HR: 0800h
AN: B11B-0153    [Abstracts]
TI: Human Influence on the Carbon Cycle in Secondary Tropical Forests
AU: * Hopkins, F M
EM: checka@berkeley.edu
AF: Lawrence Berkeley Lab, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: * Hopkins, F M
EM: checka@berkeley.edu
AF: Department of Environmental Science, Policy and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Torn, M S
EM: mstorn@lbl.gov
AF: Lawrence Berkeley Lab, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Silver, W
EM: wsilver@nature.berkeley.edu
AF: Department of Environmental Science, Policy and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AU: Marin-Spiotta, E
EM: aurios@nature.berkeley.edu
AF: Department of Environmental Science, Policy and Management, University of California, Berkeley, 151 Hilgard Hall #3110, Berkeley, CA 94720 United States
AB: Recently it has been proposed that reforestation of tropical pasture lands may be an effective way to sequester CO2, but the effects of re-forestation on the soil C pool are not well known. In an attempt to gain a better understanding of the soil C dynamics during the process of tropical forest re-growth, soil samples were collected from active pasture and 10, 30, and 80 year-old secondary forest, in the Cayey region of Puerto Rico. We are conducting a long term incubation experiment to determine the effects of future climate change and atmospheric N deposition on soil CO2 effluxes and the relative importance of pasture or forest source C in soil C losses. Pasture soils exhibited the highest rates of soil respiration, followed by the secondary forests, which tracked closely under all treatments except N addition. There were few effects of added N on CO2 effluxes; the 80 year-old forest showed the lowest rates of soil CO2 efflux under N additions. In contrast, CO2 fluxes were consistently higher in soils at elevated temperature relative to the controls. In the re-growing forests, C-13 isotope data reveal that warming also increased the proportion of C3 derived C as opposed to C4 (i.e., old pasture) derived-C in respiration. After two months of incubations, no effect of warming on 13-CO2 was seen in pasture sites. Our results indicate that soil C pools in re-growing tropical forests are highly sensitive to temperature, but soil C losses do not appear to be responsive to added N.
DE: 3322 Land/atmosphere interactions
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting