University of Michigan
Enrollment Year: 2005
Atmospheric Mentor: Mary Anne Carroll, University of Michigan
Biosphere Mentor: Don Zak, University of Michigan; Knute Nadelhoffer, University of Michigan
In order to predict the response of ecosystem productivity to increasing concentrations of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3), it is necessary to understand how such changes will affect releases of biologically reactive nitrogen (N) during organic matter decomposition. An important component of decomposition and the associated release of N is the production of fine root and mycorrhizal litter. Elevated atmospheric CO2 and elevated tropospheric O3 are likely to alter total plant allocation to fine roots and mycorrhizal fungal symbionts rich in the nitrogenous-containing compound chitin. The proportion of chitin-derived N that is made available to plants as NH4+ during decomposition depends which organisms (or classes of organisms) are responsible for its breakdown. Actinomycetes and fungi are the two groups most active in chitin degradation. Distinguishing which of these two groups dominate chitin degradation in northern hardwood forests under eCO2 and eO3 is important because actinomycetes and fungi decompose the material with differing efficiencies. If fungi dominate chitin decomposition under eCO2 and/or eO3, a greater proportion of the associated NH4+ released would potentially be available for plant uptake. However, if actinomycetes dominate chitin degradation, microbial decomposers would retain a greater proportion of the N in chitin litter that enters the soil, leaving less available for plant uptake and growth. Therefore, this proposal addresses the following two key questions on the effects of changes in atmospheric chemistry on ecosystem function:
1. How will elevated atmospheric CO2 and tropospheric O3 alter belowground plant litter biochemistry?
2. How does microbial community composition influence ecosystem nitrogen availability?
Because N availability often constrains plant growth in terrestrial ecosystems, understanding the mechanisms by which it is influenced by atmospheric chemistry is needed for better predicting ecosystem response to anthropogenic global change.
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