Chuck Pepe-Ranney edited Discussion.tex  over 9 years ago

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relative differences between planktonic and biofilm diversity found in  \citet{22237539}} compared to this study.  In %In  addition, for this study, it is important to note that biofilm community richness %richness  peaked at the intermediate treatment (C:P = 100) and appeared to decrease %decrease  over time although %although  with only two time points it was unclear how pronounced this effect was %was  (Figure~\ref{fig:rarefaction}). Since biomass of the plankton and the biofilm %biofilm  increased with increasing C subsidies the intermediate peak in OTU richness %richness  is consistent with a classic productivity-diversity relationship that has %has  been shown for many ecosystems and communities both microbial and otherwise. %otherwise.  However, as with other experiments with this result our experimental design %design  did not allow us to tell whether resources drove productivity that drove changes %changes  in diversity or whether resources drove diversity which altered productivity. %productivity.  Rather we note that, as diversity decreased in the highest C treatment %treatment  bacterioplankton and biofilm membership became increasingly similar. %similar.  This suggests that environments that contain high amounts of labile C %C  selected for fewer dominant taxa that came to dominate the biofilm community, %community,  overwhelming the species sorting mechanisms that appeared to dominate %dominate  biofilm community assembly in all other treatments. Similarly, while we %we  did not measure extracellular polymeric substances (EPS), direct microscopy showed %showed  that planktonic cells in the highest C treatment (C:P = 500) were surrounded %surrounded  by what appeared to be EPS. Because biofilm EPS appeared also to increase %increase  moving from the low to high C treatments (Figure~\ref{fig:microscope}) %(Figure~\ref{fig:microscope})  it is possible that more abundant planktonic cells %cells  were more readily incorporated into biofilms due both to increased "stickiness" %"stickiness"  of the planktonic cells as well as the biofilm itself. While we did %did  not observe flocculating DOC which has been shown to dominate high DOC environments %environments  in nature, we did measure a substantial increase in DOC in the C:P = %=  500 treatment which was more than 2-fold higher than any of the other treatments. %treatments.  Thus additional adhesion of the plankton and the biofilm may also explain %explain  the merging of the planktonic and biofilm bacterial membership in the highest %highest  C treatment. %\subsection{Lifestyle (biofilm or planktonic) Enriched OTUs}  %