT) maize line CC-2 (CC2) and its recipient variety Zhengdan958 (Z958) were compared at the tasseling and flowering stages by high-throughput sequencing of V3-V4 hypervariable regions of 16S rRNA gene (16S rDNA) amplicons via Illumina MiSeq. In addition, real-time quantitative PCR (qPCR) was also performed to analyze the nifH gene abundance between CC2 and Z958. Our results showed no significant difference in alpha/beta diversity of root-associated bacterial communities at the tasseling or flowering stage between CC2 and Z958 under field growth conditions. The relative abundances of the genera Bradyrhizobium and Bacillus including species B. cereus and B. muralis were significantly lower in the roots of CC2 than that of Z985 under field conditions. Both these species are regarded as plant growth promoting bacteria (PGPB), as they belong to both nitrogen-fixing and phosphate-solubilizing bacterial genera. The comparison of the relative abundance of nitrogen-fixing/phosphate-solubilizing bacteria at the class, order or family levels indicated that only one class Bacilli, one order Bacillales and one family Bacillaceae were found to be significantly lower in the roots of CC2 than that of Z985. These bacteria were also enriched in the roots and rhizospheric soil than in the surrounding soil at both two stages. Furthermore, the class Betaproteobacteria, the order Burkholderiales, the family Comamonadaceae, and the genus Acidovorax were significantly higher in the roots of CC2 than that of Z985 at the tasseling stage, meanwhile the order Burkholderiales and the family Comamonadaceae were also enriched in the roots than in the rhizospheric soil at both stages. Additionally, the nifH gene abundance at the tasseling stage in the rhizosphere soil also showed significant difference. The relative abundance of nifH gene was higher in the root samples and lower in the surrounding soil, which implicated that the roots of maize tend to be enriched in nitrogen-fixing bacteria.
Highlights
The global commercial cultivation of genetically modified (GM) or transgenic crops has increased about 110-folds, from 1.7 million hectares (1996) to 185.1 million hectares (2016), and has already accumulated 2.1 billion hectares or 5.3 billion acres in 21 years (ISAAA, 2017)
According to the information we got from China Soil Database, the soil type in Yuanyang, Xinxiang City belongs to fluvo-aquic soils and the soil type in Zhangqiu, Jinan City is calcic sajiang black soils which belong to lime concretion black soils
When compared the root microorganisms at same layers, the results showed that the surrounding soil samples of CC2 and Z958 shared the largest amount of Operational Taxonomic Unit (OTU) while the root samples of CC2 and Z958 shared the minimum amount of OTUs
Summary
The global commercial cultivation of genetically modified (GM) or transgenic crops has increased about 110-folds, from 1.7 million hectares (1996) to 185.1 million hectares (2016), and has already accumulated 2.1 billion hectares or 5.3 billion acres in 21 years (ISAAA, 2017). According to The International Service for the Acquisition of Agri-biotech Applications, herbicide tolerance deployed in soybean, maize, etc., has consistently been the dominant trait at 47% of the global hectarage (ISAAA, 2017) These commercial transgenic crop varieties benefited economic gains of 574 million tons valued at US$167.8 billion in 1996-2015 and provided accessible food and nutrition to the 7.4 billion global populations (ISAAA, 2017), large amounts of previous studies documented various effects of these transgenic crops on soil microbial communities especially rhizosphere bacteria (Dunfield and Germida, 2004; Liu et al, 2005; Turrini et al, 2015; Guan et al, 2016). A recently study showed that rice genotypes affect the rhizosphere microbial communities, and impact the microbial communities in the rhizoplane and endosphere (Edwards et al, 2015)
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