HR: 08:30h
AN: B41C-02    [Abstracts]
TI: The residence time of carbon in Amazonian primary forests
AU: * Trumbore, S
EM: setrumbo@uci.edu
AF: University of California, Department of Earth System Science, Irvine, CA 92612 United States
AU: Vieira, S A
EM: savieira@cena.usp.br
AF: Lab. de Ecologia IsotA��'A,A3pica, CENA/USP Av. CentenA��'A,A�rio 303, Piracicaba, SP 13416-000 Brazil
AU: Camargo, P
EM: pcamargo@cena.usp.br
AF: Lab. de Ecologia IsotA��'A,A3pica, CENA/USP Av. CentenA��'A,A�rio 303, Piracicaba, SP 13416-000 Brazil
AU: Chambers, J Q
EM: jchamber@tulane.edu
AF: Tulane University, Ecology and Evolutionary Biology, New Orleans, LA 70118 United States
AU: Higuchi, N
EM: niro@inpa.gov.br
AF: Institutio Nacional de Pesquisas da Amazonia, Andre Araujo, 1756, Manaus, AM 69011-970 Brazil
AU: Selhorst, D
EM: dselhorst@pop.com.br
AF: Setor de Estudos do Uso da Terra e MudanA��'A,Aas Globais, Parque ZoobotA��'A,A�nico Universidade Federal do Acre, Rio Branco, AC 69.915 Brazil
AU: Martinelli, L A
EM: lamartinelli@cena.usp.br
AF: Lab. de Ecologia IsotA��'A,A3pica, CENA/USP Av. CentenA��'A,A�rio 303, Piracicaba, SP 13416-000 Brazil
AB: The residence time of carbon is a major determiner of the capacity of an ecosystem to function as a source or sink of carbon. The overall residence time of carbon in primary forests is determined by (1) what fraction of photosynthetic products get respired quickly and (2) the residence time of C allocated to living plant tissues, and (3) the time each of these components takes to decay, including what fraction is oxidized to CO2 versus what becomes stabilized in soil organic matter. Using radiocarbon to determine the age of carbon in various pools in forests, we conclude that: (1) carbon use efficiency of these forests is low, with ~70% of photosynthetic products respired within a year, and only 30% allocated to growth of wood, root and leaf tissues; (2) carbon resides on average for 2-3 years in leaves and 3-10 years in fine roots; very rapid or ephemeral root turnover is assigned in our budgets to A�A�A��_sA�A<�"autotrophicA�A�A��_sA�A��_zA� respiration (3) the mean age of carbon in living trees is longer (200-260 years) than the mean residence time of carbon derived from the biomass stock divided by annual wood growth increment (40-100 years) because most of the biomass is in the largest, fastest growing, trees, while most of the individuals are smaller, slower growing, shaded trees; (4) decomposition rates are rapid, but potentially recycling of carbon in the microbial community leads to a significant decadally cycling pool in near-surface organic matter. We will summarize these findings and use them with models of carbon dynamics to estimate carbon storage and loss potential on interannual to decadal timescales. The overall age of heterotrophically respired carbon (carbon derived from microbial decomposition) is 6-10 years, with much of the time lag due to the time spent by C in living leaf and root tissues. Even when combined with 70% autotrophically respired C with residence times of <1 year, this significant time lag can lead to large interannual variation in net ecosystem exchange given relatively small, regionally coherent, shifts in gross photosynthesis. On decadal and longer timescales, the dynamics of wood and fast-cycling soil organic dominate the capacity for C storage under scenarios such as CO2 fertilization, or recovery from periodic disturbance.
DE: 1030 Geochemical cycles (0330)
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting