I conduct my dissertation research at the forested Free-Air CO2 Enrichment (FACE) experiment at Oak Ridge National Laboratory (ORNL). CO2 enrichment at ORNL FACE has more than doubled fine-root production. Further, fine roots have increased soil exploration at depths up to 60 cm, which is twice the average rooting depth in the control plots.
My dissertation research is focused on the question of whether CO2-mediated increases in fine-root litter will progressively decrease forest nitrogen availability by increasing nitrogen immobilization in soil organic matter.
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Current Projects
Changes in fine-root quantity and quality with elevated CO2:
Implications for decomposition and N cycling |
Changes in fine-root quantity and quality under scenarios of elevated CO2 have the potential to affect microbial decomposition rates, which may lead to an imbalance between fine root decomposition and production, as well as changes in C storage and N cycling. To better understand how increases in root production and proliferation at depth may affect these ecosystem processes, I am currently examining the characteristics and decomposability of fine roots grown under current and elevated concentrations of CO2 at the ORNL FACE site. |
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Increased fine-root production may increase gross N mineralization
and immobilization in a CO2 enriched deciduous forest |
Large inputs of labile organic C via plant litter can create a large biosynthetic microbial demand for N and increase microbial N immobilization, though this depends on characteristics associated with soil depth. I used an isotope dilution technique at ORNL FACE to measure CO2 effects on potential rates of gross N immobilization, mineralization, and nitrification at four 15-cm depth increments up to 60 cm within the soil profile. |
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N limitation in a sweetgum plantation:
Implications for C storage at ORNL FACE
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Soil N availability often limits net primary production in terrestrial ecosystems and is therefore predicted to constrain long-term increases in forest productivity and C storage in response to CO2 enrichment. We performed a fertilization experiment in the summers of 2004 and 2005 in a sweetgum plantation adjacent to FACE to examine the theory that sweetgum trees on the ORNL research park are limited by N availability prior to CO2 fertilization. |
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Past projects
Increased N and P availability affect N-use efficiency at
multiple ecological scales in northern peatlands |
The adaptive use of resources by plants is an important topic in ecology, and is generally expressed as a resource-use efficiency. Nitrogen-use efficiency (NUE), in particular, has been the subject of several studies, as N is the primary growth-limiting factor in many ecosystems. We examined how increases in N and P availability may affect plant NUE response at multiple ecological scales in fertilization experiments across a gradient of nutrient-limited peatland ecosystems in the Upper Peninsula of Michigan. |
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