Tables & Figures
Figure 1: Correlations between the relative abundance of each zOTU pair across samples were calculated using the maximal information coefficient (MICe). Results were visualised in Gephi with node size associated betweenness centrality and node colour with the network modularity. Edge colour is associated with negative (green), or positive (purple) correlations based on Pearson coefficients. Acidobacteria, Proteobacteria, Bacteroidetes and Actinobacteria form the backbone of microbial networks. Aspect and conductivity have significant influence over community composition with strong positive associations with transect end (orange) and strong negative correlations with transect middle (blue).
Figure 2: Distribution of bacteria (left) and micro-eukarya (right) along transects (i.e. start = 0-50, mid = 100-150, end 200-300) at Old Wallow. Microbial phyla are vertically sorted in order of decreasing relative abundance. Dominant bacterial phyla are commonly associated with arid soil communities. Micro-eukaryotes were largely unclassified however dominant taxa were associated with algal phyla, an uncommon feature within Antarctic desert soils.
Figure 3: Rarefaction curves at 100m gradients S1 Rarefaction curves of subsampled bacterial, eukaryotic and archaeal communities between sites. In all cases, asymptote was reached indicating that sufficient sampling depth had been achieved. End transects saw the highest species diversity across all domains. Start transects are second highest bacteria and archaea whilst mid transects are highest for eukarya.
Figure 4: Fluorescent In-situ hybridisation microscopy conducted on enrichment cultures displaying Diatom like morphologies. Enrichment cultures were incubated in V4 media with 10% salt, antibiotics (Streptomycin and Ampicillin) and antifungals (Natamycin and Cycloheximide). Red Fluorescent probes bind to archaea whilst green bind to bacteria. Dapi stains appear blue indicating the presence of DNA. Five different morphologies were visualised and compared to electron microscopy scans of known species. Morphologies were matched by morphology to the Diatoms of North America index.
Figure 5: Overall importance (R2 weighed) of predictors driving distrubtions of polar soil (a) bacteria and (b) micro-eukarya within Old Wallow. Bacteria and micro-eukarya showed similar predictors for the shaping of microbial communities. Overall importance plots showed SO3 to be the strongest predictor in shaping the bacterial microbiome followed by SO4, Na2O and DMF. For eukaryotes Ph was the strongest predictor followed by, SO4 SO3 and Na2O.
Figure 6: Biological and geographical bi-plots classifying spatial groups for polar soil bacteria across Old Wallow. Different colours highlight variations in species composition and turnover. Key drivers of groups at the start and end associated with Al2O3, Fe2O3 and Aspect. For communities in the mid-section of the transect Na2O and Cl were the key drivers. A distinct group at the start of the transect was predominantly driven by SO4 and SO3.
Figure 7: Biological and geographical bi-plots classifying spatial groups for polar micro-eukaryotes across Old Wallow. Different colours highlight variations in species composition and turnover. Micro-eukaryotic spatial groups were less distinct but had similar drivers as bacteria based on transect location. Communities at the start of the transect were driven by SO3, SO4 and NO3. Communities in the middle were driven by Na2O, Cl and pH. Those at the end were more driven by DMF and Aspect.
Figure 8: Boxplots representing copy numbers of bacteria and micro-eukarya within Old Wallow. Old Wallow soil DNA was extracted and qPCR was conducted to quantify copy numbers of bacteria (Eub1048f/Eub1194r) and micro-eukarya (DM568F/RM2R) to analyse microbial density at different points along the transect. Copy numbers were calculated as per a gram of soil and log ratio transformed. Bacterial 16s rRNA copy numbers were significantly higher than eukaryotic 18s rRNA copy numbers across all areas of the transect. Bacterial abundance was consistant throughout the transect whilst eukarya increased from start to finish.
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