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A collaborative research effort
between Iowa State University, the Organization for Tropical
Studies (OTS)/Duke University, Colorado State University and USDA Forest
Service for research at La Selva Biological Station in lowland Costa Rica. This research builds on results
from a long-term experimental site, with the goal of evaluating the
mechanistic bases of species-level controls over whole-forest carbon
cycling. In previous studies, three
key plant traits were identified that had the potential to influence the
ecosystem-level carbon balance: 1) carbon use efficiency (CUE, = production /
(respiration + production); 2) partitioning among plant parts that have
differences in CUE (e.g., leaves, wood); and 3) tissue biochemistry that in
turn influences residence time of organic matter, hence its dynamics. For analysis and modeling of forest carbon
budgets, which are critical components of global carbon-cycle models, it is
essential to have accurate estimates of the forest gross primary productivity
(GPP) and the partitioning of GPP among plant parts. It is also critical to evaluate the effect
of plant tissue ‘quality’, i.e. biochemical composition, on soil
carbon dynamics in experimentation unconfounded by other species traits, i.e.
physical attributes such as leaf toughness and particle size and unspecified
biochemical composition. To evaluate these plant traits, we plan a
combination of field measurements of plant-level carbon fluxes, and field and
laboratory measurements of soil carbon fluxes and stocks following a soil
manipulation experiment. Model
development of Century, a widely used, process-based ecosystem model, to
include plant-level carbon fluxes is an important component of this research.
Two independent estimates of GPP will be generated: one derived from a
plant-canopy model (MAESTRA) and one derived from field measurements, to
calibrate the monthly photosynthesis model in Century. Century will also be
used as a tool to integrate results from the soil experiment into a broader
framework. This research will be conducted primarily in the single-species
tree plantations that were established in 1988, in a randomized
complete-block design. Altogether this
research will enhance our understanding of the mechanisms by which individual
species influence the carbon balance of forest systems, and will improve our
capacity to model the biogeochemistry of tropical lands in response to
land-use and environmental change.
Results
of past research at this site and in the prior ECOS grant can be found at the
Iowa State ECOS website
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Jim Raich
Shinichi
Asao
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