Shifts in bacterial community structure associated with inputs of low molecular weight carbon compounds to soil

Low molecular weight carbon (C) substrates are major drivers of bacterial activity and diversity in the soil environment. However, it is not well understood how specific low molecular weight C compounds, which are frequently found in root exudates and litter leachates, influence bacterial community structure or if there are specific groups of soil bacteria that preferentially respond to these C inputs. To address these knowledge gaps, we added three simple C substrates representative of common root exudate compounds (glucose, glycine, and citric acid) to microcosms containing three distinct soils from a grassland, hardwood forest, and coniferous forest. CO2 production was assessed over a 24 h incubation period and, at the end of the incubation, DNA was extracted from the samples for assessment of bacterial community structure via bar-coded pyrosequencing of the 165 rRNA gene. All three C substrates significantly increased CO2 production in all soils; however, there was no relationship between the magnitude of the increase in CO2 production and the shift in bacterial community composition. All three substrates had significant effects on overall community structure with the changes primarily driven by relative increases in beta-Proteobacteria, gamma-Proteobacteria, and Actinobacteria. Citric acid additions had a particularly strong influence on bacterial communities, producing a 2-5-fold increase in the relative abundance of the beta-Proteobacteria subphylum. These results suggest that although community-level responses to substrate additions vary depending on the substrate and soil in question, there are specific bacterial taxa that preferentially respond to the substrate additions across soil types. (C) 2010 Elsevier Ltd. All rights reserved.