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“The experiment that couldn’t fail…” - M. Fisk and P. Groffman Will Kessler

Carbon and pH as controls of microbial and microarthropod communities in a northern hardwood forest. “The experiment that couldn’t fail…” - M. Fisk and P. Groffman Will Kessler Department of Natural Resources Cornell University.

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“The experiment that couldn’t fail…” - M. Fisk and P. Groffman Will Kessler

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  1. Carbon and pH as controls of microbial and microarthropod communities in a northern hardwood forest “The experiment that couldn’t fail…” - M. Fisk and P. Groffman Will Kessler Department of Natural Resources Cornell University

  2. Carbon and pH as controls of microbial and microarthropod communities in a northern hardwood forest “The experiment that couldn’t fail…” - M. Fisk and P. Groffman Will Kessler Department of Natural Resources Cornell University

  3. Question: Does pH control soil microarthropod populations indirectly through microbial communities in the northern hardwood forest?

  4. Microarthropods Microbes Forest floor substrate • Microbes:soil bacteria and saprophytic soil fungi. In northern hardwood forests fungi dominate • Microarthropods: small invertebrates occupying trophic levels above microbes in below ground food-webs. • Primarily mites (Acari) and certain insects.

  5. Experimental design Conducted in Bear Brook Watershed (west of 6), summers 2000-2001 • Forest floor pH manipulation • 667 g m-2 Calcium (CaSiO3) added as fine powder • Data Recorded from Organic horizon • Soil pH • Microbial respiration (field + lab) • Microbial biomass C + N • Microarthropod abundance

  6. Soil pH response to Ca addition

  7. Microbial respiration response to Ca addition

  8. Trend in Microarthropods? Saw weak evidence (non-significant) of a decline in microarthropods in Ca addition plots p = 0.109 p = 0.134

  9. Additional evidence across season: microarthropod decline Similar dates in consecutive years appear to have decreasing microarthropods per g dry soil p = 0.174

  10. Summary • Ca addition resulted in an increase in soil pH and respiration, but had no effect on microbial biomass. • Microarthropods showed a non-significant decreasing trend in Ca plots during the summer of 2000, continuing to 2001.

  11. Linking pH to microbial activity(3 scenarios) • Increased pH could translate to lower stress for microbes, meaning more activity, growth, and mortality. Net signal is then increased CO2, but not biomass. • Increased pH, could mean greater stress for an acidic-adapted community. Thus, CO2 signal is stress induced, and no biomass is added. • Increased pH could favor bacteria over fungi in the forest floor. Bacteria are less efficient than fungi, and would thus produce more CO2 per unit biomass.

  12. B B F F Interpretation Trophic consequence for microarthropods? Microarthropods Micro- arthropods pH increase +1

  13. Thanks! • Melany Fisk • Tim Fahey • Peter Groffman

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