Date of Award

Spring 1991

Project Type

Dissertation

Program or Major

Botany and Plant Pathology

Degree Name

Doctor of Philosophy

First Advisor

Arthur C Mathieson

Abstract

The tissue nitrogen and phosphorus composition of 59 marine macrophytes from the Great Bay Estuarine System, NH-Maine and adjacent coast is affected by a variety of environmental and biological factors; by contrast, tissue carbon is more consistent. The overall mean CNP ratio of these plants was 612:29:1, which deviated significantly from that previously recorded for phytoplankton.

The C:N:P ratios within seaweeds were more closely related to functional forms than phylogenetic relationships. Brown algae had higher C:N ratios than green and red algae. This pattern primarily resulted from the very high C:N ratios within thick bladed and coarsely branched species, which dominanted the Phaeophycean taxa evaluated. Overall, the tissue nutrient status within an alga depends upon ambient nutrient availability, as well as a plant's uptake efficiency, storage capacity, and consumption rate(s).

The present study suggests that neither N nor P limitations should be solely delineated by ratios of tissue composition. An assessment of tissue C:N ratios of marine macrophytes (mean = 21:1) and long-term ambient nitrogen and phosphorus concentrations suggests that nitrogen is the primary limiting nutrient within the Great Bay Estuarine System. On the other hand, tissue N:P ratios (mean = 29:1) suggest that phosphorus is most limiting. Based upon C:N and N:P ratios, some algae would appear to be limited by both N and P. Such a response seems questionable.

Under laboratory conditions tissue N:P ratios within both Ascophyllum nodosum and Gracilaria tikvahiae were physiologically determined, although they were somewhat affected by ambient N:P ratios. Both algae absorbed N more efficiently when ambient N:P ratios were low, while P uptake efficiency was elevated with increased ambient N:P ratios. Tissue nitrogen and phosphorus, but not carbon, were strongly affected by N or P supplements. In culture studies Chlorophyll a concentrations were mainly affected by N rather than P concentrations. The biliprotein pigments in Gracilaria were closely related to N:P ratio within the media.

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