deletions | additions       diff --git a/introduction.tex b/introduction.tex  index 09109bf..d721712 100644  --- a/introduction.tex  +++ b/introduction.tex 
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The first step in teasing out belowground C cycling dynamics is to identify microbial groups responsible for the measured process and understand the relationship between genetic diversity, community structure, and function \cite{O_Donnell_2002}. Stable-isotope probing (SIP) provides a unique opportunity to link microbial identity to activity \cite{Chen_Murrell_2010}. SIP has been utilized to expanded our knowledge of a myriad of important biogeochemical processes \cite{Chen_Murrell_2010}, yet, there remain limitations. Frequently utilized SIP-coupled molecular applications such as TRFLP, DGGE, and cloning provide insufficient resolution of taxon identity and depth of coverage and, to our knowledge, are usually conducted under the narrow scope of single substrate additions with few exceptions \cite{Lueders_2003,Chauhan_2009}. SIP studies use single substrate experimental designs to minimize isotope signal dilution, however, it detracts from how microbes may experience that substrate naturally, calling into question its environmental and biological relevance.  Degradative succession refers to the temporal changes in species or functional guilds that occurs during the sequential degradation of constituents of a nutrient resource \cite{townsend2003essentials,Bastian_2009}. The decomposition of a nutrient source is hypothesized to promote succession of active community members as compounds are sequentially degraded \cite{Biddanda_1988}. Differences in the degradation of labile C sources (ie. glucose, xylose, or sucrose) and complex C polymers (ie. cellulose or lignin) have been detected \cite{Engelking_2007,Anderson_1973,Stotzky_1961,Alden_2001,Furukawa_1996,Fontaine_2003,Blagodatskaya_2007,Jenkins_2010,Rui_2009,Fierer_2010}. A classic example of plant litter degradative succession is characterized by a series of stages in which sugar fungi dominate in stage one, followed by cellulolytic fungi in stage two, and lignin degrading fungi in the final stage \cite{Gessner_2010}. This demonstrates not only the succession of detritivores but also the sequential degradation of litter constituents starting with consumption of the most labile C sources followed by degradation of more complex and polymeric C sources. Thesesingle substrate  studies suggest that if a complex mixture of labile and polymeric C were added to soil two waves of degradation could be observed; labile C degradation early on and subsequent polymeric C degradation. We propose this temporal cascade from labile C degraders preceeding the polymeric C degraders occurs in natural microbial communities, called herein microbial community succession. "2) there It  is a common decomposition sequence independent of plant inputs or other ecosystem properties; and 3) molecular important to understand these  decomposition sequences, although consistent, sequences because as environments  are not uni- form and can be altered, resulting altered it results  in measurable and functional changes in soil C."\cite{Grandy_2008}  "We determinedthat simple substrateswere degradedby the same groups of organisms in both soils, and at similar rates, but pine litter was degraded by different microbial groups in the two soils, and C \cite{Grandy_2008} which could cumulatively have large impacts  at different rates. Thus as substrate complexity increased, the functional group responsible for its degradation became more distinct between the two soils."\cite{Waldrop_2004} a global scale.  Goldfarb then functional guild literature (fierer) then propose that phyla do not serve as a single functional unit as many clades within a phyla may respond differently.   \cite{Fierer_2012} - demonstrates that taxonomic and phylogenetic diversity does not confer functional diversity. "There has been considera- ble debate in the field of ecology as to how the taxonomic diversity of communities relates to the observed functional, or trait-level, diversity (16); we found a strong positive correlation be- tween the functional and taxonomic diversity of soil microbial communities"\cite{Fierer_2013} 
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"In correspondence with the dynamics of fatty acids, the bac- terial community showed a distinct succession during the course of residue decomposition"\cite{Rui_2009}  "dynamics of community structure seemed to be related to changes in the availability of carbon resources occurring during degradation"\cite{Bastian_2009}  "We determinedthat simple substrateswere degradedby the same groups of organisms in both soils, and at similar rates, but pine litter was degraded by different microbial groups in the two soils, and at different rates. Thus as substrate complexity increased, the functional group responsible for its degradation became more distinct between the two soils."\cite{Waldrop_2004}