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Harvard Forest Symposium Abstract 2012

• Title: Response of soil microbial community to heating and implications for the climate
• Primary Author: Jerry Melillo (Marine Biological Laboratory)
• Additional Authors: Chelsea Baldino (Marine Biological Laboratory); Frank Bowles (Research Designs); Sarah Butler (Marine Biological Laboratory); Lindsay Scott (Marine Biological Laboratory); William Werner (Marine Biological Laboratory)
• Abstract:

  During the twenty-year soil warming study at the Harvard Forest, we have observed a three-phase response to increased soil temperature. Initially, soil warming caused an increase in soil respiration in the heated plots relative to the control, and there was a significant loss of soil carbon in the heated plots (Phase I). The soil respiration delta in response to warming then declined so that after a decade, soil respiration rates in the warmed and control plots were about equal (Phase II). In year 15, soil respiration in the heated plots began to increase relative to the control plots, and the delta has grown over the last 5 years (Phase III). Over the study period, we have made a number of measurements of soil-carbon quality and indicators of microbial community structure and function. When respiration rates in both heated and control plots were equal (Phase II), labile carbon pools and microbial biomass were lower in the heated plots relative to the control (Bradford et al. 2008, Frey et al. 2008). It has been hypothesized that the decrease in microbial biomass could be because of the decrease in the size of the labile carbon pool or because of a reduction in carbon-use efficiency (Allison et al. 2010). As for the increase in soil respiration in response to warming in Phase III, the mechanism of this shift is not well understood. Our working hypothesis is that there has been a change in the microbial community, with microbes that have the capacity to produce oxidative enzymes becoming more important actors during Phase III. Preliminary measurements of extracellular enzyme potential and estimates of phenol utilization efficiency carried out during Phase III (Frey personal communication) indicate that the microbial community in warmed soils have a greater capacity to break down more recalcitrant carbon compounds. In the future, we will conduct genomic and functional analyses of soils from this long-term study in order to better understand the microbial community structure present after twenty years of warming.

• Research Category: Large Experiments and Permanent Plot Studies
  Soil Carbon and Nitrogen Dynamics