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Biomass, depth distribution, and nitrogen concentration of fine roots in northern forests exposed to elevated atmospheric CO2 and tropospheric O3
AuthorKeller, Richard Kyle
AdvisorPregitzer, Kurt S
Natural Resources and Environmental Science
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As global levels of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) increase, it is important to understand how these two gases will affect forest carbon (C) sequestration. Although fine roots are a small portion of the overall forest C pool, their function is key in nutrient acquisition and the formation of soil C, ultimately linking forest productivity and soil. Exposure to increased CO2 is known to stimulate forest productivity and fine root biomass, while tropospheric O3 is phytotoxic and increased O3 has been shown to decrease root biomass. The Aspen FACE (free-air CO2 enrichment) experiment was designed to better understand the forest response to elevated CO2 and O3. Here, we describe the response of fine root biomass, distribution, and nitrogen (N) concentrations after eleven years of treatment with elevated CO2 and/or O3 concentrations. Fine roots were collected through incremental soil cores in the experimental treatments and across the community subplots to a depth of 1 meter.No effects of elevated CO2 or O3 were observed on root biomass or root depth distribution. The previously observed effects of CO2 and O3 disappeared indicating a transient response through time. The results suggest that elevated CO2 in future climates may cause a stimulation of fine roots, but that stimulation is transient. Similarly, the effects of elevated O3 also diminished with time, indicating that O3 may only decrease fine root biomass in young forests. However, the effects of community and community interaction with elevated CO2 and O3 treatments on root N indicate differential species responses, with the potential to shift the species composition of future forests. This research supports the idea that climate change will affect our future forests, but not always in the way we predicted.