Phylogenetic trees of OTUs passing sparsity threshold for
\textit{Proteobacteria} \textbf{A} and 
\textit{Firmicutes} \textbf{B}. $^{15}$N-responders are identified by dots present in
column \textbf{i}. Log$_{2}$ of OTU proportion fold change (labeled:control
samples) for each OTU are presented as a heatmap in column \textbf{ii} with
results from days 2 and 4 on the left and right sides of the column
respectively. High fold change values indicate $^{15}$N incorporation.
Presence/absence of OTUs (black indicates presence) in lichen, light, or dark
environmental samples \citep{Garcia_Pichel_2013} is shown in column
\textbf{iii}.  Presence/absence of OTUs (black indicates presence) in crust and
below crust samples \citep{Steven_2013} is shown in column \textbf{iv}.