Relationships Between Microbial Community Structure and Soil Processes Under Elevated Atmospheric Carbon Dioxide
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There is little current understanding of the relationship between soil microbial community composition and soil processes rates, nor of the effect climate change and elevated CO2 will have on microbial communities and their functioning. Using the eastern cottonwood (Populus deltoides) plantation at the Biosphere 2 Laboratory, we studied the relationships between microbial community structure and process rates, and the effects of elevated atmospheric CO2 on microbial biomass, activity, and community structure. Soils were sampled from three treatments (400, 800, and 1200 ppm CO2), a variety of microbial biomass and activity parameters were measured, and the bacterial community was described by 16S rRNA libraries. Glucose substrate-induced respiration (SIR) was significantly higher in the 1200 ppm CO2 treatment. There were also a variety of complex, nonlinear responses to elevated CO2. There was no consistent effect of elevated CO2 on bacterial diversity; however, there was extensive variation in microbial community structure within the plantation. The southern ends of the 800 and 1200 ppm CO2 bays were dominated by β-Proteobacteria, and had higher fungal biomass, whereas the other areas contained more α-Proteobacteria and Acidobacteria. A number of soil process rates, including salicylate, glutamate, and glycine substrate-induced respiration and proteolysis, were significantly related to the relative abundance of the three most frequent bacterial taxa, and to fungal biomass. Overall, variation in microbial activity was better explained by microbial community composition than by CO2 treatment. However, the altered diversity and activity in the southern bays of the two high CO2 treatments could indicate an interaction between CO2 and light.
KeywordsPhotosynthetically Active Radiation Clone Library Microbial Community Structure Microbial Community Composition Eastern Cottonwood
We gratefully acknowledge Spring Strahm, Laura Dane, and Richard Wilson for logistical and laboratory assistance, and Dr. Barry Osmond for his skilled coordination of research efforts at B2L. The comments of two anonymous reviewers were very helpful in revising this manuscript. Financial support was provided by the Packard Foundation and the Office of the Executive Vice Provost, Columbia University (Dr. Michael Crow). We especially would like to thank Mr. Edward P. Bass for making this study possible.
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