HR: 1340h
AN: B13C-0248    [Abstracts]
TI: The Effects of N Addition on the Belowground C Cycle in two Temperate Forests
AU: * Nowinski, N S
EM: nnowinsk@uci.edu
AF: University of California-Irvine, 3200 Croul Hall, Irvine, CA 92697 United States
AU: Trumbore, S
EM: setrumbo@uci.edu
AF: University of California-Irvine, 3200 Croul Hall, Irvine, CA 92697 United States
AU: Fernandez, I
EM: ivanjf@maine.edu
AF: University of Maine, 5722 Deering Hall, Orono, ME 04469-5722 United States
AU: Magill, A
EM: alison.magill@unh.edu
AF: Unversity of New Hampshire, 481 Morse Hall, Durham, NH 03824 United States
AU: Rustad, L
EM: rustad@maine.edu
AF: University of Maine, 5722 Deering Hall, Orono, ME 04469-5722 United States
AU: Szillery, J
EM: johanna.szillery@umit.maine.edu
AF: University of Maine, 5722 Deering Hall, Orono, ME 04469-5722 United States
AB: Human activities such as fossil fuel combustion, fertilizer-use, industrial ammonia and biomass burning have roughly doubled the amount of biologically active nitrogen entering ecosystems each year. N is essential for growth and is the limiting nutrient in many ecosystems. Additionally, N availability has been shown to affect plant, root and soil respiration. For several temperate forests, experimental addition of N is associated with a decline in soil CO2 efflux. This decline could be due to either (1) decreased allocation of C to root metabolism and growth because N demand of plants can be met with less energy expended belowground, or (2) decreased rates of organic matter supply or decomposition due to changes in leaf or root tissue chemistry, or to changes in the decomposer community. We use radiocarbon measurements in soil organic matter, heterotrophically respired CO2, and soil respiration to distinguish between these two hypotheses. Atmospheric 14C peaked in the 1960s due to atomic weapons testing and has subsequently been declining. Differences in 14C of soil organic matter and fine roots sampled in control versus N addition plots can be used to determine if turnover differs between these pools by treatment. In temperate forests heterotrophic respiration is distinguishable from autotrophic respiration by its 14C content, so radiocarbon measurements in respired CO2 can be used to estimate the contribution of root respiration to overall CO2 efflux We will report measurements made at two sites: (1) the Bear Brook watershed in eastern Maine, which consists of 2 10ha plots, a reference and another that receives 34 kg N ha-1 yr-1 with sections of hardwood and conifer stands in each plot, and (2) N amendment plots at the Harvard Forest in central Massachusetts, which consist of 6 0.09ha plots, a control, a plot receiving 50 kg N ha-1 yr-1, and one receiving 150 kg N ha-1 yr-1 in both conifer and hardwood stands. Data on root and litter/soil C dynamics on a series of timescales will be presented, together with implications for C storage in ecosystems subjected to anthropogenic N deposition.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting