Increased forest growth in response to rising atmospheric concentrations of CO2 may mitigate a portion of fossil fuel emissions, especially if carbon is sequestered in longlived biomass or soil pools. Greater carbon uptake under elevated atmospheric [CO2] in forested ecosystems may facilitate the production of small diameter (i.e. “fine”) roots used for nutrient acquisition. Increased fine-root production in forested ecosystems may affect soil carbon storage and nitrogen cycling because fine roots live and die in the span of a year. My dissertation research took advantage of a long-term, on-going Free-Air CO2-Enrichment experiment in a sweetgum (Liquidambar styraciflua L.) forest stand at Oak Ridge National Laboratory to investigate the causes and consequences of increased fine-root production under elevated [CO2]. To examine the premise that N limitation was the cause of increased fine-root production in the CO2-enriched sweetgum stand, I fertilized plots in an adjacent sweetgum plantation with 200 kg ha-1 of N as urea. The relative C flux to wood production that I observed in the fertilized treatment is consistent with the premise that increased root production in the adjacent FACE experiment is in response to N limitation. To examine the consequencesof increased fine-root production under elevated [CO2], I: (1) quantified fine-root biomass and N inputs at several soil depths using a long-term minirhizotron data set combined with continuous, root-specific measurements of root mass per unit length and [N], and (2) allowed fine roots grown under current and elevated [CO2] to decompose in a common garden experiment by modifying existing litterbag methodology. I found that C and N inputs via root mortality were doubled under elevated [CO2], and half of the inputs were below 30 cm soil depth. However, CO2-enrichment had no effect on fine-root chemistry or decomposition rate, and therefore more root detritus may be incorporated into long-lived soil organic matter under elevated [CO2]. Quantification of the effects of elevated CO2 on the fate of a greater quantity of fine-root detritus, especially at depth in the soil, will provide critical information needed for predicting processes such as long-term soil C storage and N cycling in response to environmental change.
| Identifer | oai:union.ndltd.org:UTENN/oai:trace.tennessee.edu:utk_graddiss-1517 |
| Date | 01 August 2008 |
| Creators | Iversen, Colleen Marie |
| Publisher | Trace: Tennessee Research and Creative Exchange |
| Source Sets | University of Tennessee Libraries |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations |
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