HR: 14:40h
AN: B53B-05    [Abstracts]
TI: Quantification of Calcium Isotope Fractionation in Ectomycorrhizal Trees
AU: * Hoff, C J
EM: choff@cisunix.unh.edu
AF: UNH Dept. of Earth Sciences, James Hall, Durham, NH 03824 United States
AU: Bryce, J G
EM: julie.bryce@unh.edu
AF: UNH Dept. of Earth Sciences, James Hall, Durham, NH 03824 United States
AU: Hobbie, E A
EM: erik.hobbie@unh.edu
AF: UNH Complex Systems Research Center, Morse Hall, Durham, NH 03824 United States
AU: Colpaert, J V
EM: jan.colpaert@luc.ac.be
AF: Limburgs Universitair Centrum, Environmental Biology Universitaire Campus, Diepenbeek, B-3590 Belgium
AU: Bullen, T D
EM: tdbullen@usgs.gov
AF: USGS Branch of Regional Research, Water Resources Division, MS 420, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Calcium plays a significant role in many forest ecosystem processes and is required for plant growth. Within plants, calcium is a critical component of cell walls and membranes, signaling processes, and charge balances (1). Current efforts to quantify Ca cycling in ecosystems rely on large-scale ecosystem manipulations (e.g., 2) or mass balances (e.g., 3) and indirect chemical proxies, Ca/Sr or Sr isotopic systems (e.g., 4). The measurement of Ca isotopes may provide more direct information about the calcium sources and fluxes within and between the geological (mineral and soil) and biological (fungi and plants) components of terrestrial ecosystems. To examine calcium isotopic variability systematically, we measured the fractionation between roots and needles in cultured Scots pine ( Pinus sylvestris) seedlings. Our samples include roots and needles from trees grown at low or high nutrient supply rates (3% or 5% per day). Because mycorrhizal fungi are intimately involved in plant nutrient supply, we also tested whether mycorrhizal colonization by Suillus bovinus affected calcium isotopic fractionation. Initial results demonstrate that at a low nutrient supply rate there is a small but measurable fractionation (averaging 0.58 ‰) between the roots and needles of individual trees; the needles are enriched in ⁴⁰Ca compared to the roots. The root-needle fractionation is unaffected by mycorrhizal colonization. Ongoing analyses will address both the consistency of the root-needle fractionation and the impacts of nutrient supply rate on fractionation. Preliminary results suggest that higher nutrient supply rates lead to decreased root-needle fractionation. Analyses underway will also address whether different fungal species ( Thelephora terrestris) affect the documented root-needle fractionation. Isotope signatures of calcium source materials will complete our sample suite and will be used to assess fractionation during uptake. Ultimately, the results of this study will provide important insights into models of calcium isotope fractionation mechanisms as well as calcium cycling in forest ecosystems. (1) White, P.J. and M.R. Broadley. 2003. Annals of Botany. 92:487-511. (2) Peters, S.C., et al. 2004. Biogeochem. 67: 309-329. (3) Schmitt, et al. 2003. EPSL. 6731: 1-16. (4) Blum, J.D., et al. 2002. Nature. 417: 729-731.
DE: 0400 BIOGEOSCIENCES
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Biogeosciences [B]
MN: Fall Meeting 2005