THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
Dear Friends and Colleagues
Assessing the Risks of GM Crops to Soil Microorganisms
Soil microorganisms are the link between soil and plants, integrating these two systems. Plant–microorganism interactions in the rhizosphere soil are a major factor in the regulation of plant growth and development. The core effect of growing GM plants on soil is the change in soil ecosystem function, especially the effects on microbial communities. With the increase in cultivation of various GM plants (e.g., insect-resistant or disease-resistant plants) and the release of their expression products (e.g., Bt protein) into the soil ecosystem, soil microbial diversity and eventually agricultural production systems could be adversely impacted. Moreover, foreign genes may change the genetic and functional properties of soil microorganisms via horizontal transfer.
A new review focuses on the recent advances in the understanding of the effects of GM plants on soil microbial communities and in the applied research and detection technologies to analyse those effects. It finds that many studies on the effects of GM plants on soil microorganisms have been carried out on different GM plants in different environments and analyzed with different methods. Furthermore, most of the research conclusions were obtained on the basis of a 1-year cultivation period, which is too short a time frame to evaluate the ecological risk of GM plants. The limitations of current research methods are an important reason for the discrepant conclusions in various studies. The effects of GM plants with stacked traits on soil microorganisms may be even more complicated in comparison with single-trait crops in future biosafety assessments.
Nevertheless, species abundance and diversity of soil microbes comprise an important reference parameter in the safety evaluation of GM plants. Because of the limitations of current studies, further research at a more specific level is necessary to assess the correlation among the components and functions of soil microbial communities, the response of soil microbial structure and function to natural fluctuations in the soil system, the extent of the influence of GM plants on soil microbes, and the limitations of these various risks.
Please find below the Abstract, and Conclusion and Perspectives, of the review.
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DO GENETICALLY MODIFIED PLANTS AFFECT ADVERSELY ON SOIL MICROBIAL COMMUNITIES?
Zheng-jun Guan, Shun-bao Lu, Yan-lin Huo, Zheng-Ping Guan, Biao Liu,and Wei Wei
Agriculture, Ecosystems and Environment 235 (2016) 289–305
http://www.sciencedirect.com/science/article/pii/S0167880916305357
Abstract
With the increase in the number of commercial applications and larger cultivation areas of genetically modified (GM) plants, their biosafety for soil microorganisms has become a controversial issue. The effects on the diversity and abundance of soil microorganisms are important components of evaluation of the biosafety risks of GM plants. So far, no definite conclusions have been drawn about whether GM plants can negatively affect soil microorganisms. In this review, we discuss the advances that have been made in recent years in the research into the effects of GM plants on soil microbial communities. It has been argued that foreign gene products that are released from the residue of GM plants into soil by root exudation may affect soil microbial communities. Moreover, foreign genes may change the genetic and functional properties of soil microorganisms via horizontal transfer. The advantages and disadvantages of various detection technologies—from classical culture-dependent methods to modern molecular protocols—are reviewed here. To accurately and comprehensively evaluate the effects of GM plants on microorganisms, we discuss the factors that should be considered in the assessment of risks of GM plants for soil microorganisms (e.g., foreign proteins, marker genes, plant varieties, and environmental factors), as well as the problems and prospects related to biosafety assessment platforms for GM plants.
Conclusion and Perspectives
Soil microorganisms play essential roles in agricultural production systems. With the increase in cultivation of various GM plants (e.g., insect-resistant or disease-resistant plants), soil microorganisms will be exposed to risks that may eventually adversely affect agricultural production systems. The introduction of foreign genes into GM plants may affect species diversity and amounts of root exudates, alter micro-ecological environments in the soil, and can strongly influence the soil ecosystem functions. Therefore, the core effect of growing GM plants on a soil is the change in soil ecosystem function, especially the effects on the related microbial communities. Some investigators believe that no inherent connection exists between the diversity and function, and the abundance of the species was found to not affect soil function substantially (Bardgett, 2002). There is no direct evidence showing that soil microbial diversity is related to soil ecosystem function. That is, a decrease in microbial diversity does not necessarily worsen soil ecosystem function, but the change in certain key species may matter (Tilman et al., 2001). On the other hand, Bender et al. (2016) synthesized the potential of soil organisms to enhance ecosystem service delivery and demonstrated that soil biodiversity promotes multiple ecosystem functions simultaneously (i.e., ecosystem multifunctionality). Current techniques and methods may not be effective enough to obtain the relevant evidence, or the available data may be inadequate to draw such conclusions. For example, soil ecosystem function may have correlations only with a few microbial species or show functional redundancy (Loreau et al., 2001). Nevertheless, the species abundance and diversity of soil microbes comprise an important reference parameter in the system of safety evaluation for GM plants and may represent a key element of the biosafety assessment of animal and plant diversity.
Many studies on the effects of GM plants on soil micro-organisms have been carried out, and obvious differences among these studies have been noted. These studies, however, were conducted on different GM plants, and in different environments, and the resulting data were analyzed with different methods characterized by specific detection thresholds. For example, a DGGE, T-RFLP or SSCP profile may reveal the diversity manifesting as 25–40 most abundant microorganisms, whereas a 454 or Illumina-based approach easily detects easily 2000–5000 different organisms in a rhizosphere. Thus, assuming that the same number of replicates are analyzed, the latter methods have a much higher probability to detect significant differences between a GM plant and the comparator but also between non-GM varieties or different plant growth stages. Furthermore, most of research conclusions were obtained on the basis of a 1-year cultivation period. In view of various factors, it is not enough to evaluate the ecological risk of GM plants in a short trial time frame. Furthermore, more stacked traits of GM plants are expected to be developed in future agricultural practice. Multiple transgenic products and other secondarily metabolized components can be released into soil and affect the soil microbial communities. Other agricultural practice changes, e.g. application of an herbicide in the case of herbicide-resistant plant stacked with other traits, may also influence the soil microbes. Therefore, the effects of GM plants with stacked traits on soil microorganisms may be more complicated in comparison with single-trait crops in future biosafety assessments.
Because of the limitations of current studies, further research at a more specific level is necessary to assess the correlation among the components and functions of soil microbial communities, the response of soil microbial structure and function to natural fluctuations in the soil system (e.g., the season, climate, rotation, and pesticide use), the extent of the influence of GM plants on soil microbes, and the limits of these various risks. The limitations of current research methods are another important reason for the discrepant conclusions in various studies. On the basis of the findings presented above and existing standardized evaluation protocols (Birch and Wheatley, 2005), the discussion and analyses as well as an assessment of safety assessment of GM plants for soil microbes should involve a better evaluation method and theoretical system for analysis of soil microecology, with objective and scientific verification. The combined application of traditional culture methods, modern biochemistry, and molecular biological technologies should probably be able to circumvent the drawbacks of each method and help to fully exploit the complementary advantages. Especially, the development and improvement of NGS technologies (such as 454- pyrosequencing and Illumina MiSeq sequencing) and DNA meta-barcoding will help to better evaluate the effects of GM plants on soil microorganisms. In addition, for GM plants of different species, a case study should be conducted by combining long-term fixed plot tests. Risk assessment of the safety of GM plants is a long term and difficult task. A better understanding of the advantages and disadvantages of cultivation of GM plants can be obtained over time and mostly depends on the progress of technologies and knowledge in the scientific community.