Recently Deglaciated High-Altitude Soils of the Himalaya: Diverse Environments, Heterogenous Bacterial Communities and Long-Range Dust Inputs from the Upper Troposphere

<div><p>Background</p><p>The Himalaya with its altitude and geographical position forms a barrier to atmospheric transport, which produces much aqueous-particle monsoon precipitation and makes it the largest continuous ice-covered area outside polar regions. There is a paucity of data on high-altitude microbial communities, their native environments and responses to environmental-spatial variables relative to seasonal and deglaciation events.</p><p>Methodology/Principal Findings</p><p>Soils were sampled along altitude transects from 5000 m to 6000 m to determine environmental, spatial and seasonal factors structuring bacterial communities characterized by 16 S rRNA gene deep sequencing. Dust traps and fresh-snow samples were used to assess dust abundance and viability, community structure and abundance of dust associated microbial communities. Significantly different habitats among the altitude-transect samples corresponded to both phylogenetically distant and closely-related communities at distances as short as 50 m showing high community spatial divergence. High within-group variability that was related to an order of magnitude higher dust deposition obscured seasonal and temporal rearrangements in microbial communities. Although dust particle and associated cell deposition rates were highly correlated, seasonal dust communities of bacteria were distinct and differed significantly from recipient soil communities. Analysis of closest relatives to dust OTUs, HYSPLIT back-calculation of airmass trajectories and small dust particle size (4–12 µm) suggested that the deposited dust and microbes came from distant continental, lacustrine and marine sources, e.g. Sahara, India, Caspian Sea and Tibetan plateau. <i>Cyanobacteria</i> represented less than 0.5% of microbial communities suggesting that the microbial communities benefitted from (co)deposited carbon which was reflected in the psychrotolerant nature of dust-particle associated bacteria.</p><p>Conclusions/Significance</p><p>The spatial, environmental and temporal complexity of the high-altitude soils of the Himalaya generates ongoing disturbance and colonization events that subject heterogeneous microniches to stochastic colonization by far away dust associated microbes and result in the observed spatially divergent bacterial communities.</p></div

Non-metric multidimensional scaling ordination of microbial communities sampled from 5000–6000 m altitudinal gradient.

<p>(•) 6000 m, (▴) 5800 m, (×) 5600 m, (_*) 5400 m, (+) 5200 m, (▪) 5000 m. Horizontal transect formed significant groups (NP-MANOVA, p<0.05). Filled symbols denote barren soils. Individual samples connected by lines define convex hull surface area of NM-MDS scores of microbial community characteristics as a measure of community-space covered.</p

Variance partitioning of environmental and spatial factors shaping microbial communities at the three phylogenetic levels (OTU, Order, Phylum).

<p>Variance partitioning of environmental and spatial factors shaping microbial communities at the three phylogenetic levels (OTU, Order, Phylum).</p

Conditional effects of environmental variables selected by forward selection in redundancy analysis (RDA) as determined by 4999 Monte Carlo permutations under the full multivariate model at the three taxonomic levels.

<p>Only the relevant environmental factors are listed.</p

The relationship between dust particle number and microbial abundance during 2002, 2005 and 2006 sampling campaigns.

<p>(•) 6000 m, (▴) 5800 m, (□) 5600 m, (○) 5400 m, (?) 5200 m, (▪) 5000 m. () 6000 m autumn 2005; () 6000 m spring 2006.</p

Non-metric multidimensional scaling ordination of 6000 m microbial communities sampled in autumn of 2002 (▾), 2005 (▪) and in spring 2006 (•) next to corresponding 2005 autumn (□) and spring 2006 (○) dust samples.

<p>Note - no significant groups could be identified using NP-MANOVA (0.05</p

Distance-decay relationships in the non-continuous permafrost soils of the 1000 m altitude gradient.

<p>Pairwise dissimilarities (Bray-Curtis index) of microbial communities were plotted as a function of the distance (vertical plus horizontal) between the sampling locations.</p