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Harvard Forest Symposium Abstract 2011

  • Title: Seasonal, Biogeochemical, and Microbial Response of Soils to Simultaneous Warming and Nitrogen Additions
  • Primary Author: Alix Contosta (University of New Hampshire - Main Campus)
  • Additional Authors: Serita Frey (University of New Hampshire - Main Campus); Melissa Knorr (University of New Hampshire - Main Campus)
  • Abstract:

    Climate warming and N deposition are global environmental threats that could alter soil microbial communities and the biogeochemical processes they perform. Few studies have examined interactive effects of elevated temperatures and N inputs. Many studies have also not considered the role that season plays in mediating the response of soils to warming and N. Finally, most research has not linked changes in the soil microbial community with ecosystem-scale dynamics. One objective of this study was to examine season-specific microbial and biogeochemical responses to simultaneous warming and N additions. Another aim was to investigate whether warming and N can restructure microbial communities in such a way as to alter ecosystem processes. The research occurred at the Soil Warming × Nitrogen Addition study at the Harvard Forest, and included four treatments: control, warming, warming × N, and N additions only. Soil respiration and N mineralization were measured continuously for two years, from May 2007 through April 2009. Further monthly respiration measurements were made during the growing seasons of 2009 and 2010. During winter, spring, summer, and fall of 2008, labile carbon, enzyme activity, microbial biomass, and microbial community composition were quantified. In October of 2009 and 2010, soils were re-sampled for microbial biomass and community composition. Finally, a wood decomposition study was conducted from 2007 through 2009 at the field site to examine changes in both wood decay and the fungi performing the decay.



    For the 2007 through 2009 sampling period, results indicated season-specific responses of soil respiration, N mineralization, and microbial biomass to the experimental manipulations. Soil respiration and N mineralization increased with warming and N additions, even during winter. By contrast, microbial biomass declined with warming and N and this decline primarily occurred in autumn. Where warming × N occurred together, warming appeared to moderate the negative effect of N additions on soil respiration and microbial biomass. Regarding the decomposition experiment, N additions suppressed wood decay while warming had no effect. The combination of warming × N was synergistic, accelerating wood decay beyond either treatment on its own. Lower decay rates in fertilized plots were not associated with a concomitant change in the structure of the fungal community colonizing the wood. Overall, the findings from the 2007 to 2009 data collection suggest that anthropogenic stressors and seasonal changes can interact to affect soil microbial communities and biogeochemical cycles.



    Field season measurements of soil respiration from 2009 and 2010 indicate that both warming and N additions have continued to stimulate CO2 flux, with warming treatments having a stronger effect on respiration than N additions alone. We are currently analyzing soil samples from the autumns of 2009 and 2010 for microbial biomass and community composition.

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