deletions | additions       diff --git a/introduction.tex b/introduction.tex  index fbbe793..5546151 100644  --- a/introduction.tex  +++ b/introduction.tex 
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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. These single 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.   " In addition, the analysis by phylogenetic and ecological groups, suggest that the communities respond in a similar trajectory of initial colonization first by heterotropic generalists and later specialists. "\cite{L_pez_Lozano_2013}  "Resource availability is also likely to be a funda- mental driver of microbial succession, but the limiting resources and environmental factors regulating succession will be more complex given the far greater physiological diversity contained within microbial communities and the breadth of environments in which succession can occur. During endoge- nous heterotrophic succession, labile substrates will be consumed first, supporting copiotrophic microbial taxa that are later replaced by more oligotrophic taxa that metabolize the remaining, more recalcitrant, organic C pools in the later stages of succession (Rui et al., 2009)."\cite{Fierer_2010}  "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}  "For bacterial succession, an increase in the proportion of Proteobacteria from winter to spring was observed, whereas that of Actinobacteria and Verrucumicrobia decreased (Figure 1b). Changes in the respective group abundances were validated by a PLFA analysis, which showed similar trends (Figure 2). A reduction of Actinobacteria was unexpected, because they are known to be involved in decomposition of organic materials, and thus are important for organic matter turnover and C cycle (Kirby, 2006). In other studies, an increase in the abundance of Actinobacteria has been shown during later stages of litter decomposition (Torres et al., 2005; Snajdr et al., 2011). The same accounts for the absence of Acidobacteria; members of this bacterial phylum can degrade various polysaccharides in- cluding cellulose and xylan (Ward et al., 2009). Based on RNA sequencing, Baldrian et al. (2012) found Acidobacteria to be the main bacterial group that was enriched in an active litter inhabiting community."   "Different models for C-acquisition propose a sequential decomposition of polysaccharides, starting with hemicellulose and cellulose degrada- tion followed by the removal of lignin (Berg and Mcclaugherty, 2008; Snajdr et al., 2011). " \cite{Schneider_2012}  
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"2) there is a common decomposition sequence independent of plant inputs or other ecosystem properties; and 3) molecular decomposition sequences, although consistent, are not uni- form and can be altered, resulting 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 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}  -------  " In addition, the analysis by phylogenetic and ecological groups, suggest that the communities respond in a similar trajectory of initial colonization first by heterotropic generalists and later specialists. "\cite{L_pez_Lozano_2013}  "Resource availability is also likely to be a funda- mental driver of microbial succession, but the limiting resources and environmental factors regulating succession will be more complex given the far greater physiological diversity contained within microbial communities and the breadth of environments in which succession can occur. During endoge- nous heterotrophic succession, labile substrates will be consumed first, supporting copiotrophic microbial taxa that are later replaced by more oligotrophic taxa that metabolize the remaining, more recalcitrant, organic C pools in the later stages of succession (Rui et al., 2009)."\cite{Fierer_2010}  "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}