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Harvard Forest REU Symposium Abstract 2008

  • Title: Soil warming and nitrogen additions influence brown food webs.
  • Author: Johanna L Weaver (Oberlin College)
  • Abstract:

    Two anthropogenic effects: added nitrogen (+N) in rainfall and increased temperature (+Heat) through increasing CO2, are widespread in northern temperate forests but the combined impact of heat and nitrogen additions on community structure is still unknown. We tested their effects on the community structure of a brown food web (decomposer microbes and their consumers) in a New England forest. We tested two hypotheses. First, ectotherms are heat limited, so activity of arthropods will increase with +heat. Second, decomposer populations are N-limited, and feed arthropods, hence +N should in turn increase arthropod abundance. At the Harvard Forest six replicates of four treatments (+N, +Heat, +N +Heat, Control) were applied to 3x3 m plots, beginning in the Fall of 2006. From April – July 2008 we measured activity density of four common taxa —two predators: ants and spiders, and two microbivores: collembola and mites— using two pitfall traps per plot over 48 hours. Taxa responded differently. Ants and collembola increased on +heat plots. Acari abundance increased on +N and +heat plots, but decreased again on +heat +N plots. Spiders did not vary with either treatment. Thus two common taxa, a microbivore and a predator, appear to increase in local activity with warming. The lack of +N effects may reflect the lack of N-limitation of decomposers and/or increased shading of +N plots. After two years, warming appears to have a larger effect on this brown food web than nitrogen deposition.

  • Research Category: Large Experiments and Permanent Plot Studies