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Ashley Campbell edited Results & Discussion.tex
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The \textsuperscript{13}C-incorporation reveals temporal dynamics of C degradation demonstrated by \textsuperscript{13}C-xylose incorporation at days 1, 3, and 7 and \textsuperscript{13}C-cellulose incorporation at days 14 and 30 (\href{https://www.authorea.com/users/3537/articles/3612/master/file/figures/ordination_all1/ordination_all1.png}{Fig. 1B}), as expected \cite{Amelung_2008}. The bulk community amplicons support the temporal dynamics observed in the gradient fraction amplicons by demonstrating significant (pval) microbial community changes over time. Although within a single time point, the bulk community demonstrated no significant difference between treatments (\href{https://authorea.com/users/3537/articles/8459/master/file/figures/bulk_ordination/bulk_ordination.png}{Fig. S2}).
The temporal dynamics reveal the composition of Heavy fraction amplicon pools from samples that received \textsuperscript{13}C-xylose
assimilating amplicons are different for each of the days the label is detected based diverged from corresponding controls on
their separate distributions for each of the time points days 1 through 7 (\href{https://www.authorea.com/users/3537/articles/3612/master/file/figures/ordination_all1/ordination_all1.png}{Fig.
1B}). The disappearance of the \textsuperscript{13}C-xylose incorporation signature (relative to control) for 1}). Furthermore, amplicon pool composition varied across these days
(\href{https://www.authorea.com/users/3537/articles/3612/master/file/figures/ordination_all1/ordination_all1.png}{Fig. 1B}) indicating dynamic changes in \textsuperscript{13}C-xylose assimilation with time. At day 14 and 30
result heavy fractions from
loss of \textsuperscript{13}C-label \textsuperscript{13}C-xylose labeled samples are no longer differentiated from corresponding controls indicating that {13}C is no longer detectable in
DNA over time. This occurs by dilution of \textsuperscript{13}C-label out DNA. The decline in \textsuperscript{13}C-labelling of
the DNA
when a switch is likely due to isotopic dilution resulting from
\textsuperscript{13}C assimilation of unlabeled C and/or due to
\textsuperscript{12}C substrate utilization takes place during biomass cell turnover
and/or predation. resulting from mortality.
\textsuperscript{13}C-cellulose incorporation isn't detected until day 14 and amplicon composition is consistent for both days 14 and 30 (\href{https://www.authorea.com/users/3537/articles/3612/master/file/figures/ordination_all1/ordination_all1.png}{Fig.
1B}). 1}). The consistency of amplicon composition for cellulose degradation over time compared to xylose suggests a wider array of microorganisms utilize xylose, whereas, cellulose utilization occurs in a select few. This is consistent with long standing notions that more microorganisms are capable of utilizing simple carbohydrates than complex C substrates. Overall patterns of C degradation observed in this study demonstrate different microbial community members are responsible for the consumption of these two substrates; xylose is consumed quickly, whereas, cellulose decomposition takes longer. This suggests a pattern of microbial community transition accompanying the decomposition process. This is consistent with
\cite{Engelking_2007} Engelking \textit{et al.}\cite{Engelking_2007} who observed as much as 75\% of labile C respired or converted into microbial biomass in the first 5 days of decomposition, whereas, cellulose degraders take longer to respond \cite{Hu_1997} with less than 42\% of cellulose metabolized over the first 5 days of incubation \cite{Engelking_2007}.
\textbf{Differential C utilization by taxa.} Individual OTUs that assimilated \textsuperscript{13}C-substrates were identified using the DESeq framework \cite{Anders_Huber_2010} to analyze differential representation in heavy fractions (\href{https://www.authorea.com/users/3537/articles/3612/master/file/figures/l2fc_fig1/l2fc_fig.pdf}{Fig. 2}). There were 43 and 35 unique OTUs that significantly (\textit{p}-value \textless 0.10) assimilated \textsuperscript{13}C-xylose and \textsuperscript{13}C-cellulose, respectively; herein called 'responders' (\href{https://www.authorea.com/users/3537/articles/8459/master/file/figures/OTU_screening_schematic/OTU_screening_schematic.pdf}{Fig. S2}, \href{https://www.authorea.com/users/3537/articles/8459/master/file/figures/l2fc_fig_pVal/l2fc_fig_pVal.png}{Fig. S3}). Overall, we found xylose responders were from higher rank abundances than cellulose responders, however, cellulose responders exhibited a greater change in buoyant density (i.e. assimilated more \textsuperscript{13}C) than xylose responders in response to isotope incorporation (Figure 3).