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Harvard Forest Symposium Abstract 2010

  • Title: Interactive Effects of Soil Warming and Nitrogen Additions on the Soil Microbial Community
  • 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:

    Soil warming studies are typically single factor experiments that examine the effect of increased temperatures on soil carbon and nutrient fluxes. Many of these studies do not quantify the microbial community that performs these fluxes. In addition, most do not represent a scenario where increased temperatures take place along with other disturbances such as nitrogen deposition. The objective of this study was to examine the interactive effects of warming and nitrogen fertilization on the soil microbial community. The research occurred at the Soil Warming ×Nitrogen Addition Experiment at the Harvard Forest in Petersham, MA. The experiment included four treatments: control, heat, heat + N, and N only. Since August 2006, heated plots have been warmed to 5°C above ambient using buried cables, and monthly additions of aqueous NH4HO3 have fertilized plots at a rate of 5 g N m-2 y-1. Soils were sampled in January, April, July, and October 2008, and phospholipid fatty acid analysis was used to examine microbial biomass and microbial community composition. Results indicate that the soil microbial community responded most strongly to warming and/or N additions in October, when fungal and bacterial biomass was suppressed in all the experimental manipulations. The N only plots displayed the largest decrease in biomass, followed by heat + N, and then the heat only treatment. These reductions could account for the long-term acclimation and/or decline of soil CO2 respiration observed in many soil warming and N fertilization experiments. In addition, the N only plots showed a significant change in microbial community composition in October 2008, while the heat+N plots displayed a community composition intermediate between the heat only and the N only treatments. The more moderate decrease in biomass and the smaller shift in community composition in the heat + N plots as compared to the N only treatment suggest that increased temperatures alleviate the negative effect of N fertilization on the soil microbial community.

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