HR: 1340h
AN: B23A-0946    [Abstracts]
TI: Whole Ecosystem Low-level 14C Pulse Labeling and CO2 Flux Measurements in a Boreal Forest
AU: * Carbone, M
EM: mcarbone@uci.edu
AF: University of California, Dept. Earth System Science 3200 Croul Hall, Irvine, CA 92697-3100 United States
AU: Trumbore, S
EM: setrumbo@uci.edu
AF: University of California, Dept. Earth System Science 3200 Croul Hall, Irvine, CA 92697-3100 United States
AU: Czimczik, C
EM: czimczik@uci.edu
AF: University of California, Dept. Earth System Science 3200 Croul Hall, Irvine, CA 92697-3100 United States
AU: McDuffee, K
EM: kcmduffe@uci.edu
AF: University of California, Dept. Earth System Science 3200 Croul Hall, Irvine, CA 92697-3100 United States
AU: McMillan, A
EM: mcmillaa@uci.edu
AF: University of California, Dept. Earth System Science 3200 Croul Hall, Irvine, CA 92697-3100 United States
AB: We developed a large volume, low level, 14C pulse-chase, field labeling method to determine the timing and contribution of recent photosynthetic products to total ecosystem respiration in a poorly drained black spruce forest stand in Manitoba, Canada. The site is part of a chronosequence of black spruce stands located in the BOREAS Northern Study Area (55N, 98W), and time since fire is 40 years. The radiocarbon addition was designed to produce a 14C signature of ~1500 times Modern for CO2 at ambient levels inside the ~37,000 L volume light chamber. At this level of labeling, the radioactivity in our 14C source (acidified sodium bicarbonate solution with specific activity of ~30 nCi/g) and in the chamber were well below levels that are regulated. We labeled two chambers in August 2004. The vegetation inside the first (37,000 L) chamber included black spruce trees (ranging from seedlings to 4 m tall) with feather moss and shrub understory. A second 14CO2 label was applied in a smaller chamber (500 L) containing only feather mosses. Both chambers were constructed from polyethylene plastic that allowed for 70 percent transmission of PAR. For seven days following the label, we measured the quantity and 14C content of soil respiration with small (10 L) dark chambers, above-ground respiration with branch bags, and total ecosystem respiration with a dark chamber. Live root and moss 14C content were measured by field incubations. Additionally, soil gas 14C content at two depths within the moss/organic layer was measured. Radiocarbon measurements are made using Accelerator Mass Spectrometry, which allows us to easily distinguish the presence of the label in small amounts (mg) of material. We will report the radiocarbon (delta 14C) signature of individual respiration sources. Preliminary results show that we can use these isotopic signatures to follow the labeled contribution of respiration from individual sources (moss, root/root exudates, and needle) to total ecosystem respiration. We plan on using this information to separate moss respiration from soil respiration, and furthermore, to partition fast from slow cycling soil respiration sources in this ecosystem. We will attempt to scale small chamber and branch bag respiration fluxes and 14C content to large (37,000 L) chamber measurements. Additionally, the large chamber CO2 flux measurements will be compared with eddy covariance measurements taken concurrently at the same site.
DE: 4805 Biogeochemical cycles (1615)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting