Microbial communities are responsible for decomposing soil organic carbon and mediating rates of carbon flow through an ecosystem. Due to the diversity of soil microorganisms, it has been notoriously difficult to characterize functional traits of microbial taxa, especially with regards to broadly distributed processes such as carbon assimilation and mineralization. Microorganisms can exhibit phylogenetic organization in their habitat preferences and life-strategies suggesting phylogeny might be linked to function. The overall objective of our study was to determine if substrates utilization is phylogenetically clustered in microorganisms and if this patterns of substrate use are consistent across soils with differing organic matter. Soils were sampled from the Detritus Input and Removal Treatment plots in Harvard Forest (Petersham, Ma) with the following treatments: normal litter inputs, double litter inputs, and no litter inputs. We used parallel incubations with 13C-labelled glucose and cellulose as well as no substrate added controls. Quantitative stable isotope probing was used to measure taxon-specific substrate assimilation into microbial biomass. Since the ecology and metabolic capabilities of soil microorganisms are important to ecosystem process rates, understanding who’s there as well as what are they doing will further our understanding of carbon flux within an ecosystem.
Results/Conclusions:
Historical litter input altered the decomposition rates of glucose and cellulose. Decomposition of glucose was most rapid in the normal litter treatment and slowest in no litter treatment. Conversely, the double litter treatment had the most rapid rate of cellulose decomposition. Approximately 40% of glucose was mineralized within the first week of incubation while cellulose decomposed more slowly with 60% remaining by 3 weeks. Differences in decomposition of glucose and cellulose corresponded with 13C incorporation by soil microorganisms. The majority of microbial taxa assimilated 13C-glucose into their DNA while 13C-cellulose incorporation was restricted to a few groups. Since most microorganisms are able to utilized glucose, we found that amount of glucose assimilation to be more dependent on the microorganisms’ life strategies. For example, fast growing families such as Psuedomonadacea, Micrococcaceae, and Xanthobacteraceae had a greater proportion of 13C enrichment. Cellulose utilization appeared to be restricted to specialized groups such as Cytophagaceae and Sphingomonadaceae. Generally, closely related phylotypes exhibited similar amount of 13C assimilation, however some groups were functionally coherent (e.g., Micrococcaceae) and others were more dispersed (e.g., Cytophagaceae). Taken together, these results indicate substrate assimilation can cluster according to phylogeny even across different organic matter inputs.