PARENT SESSION
Oral Session # 12: Biogeochemistry I: Carbon Dioxide Cycling.
Presiding: D Markewitz
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.
Ecological controls over net ecosystem productivity in a Central Amazon forest.
Chambers, Jeffrey *,1, 2, 3, Toledo, Ligia2, da Silva, Roseana2, Tribuzy, Edgard2, Martins, Liliane2, dos Santos, Joaquim2, Higuchi, Niro2, Trumbore, Susan1, 1 University of California, Irvine, CA, USA2 Instituto Nacional de Pesquisas da Amazonia, Manaus, Amazonas, Brazil3 Tulane University, New Orleans, LA, USA
ABSTRACT- We have carried out extensive field studies of net ecosystem productivity (NEP) components in a Central Amazon forests including: (i) monthly tree growth for over three years using dendrometer bands, (ii) precipitation and litter quality controls over coarse woody debris decomposition and respiration, (iii) precipitation control over respiration from fine surface litter, (iv) tree growth response to disturbance from a logging experiment, (v) maximum tree age using radiocarbon dating, and (vi) tree allometry based on data from hundreds of harvested trees. These data, along with additional published data, were used to construct an individual-based stochastic-empirical model (coded in Java) that simulates the carbon cycling dynamics of live trees, dead trees and surface litter. This model was used to explore a number of ecological controls over aboveground NEP (ANEP). First, in response to an assumed 25% increase in aboveground net primary productivity linked to the known and expected rise in atmospheric CO2 (fertilization response,) the forest acted as a small net carbon sink (0.2 Mg C ha-1 yr-1) for about 200 years, which is considerably less than previously reported for this forest. Second, forest carbon balance was more sensitive to changes in ANEP driven by a simulated increase in tree mortality rates, than a CO2 fertilization response. Third, seasonal variability in ANEP was more strongly controlled by surface litter (coarse and fine) respiration driven by moisture availability, than by seasonal changes in tree growth and woody tissue production. In addition, tree growth exhibited a strong seasonal cycle that was only partially explained by actual precipitation variables, underscoring the importance of phenology in controlling seasonality in ANEP.
Key words: biogeochemistry, tropical, NEE