1 / 19

Carbon and pH as Controls of Microbial and Microarthropod Communities in a Northern Hardwood Forest

This study examines the effects of carbon availability and pH on soil microbial and microarthropod communities in a northern hardwood forest. The experiment was conducted at the Hubbard Brook Experimental Forest in New Hampshire from 2000-2001. Results showed that calcium addition increased soil pH and respiration, but had no effect on microbial biomass. There was a non-significant decreasing trend in microarthropods in the summer of 2000, continuing to 2001.

phillipsr
Télécharger la présentation

Carbon and pH as Controls of Microbial and Microarthropod Communities in a Northern Hardwood Forest

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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. Question(s): • Does carbon availability • Does pH control soil microarthropod populations indirectly through microbial communities in the northern hardwood forest?

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

  4. C addition Ca addition C & Ca addition Control Experimental design Conducted at the Hubbard Brook Experimental Forest (HBEF) NH, summers 2000-2001. • In this study, I manipulated:  •  Forest floor carbon availabilityGlucose/Cellulose addition • Forest floor pH, Calcium (CaSiO3) addition 4 Treatment Plots at each of 5 sites

  5. Addition timeline: Summer 2000 Ca+ C+ C+ C+ C+ C+ 5-Jun 14-Jun 28-Jun 13-Jul 23-Jul Ca+ : Calcium addition performed; 667 g Ca m-2 C+: Carbon addition performed; totaling 120 g C m-2 for summer Background figures at Hubbard Brook: • Microbial biomass: 28 g C m-2 • Annual C input to organic soil: 250 g C m-2 (litter, roots, exudates)

  6. Calcium:added as ground wollastonite powder, sifted over each plot like flour. Carbon: mixed in 3L water solution and sprayed over plots with a backpack sprayer. Control plots received equivalent amounts of water throughout study.

  7. Data recorded: WhatWhen • Soil pH 2000-2001 • Microbial respiration (field) 2000 • Microbial respiration (lab) 2000 • Microbial biomass C 2000 • Microbial biomass N 2000 • Microarthropod abundance 2000-2001

  8. High hopes… • Expected increased pH in Ca addition plots • Expected to see positive response in microbial respiration as C availability increased • Curious about microbial biomass with respect to C availability • Curious about abundance of microarthropods with respect to both C availability and pH

  9. Bummer! No significant response in C plots: Respiration (e.g. ) Biomass C Biomass N Microarthropods However; lack of response to C addition allowed a statistical regrouping of data into Ca and no-Ca blocks…

  10. Soil pH response to Ca addition

  11. Microbial respiration response to Ca addition

  12. Microbial biomass C

  13. Trend in Microarthropods? Saw weak evidence (non-significant) of a decline in microarthropods in Ca addition plots

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

  15. Summary • No observed C addition effect (microbial respiration, biomass, or microarthropods). • 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 the summer of 2000, continuing to 2001.

  16. 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.

  17. Interpretation • Raised pH in Ca addition plots may have shifted the microbial community, resulting in a decrease in the fungal to bacterial ratio (F:B). • In addition to increased respiration, a lower F:B in Ca plots could explain the negative trend in microarthropods (primarily fungivorous).

  18. B B F F Interpretation (ctd.) Trophic consequence for microarthropods? Microarthropods Micro- arthropods pH increase +1

  19. Thanks! • Melany Fisk • Tim Fahey

More Related