HR: 1340h
AN: B23A-0945    [Abstracts]
TI: The Source of Carbon for Root Respiration
AU: * Cisneros-Dozal, L
EM: cisnerol@uci.edu
AF: University of California, Department of Earth System Science 3200 Croul Hall, Irvine, CA 92697 United States
AU: Trumbore, S
EM: setrumbo@uci.edu
AF: University of California, Department of Earth System Science 3200 Croul Hall, Irvine, CA 92697 United States
AU: Zheng, S
EM: szheng@uci.edu
AF: University of California, Department of Earth System Science 3200 Croul Hall, Irvine, CA 92697 United States
AB: In the Enriched Background Isotope Study (EBIS) that took advantage of a whole-ecosystem radiocarbon label that occurred in the temperate forest near Oak Ridge, Tennessee, we measured the radiocarbon signature of total soil respiration, heterotrophic respiration and root respiration, at different times during the last 3 growing seasons (2002-2004). By applying a mass balance approach, the relative and absolute contributions of heterotrophic and root respiration to total soil respiration were estimated. In contrast to heterotrophic respiration, root respiration seemed to be less affected by changes in soil moisture and temperature but rather showed a link to photosynthetic activity with a very similar pattern during the growing season as that of leaf area index. The radiocarbon signature of root respiration was very dynamic with low values in spring compared to the summer. The sources of variation can include changes in the local atmospheric signature and/or changes in the source of C being respired. Two different sites with different values and patterns of local atmospheric radiocarbon signature showed the same pattern in radiocarbon signatures of root respiration indicating that the source of variation was phenological. Low values during the spring could indicate the use of stored carbohydrates switching to more recent photosynthetic products as the summer progresses. As a first attempt to elucidate the source of C respired by roots, we will compare the radiocarbon content of starch, cellulose and soluble sugars in roots to that of bulk root material and root respired CO$_{2}$. These radiocarbon signatures can help us identify the pool of C that is most likely being respired by roots during the growing season. A better understanding of the source of C for root respiration has implications for understanding the role of root respiration in C cycling in temperate forests, specifically the timescale over which carbon is fixed through photosynthesis and returned to the atmosphere by root respiration.
DE: 4805 Biogeochemical cycles (1615)
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting