Modeling growth and production dynamics of spartina alterniflora
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The goal of this work is to investigate the growth and production dynamics of the dominant salt marsh grass in the southeastern United States, Spartina alterniflora, including documenting non-structural carbohydrate pools and investigating seasonal changes in translocated biomass between above- and below-ground tissues. In Chapter 2, the dynamics of several non-structural carbohydrates (NSC) stored in S. alterniflora is investigated. Results show that sucrose is the dominant NSC in both above- and below-ground tissues and that the total NSC as a percentage of total biomass is highest in the summer through to early winter. The study suggests that sucrose is likely used for long-term storage whereas glucose is preferentially utilized for short-term storage. In Chapter 3, the growth and production dynamics of short, medium, and tall height forms of S. alterniflora are investigated using a phenology-based growth model (PG model), which includes the effects of light, temperature, and salinity on plant production. The model is used in combination with field observations of biomass to estimate values of physiological parameters such as mass-specific rates of carbon translocation. Once parameterized, the model is used in forward mode to predict whole-plant production, growth, respiration, mortality, and translocation. Model results indicate that the short height form of S. alterniflora translocates a higher proportion of photosynthates or remobilization of assimilates to below-ground tissues during periods of growth and senescence periods than medium or tall S. alterniflora, although the absolute amount of carbon translocation to below-ground tissues is greatest in the tall form of S. alterniflora because of its larger above-ground biomass. In Chapter 4, the model is used to compare the production and translocation dynamics of S. alterniflora along a latitudinal gradient using sites in Delaware, South Carolina, and Louisiana. Model results indicate that photosynthates make up the main source of carbon translocated to below-ground tissues at low latitudes, whereas at high latitudes, both photosynthates and remobilization of assimilates in senescing shoots are preferentially used. This shows the importance of taking into account the different translocation dynamics of the plants when comparing growth and production across sites at different latitudes.