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Harvard Forest Symposium Abstract 2010

  • Title: Response of soil microbial community to 19 years of warming: a preliminary study
  • Primary Author: Chelsea Vario (Dartmouth College)
  • Additional Authors: Sarah Butler (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory); Rose Smith (Marine Biological Laboratory)
  • Abstract:

    To date several key changes have been observed through the long term soil warming experiment at the Harvard Forest. During the first few years of heating, soil respiration was greatly accelerated compared to the control plots (Melillo et al. 2002), but the heating effect slowed during years 5-12. In a study focused on the first twelve years of the experiment, Frey et al. (2008) reported a 45% decrease in active microbial biomass on the heated plots, including reductions in total fungal and arbuscular micorrhizal biomarkers. After fifteen years of warming, Bradford et al. (2008) found a significant decrease in labile carbon on the heated plots and suggested that both substrate limitation and thermal adaptation of the microbial community played a part in the reduction of carbon dioxide release. However, since year 13 of the experiment, respiration rates have begun to rise again. This has suggested further adaptation of the microbial community which may be leading to the metabolism of more recalcitrant forms of carbon, such as lignin. To explore this possibility both time-series and rapid analysis extracellular enzyme assays were performed on soils from the heated and control plots. On three occasions throughout 2009, extracellular enzyme assays were conducted for two oxidative enzymes—phenol oxidase and peroxidase, which break down lignin. On one occasion samples were collected for time-series incubations, in which soils were amended with lignin and nitrogen and assayed over an 18 day period. “Snap shot” assays did not reveal differences in the enzyme dynamics in the heated and control soils, but the incubation experiments revealed differences in the response of heated versus control soils. When amended with lignin, heated soils responded with increased respiration and enzyme activity rates, while control soils were not affected. This finding suggests that soils exposed to two decades of heating were primed to break down more recalcitrant forms of carbon. Further studies are being conducted to verify that heated soils are capable of respiring older, more recalcitrant forms of carbon that would otherwise remain in the terrestrial carbon pool.

  • Research Category: Forest-Atmosphere Exchange, Large Experiments and Permanent Plot Studies, Soil Carbon and Nitrogen Dynamics