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USING STABLE ISOTOPES AND MECHANISTIC MODELS TO EXAMINE CARBON RESOURCE PARTITIONING IN THALASSIA TESTUDINUM AND ZOSTERA MARINA
Citation:
Kaldy, J E., P M. Eldridge, AND C P. Andersen. USING STABLE ISOTOPES AND MECHANISTIC MODELS TO EXAMINE CARBON RESOURCE PARTITIONING IN THALASSIA TESTUDINUM AND ZOSTERA MARINA. Presented at Seagrass 2004, North Queensland, Australia, September 25-27, 2004.
Description:
Natural and anthropogenic stress negatively impact seagrass production and ecosystem function. Our goal is to better understand seagrass response to reduced light, nutrient and organic loading at a variety of ecological scales (individual to landscape) in order to help develop protective criteria for seagrass. This requires a detailed understanding of carbon resource partitioning. Mechanistic models are one method of integrating complex data sets to elucidate underlying processes. We used inverse analysis of Thalassia testudinum above- and below-ground biomass, and growth data to determine carbon allocation to various plant (leaves, rhizomes and roots) and geochemical (DOC, DIC) compartments. Our model results and stable isotope (13C) tracer experiments suggest that about 12% of T. testudinum gross primary production was exuded from the roots/rhizomes and that this carbon can support almost 40% of sediment bacterial carbon demand. The Thalassia inverse analysis predicted carbon flux based on biomass and growth rates but was unable to differentiate between structural (cell walls) and non-structural carbohydrates (reducing and non-reducing sugars). Our current inverse analysis for Zostera marina explicitly differentiates structural carbon from non-structural sugars. This innovation permits detailed assessment of the carbon source-sink relationships (transport vs storage vs growth) within the shoots, rhizomes and roots. Initial model simulations indicated that a large proportion of photosynthate was allocated to Z. marina below-ground tissues. In situ 13C pulse-chase tracer experiments were conducted to quantify carbon allocation and preliminary results indicate that enriched carbon was transported to below-ground tissues within hours. Ongoing compound specific isotope analyses of reducing and non-reducing sugars from the tracer experiments will provide further insight to the transport and storage of photosynthate. This research program is advancing our scientific understanding of how these plants function physiologically and how they respond to stressors, thus improving our capacity to manage and protect seagrass resources.