\section{Introduction}
% Fakesubsubsection:Biofilms are diverse and complex
Biofilms are diverse and complex microbial consortia, and, the biofilm
lifestyle is the rule rather than the exception for microbes in many
environments. Large and small-scale biofilm architectural features 
play an important role in their ecology and influence their role in
biogeochemical cycles \citep{17170748}. Fluid mechanics impact biofilm
structure and assembly \citep{hoedl_2011,19571890, 14647381}, but it is less
clear how other abiotic factors such as resource availability affect biofilm
assembly. Aquatic biofilms initiate with seed propagules from the planktonic
community \citep{hoedl_2011, 22120588}. Thus, resource amendments that
influence planktonic communities may also influence the recruitment of
microbial populations during biofilm community assembly.

% Fakesubsubsection:In a crude sense, biofilm and planktonic microbial
In a crude sense, biofilm and planktonic microbial communities divide into two
key groups: oxygenic phototrophs including eukaryotes and cyanobacteria
(hereafter "photoautotrophs"), and heterotrophic bacteria and archaea. This
dichotomy, admittedly an abstraction (e.g. non-phototrophs can also be
autotrophs), can be a powerful paradigm for understanding community shifts
across ecosystems of varying trophic state \citep{Cotner_2002}. Heterotrophs
meet some to all of their organic carbon (C) requirements from photoautotroph
produced C while simultaneously competing with
photoautotrophs for limiting nutrients such as phosphorous (P) \citep{379}. The
presence of external C inputs, such as terrigenous C leaching from the
watershed \citep{Jansson_2008, Karlsson_2012} or C exudates derived from
macrophytes \citep{Stets_2008, Stets_2008b}, can alleviate heterotroph reliance
on photoautotroph derived C and shift the heterotroph-photoautotroph
relationship from commensal and competitive to strictly competitive
\citep[see][Figure~\ref{fig:conceptual}]{Stets_2008}. Therefore, increased
C supply should increase the resource space available to heterotrophs and
increase competition for mineral nutrients decreasing nutrients available for
photoautotrophs (assuming that heterotrophs are superior competitors for
limiting nutrients as has been observed
\citep[see][Figure~\ref{fig:conceptual}]{COTNER_1992}). These dynamics should
result in the increase in heterotroph biomass relative to the photoautotroph
biomass along a gradient of increasing labile C inputs. We refer to this
differential allocation of limiting resources among components of the microbial
community as niche partitioning.

% Fakesubsubsection:While these gross level dynamics have been discussed
While these gross level dynamics have been discussed conceptually
\citep{Cotner_2002} and to some extent demonstrated empirically
\citep{Stets_2008}, the effects of biomass dynamics on
photoautotroph and heterotroph membership and structure has not been directly
evaluated in plankton or biofilms. In addition, how changes in planktonic
communities propagate to biofilms during community assembly is not well
understood. We designed this study to test if C subsidies shift the
biomass balance between autotrophs and heterotrophs within the biofilm or its
seed pool (i.e. the plankton), and, to measure how changes in biomass pool size
alter composition of the plankton and biofilm communities. Specifically, we
amended marine mesocosms with varying levels of labile C input and evaluated
differences in photoautotroph and heterotrophic bacterial biomass in plankton
and biofilm samples along the C gradient. In each treatment we characterized
plankton and biofilm community composition by PCR amplifying and DNA sequencing
16S rRNA genes and plastid 23S rRNA genes.






    
    