Abstract
BackgroundBacillus thuringiensis (Bt) crops have been cultivated at a large scale over the past several decades, which have raised concern about unintended effects on natural environments. Microbial communities typically contain numerous rare taxa that make up the majority of community populations. However, the response of dominant and rare taxa for fungal diversity to the different root environments of Bt plants remains unclear.ResultsWe quantified fungal population sizes and community composition via quantitative PCR of ITS genes and 18S rRNA gene sequencing of, respectively, that were associated with Bt and conventional cotton variety rhizosphere soils from different plant growth stages. qPCR analyses indicated that fungal abundances reached their peak at the seedling stage and that the taproots and lateral root rhizospheres of the Bt cotton SGK321 were significantly different. However, no significant differences in population sizes were detected between the same root zones from Bt and the conventional cotton varieties. The overall patterns of fungal genera abundances followed that of the dominant genera, whereas overall patterns of fungal genera richness followed those of the rare genera. These results suggest that the dominant and rare taxa play different roles in the maintenance of rhizosphere microhabitat ecosystems. Cluster analyses indicated a separation of fungal communities based on the lateral roots or taproots from the three cotton varieties at the seedling stage, suggesting that root microhabitats had marked effects on fungal community composition. Redundancy analyses indicated that pH was more correlated to soil fungal community composition than Bt protein content.ConclusionsIn conclusion, these results indicate that dominant and rare fungal taxa differentially contribute to community dynamics in different root microhabitats of both Bt and conventional cotton varieties. Moreover, these results showed that the rhizosphere fungal community of Bt cotton did not respond significantly to the presence of Bt protein when compared to the two conventional cotton varieties.
Highlights
Bacillus thuringiensis (Bt) crops have been cultivated at a large scale over the past several decades, which have raised concern about unintended effects on natural environments
Fungi living in the rhizosphere can impact health, nutrition, and productivity of plants in agricultural ecosystems [8, 9], and understanding how fungal communities are affected by Bt crop cultivation is an essential aspect of elucidating soil biological processes at work in the rhizosphere by exposure to Bt proteins produced by Bt cotton
The population size of rhizosphere fungi associated with the taproot of SGK321 at the seedling stage was significantly higher compared to the lateral roots, suggesting that the root microhabitat was influential
Summary
Bacillus thuringiensis (Bt) crops have been cultivated at a large scale over the past several decades, which have raised concern about unintended effects on natural environments. GM Bt crops produce insecticidal recombinant Cry1Ac protein, typically in their root tissue. Such recombinant products may potentially enter the rhizosphere as an additional nutrient source for the soil microbial community. Fungi living in the rhizosphere can impact health, nutrition, and productivity of plants in agricultural ecosystems [8, 9], and understanding how fungal communities are affected by Bt crop cultivation is an essential aspect of elucidating soil biological processes at work in the rhizosphere by exposure to Bt proteins produced by Bt cotton. The communities identified appeared to be less taxonomically rich, and changes in the relative abundance of species were easy to overlook based on plate counts of cultivable organisms [11]
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