Rhizospheric Bacterial Community of Endemic Rhododendron arboreum Sm. Ssp. delavayi along Eastern Himalayan Slope in Tawang

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.

Rhizosphere Microbiome of Arid Land Medicinal Plants and Extra Cellular Enzymes Contribute to Their Abundance

“…Similarly, increased abundance of Proteobacteria and decreased presence of Acidobacteria in the plant-rhizosphere samples with respect to different hosts were previously found with Agave species [27], suggesting a major community structure associated with the arid land plants. These have also been reported in some of the important medicinal plants, such as Panax ginseng [66], Thymus zygis [36], Polygonum cuspidatum [33], Rhododendron arboretum [35], Sapindus saponaria [53], Taxus baccata and Aloe vera [34,67]. Nonetheless, distribution of phyla including Chloroflexi, Planctomycetes, and Firmicutes in C. austroarabica rhizosphere and Cyanobacteria in A. obesum rhizosphere were significantly different, suggesting host-specific microbe management as indicated by Berendsen et al [17].…”

“…decipiens Buchen., and Rhizoma arisaematis [28,29] showed remarkably high and diverse rhizosphere colonization with Actinobacteria [30]. In addition, some of the recent studies have elucidated the rhizosphere communities of Rehmannia glutinosa [31], Rumex patientia [32], Polygonum cuspidatum [33], Aloe vera [34], Rhododendron arboretum [35], and Thymus zygis [36]. These studies have been restricted to the bacterial communities and did not include fungi, and a few studies used high-throughput next-generation sequencing.…”

Investigation of an Elevational Gradient Reveals Strong Differences Between Bacterial and Eukaryotic Communities Coinhabiting Nepenthes Phytotelmata

“…The extent to which microbes follow the same macroecological trends established in plants and animals (macro-organisms or "macrobes") remains partially unresolved. One major line of thought on microbial macroecology is the Baas-Becking hypothesis: "everything is everywhere, and the environment selects", suggesting that bacteria are not dispersal-limited and thus not subject to the broad-scale spatial structuring seen in macrobes [7][8][9][10][11][12]. However, this view is controversial [13][14][15][16][17], and may not apply to eukaryotic microbes [18,19].…”

“…Microbes have not been as extensively studied in the context of elevational gradients, but the past decade has seen an increasing number of studies examining elevational patterns of bacteria in soil [6,[8][9][10][11][12][20][21][22] and to a lesser extent, aquatic habitats [23][24][25][26]. Similar studies have also been conducted for fungi [27][28][29][30][31][32][33][34][35] and protists [18,[36][37][38][39].…”

O genótipo do hospedeiro e as condições ambientais como moduladores da comunidade bacteriana associada

“…Plantas pouco estudadas e de ocorrência restrita, como as endêmicas, são alvos para a bioprospecção de novos produtos (Debnath et al, 2016). Neste tipo de exploração, sugere-se que o processo evolutivo ocorrido entre as espécies (plantas e bactérias) foram primordiais para determinar uma forte e restrita associação entre os organismos e a sobrevivência de ambos em ambientes com condições bióticas e abióticas variáveis 23°27'34,43''; W 45°01'11,40''); ambiente de Intermédio, distante cerca de 600 metros do mar (S 23°27'35,4''; W 45°02'18,6''); e um ambiente de Mata (Mata Atlântica), distante 6 km do mar (S 23°27'34,63''; W 45°01'11,32'') Lâmina elíptica e lanceolada, 7-42,2 X 2,2-16,5 cm, ereta a patente em relação ao caule, ápice agudo, obtuso.…”