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Harvard Forest Symposium Abstract 2014

  • Title: Response of Soil CO2 Emissions and Nitrogen Mineralization to 22 Years of Experimental Warming
  • Primary Author: Jerry Melillo (Marine Biological Laboratory)
  • Abstract:

    The Prospect Hill soil warming experiment was designed to examine the effects of soil warming on soil carbon and nitrogen cycling. More recently, we have also begun examining microbial responses to warming, including changes in community structure. We observed a strong increase in soil respiration during the first 10 years of warming (Phase I), followed by a decrease back to control levels (Phase II, years 11-15). During Phase II we measured lower labile carbon pools and lower microbial biomass in the heated relative to the control plots. Following Phase II and through the present, we have observed respiration rates from the heated plots once again climbing above those from the control plots, which we are calling Phase III.

    In addition to increasing CO2 emissions, soil warming also stimulated nitrogen mineralization during Phase I. Periodic measurements of nitrogen mineralization during Phases II and III showed no stimulatory effect of soil warming. This lack of a long-term N cycle response to soil warming has implications for ecosystem-level carbon storage. We are studying these ecosystem-level implications with a second soil warming experiment at the Barre Woods site at Harvard Forest.

    Preliminary soil genomic studies being conducted by our collaborators Kristen DeAngelis and Jeffery Blanchard of UMass, Amherst, indicate that warming is changing microbial community structure, especially in the forest floor, where we have observed significant soil carbon mass loss. Laboratory incubations of soils from the heated and control plots conducted by Serita Frey of the University of New Hampshire suggest that soil warming differentially affects the decay of different classes of organic compounds - see Frey et al. Nature Climate Change 3:395-398. Multiple lines of evidence indicate microbial adaptation to soil warming, including laboratory studies (Bradford et al. 2008, Ecology Letters 11:1316-1327) and field measurements. The relative importance of changes in microbial structure in the adaptation to warming is not yet known.

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