Abstract
Information on rhizosphere microbiome of endemic plants from high mountain ecosystems against those of cultivated plantations is inadequate. Comparative bacterial profiles of endemic medicinal plant Rhododendron arboreum Sm. subsp. delavayi rhizosphere pertaining to four altitudinal zonation Pankang Thang (PTSO), Nagula, Y-junction and Bum La (Indo-China border; in triplicates each) along cold adapted Eastern slope of Himalayan Tawang region, India is described here. Significant differences in DGGE profile between below ground bulk vs. rhizospheric community profile associated with the plant was identified. Tagged 16S amplicon sequencing from PTSO (3912 m) to Bum La (4509 m), revealed that soil pH, total nitrogen (TN), organic matter (OM) significantly influenced the underlying bacterial community structure at different altitudes. The relative abundance of Acidobacteria was inversely related to pH, as opposed to TN which was positively correlated to Acidobacteria and Proteobacteria abundance. TN was also the significant predictor for less abundant taxonomic groups Chloroflexi, Gemmatimonadetes, and Nitrospirae. Bum La soil harbored less bacterial diversity compared to other sites at lower altitudes. The most abundant phyla at 3% genetic difference were Acidobacteria, Actinobacteria, and Proteobacteria amongst others. Analysis of similarity indicated greater similarity within lower altitudinal than higher altitudinal group (ANOSIM, R = 0.287, p = 0.02). Constraining the ordination with the edaphic factor explained 83.13% of variation. Unique phylotypes of Bradyrhizobium and uncultured Rhizobiales were found in significant proportions at the four regions. With over 1% relative abundance Actinobacteria (42.6%), Acidobacteria (24.02%), Proteobacteria (16.00%), AD3 (9.23%), WPS-2 (5.1%), and Chloroflexi (1.48%) dominated the core microbiome.
Highlights
The plant microbiome refers to the composite community of microbes associated with plants (Mendes et al, 2013)
We assessed the rhizospheric bacterial community of endemic medicinal plant R. arboreum Sm. subsp. delavayi and its association with soil properties at a high altitude region upstream of Tawang, India situated in the eastern slope of the Himalaya
DGGE profiles of bulk soil and rhizospheric soil ruled out the possibility for specific bacterial group selection by the dry, cold Himalayan soils and emphasized on the phenomenon of “rhizosphere effect.”
Summary
The plant microbiome refers to the composite community of microbes associated with plants (Mendes et al, 2013). By altering composition of below-ground microbial community with treatments, the authors showed Brassica rapa plants associated with simplified, less diverse microbial community compared to plants with highly diverse complex microbial community, were smaller, had reduced chlorophyll content, produced less flower and had less fecundity Such reports relate to the reciprocal interactions that exist between the plant and associated microbes in modulating each other. Shen and Wang (2011) showed that transplanted seedlings of endemic and critically endangered Euryodendron excelsum with native arbuscular mycorrhizal fungi enhanced survivability by 80% compared to 46% on their own Such studies suggest that below ground microbial communities may play important role in determining diversity, productivity and composition of above ground plant community. Microbiome studies of endemic medicinal plants are still primitive
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