OOS 40-10 - Chronic atmospheric N deposition decreases microarthropod density in a northern hardwood ecosystem

Thursday, August 11, 2011: 4:40 PM
17A, Austin Convention Center
Huijie Gan , Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI
Mark D. Hunter , Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI
Donald R. Zak , Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI
Background/Question/Methods

Nitrogen (N) deposition can negatively impact litter decomposition by slowing the rate of microbial decay.  Soil arthropods, which also mediate important functions during litter decomposition, could also be negatively impacted, especially if the slowing of microbial decay decreases the flow of energy in the soil food web.  In order to study the influence of N deposition on soil arthropod communities and decomposition, 96 litter bags with aspen litter were placed in the forest floor of a sugar maple dominated forest that is designated for long term N deposition study (3 plots have received ambient N deposition and the other 3 plots have received an additional 30Kg N / ha/yr since 1994). Litter bags were retrieved at 2 months, 4 months, 14 months and 16 months and the arthropods were extracted using modified Tullgren funnels. The arthropods were enumerated under microscopes with the dominant group Oribatida identified to species. 

Results/Conclusions

Simulated N deposition stimulated mass loss, consistent with the hypothesis that the initial stages of litter decay are accelerated by high N availability. While there was no difference in arthropod density between ambient and simulated N deposition treatments, oribatid mite species richness was greatly reduced in the litter bags exposed to simulated N deposition.  The association of higher decomposition rate and lower oribatid mite richness in litterbags exposed to simulated N deposition suggests that faster decay may offer less diverse resources to support the oribatid mites community.  We hypothesize that microbial diversity is generally lower under faster rates of litter decay. However, understanding changes in oribatid mite communities will require further study of the interaction between saprotrophic microbial communities and arthropod communities.

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