Abstract
Karst topography is formed from the dissolution of soluble rocks, such as limestone and dolomite. In soils of such a landform, excessive contents of exchangeable calcium seriously limit the growth of vegetations. Researches have proved that rhizosphere microorganisms and endophytes help host plants to adapt to various adverse environments. The adaptive capacity of plants that grow in adverse environment with salt, drought, thermal and heavy metal stresses partially or completely comes from symbiotic microorganisms. By using the high-throughput amplicon sequencing, the bacterial community structures in soil with high calcium contents and roots and leaves of Cochlearia henryi that is commonly seen in karst area were analyzed. The bacteria community structures in these three compartments showed obvious differences. This indicates that C. henryi, which is adaptive to high calcium stress, selectively co-exists with specific bacteria. Although the bacteria community structures in these three compartments differed significantly, there were 73 operational taxonomic units (OTUs) shared by karst soils as well as roots and leaves of C. henryi. The phylogenetic diversity of these 73 OTUs differed significantly from that of overall OTUs detected. There were also obvious differences in KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways and abundance values between the 73 OTUs and overall bacterial communities. A large number of OTUs shared by the karst soils, roots and leaves of C. henryi had close genetic relationship with known stress-resistant bacterial strains. Our results showed that the functional bacteria can be predicted by exploring core bacteria, bacteria shared by soils, adaptable plant roots and leaves. This information will potentially accelerate studies on natural microbial communities which can promote the adaptive capacity of host plants to high calcium stress, and will be valuable for finding microbial strains for field application in karst topography.
Highlights
Rhizosphere microorganisms and endophytes can help host plants to adapt to various adverse environments [1]
The Venn diagram showing the shared or specific operational taxonomic units (OTUs) of each sample or compartment was generated using the Venn Diagram package in R (v3.3.2), The core OTUs shared by the high calcium soil, roots and leaves of C. henryi were screened in accordance with the results of Venn diagram
The organic nutrient substances, such as carbon and nitrogen which are important components for plant growth were lower than those of nutrient soils, showing a considerable degree of infertility. These results indicated that karst bulk soils in Huajiang county are alkaline and infertile with high calcium content, which points to a functional role of determinant factors, such as symbiotic bacterial community, in plant growth in these soils
Summary
Rhizosphere microorganisms and endophytes can help host plants to adapt to various adverse environments [1]. Microorganisms in the karst soils faces calcium stress and endophytes in the roots and leaves of C. henryi must adapt to their host. Data on the physiological and ecological effects of C. henryi rhizosphere microorganisms and endophytes in karst regions, a unique ecological system with high calcium content, are unknown, if not, limited and needs extensive scrutiny. “Core” operational taxonomic units (OTUs) shared by karst soils, as well as roots and leaves of C. henryi were identified. We expected that these OTUs should be adaptive to calcium stress and involved in the adaptability of C. henryi to karst ecosystem. We compared the phylogenetic diversity and functional profiling of the “core” OTUs and that of the overall OTUs and observed significant differences
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