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Harvard Forest Symposium Abstract 2013

• Title: Response of Soil Microbial Community to Heating and Implications for the Climate
• Primary Author: Chelsea Baldino (Marine Biological Laboratory)
• Additional Authors: Frank Bowles (Research Designs); Sarah Butler (Marine Biological Laboratory); Serita Frey (University of New Hampshire - Main Campus); Jerry Melillo (Marine Biological Laboratory); Lindsay Scott (Marine Biological Laboratory); Rose Smith (Marine Biological Laboratory); William Werner (Marine Biological Laboratory)
• Abstract:

  Chelsea Baldino, Ecosystems Center, MBL
  
  Prospect Hill 21-year-old Soil Warming Experiment
  
  Abstract, Harvard Forest Annual Ecology Symposium 2013
  
  
  
  During the twenty-second year of soil warming at our Harvard Forest Prospect Hill site, we have continued to observe an increase in carbon dioxide emissions from our heated plots relative to our control plots. Throughout the years, we have witnessed respiration go through three phases. Initially, soil warming caused an increase in soil respiration in the heated plots relative to the control, causing a significant loss of soil carbon in the heated plots (Phase I). The soil respiration difference between heated and control then declined so that after around a decade, soil respiration in the heated and control plots was about equal (Phase II). In around year 15, soil respiration in the heated plots began to increase relative to the control plots, and the delta has now been positive again for the past six years (Phase III) (Fig. 1). Throughout the study period, we have made a number of measurements of soil-carbon quality and indicators of microbial community structure and function to determine why respiration has behaved this way.
  
  
  
  When respiration rates in both heated and control plots were equal (Phase II), microbial biomass was lower in the heated plots relative to the control, which we hypothesized was because of a decrease in the size of the labile carbon pool or because of a reduction in carbon-use efficiency (Bradford et al. 2008, Frey et al. 2008, Allison et al. 2010). As for the increase in soil respiration in Phase III, we hypothesize that since there is less labile carbon available to the microbes, a shift in the microbial community to organisms capable of breaking down recalcitrant carbon has now occurred. This hypothesis is supported by preliminary results, which show that heated plots have significantly higher microbial diversity than control plots, suggesting that new microbial species have moved in to these plots (DeAngelis, unpublished). Also, at incubation temperatures of 15°C and 25°C, soils amended with phenol had significantly higher microbial carbon-use efficiency in the heated plots than the control, which means it is possible that the microbial community in the heated plots has adapted to breaking down recalcitrant compounds more efficiently (Frey at al. 2012). This increased efficiency means that microbes are spending less carbon on respiration and thus are incorporating more carbon into their own biomass, which may explain why we have seen an increase in respiration again in recent years. In the future, we will be conducting genomic and functional analyses of soils at Prospect Hill with collaborators at UMass Amherst and the University of New Hampshire in order to better understand the microbial community structure.
  
  
  
  References:
  
  Allison, S. D., M. D. Wallenstein, et al. 2010. Soil-carbon response to warming dependent on
  
  microbial physiology. Nature Geoscience 3: 336-340.
  
  
  
  Bradford, M. A., C. A. Davies, et al. 2008. Thermal adaption of soil microbial respiration to
  
  elevated temperatures. Ecology Letters 11: 1316-1327.
  
  
  
  Frey, S.D., R. Drijber, et al. 2008. Microbial biomass, functional capacity, and community
  
  structure after 12 years of soil warming. Soil Biology and Biochemistry 40: 2904-2907.
  
  
  
  Frey, S.D, J. Lee, et al. 2012. The temperature response of soil microbial efficiency and its
  
  feedback to climate. Nature Climate Change (Advance Online Publication).
  
  

• Research Category: Forest-Atmosphere Exchange
  Group Projects
  Soil Carbon and Nitrogen Dynamics


• Figures:
CLB LTER 2013 Abstract Fig. 1.jpg