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  Very few studies have previously evaluated the relationship among membership and or diversity of the plankton and the biofilm community from complex environmental microbial communities. One notable study looked at planktonic community composition and biofilm formation on glass beads placed for three weeks in two boreal freshwater streams \cite{22237539}. While that study system is markedly different than our study, the analyses and questions addressed in each study were very similar. Both studies concluded that the biofilm community membership was most likely driven by species sorting over mass effects. However, in the \citet{22237539} study the authors reported that planktonic diversity was significantly higher relative to biofilm diversity (the opposite of what we found in our study). Given the differences in the study systems, this result is not suprising. While biofilm communities were establishsed on glass beads in \citet{22237539} and glass slides (this study) over a similar time period (~21 days, \citet{22237539} and ~17 days this study) the origin of the planktonic community in each study was very different. The \citet{22237539} study was conducted in a boreal stream during snow melt when connectivity between the terrestrial and aquatic habitats was high and potentially highly variable depending on how hydrologic pathways differed among precipitation events. A separate study conducted in alpine and sub-alpine streams of the Rocky Mountains clearly showed that stream plankton communities reflected localized precipitation events and could be traced largely to sources of soil communities of drainages within the watershed \cite{22626459}. While planktonic communities in lake ecosystems can be linked to soil communities in the watershed, as residence time of the system slows the relative influence of species sorting increases. Thus, in headwater ecosystems stream plankton communities can often be composed primarily of soil organisms \cite{22378536}. In addition to the diverse source communities the \cite{22237539} study sampled the plankton community at multiple timepoints and integrated the samples before sequencing, further increasing community richness as compared to the current study where the plankton community was sampled and analyzed only at two independent timepoints. Indeed, when we pool OTU counts from all planktonic libraries and compare the rarefaction curve of the pooled planktonic libraries (algae and bacteria) against sample-wise biofilm libraries, we find more total bacterial and algal planktonic OTUs than in any given single biofilm sample. It appears, however, that some sample-wise bacterial biofilm rarefaction curves may exceed the integrated planktonic curve upon extrapolation and most exceed the integrated planktonic curve at sampling depths where data is present for the biofilm and itegrated planktonic library. This supports our conclusion that temporal heterogenetity in teh plankton was not sufficient to explain the higher diversity in the biofilm sample.  Our study provides an additional detailed analysis of biofilm community assembly mechanisms consistent with what has been previously reported. Additionally, we evaluated how resource subsidies potentially alter the seed pool (the plankton) and the biofilm community. Interestingly, biofilm community richness peaked at the intermediate treatment (C:P = 100) and appeared to decrease over time although with only two time points it was unclear how pronounced this effect was. Since biomass pools for the plankton and the biofilm increased with increasing carbon subsidies the intermediate peak in OTU richness is consistent with a classic productivity-diversity relationship that has been shown for many ecosystems and communities both microbial and otherwise (REFS). otherwise.  Interestingly, as diversity decreased at the high end of the carbon subsidy gradient bacterial plankton and biofilm membership became increasingly similar. This suggests that enviornments that contain high amounts of labile carbon selected for fewer dominant taxa that then also came to dominate the biofilm community. While we did not measure extracellular polymeric substances (EPS), direct microscopy showed that cells in the highest carbon treatment (C:P = 500) were surrounded by what appeared to be EPS. Because biofilm EPS appeared also to increase moving from the low to high carbon treatments (Figure 3) it is possible that planktonic cells were more readily incorporated into biofilms due both to increased "stickiness" of the planktonic cells as well as the biofilm itself. While we did not observe floculating DOC which has been shown to dominate high DOC environments in nature, we did measure a substanial increase in DOC in the C:P = 500 treatment which was more than 2-fold higher than any of the other treatments. \subsection{Sample Class Enriched OTUs}