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CD-08 Abstract

Carbon Dynamics in Vegetation and Soils Along the Eastern LBA Transect

Plínio Barbosa de Camargo — USP - Universidade de Sao Paulo (SA-PI)
Susan E. Trumbore — University of California (US-PI)

Objectives





We will combine radiocarbon with more traditional measures of C inventory and fluxes to

study the stocks, allocation and turnover of carbon at intensive study sites along the

eastern LBA transect. In spite of their importance to regional and global C budgets, the

understanding of C residence times in vegetation, detritus and soils is very poor in

tropical ecosystems. In particular, the roles of woody biomass and detritus, which contain

large amounts of C with decadal or longer turnover times, need to be better quantified and

are amenable to study with radiocarbon. We will focus on 5 specific components of

stand-level C cycling at several intensive study sites:







  1. quantifying of C uptake rates in growing trees using bomb radiocarbon in concert with

    diameter increment measurements to determine the average rate (and variability) of tree

    growth over the past 3 decades


  2. determining age demographics of tree populations, using radiocarbon to determine tree

    age


  3. assessing the rate of production and decomposition of dead wood debris using permanent

    plot and decomposition rate experiments


  4. using radiocarbon in fractionated organic matter together with measures of C fluxes and

    stocks in soils to determine the amount and turnover time of C in fast-cycling and

    mineral-stabilized organic matter in soils


  5. Using 14C measurements in respired CO2, microbial biomass, and

    soil organic matter to partition total soil CO2 efflux into components from

    metabolic respiration and heterotrophic decomposition.






We will combine these with measurements of litterfall, root dynamics and CO2

fluxes by other groups to produce site-specific models of C cycling for comparison with

eddy correlation measurements of net ecosystem production (NEP).






Our data will provide process-level understanding needed to apportion eddy correlation

measurements of whole-canopy net CO2 flux into above- and below- ground

components and to predict what factors may cause inter-annual variability in net C

balance. Our studies of tree age demographics will scale this understanding to larger

areas, and help determine the best way to extrapolate NEP measurements in space and in

time. At the global scale, our measurements of the time lag between C uptake by

photosynthesis and loss by decomposition are needed to test ecosystem C models.

Additionally, our work with tree demographics will have implications for forestry

management, since our preliminary results show some large, economically valuable trees are

very old (1000 years).

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