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CARBON AND NITROGEN ALLOCATION MODEL FOR THE SEAGRASS THALASSIA TESTUDUNUM IN LOWER LAGUNA MADRE
Citation:
Eldridge, P M. AND J Kaldy. CARBON AND NITROGEN ALLOCATION MODEL FOR THE SEAGRASS THALASSIA TESTUDUNUM IN LOWER LAGUNA MADRE. Chapter II, Dunton (ed.), Effects of Dredge Deposits on Seagrasses: An Integrative Model for Laguna Madre. U.S. Army Corps of Engineers, Galveston, TX, I:II-1-26, (2003).
Description:
Inverse modeling methods are a powerful tool for understanding complex physiological relationships between seagrasses and their environment. The power of the method is a result of using ranges of data in a system of constraints to describe the biological system, in this case, the flow of carbon and nitrogen through Thalassia testudunum (Turtle grass). Carbon flows represent energy flow while, nitrogen flows are a surrogate for the nutritional state of the plant. We use field measurements and literature values of production, growth and turn-over rates, etc. to develop the data and constraint systems. The model uses an optimization routine to calculate a complete set of physiological flows within the plant based on measured rate processes. This optimization routine is a "least-squares analysis" which solves for the shortest flow network that is consistent with all constraints. The result is a partitioning of material fluxes (i.e., carbon and nitrogen) that satisfies the rates of production, growth and turn-over of the different compartments as delineated by empirical measurements. Model results indicate that assimilated carbon was equally partitioned between leaves and below-ground tissues and that the flow was unidirectional during the summer months. Losses to dissolved organic carbon (DOC) from the root/rhizome module were substantial and may contribute to the high DOC concentrations measured in the sediments. Nitrogen assimilation occurred in the below-ground model and model results indicate that internal recycling, particularly from the leaves, in important. Losses of dissolved organic nitrogen (DON) were minimal, indicating that Thalassia testudunum uses nitrogen efficiently.
We ran a tracer analysis to determine the exchangeable pool size within each seagrass module (leaves, short shoot, root/rhizome), and accumulation within biogeochemical pools. Thus, using measured growth rates etc. we were able to model the flow of carbon and nitrogen through th