Hopkins Marine Station Student Paper

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Title: Effects of nitrogen stress on photosynthetic pigments of the subtidal red algae, Rhodymenia pacifica
Student Author(s): Thornber, Carol
Faculty Advisor(s): Watanabe, James
Pages: 22
Location: Final Papers Biology 175H
Date: June 1994
Abstract: The purpose of this experiment was to determine if there is a relationship between lowered nitrate levels in seawater and subsequent degradation of phycobilins in Rhodymenia pacifica when grown under adequate light. Phycobilins, accessory photosynthetic pigments, are often degraded under nitrate stress because of their high nitrogen content. In this experiment, the subtidal red alga R. pacifica was placed in tanks of artificial seawater with varying nitrate concentrations (0, 10, and 20 uM) and the phycobilin levels of these thalli were traced over five weeks. Phycobilin levels in the thalli in all treatments decreased significantly among weeks and treatments. Thalli given no nitrate had lower phycobilin levels than the 10 and 20 uM treatments, whose levels decreased at approximately the same rate. Additional thalli were grown in natural seawater with identidal experimental conditions; their phycobilin levels decreased less markedly over time. All thalli except for those in natural seawater began to turn green at their tips after approximately two weeks; this green tissue was very weak and degraded when it was touched. Chlorophyll a levels of all samples remained constant throughout the experiment, and there was no growth of any thalli. Elemental analysis of the tissues was performed; there was a significant increase in percent carbon in all treatments over time, but no significant changes in percent nitrogen. In conclusion, there is a definite trend which shows that decreased nitrate concentrations do lower phycobilin concentrations over time. However, there presence of green thalli tissue suggests that there may have been other factors involved as well.